The effect of considering dissipation in the model for the metallic component of metallo-dielectric photonic crystals is studied. The study has been carried out with the Transfer-Matrix Method with the help of the TRANSLIGHT software package. The influence of the filling fraction and of the background dielectric constant on the width of the second band gap and on the cut-off frequency for E-polarization has been analyzed. The influence of different levels of dissipation on the transmittance and reflectance spectra and on the absorption has been calculated, with special attention to the absorption induced at the plasmonic resonances in H-polarization.

Limiting factors for short-wavelength QCL designs are discussed, and a model is described to predict the short-wavelength limit for strain-balanced QCL structures. High performance is predicted at wavelengths as short as 3.0mm based on a conduction band offset of 0.9 eV in the GaInAs/AlInAs materials. Recent work is presented on the growth of strained materials using gas-source molecular beam epitaxy to investigate the model predictions. Advanced material characterization, including HR-STEM, high-resolution x-ray diffraction, photoluminescence, atomic force microscopy, and wafer-scale uniformity and repeatability are demonstrated for strain-balanced QCL structures. Laser testing results are presented for QCLs operating at ~4.8mm, and lastly, predictions for further performance improvement at short wavelengths are discussed.

In this paper we model vertical cavity surface-emitting lasers (VCSELs) that are optically pumped with circularly polarised light. This pumping scheme produces partial spin alignment of electrons since right-circular polarisation (RCP) excites spin-down electrons and left-circular polarisation excites spin-up electrons. The two spin populations are coupled through spin relaxation with a characteristic time in the order of 1-100 ps. RCP and LCP lasing emission from these populations are coupled through linear birefringence and gain anisotropy (dichroism), each with their own characteristic rates. The well-known spin-flip model (SFM) describes these processes in terms of four rate equations (one each for the complex RCP and LCP fields, one each for spin-up and spin-down electrons). For the special case when the two circularly-polarised field components have the same frequency and maintain a constant phase difference, these may be recast in terms of optical intensities, thus leading to an efficient method for numerical solution in the steady state. We have used this method to systematically investigate the influence of spin relaxation, birefringence and dichroism, and pump ellipticity on the VCSEL output. It is found that the spin relaxation time and the ellipticity of the optical pump have the strongest effect. The method can also be used to investigate the accuracy of approximate solutions of the SFM equations that have been proposed in the literature.

Lasing emission is demonstrated at room temperature in the entire spectral region from 1.29 to 1.52 microns using GaInNAs/GaAs quantum well (QW) laser diodes (LD) grown by molecular beam epitaxy on GaAs substrates. The separate confinement heterostructures (SCH) is made up by AlGaAs cladding layers, a GaInNAs-based QW and GaAs barriers. To achieve lasing emission from 1.29 to 1.52 microns the In in the QW content is maintained at 40%, while the N content is varied from 1.3 to 3.3%. With this structure, the threshold current density (Jth) and external differential quantum efficiency (hd) at 1.29 microns are 685 A/cm² and 45 %, respectively. Increasing the wavelength to reach 1.5 micron emission degrades these figures to Jth=2890 A/cm² and hd=23% at 1.49 microns, and to Jth=4060 A/cm² and hd=16% at 1.52 microns, which still represent a very large improvement with respect to previous reports of LDs based on the quaternary. Even though adding N to the structure decreases the internal quantum efficiency (hi), from 75% to 50%, this figure does not change with increasing wavelengths up to 1.44 microns. The differential modal gain also degrades as a result of adding N to the QW, but like the case of hi, does not change significantly with increasing wavelength. Thus, achieving long wavelength emission up to 1.55 micron emission starts to become viable, even with simple LD structures.

The influence of carrier localization on the opto-electronic properties of GaInNAs/GaAs quantum well (QW) light emitting diodes (LED) and laser diodes (LD) grown by molecular beam epitaxy is studied. The external quantum efficiency of the LEDs at low temperature is found to be strongly affected by emission from localized states, and its evolution with the injected current is modified compared to the typical one of a QW LED. The light-current characteristics of GaInNAs LDs are measured for different temperatures between 15 and 295 K, and an anomalous behaviour of the threshold current with temperature is obtained comparing to a reference InGaAs laser. In particular, a negative or infinite T0 is obtained at very low temperatures, followed by a region of very small T0. In addition, if the temperature is further increased, a change to a higher T0 is obtained at a temperature which is in the range of the typical delocalization temperatures in GaInNAs QWs. All these features are attributed to the influence of carrier localization. The temperature induced changes in the relative carrier population of the localized states and the band edge states change the lineshape of the gain spectrum and its peak value, and consequently the threshold current of GaInNAs QW lasers.

Photonic crystal devices are now being produced for a variety of functions-and the need to provide thermal control of the behaviour suggests the use of thermo-optic effects. It has emerged that thermo-optic effects can provide useful modulation, switching and tuning capability. Future trends indicate fast, low-power, thermo-optically operated photonic crystal and photonic wire devices-and the possibility of simultaneous athermal characteristics.

In this paper we review the fabrication and characterisation techniques of m icrostructured optical fibre (M OF) tapers, their fundam ental waveguiding properties and potential applications. W e fabricate photonic crystal fibre tapers without collapsing the air-holes, and confirm this along the taper with a non-invasive probing technique. We then describe the fundam ental property of such tapers associated with the leakage of the core m ode that leads to long wavelength loss. We also revisit the waveguiding properties in another form of tapered MOF photonic wires, which transition through waveguiding regimes associated with how strongly the mode is isolated from the external environment. We explore these regimes as a potential basis for evanescent field sensing applications, in which we can take advantage of controlled airhole collapse as an extra dimension to these photonic wires.

Most numerical analysis of waveguide propagation in photonic crystal fibers are based on ideal structures with full discrete rotational symmetry and periodic boundary conditions to reduce the computational domain. However fabrication defects can yield some kind of disorder appearing as small random displacements in the air-hole distribution in the fibre cladding. The effects introduced by this disorder on the eigenmodes and propagation constants can be studied by the numerical solution of the whole cross-section of the photonic crystal fibre. Here, the finite element method is applied to the solution of the two-dimensional scalar Helmholtz equation. Nonsymmetrical meshes obtained by Delaunay triangulation are used, and a perfect matched layer is introduced outside the air-hole distribution in order to reduce the effects of spurious evanescent modes. For monomode fibres, the weak disorder only changes slightly the effective propagation constant and the field. However, for multimode fibre, the field profile of the higher-order modes deforms significantly even in the presence of weak disorder. The field profile of the fundamental mode adapts to the first row of air-holes with only small changes. But for multimode fibres the degeneracy of the high-order mode profiles, which follows from a group theory analysis of the full discrete symmetry of the fibre, is broken by the disordered air-hole distribution. Surprisingly, the effective propagation constant only suffers small changes. In summary, the results are similar to those obtained in recent experiments on multi-mode propagation in photonic crystal fibres.

We report on the investigation of planar photonic crystal waveguide transitions with a scanning near-field optical microscope (SNOM) in collection mode. An abrupt and a gradual taper design intended to couple light from a W3 (three missing rows of holes) to a W1 waveguide were fabricated in a InGaAsP slab waveguide. SNOM measurements reveal that a taper design can efficiently funnel light into the W1 waveguide. For both designs a suppressed coupling of light into the W1 waveguide is measured for a frequency which corresponds to a mode crossing which we determined by 3D plane wave simulations.

In this paper we propose the design and the fabrication of 90° bend ridge waveguide (WG) assisted by a two-dimensional photonic crystal (2D-PC). 2D-PCs act as efficient mirrors along the boundaries of the bend ridge thus reducing the in-plane losses. The ridge waveguide consists of a 3 μm x 0.75 μm titanium dioxide core on a silica bottom cladding. The 2D-PC structure surrounding the bend waveguide is composed of a triangular array of circular dielectric pillars having a height of 0.75 μm. The titanium dioxide waveguiding core layer is covered with PMMA in order to create a quasi-symmetric structure. A photonic band gap centered around 1.3 μm is obtained by a PC radius r = 0.33a and lattice period a = 0.450 μm. The design of the whole structure is subsequently optimized by using a 3D Finite Difference Time Domain based computer code. The ridge waveguide assisted by a 2D-PC has been fabricated by using electron beam lithography and reactive ion etching. For the pattern transfer we have used about 50 nm thin layer Cr metal etch mask obtained by means of a lift-off technique based on the use of bi-layer resist (PMMA/MMA). The presence of the 2D-PC around the bend waveguide leads to a sharp increase of the transmission efficiency around 1.3 μm for curvature radius of 2.5 μm. The bend transmission results to be in the range between 0.76 and 0.85 when the thickness of the ridge WG and of the 2D-PC pillars is between 0.75 and 1.3 μm. This value is more than twice with respect to the bend waveguide without 2D-PC.

Efficient polymer based organic light emitting devices (PLEDs) are fabricated by spin coating method. The emitting layer consists of polymer host and phosphor dopant. The energy transfer and charge carrier trapping of poly(9,9-dioctylfluorene) (PFO)-based PLEDs doped with red emissive phosphor tris(1-phenylisoquinoline) iridium (III) [Ir(piq)3] by applying the voltage pulse on devices has been discussed. The emission from the host has been observed under a short pulse of 100 ns was applied. In order to change the electroluminescent (EL) spectrum, PFO-based white-light-emitting PLEDs have been demonstrated utilizing the different pulse width and frequency. The maximum luminance of 4,800 cd/m² and the Commission Internationale de L'Eclairage (CIE) coordinates of the ideal white light (0.33, 0.35) at the pulse width and frequency of 100 ns and 1 kHz, respectively, were obtained.

The mode coupling of organic distributed feedback lasers is enhanced by using a distributed feedback grating that is etched into a thin layer of titanium dioxide (TiO₂). The use of TiO₂ increases the index contrast in the grating and the confinement in the waveguide. The enhanced mode coupling results in larger feedback given to the lasing modes, which lowers the laser threshold and allows smaller devices to be built. The lasing threshold of the TiO₂-enhanced devices is twice as low as that of conventional devices whose grating is etched directly into the quartz.

The optoelectronic properties of a new type of organic light-emitting diode have been measured, which incorporates in the active layer a molecule containing as well an electron conducting and blue emitting oxadiazole group and a hole conducting carbazole group. The investigated device consists of this active oxadiazole/carbazole layer deposited by spin-coating on transparent conductive oxide (TCO) covered glass substrate and top aluminium contacts for electron injection. We compared two types of devices, with and without the insertion of a 40nm thick spin-coated PEDOT layer as hole injector between the active and the TCO layer. Stable blue emission has been observed only for the device with inserted PEDOT layer with an inset of the light emission at an applied voltage of 10V. For devices without PEDOT layer a much higher threshold voltage for light emission and a lower quantum efficiency as compared to the device with intermediate PEDOT layer has been found.

We report data on a new nanophotonic device based on a 2-D slab silicon photonic crystal (PC) matrix composed of a periodic array of high index silicon pillars embedded within a flexible low index polyimide matrix. To our knowledge, for the first time, negative refraction based on the superprism effect is reported in a 2-D silicon-based photonic crystal device. This work has a huge potential in various applications employed within silicon-based photonic crystal systems such as super-lenses, tunable filters, and optical switches. The device, designed for 1.54 μm infrared light, is composed of a triangular array of silicon pillars of diameter 400 nm with a lattice spacing of 616 nm embedded in a thin 400 nm thick polyimide matrix. Small changes in the incoming angle of light can produce large changes in the direction of the outgoing light near zero stress. Silicon pillars are formed by RIE etching and polyimide is then spun on, baked and etched to form the PC device. The PC matrix is then released from the oxide with a BOE etch. Samples with incident angles in the range of 0° ~ 8° have been tested. Strong negative refraction on the order of 50° is seen in the PC with the incident angle of 8°. This is in close agreement with the simulated results and clearly demonstrates the effectiveness of the photonic crystal device.

In this paper, the interactions of pulsed and continuous wave Gaussian beams with a photonic crystal that has a negative effective refractive index are considered. Subwavelength focusing of incident Gaussian beams with a photonic crystal slab due to the negative refraction is discussed theoretically. Negative angle of refraction behaviour associated with the negative index of refraction exhibited by the PC slab is also shown. All our simulations are carried out by using the finite difference time domain (FDTD) method.

The beam at the exit surface of a Photonic Crystal (PhC) slab can be periodically modulated, in positive or in negative direction, changing the slab thickness. The thickness in negative refraction on PhC's is not always appropriately considered, in spite of an always increasing literature in this subject. This effect is well known in x-ray diffraction, in the most comprehensive version: the Dynamical Diffraction Theory (DDT). Thickness dependence is a direct result of the so-called Pendellosung phenomenon and is linked to a periodic exchange, inside the crystal, of the energy among direct beam (or positively refracted) and diffracted beam (or negatively refracted). It represents an outstanding example of the application of the result of DDT as a tool for the analysis of s electromagnetic interaction in PhC's.

Colloidally synthesized CdSe/ZnS core/shell semiconductor nanocrystals (NCs) show highly efficient, narrow-width and size-tunable luminescence. Moreover, they can be incorporated in polymer matrices and deposited on solid substrates by means of spin-coating techniques. When embedded between two mirrors a NCs/polymer blends microcavity is realised, thus allowing to tailor the photoluminescence spectrum of these emitters. By virtue of the quantized photonic and electronic density of states, colloidal quantum dots embedded in a single mode vertical microcavity are good candidates for the fabrication of high-efficiency emitting devices with high spectral purity and directionality. In this paper, we have applied a new organic-inorganic hybrid technology for the fabrication by imprint lithography (IL) of vertical microcavities that embed colloidal quantum dots. Two dielectric distributed Bragg reflectors (DBR) are evaporated on two different substrates. The active organic layer (NCs/polymer blend) is spin coated on the first DBR, whereas a lithographic pattern is realized on the second DBR, used as the IL mold. The two parts are then assembled together in an IL process in order to create a vertical microcavity. The fine control of the thickness of the active material waveguide layer can be achieved through the mold patterning depth and the IL process parameters. All the fabrication steps have been engineered in order to decrease the thermal stress of the active layer. The effectiveness of this technology is demonstrated by the room temperature photoluminescence (PL) spectra, recorded on the fabricated microcavity, which show a sharp emission peak with a line width of 4.15 nm.

RGB-OLED-displays can be realized by at least three different approaches: Color from white, color from blue or patterning of red, green and blue OLEDs, which is favorable for reasons of higher efficiency and lower costs. Common patterning techniques like photolithography cannot be applied due to the degradation of the OLEDs after the exposure to solvents. Shadow masking which is currently widely applied is not applicable for bigger substrate sizes of future mass production tools. Therefore a novel approach for patterning of organic semiconductors will be demonstrated. The laser induced local transfer (LILT) of organic small molecule materials allows for mass production of high resolution RGB-OLED-displays. An infrared absorbing target is coated with the desired emitting material, which is placed in a short distance in front of an OLED substrate. A scanner deflects and focuses an infrared laser beam onto the target. By adjusting scanning speed and laser power accurately the target locally heats up to a temperature where the organic material sublimes and will be deposited on the opposite OLED substrate. By repeating this for red, green and blue emitting materials a RGB-OLED-display can be realized. For process evaluation and development a LILT-module has been built, incorporating two custom vacuum chambers, several lift and transfer stages, a high-speed high-precision scanner and an infrared continuous-wave laser (cw). This module is designed to be part of a future inline deposition system for full-color OLED displays. In the first experiments it could be observed, that the pattern resolution is strongly dependent on the scanning speed, exhibiting minimum feature sizes of 40μm. It can be deducted that this is due to the laser's beam profile (TEM00), which allows for the smallest focus possible, but may not allow for rugged process conditions suitable for production. Rectangular steep-edged beam profiles may overcome this problem.

Realization of enhancement of second-harmonic generation (SHG) in three-dimensional (3D) photonic crystals utilizing nonlinear diffraction is demonstrated. The samples are composed from close-packed silicon oxide spheres with diameter of 250 to 300 nm in each sample forming an ordered fcc opal matrix. The opal voids are filled by noncentrosymmetric gallium nitride and centrosymmetric silicon with filling factor close to unit. The photonic band gap (PBG) is obtained for light reflected from the (111) face and localized in the spectral region from 800 to 950 nm for different samples. SHG spectra show pronounced peaks as the fundamental radiation is tuned across the photonic band gap. The intensity enhancement in SHG is about 100 and the spectral width of the SHG resonances is approximately 15 nm. The SHG enhancement is attributed to combination of linear diffraction of the fundamental radiation from the (111) opal layers and nonlinear diffraction utilizing the 3D periodicity of the quadratic susceptibility of silicon and gallium nitride nanocrystals in opal voids. The spectral position of the SHG peak is slightly red-shifted in comparison with the PBG center and attributed to condition of the group velocity minima.

A simple and cost-effective integrated synthesizer of fast light pulses has been designed, analyzed and tested for the characterization of the time response of photo-multipliers (PMT). This synthesizer consists of an integrated pulse generator based on Schmidt Trigger Inverters, a broadband matching network and a high speed LED. It enables the generation of pulses as short as less than 10 ns with variable pulse width, amplitude and repetition frequency. In order to accurately know the shape of the pulses applied to the PMT under test, a circuital model of the LED has been developed and verified at frequencies up to 2 GHz. This model accounts for the nonlinear behavior of the LED capacitance as well as the package parasitics. The influence of the mismatch at the different frequency components of the synthesized pulse has been investigated. The pulse transmitter has been used to test the time response of MAGIC telescope pixels.

InGaN/GaN Multiple Quantum Well (MQW) structures have been grown on sapphire substrates by low pressure metalorganic chemical vapor deposition (MOCVD), for wide range of blue, blue-green and green light emission device application. The compositions and sizes within QWs were designed according to the requirements on the LED performance. Samples were investigated by a variety of characterization techniques. Optimization of the growth parameters and process was realized and evidenced by high resolution X-ray diffraction (XRD) measurements. High quality of MQW wafers have been achieved with excellent characteristics, showing XRD multiple satellite peaks up to 10th order due to the quantum well superlattice confinements and fine fringe structures among satellite peaks. Transmission electron microscopy confirmed the sharp MQW structures and dimensional parameters, and revealed the V-shape defects. Optical properties were further studied and Quantum confined Stokes effect was observed from photoluminescence and photoluminescence excitation measurements.

Light emitting devices for the infrared spectral region are used in a lot of application fields. In the mid infrared (MIR) region, where a lot of gases show strong absorptions, the optical output power of inexpensive emitters in the relevant wavelength range is too low. An optically pumped emitter for the MIR region around 4 μm based on narrow gap semiconductors is demonstrated. The pumping takes place using inexpensive near-infrared (around 1 μm) high power continuous wave (cw) semiconductors laser. The radiation is converted by the narrow gap semiconductor into the MIR region as spontaneous emission. Molecular beam epitaxy (MBE) grown IV-VI lead chalcogenide-based compounds, especially PbSe, are applied for frequency conversion. The structural and optical quality of these thin film materials is characterized mainly by X-ray defraction measurements (XRD) and photo luminescence (PL) spectroscopy. For high radiation efficiency the outcoupling of the light is enhanced by surface structuring. Useful structures generating high photoluminescence intensity are characterized by IR imaging with an IR camera system being sensitive in the spectral region of interest. Due to the high pumping powers the device design-especially the thermal management of the active PbSe film-plays an important role. We will present a preparation technique for optically pumped, surface structured PbSe emitters in transmission geometry exploiting the transparency of the substrates and glues in the relevant wavelength region. The measured total emission power of the emitters exceeds 0.5 mW. Using an optimised design total emission powers up to 2 mW were achieved.

Liquid crystals are customarily used in several kinds of flat panel displays. Besides usual nematic liquid crystals, smectic tristate antiferroelectric liquid crystals have shown analogue grayscale and full color video rate at high-end devices with passive multiplexing. These devices ultimately are intended to be applied to small size devices on microdisplay applications. When a symmetric driving signal is applied, the electrooptic response of the devices usually consists of two symmetric hysteresis lobes. An asymmetric hysteresis cycle can be developed by using dissimilar aligning layers onto the two glass plates of the cell. This kind of devices can lead to analogue optical multistability, i.e., devices whose optical transmission may be arbitrarily set and maintained reducing or eliminating the bias voltage. In this work, a study of the asymmetric behavior of cells filled with commercial antiferroelectric liquid crystal is presented. Optical hysteresis cycles have been obtained applying a low frequency triangular waveform to the devices. Analogue grayscales have been generated only at one lobe of the hysteresis cycle. Electrical characterization has been carried out measuring the switching current of the cells test. Multiplexed driving waveforms have been applied with and without bias voltage in order to evaluate the stability of the optical transmission for video rate working. Results demonstrating analogue optical multistability on asymmetric antiferroelectric cells have been obtained. Narrow dynamic ranges, compatible with standard electronics for dynamic grayscale in data columns have been found. Preliminary measurements of the frequency dependence of impedance have been obtained on the capacitive device.

We report a true left-handed (LH) behavior in a composite metamaterial consisting of periodically arranged split ring resonator (SRR) and wire structures. The magnetic resonance of the SRR structure is demonstrated by comparing the transmission spectra of SRRs with that of closed SRRs. We confirmed experimentally that the effective plasma frequency of the LH material composed of SRRs and wires is lower than the plasma frequency of the wires. A well-defined left-handed transmission band with a peak value of -1.2 dB (-0.3 dB/cm) is obtained. We also report the transmission characteristics of a 2D composite metamaterial (CMM) structure in free space. At the frequencies where left-handed transmission takes place, we experimentally confirmed that the CMM structure has effective negative refractive index. Phase shift between consecutive numbers of layers of CMM is measured and phase velocity is shown to be negative at the relevant frequency range. Refractive index values obtained from the refraction experiments and the phase measurements are in good agreement. The experimental results agree extremely well with the theoretical calculations.

We numerically investigate, the unique features of imaging by a superlens made of a photonic crystal slab that possesses the property of negative refraction. We confirm earlier finding that a photonic crystal slab lens can provide the imaging of a point source. We prove that the resolution of such a slab lens can be improved by optimizing the air hole radius as well as the refractive index of the high index material. It is found that by decreasing the radius of the air holes, the spatial resolution is improved significantly. It is also shown that for the case of two sources, the resolution of such a photonic crystal lens can be made indeed better than the radiation wavelength. The finite difference time domain (FDTD) method is used in our numerical simulations.

We demonstrate an ultra sensitive method for Two Photon Fluorescence (TPF) excitation using resonant Grating Waveguide Structures (GWS). In its basic configuration, a GWS consists of a substrate, a waveguide layer and an additional grating layer. When illuminated with laser light under resonant conditions, the GWS reflects all light and leads to very high local surface intensities. This field enhancement can be exploited for TPF spectroscopy, without the need for a highly intense, focused laser light. We present the enhanced TPF signal obtained from a 23 nM drop of tetramethylrhodamine (TMR) on the top of high-finesse resonant polymeric GWS. The resonant behaviour of the GWS was tested for normal incidence with TE polarization illumination. As expected, the transmission spectral profile has a dip at resonant wavelength. The TPF spectra of TMR molecules were observed for different excitation wavelengths. Close to resonance, TPF intensity increases and the maximum signal is obtained when the excitation wavelength coincides with the resonance wavelength of the GWS. These results clearly indicate that the huge field localization at grating surface is responsible for the TPF excitation. We obtained a detection limit down to picomolar concentration of the dye molecules, offering the possibility of a highly sensitive, compact and non-destructive tool for widespread biochemical applications.

Semiconductor Optical Amplifiers (SOAs) have mainly found application in optical telecommunication networks for optical signal regeneration, wavelength switching or wavelength conversion. The objective of this paper is to report the use of semiconductor optical amplifiers for optical sensing taking into account their optical bistable properties. As it was previously reported, some semiconductor optical amplifiers, including Fabry-Perot and Distributed-Feedback Semiconductor Optical Amplifiers (FPSOAs and DFBSOAs), may exhibit optical bistability. The characteristics of the attained optical bistability in this kind of devices are strongly dependent on different parameters including wavelength, temperature or applied bias current and small variations lead to a change on their bistable properties. As in previous analyses for Fabry-Perot and DFB SOAs, the variations of these parameters and their possible application for optical sensing are reported in this paper for the case of the Vertical-Cavity Semiconductor Optical Amplifier (VCSOA). When using a VCSOA, the input power needed for the appearance of optical bistability is one order of magnitude lower than that needed in edge-emitting devices. This feature, added to the low manufacturing costs of VCSOAs and the ease to integrate them in 2-D arrays, makes the VCSOA a very promising device for its potential use in optical sensing applications.

Resonant noble metal nanoparticles with dimensions of a few tens of nanometers and sustaining Localized Surface Plasmon (LSP) modes have been recently proposed as good candidates for increasing both integration and sensitivity compared to conventional extended thin metal films. Very recently several groups have reported results of sensing with a single nano-particle. The study we present contains two main parts. First, using randomly distributed colloidal gold spheres, we demonstrate the ability of LSP sensors for monitoring quantitatively and without the use of any label, the binding between small organic molecules and antibodies with real-life applications. In a second part, the Fourier Modal Method (FMM) is used to model controlled geometries of particles that allow for optimizing the sensor properties. In particular, we show that the electromagnetic coupling within a periodic 2D particle array can be optimized to increase the field localization and thus the sensitivity of the sensor.

A Radio-Frequency (RF) Ring Resonator (RR) Fibre-Optic sensor (FOS) configuration is theoretically analyzed and a specific example to show the principle of operation is reported: an intensity-encoded fiber-optic sensor prototype based on the optical losses due to fibre curvature. The proposed configuration can be used for self-referencing purposes and to improve sensitivity as regards the measurand in any intensity fibre-optic sensor. Light intensity fluctuations to be measured are converted to ring resonator losses that produce high amplitude variations of the transfer function of the ring resonator. The use of an Erbium-Doped Waveguide Amplifier (EDWA) offers the theoretical possibility of increasing sensitivities to the greatest extent previously reported. A proper selection of the ring resonator point of operation is achieved using an optical attenuator, a variable coupling ratio coupler and an EDWA if needed. Modulation of the optical carrier by a RF signal allows overcoming possible instabilities due to environmental perturbations and simplifying the detection electronics. Two self-reference techniques to overcome unwanted source and local intensity fluctuations are developed. Both self-referencing techniques avoid possible intensity fluctuations because of long leads perturbations, in case of remote operation. Temperature effect on the measurements is also discussed.

Intense optical fields can induce significant forces "between" particles. In analogy with atomic physics, the resonant modes of a single particle play the role of electronic orbitals and, like their electronic counterparts, could lead to bonding and antibonding interactions between neighboring particles. In absence of absorbing or "Mie"-like resonances, light forces on small particles are, in general, very small. However, as we will show, when the fields are confined in quasi-one-dimensional waveguide structures, the coupling of the scalar dipolar field with the waveguide modes leads to a resonant total reflection close to the threshold of a new propagating mode. These resonant modes are shown to lead to unusual strong optical interactions between particles.

The trapping of micro-objects by optical radiation forces, so-called optical tweezers, has become widely used in physical, chemical and biological experiments where accurate and non-invasive manipulation is required. Recent advances in beam shaping render it possible for instance to rotate or to dynamically manipulate independently several elements. Today, one of the remaining challenges of conventional optical tweezers is the direct manipulation of systems with sizes belonging to the sub-wavelength or Rayleigh regime. Indeed, the diffraction limit prevents in that case from achieving a commensurable trapping volume and thus does not allow for minimizing the fluctuations in position of the trapped object due to its strong Brownian motion. In order to overcome this limitation, it has been proposed to use evanescent fields instead of the usual propagating fields. Recent advances in optics of noble metal nano-structures have recently provided new configurations to achieve nano-optical tweezers. Especially, tightly localized modes resulting from the coupling between resonant noble metal nanostructures may offer the gradient forces able to trap and manipulate Rayleigh objects. In this work, we calculate the radiation forces exerted on a nanometric dielectric sphere when exposed to a patterned optical near-field landscape at an interface decorated with resonant gold nanostructures. By comparing their magnitude with other forces that affect the movement of the particle, we discuss the practical ability of our configuration for multiple parallel optical manipulation.

In this paper, different optical configurations based on ring resonators and a reflective section in the feedback path, are proposed in order to show the feasibility of their applications in different fields. Additionally, the use of optical amplification in some of the configurations offers the possibility of improving the device insensibility to fabrication tolerances and gives flexibility to the designs. In the compounds configurations that use reflective elements in the ring resonators, such as Sagnac configurations and Bragg Gratings, tuning is achieved by changing the coupling ratio of a coupler apart from conventional tuning by changing the equivalent loop length, using temperature or injection current. Applications as tunable filters in DWDM networks and lasers will be discussed. The reported structures can be integrated in InP or silicon technology, because photonics circuits with equivalent components have already been developed. Some of them are a monolithically integrated Sagnac interferometer for an all-optical controlled-NOT gate. Integrated optic devices have higher free spectral ranges, thus complying with applied standards on DWDM networking. Theoretical analysis is presented to identify and emphasize the design parameters of each configuration as regards its application of interest. Measurements on fibre optic prototypes for showing the principle of operation and validating the theoretical models are reported in [24].

A 2x2 optical switch for plastic optical fibre (POF) has been developed, able to work for both 660 and 850nm simultaneous and independently of the input light's polarization, improving previous developments. The device has four bidirectional optical ports, and is able to switch from each port to any other. In this way, there are three operation modes: straight (each input connected to the corresponding output), crossed (inputs and outputs crosses) and closed (inputs connected on the one part, and output connected on the other part). As the device is bidirectional, inputs and outputs are interchangeable. The switching process is carried out by a set of Polarized Beam Splitters, Liquid Crystal cells, λ/4 plates, lens and mirrors. An electronic circuitry has been developed to control the state of the optical switch, which is shown in a Liquid Crystal Display. The system has been tested for both 660nm and 850nm, and the optical switch exhibits miliseconds switching times, an optical interchannel crosstalk better than -25 dB, and low power consumption. Applications of the switch include systems where a redundant path is needed to guarantee communication, such as safety systems in automobiles, LANs, telemedicine, heavy machinery in the industry along with coarse WDM GI (graded index) POF networks. Device size reduction is under development.

In this paper we describe a new class of tunable interferometric MOEMS devices able to perform tunable wavelength selective beam steering. These GEMOEMS (Grating Enhanced Micro Opto Electro Mechanical Systems) devices comprise a diffraction grating etched on top of a selective and tunable vertical interferometric MOEMS filter. The underlying filter reflects the transmitted orders with controllable amplitude and phase so that they interfere with the reflected orders and modulate the diffraction efficiency distribution into these reflected orders. Our first demonstrator is a 1X2 optical switch designed for operation over the C-band (1530-1560 nm). The diffraction efficiency in the reflected orders is controlled by changing the distance from the grating to a Bragg mirror via an electrostatic actuation of the suspended grating membrane. The devices are fabricated using a multiple InP-air-gap MOEMS technology based on the sacrificial etching of an InP / InGaAs stack. The grating is realized using an electron-beam lithography step. The simulated performances on the C-band show low insertion loss (less than 0.3dB), low ripple (0.15dB), reasonable cross-talk (-15dB), and an estimated switching time around 10μs. These characteristics make such an optical switch a solid contender of a rotating mirror, with the advantage of a much faster response. In this presentation, we introduce the general physical principles of GEMOEMS and describe the design, simulation, fabrication and preliminary experimental results for a simplified 1x2 optical switch. We also propose other prospective devices such as add-drop filters.

In previous studies, it was shown that using a Y waveguide, a twin laser output signal could be mixed and coupled to a fiber. The need to adapt the dimensions of the Y waveguide and apply the more restrictive conditions of a coherent regime for laser emission and waveguide mixing, led us to try an MMI coupler to focus the output signal. Herein, ideal 2x1 MMI for this purpose are presented in schematic form. Using a TE mode approximated with Gaussian distributions for the twin laser output signal (the input signal to the MMI coupler), an optimally focused output signal requirement is considered. Possible longitudinal and width dimensions for the couplers are calculated. Similar values of the MMI refraction index to the laser magnitude values were assumed to avoid the drop in transmission produced by reflections at the boundary surface. We also assumed no air gap between the laser and MMI coupler. The functioning of these ideal devices for coherent and incoherent twin laser emission is discussed.

When the emission of light by molecules, excitons etc. takes place close to a thin metallic film, coupling of power to surface plasmon-polariton (SPP) modes supported by the metal film often dominates. We explore the nature of the SPP modes and examine how the energy lost to them can be recovered through the use of periodic, wavelength scale microstructure. We show that the photoluminescence emission from a structure containing is much stronger than that from a similar planar structure. We look at the importance of the exact details of the microstructure on the emission process.

We report on the concept, generation and first observations of focused surface plasmons on shaped gratings. The gratings patterns are engineered to perform functions such as focusing or directing through noncolinear grating-assisted phasematching. We present local probing of the plasmon propagation by phase sensitive PSTM of the field distribution on engineered gratings showing the focusing of plasmons.

In the ongoing general trend for miniaturization, there is an increasing interest in the manipulation of electromagnetic fields at the nanometer scale. A main obstacle to this goal is the diffraction limit that prevents from focussing light down to volumes much smaller than the incident wavelength. In order to overcome this limitation, it has been proposed to deal with evanescent fields instead of the conventional propagating beams. Especially, plasmon fields bound at a noble metal interface or around metal nanostructures have shown to be very suitable to control the light confinement down to the nanometer scale. In this work we investigate the near-field coupling in finite metal particle chain geometry. The Green Dyadic method is used to demonstrate that high enhancement factors can be achieved by exploiting the in-plane forward scattering of the particles, with no need for cumbersome geometries with nanometer features.

The study of the Vertical-Cavity Semiconductor Optical Amplifiers (VCSOAs) for optical signal processing applications is increasing his interest. Due to their particular structure, the VCSOAs present some advantages when compared to their edge-emitting counterparts including low manufacturing costs, high coupling efficiency to optical fibers and the ease to fabricate 2-D arrays of this kind of devices. As a consequence, all-optical logic gates based on VCSOAs may be very promising devices for their use in optical computing and optical switching in communications. Moreover, since all the boolean logic functions can be implemented by combining NAND logic gates, the development of a Vertical-Cavity NAND gate would be of particular interest. In this paper, the characteristics of the dispersive optical bistability appearing on a VCSOA operated in reflection are studied. A progressive increment of the number of layers compounding the top Distributed Bragg Reflector (DBR) of the VCSOA results on a change on the shape of the appearing bistability from an S-shape to a clockwise bistable loop. This resulting clockwise bistability has high on-off contrast ratio and input power requirements one order of magnitude lower than those needed for edge-emitting devices. Based on these results, an all-optical vertical-cavity NAND gate with high on-off contrast ratio and an input power for operation of only 10W will be reported in this paper.

The importance of nonlinear optical devices is increasing due to their hopeful characteristics such as small size, high speed or even low power consumption. These devices integrated in all-optical systems achieve the best results because of the elimination of optoelectronic or electro optic conversions that imply great reductions in these advantages. Therefore the main effort should be directed to make as many functions as possible by optical means. Among these functions, wavelength conversion or amplification seem to be likely to implement with a nonlinear device. In this work a structure called Semiconductor Semimagnetic Microcavity (SSM), for optical amplification and wavelength conversion, is introduced and studied. This study requires a suitable method for nonlinear series devices. It must take into account each wave and its relationship with the others. An Extended Yeh matrix is appropriate for the characterization of this structure. The method reveals that if the microcavity is exposed to an input signal and a pumping input signal and also matches the conditions of degenerate four-wave mixing, another wave at a different wavelength appears. What is more, the original input signal becomes greatly amplified depending on the pumping input signal. The process of obtaining these results with the Extended Yeh matrix applied to a SSM is shown. Optical wavelength conversion and optical amplification in a microcavity is demonstrated by means of this matricial method.

Electrochromic (EC) materials are used mainly for domotic applications, such as transparency controlled windows or rear-view mirrors in cars. The device construction is a sandwich of electrochemical compounds, which change their optical properties when applying voltage. Although the changes that are used in the applications take place in the visible, there are also changes in the near infrared region. In the last years, some works have proposed their use in fiber optic applications, mainly as optical modulators or VOAs (Variable Optical Attenuator). EC devices have usually slow responses (several seconds) and low transmittance range, specially the organic ones. The slow response is the major drawback for their use as modulators. But in NIR transmittance ranges, there are promising results in materials like ruthenium or PEDOT (poly(3,4-ethylenedioxythiophene)). In this work, we will study the possible use in VOAs of new EC devices developed with the minimum number of layers, by their response in telecommunications wavelengths. These devices are manufactured in such a way that the integration in fiber optic devices is an easy task. The minimum number of layers and the easy construction are improvements over the existing possibilities. PEDOT is the EC material on these devices, and different manufacturing ways are compared in order to detect the best possible candidate to use.

Photonic crystal fibres consist of a number of air capillaries surrounding by either a solid or an air core. The airhole distribution allows the control of the fibre properties such as dispersion, birefringence and nonlinearities. For the manufacturing of these fibres, a preform with the required hole pattern is heated in a furnace and drawn down in a drawing tower, being essential that the air-structure of the preform be retained in the final fibre. The holes in the preform affect the heat conduction during the heating process and may result in surface tension forces and distorsion of the structure. A numerical simulation of the heat transfer during the preform heating is presented. Both finite element and volume element methods were developed for the two-dimensional axisymmetric linear heat equation with nonlinear boundary conditions accounting for the radiative heat transfer at the external surface by means of the Stefan-Boltzmann law. The heating time required to reach a uniform temperature distribution within the preform was determined for several hole distributions including high numerical aperture fibres. The main result is that the microstructured preform heats up faster or slower than the solid one, depending heavily on both the preform's air void fraction and distance of the exterior hole ring to the boundary. A detailed explanation of these facts is given. Since the outer part of the preform reaches the fibre draw temperature before the central part, a distorsion of the hole structure of the resulting fibre can result, therefore, a careful optimization of the heating process is a due requirement in photonic crystal fibre fabrication in order to avoid any such asymmetries.

A new differential theory is developed for studying mode propagation in microstructured optical fibers (MOFs) with arbitrary cross section. The present method called Fast Fourier Factorization initially applied on gratings has been generalized to anisotropic and/or inhomogeneous media described in cylindrical coordinates. Thus, a new formulation of Maxwell equations are written in a truncated Fourier space taking account to the development truncations and discontinuities of opto-geometrical quantities. In the case of isotropic and homogeneous medium, the achieved first order differential set may be resolved with suitable algorithm which changes the boundary-value problem into an initial-value problem. To avoid numerical contaminations, the S-propagation algorithm is used. The numerical implementation of the FFF method is validated by comparison with the results computed with the Multipole Method for a six hole MOF. Then, new results for a MOF profile that cannot be directly studied with the Multipole Method are given.

We report on optical analogues of well-known electronic phenomena such as Bloch oscillations and electrical Zener breakdown. We describe and detail the experimental observation of Bloch oscillations and resonant Zener tunneling of light waves in static and time-resolved transmission measurements performed on optical superlattices. Optical superlattices are formed by one-dimensional photonic structures (coupled microcavities) of high optical quality and are specifically designed to represent a tilted photonic crystal band. In the tilted bands condition the miniband of degenerate cavity modes turns into an optical Wannier-Stark ladder (WSL). This allows an ultrashort light pulse to bounce between the tilted photonic band edges and hence to perform Bloch oscillations, the period of which is defined by the frequency separation of the WSL states. When the superlattice is designed such that two minibands are formed within the stop band, at a critical value of the tilt of photonic bands the two WSLs couple within the superlattice structure. This results in a formation of a resonant tunneling channel in the minigap region, where the light transmission boosts from 0.3% to over 43%. The latter case describes the resonant Zener tunneling of light waves.

We present an experimental work on porous silicon-based optical devices. Notch filters and planar waveguides are fabricated and characterized. Three different types of filters are shown, the first one is a stop band filter in the 1.5 micron region, where improvements have been performed (smoothing of the index profile, apodization and index matching). The second is a double Notch filter in the IR range, which blocks two different frequencies. Finally Notch filters in the visible range are shown, where porous silicon has been completely oxidized. Double layer waveguides are fabricated and characterized by atomic force microscopy, luminescence and prism coupling techniques. All the results shown are compared with numerical calculations. The photoluminescence changes and the refractive index variations for different annealing times are modeled in terms of oxidation of silicon and slow condensation of the porous structure.

Novel nonlinear optical polymeric film-producing nanocomposites based on bis(arene)chromium complexes incorporated into a CN-containing matrix have been developed. Polymer-precursors were prepared by the reaction of Cr(EtnC6H6?n)2 mixtures (n = 1,2,3) with CN-containing vinyl monomers (acrylonitrile, crotononitrile and ethylcyanoacrylate). The nonlinear-optical measurements in the absence of external electrical fields showed a "natural" anisotropy resulting from self-organization taking place during the film formation process. Measurements by the spectrally-resolved two-beam coupling method confirmed that the test composites exhibited a significant cubic nonlinear optical susceptibility of the ultra-fast electronic type.

Colloidal liquids usually appear turbid due to the strong multiple scattering of electromagnetic waves from the particles in suspension. As the concentration increases, particle interactions induce positional correlations which generally lead to a reduced optical density (higher transparency). However, the optical properties of a colloidal liquid can be manipulated by tuning the interaction potential between particles. In the presence of repulsive interactions, colloidal liquids show fascinating photonic properties despite their overall disorder. Short range structural order enhances the scattering strength at certain configurations while at the same time the total light transmission shows strong wavelength dependence, reminiscent of photonic crystals. The tunable optical properties of these photonic liquids suggest potential applications such as transparency switches or improved sunblockers. On the other hand the interplay between order and disorder and the scattering properties of these systems are strikingly similar to those discussed in the transport of electrons in liquid metals. Close to the Bragg condition the transport cross section becomes anisotropic and the transmission coefficient is reduced. In materials with high refractive index mismatch such an effect might open an alternative pathway to localization of light.

We analyze the impact of slow intraband relaxation and strong carrier localization on the characteristics of quantum dot (QD) lasers. Relatively long intraband relaxation times and population filling of the QD ground state lead to carrier pile-up on excited states, reducing the laser efficiency and maximum output power. Strong carrier localization in the QDs and consequently large thermal hopping time within the QD ensemble results in the absence of quasi-thermal equilibrium under lasing conditions, as evidenced by stimulated and spontaneous emission spectra. The impact of these specific physical characteristics of QD active regions on the laser high-frequency modulation properties is analyzed, particularly with regards to the differential gain, the gain compression and the linewidth enhancement factors.

Surface-grating distributed Bragg reflector (DBR) lasers have been explored and developed for fiber communications since last decade. These single-growth-step lasers have the advantage of no crystal re-growth as required in buried-grating lasers, making fabrication simpler. As to the device characterization, it has been known that Bragg reflectivity strongly affects threshold current, side-mode suppression ratio, and slope efficiency of a DBR laser. Unfortunately, precisely measuring the Bragg reflectivity is usually not feasible, since it is difficult to couple sufficient power under subthreshold condition for a stop-band measurement. On the other hand, either Bragg reflectivity or coupling coefficient obtained from theoretical calculations may deviate from the actual situation substantially, mainly because estimations of the coupling coefficient and the grating losses are not easy to achieve. Instead, we have characterized DBR lasers differently by using a novel self-consistent method. In the approach, the measurement for mode spacing at the Bragg peak was carried out, the coupling coefficient and the grating losses were then localized through the relation between effective and real grating lengths of the lasers. These precisely estimated device parameters were further put into the calculations of Bragg reflectivity, side-mode suppression ratio, threshold current density, and slope efficiency for the lasers. It was found that the optimal coupling strength, i.e. , for the highest side-mode suppression falls in the region between 1.0 and 1.2 with a laser geometry of La = 200 μm and Lg = 500 μm. Exact value of the above strength can be obtained, if a precise grating loss is given. Because the mode-spacing under the subthreshold would reflect the mechanism of gain-loss competition inherent in the laser cavity, and the estimations were repeatedly checked by experimental results during computation, we believe our results would be relatively more accurate than those obtained by using other methods. Detailed comparison among similar researches will be demonstrated on the conference. From our analyses, it can be found that operating at the optimal coupling strength not only provides the highest SMSR, but also gives acceptable slope efficiency and, however, would also come along with inevitable penalty of the threshold current, which is resulting from the higher DBR mirror loss with a shorter effective cavity length under the weaker Bragg reflection. An acceptable compromise can be made, if a slight increase, beyond the optimal coupling strength, is appropriately selected.

Recent progress in the development of 1.3 mm InAs/InGaAs/GaAs dots-in-a-well (DWELL) laser structures has led to efficient CW room temperature laser operation with low current thresholds. However, present devices suffer from non-ideal temperature characteristics due to gain saturation, consequence of the finite dot density and carrier escape due to the small energy separation between the quantum dot (QD) ground and first-excited states. In order to improve device performance, we have examined methods to increase the QD quality and density. In these studies, we have examined the effect of different growth parameters which strongly modify the InAs QDs structure such as temperature and thickness of barrier layers and thickness and composition of the well. Analysis by Transmission Electron Microscopy (TEM), Photoluminescence (PL) and atomic force microscopy (AFM) have identified the presence of defects arising from the complex interaction of QDs, which propagate through the structure into the upper regions being the primary cause of the poor electronic device characteristics. The use of optimized growth has allowed, however, the fabrication of a defect free five layer-stacked structure with record low threshold current density.

A Raman and photoluminescence study of a thermally annealed free-standing film of silica containing Si nanocrystals is reported with emphasis on laser-induced thermal effects. The Si-rich silica film on a Si substrate was prepared by a molecular beam deposition method and annealed at 1150 °C for 1 hour in an oven, which promoted Si nanocrystals. Then the Si substrate was partially chemically etched producing free-standing film areas with typical dimensions of 2 mm x 2 mm and thickness of 1.4 μm. For the free-standing film, we observed laser-induced (Ar⁺ laser at 488 nm) thermal effects on the light-emitting and optical properties. In fact, the light emission dramatically increases with the laser intensity, up to 4 orders of magnitude at 840 nm when the laser power increases from ~100 to 200 mW, and the absorption coefficient rises considerably as well. The anti-Stokes to Stokes Raman intensity ratio suggests a very high temperature of the free-standing silica film containing Si nanocrystals (~1200 K) upon exposure to a laser power of 100 mW focused to a ~40 μm spot, and the temperature probably rises up to ~2000 K for exposure to a laser power of 200 mW. The light emission measured at the high excitation powers is similar to blackbody radiation although some quantitative deviations occur for the temperature dependence. The Ar⁺ laser annealing strongly increases the crystalline Raman peak showing that thermal annealing at 1150 °C does not finish structural reorganization of the SiO_x material. In the waveguiding detection geometry, the spectral narrowing of the photoluminescence is observed and used to estimate the refractive index.

Macroporous silicon structures have been fabricated by electrochemical etching. Such fabrication process is known to result in the presence of a thin microporous Si layer at the walls of the macropores and at the surface. Photoluminescence measurements conducted in plan-view and cross-section exhibit a wide emission peak around 650nm which can be attributed to the microporous Si. The combination of a photonic crystal and a light emitter in one structure represents a potential for applications that has not been studied previously. This preliminary study shows the influence of the main fabrication parameters, namely the current density and the etchant solution, on the emission properties of the microporous Si layer.

Light emitting devices based on high-efficiency photoluminescence (PL) fluorescent nanocrystals have been investigated in terms of the generation of light from the structure using a variety of deposition methods. An automated modified layer-by-layer (LbL) self-assembly technique has been employed to produce multilayers of thiol-capped red fluorescing CdTe nanocrystals. Indium-tin-oxide (ITO) and aluminium electrodes were used as the electrodes. Morphological characterization was carried out through Schottky field effect (SFEG) SEM and atomic force microscopy (AFM). The structures built presented clear red electroluminescence (EL) to the naked eye. Turn on voltages were found to be in the range of 3-6 volts while the onset current was in the order of tens of microamperes. The role of structure homogeneity, the presence of pinholes and lifetime extension were features addressed during this investigation. Samples with a lifetime of continuous operation in air longer than 60 minutes and highly stable EL spectra were achieved; EL was visible to the unaided eye, although the brightness was still below the commercial standards and has not yet been qualified.

In silicon, direct electronic transitions leading to light emission have a low probability of occurrence due to the momentum mismatch between upper and lower electronic levels. Until recently, this had prevented the realization of the long waited silicon optical amplifier and laser. Raman scattering, which describes the interactions of light with vibrational levels, can be used as a way to bypass the indirect band structure of silicon and to obtain amplification and lasing. The Raman approach is very appealing because device can be made in pure silicon with a spectrum that is widely tuneable though the pump laser wavelength. While a new research topic, amplifiers with pulsed gain of 20dB and CW gain of 3 dB have already been demonstrated. Using parametric Raman coupling, wavelength conversion from 1550nm to 1300nm has been achieved. A distinguishing feature of silicon Raman devices, compared to fiber devices, is the electronic modulation capability. By integrating a p-n junction with the silicon gain medium, electrically switched lasers and amplifiers have already been demonstrated. These have many exciting applications. For example, the laser can be directly modulated to transmit data, and can be part of a silicon optoelectronic integrated circuit. At the same time, electrically switched amplifiers represent loss-less optical modulators.

We report on the recent progresses of our work on the design, fabrication and integration of micro/nano-scale photonic devices and optical waveguide arrays for optical printed circuit boards (O-PCBs) and VLSI photonic applications. The waveguides are designed and fabricated by thermal embossing and ultraviolet (UV) radiated embossing of polymer materials. The photonic devices include vertically coupled surface emitting laser (VCSEL) microlasers, microlenses, 45-degree reflection couplers, directional couplers, arrayed waveguide grating structures, multimode interference (MMI) devices and photodetectors in micro/nano-scale. These de-vices are optically interconnected and integrated for O-PCB assembly and VLSI micro/nano-photonics. De-tailed procedures of fabricating and implementing these devices and assembly of O-PCB are described. The O-PCBs are to perform the functions of transporting, switching, routing and distributing optical signals on flat modular boards or substrates. We report on the result of the optical transmission performances of these as-sembled O-PCBs up to 2.5 Gbps and 10 Gbps. For the design, fabrication, and VLSI integration of nano-scale photonic devices, we used photonic crystal structures. Characteristics of these devices are also described.

We have demonstrated a planar waveguide-based tunable integrated optical filter in indium phosphide (InP) with on-chip micro-electro-mechanical (MEMS) actuation. An air-gap Fabry-Perot resonant microcavity is formed between two waveguides, whose facets have monolithically integrated high-reflectivity multilayer InP/air Distributed Bragg Reflector (DBR) mirrors. A suspended beam electrostatic microactuator attached to one of the DBR mirrors modulates the microcavity length, resulting in a tunable filter. The DBR mirrors provide a broad high-reflectivity spectrum, within which the transmission wavelength can be tuned. The in-plane configuration of the filter enables easy integration with other active and passive waveguide-based optoelectronic devices on a chip and simplifies fiber alignment. Experimental results from the first generation of tunable optical filters are presented. The microfabricated filter exhibited a resonant wavelength shift of 12nm (1513-1525nm) at a low operating voltage of 7V. A full-width-half-maximum (FWHM) of 33 nm was experimentally observed, and the quality factor was calculated to be 46. Several improvements of the MEMS actuator, waveguide, and optical cavity design for the future devices are discussed.

Silicon optical receivers, operating at the optical communication wavelengths in the 1.3-1.55 μm range, have attracted much research effort. Unfortunately, the performance of the devices proposed in literature are poor because this wavelength range is beyond the absorption edge of silicon. In order to extend the maximum detectable wavelength, the most common approach, in the realization of Si-based detectors, is the use of silicon-germanium layers on silicon, anyway, requiring processes non compatible with standard CMOS technology. In this paper, with the aim to extend the operation of silicon-based photo-detectors up to the 1.3-1.55 μm range, an alternative approach is investigated: we propose the design of a resonant cavity enhanced Schottky photodetector based on the internal photoemission effect. The device fabrication is completely compatible with standard silicon technology.

Microspheres possess high quality factor morphology-dependent resonances, i.e., whispering gallery modes. These resonances have narrow linewidths necessary for applications to compact optoelectronic devices for wavelength division multiplexing. The morphology dependent resonances have high quality factors of 104 and 105 with channel spacings of 0.14 nm in glass and 0.05 nm in silicon microspheres.

Photonic crystal microcavities are defined by the spatial arrangement of materials. In the analysis of their spatial-temporal mode distributions Finite-Difference Time-Domain (FDTD) methods have proved its validity. The output of the FDTD can be seen as the realizations of a multidimensional statistic variable. At the same time, fabrication tolerances induce an added and unavoidable variability in the performance of the microcavity. In this contribution we have analyzed the modes of a defective photonic crystal microcavity. The location, size, and shape of the cylinders configuring the microcavity are modelled as having a normal distribution of their parametric descriptors. A principal component analysis is applied to the output of the FDTD for a population of defective microcavities. The relative importance of the defects is evaluated, along with the changes induced in the spatial temporal distribution of electromagnetic field obtained from the calculation.

We present a detailed study of the localized coupled-cavity modes in a photonic molecule formed from two dielectric spherical microcavities with CdTe nanocrystals, which show a multi-peak narrowband modal structure resulting from lifting of the mode degeneracy with respect to the azimuthal quantum number. The waveguiding through the coupled microcavities and wavelength switching effect is demonstrated. The feasibility of photonic molecules as the basis for a multi-channel, wavelength-tunable optical delay device is analysed.

A single photon source which generates transform limited single photons is highly desirable for applications in quantum optics. Transform limited emission guarantees the indistinguishability of the emitted single photons. This, in turn brings groundbreaking applications in linear optics quantum information processing within an experimental reach. Recently, self-assembled InAs quantum dots and trapped atoms have successfully been demonstrated as such sources for highly indistinguishable single photons. Here, we demonstrate that nearly transform limited zero-phonon-line (ZPL) emission from single molecules can be obtained by using vibronic excitation. Furthermore we report the results of coincidence detection experiments at the output of a Michelson-type interferometer. These experiments reveal Hong-Ou-Mandel correlations as a proof of the indistinguishability of the single photons emitted consecutively from a single molecule. Therefore, single molecules constitute an attractive alternative to single InAs quantum dots and trapped atoms for applications in linear optics quantum information processing. Experiments were performed with a home-built confocal microscope keeping the sample in a superfluid liquid Helium bath at 1.4K. We investigated terrylenediimide (TDI) molecules highly diluted in hexadecane (Shpol'skii matrix). A continuous wave single mode dye laser was used for excitation of vibronic transitions of individual molecules. From the integral fluorescence, the ZPL of single molecules was selected with a spectrally narrow interference filter. The ZPL emission was then sent to a scanning Fabry-Perot interferometer for linewidth measurements or a Michelson-type interferometer for coincidence detection.

We report on a guided wave asynchronous heralded photon source based on the creation of non-degenerate photon pairs by spontaneous parametric down conversion in a Periodically Poled Lithium Niobate waveguide. We show that using the signal photon at 1310\nm as a trigger, a gated detection process permits announcing the arrival of single photons at 1550nm at the output of a single mode optical fiber with a high probability of 0.37. At the same time the multi-photon emission probability is reduced by a factor of 10 compared to poissonian light sources.

Optical microcavities that contain single quantum dots have promising applications in quantum cryptography as sources of single photons. The realisation of efficient devices relies on the ability to fabricate electrically-pumped, high Q factor (Q>2000), wavelength-sized microcavities. In this work two approaches-oxide confined and micropillar structures-are compared by optical simulation. The modification of the spontaneous emission-Purcell factor and emission coupling efficiency-in such devices is treated semiclassically here, assuming the weak coupling regime. Hence, the spontaneous emission rate and direction may be computed using the effective mode volume, resonant wavelength, and quality factor of the optical modes in the microcavity. In the context of this work, the optical modes of rotationally symmetric microcavities are determined by solving Maxwell's vectorial wave equation in the frequency domain employing vectorial finite elements, subject to an open boundary, taking into account diffraction and radiation of electromagnetic waves. Consequently, the spontaneous emission properties of realistic microcavities without any restrictions regarding structure and size may be investigated. The optical mode solver is first calibrated with measured electroluminescence spectra of an oxide confined microcavity structure with oxide diameters ranging from 2.4 um to 0.7 um. Excellent agreement is achieved between measurements and simulations, which assures the predictive capability of the optical mode solver. For oxide confinements with diameters smaller than 1 um strong degradation of the Q factor and, hence, the Purcell factor is observed. Excessive diffraction losses are identified as the main cause of this effect in the present design. Furthermore, the advantages of micropillar structures with respect to this issue are demonstrated.

Recent advances in electro-optic transmitters for improved transmission performances are presented, with special focus on lithium niobate based devices for extended reach applications.

In this work we have built an electro-optical system for the transmission of low frequency analogue signals through optical fibre. The main goal was to achieve minimum pulse distortion with maximum dynamic range. The system has been used in the framework of the MAGIC telescope experiment for the transmission of the analogue output from a photo-multiplier dedicated to optical observation of astrophysical objects, in particular pulsars. The received signal polarizes an infrared LED (λ=850 nm), which converts the pulse into an optical analogue pulse. The electro-optical pulse is transmitted by means of a multi-mode optic fibre and finally amplified and filtered by the optical receiver. The whole system has been tested using a pulse generator resembling the type of pulsed signal we expect from pulsars, that is with period of about tens of milli-seconds and few milli-seconds wide. The system was calibrated in order to: a) obtain a fixed relation between the received pulse and the final data and b) enhance the dynamic range and low distortion. In what follows, we show the behaviour of the optical transmitter under different pulse shapes, amplitude and frequencies up to several hundred Hz. The electro-optical system has been mounted on the MAGIC telescope and tested successfully with the observation of the pulsed optical signal from the Crab pulsar.

Laser micromachining of semiconductor and Transparent Conductive Oxides (TCO) materials is very important for the practical applications in photovoltaic industry. In particular, a problem of controlled ablation of those materials with minimum of debris and small heat affected zone is one of the most vital for the successful implementation of laser micromachining. In particular, selective ablation of thin films for the development of new photovoltaic panels and sensoring devices based on amorphous silicon (a-Si) is an emerging field, in which laser micromachining systems appear as appropriate tools for process development and device fabrication. In particular, a promising application is the development of purely photovoltaic position sensors. Standard p-i-n or Schottky configurations using Transparent Conductive Oxides (TCO), a-Si and metals are especially well suited for these applications, appearing selective laser ablation as an ideal process for controlled material patterning and isolation. In this work a detailed study of laser ablation of a widely used TCO, Indium-tin-oxide (ITO), and a-Si thin films of different thicknesses is presented, with special emphasis on the morphological analysis of the generated grooves. The profiles of ablated grooves have been studied in order to determine the best processing conditions, i.e. laser pulse energy and wavelength, and to asses this technology as potentially competitive to standard photolithographic processes. The encouraging results obtained, with well defined ablation grooves having thicknesses in the order of 10 μm both in ITO and a-Si, open up the possibility of developing a high-performance double Schottky photovoltaic matrix position sensor.

Much attention is currently being paid to the materials and processes that allow one to directly write or to imprint waveguiding structures and/or diffractive elements for optical integrated circuits by exposure from a source of photons, electrons or ions. Here a brief overview of the results achieved in our laboratories is presented, concerning the fabrication and characterization of optical guiding structures based on different materials and exposure techniques. These approaches include: electron and ion beam writing of waveguides in (poly)-crystalline lithium fluoride, uv-laser printing of waveguides and gratings in photorefractive glass thin films, and fs-laser writing in tellurite glasses. Properties and perspectives of these approaches are also discussed.

A scalable multatom entangled system, capable of high-performance quantum computations, can be realized by resonant dipole-dipole interacting dopants in a solid state host. In one realization, the qubits are represented by ground and subradiant states of effective dimers formed by pairs of closely spaced two-level systems (TLS). Such qubits are highly robust against radiative decay. The two-qubit entanglement in this scheme relies on coherent excitation exchange between the dimers by external laser fields. This scheme is challenging because of the nanosize control and addressability it requires. Another realization involves dipole-dipole interacting TLS whose resonance frequency lies in a photonic band gap of a dielectric photonic crystal. A sequence of abrupt changes of the resonance frequency can produce controlled entanglement (logic gates) with improved protection from radiation decay and decoherence.

One of the most important optical properties of photonic crystals is that the waveguide dispersion relations can be tailored and allow for many non-conventional applications such as guiding and processing of the light signal. On the other hand, a variety of physical phenomena make liquid crystals (LC's) one of the most interesting subject of modern fundamental science. Moreover, in the last years, it has been proved that in order to obtain active tuning of the photonic crystals device a very promising approach can be achieved by infiltrating photonic structure with liquid crystals. On this line of argument, in this paper, the design of an electro-optical switch based on 2D silicon photonic band-gap structure and using liquid crystals as active medium is presented. We consider a T-junction PhC diplexer in two dimensional photonic crystals composed of silicon rods with square lattices with nematic liquid crystals as background. We prove that a range of frequency can propagate in both left and right waveguide of T-junction or in only one of them by applying an external electric field reorienting the liquid crystal.

Optoelectronic integrated circuits (OEICs) offering high bandwidth and high sensitivity as well are needed for the pickups of optical storage systems of the next generation, such as Blu-Ray or HDDVD. High bandwidth is necessary to enable high data transfer rates between the disk and the processing device, and high sensitivity allows to operate at low optical power and to deal with the lower efficiency of the photodiodes for blue light. Two methods will be presented to increase the bandwidth of the OEIC while maintaining high sensitivity. The first approach reduces the parasitic capacitance by placing the feedback resistor in a low-doped region. By this way the parasitic capacitance of the resistor is combined in series with the small depletion-layer capacitance of the low-doped region, which results in a drastically reduced effective capacitance. Using this method the 3dB-frequency of a standard one-stage transimpedance amplifier is increased by 55% from 67MHz to 104MHz. In the second approach the feedback resistor is replaced by a network that consists of two resistive voltage dividers that are coupled via a capacitor. Using such a capacitive-coupled voltage divider (CCVD) the feedback path is split into a low- and a high-frequency path and the effective band-limiting RC-constant is reduced. A bandwidth of 378MHz could be achieved. With a measured transimpedance of 212kΩ this results in a GBW of 80.3THzΩ.

Supercontinuum (SC) generation in optical fibers and waveguides is a phenomenon of increasing interest that has found applications in fields like time-resolved spectroscopy, ultrashort pulse compression, multiwavelength optical sources for WDM and optical frequency metrology. Most of the experiments performed up to now have been accomplished using femtosecond or picosecond-pulsed laser sources and special fibers such as highly-nonlinear photonic crystal fibers. Supercontinuum generation using continuous-wave laser sources was demonstrated only recently, but the initial results demonstrate that high power density (>1 mW/nm), broadband supercontinuums (more than 250 nm) can be achieved with good long-term stability. In this paper we show different experimental setups to produce continuous-wave supercontinuums in optical fibers. We show how the supercontinuum varies depending upon the pump source used in the experiment. We believe that such an incoherent source can have very interesting applications in optical fiber and component characterization, fiber sensing and optical coherence tomography for biomedical applications. As a sample application, we show that this source can be used to measure polarization mode dispersion (PMD) in optical fibers very accurately and with an extremely large dynamic range (>200 km).

The optical damage behaviour of different LiNbO₃ optical waveguides has been experimentally studied by measuring the intensity output of a single beam as a function of the intensity input. Parallel measurements of photovoltaic currents have been carried out as a function of the input intensity and they have been correlated with the optical damage data. The following LiNbO₃ guides have been studied and compared: proton exchanged (PE) belonging to the phases alpha, beta₁, beta₂ and reverse proton exchanged (RPE), and Zn in-diffused waveguides. The greatest intensity thresholds for optical damage, about 2x10³ times greater than that of the substrate, have been obtained in RPE guides (they support ordinary polarization and have similar nonlinear optic activity as the substrate) and beta₂ guides which support extraordinary polarization (they have no nonlinear optic activity). On the other hand, the lowest photovoltaic currents have been measured in beta_1,2-phases. As a function of the light intensity, the photovoltaic current exhibits a superlinear behaviour, strong in alpha-phase and weaker in Zn in-diffused and RPE guides. The results for optical damage are discussed in connection with those of photovoltaic currents, paying particular attention to the main mechanisms involved.

The technique of fabrication of one-dimensional anisotropic photonic crystals and microcavities based on porous silicon with birefringence has been developed. The spectra of linear reflectance demonstrate presence of photonic band gap (PBG) and microcavity mode located in the center of PBG. Their spectral position is tuned upon the sample rotation around its normal and/or rotation of incident light polarization plane. Enhancement of second- and third-harmonic generation for the fundamental wavelength resonant to the long wavelength edge of PBG due to phase matching is observed by angular spectroscopy. The angular positions of second- and third-harmonic peaks are determined by porous silicon dispersion and shifted for different polarisation of the fundamental wave due to the dielectric function anisotropy.

Light propagation through vortex matter in atomic Bose-Einstein condensates is examined. It is shown that vortex matter can be used as a photonic crystal by a refractive index enhancement scheme. Band structure of the vortex lattice is numerically calculated. Index enhanced vortex matter is shown to exhibit large refractive index contrast with the dilute thermal gas background in the vortex core. Depending on the depth of the index contrast full or directional photonic band gaps are found in the band structure. Experimental parameters required to generate band gaps in the visible region of the electromagnetic spectrum are calculated.

In recent years quantum information research has lead to the discovery of a number of remarkable new paradigms for information processing and communication. These developments include quantum cryptography schemes that offer unconditionally secure information transport guaranteed by quantum-mechanical laws. Such potentially disruptive security technologies could be of high strategic and economic value in the future. Two major issues confronting researchers in this field are the transmission range (typically <100km) and the key exchange rate, which can be as low as a few bits per second at long optical fiber distances. This paper describes further research of an approach to significantly enhance the key exchange rate in an optical fiber system at distances in the range of 1-20km. We will present results on a number of application scenarios, including point-to-point links and multi-user networks. Quantum key distribution systems have been developed, which use standard telecommunications optical fiber, and which are capable of operating at clock rates of up to 2GHz. They implement a polarization-encoded version of the B92 protocol and employ vertical-cavity surface-emitting lasers with emission wavelengths of 850 nm as weak coherent light sources, as well as silicon single-photon avalanche diodes as the single photon detectors. The point-to-point quantum key distribution system exhibited a quantum bit error rate of 1.4%, and an estimated net bit rate greater than 100,000 bits-1 for a 4.2 km transmission range.

This work is devoted to the first experimental observation of optical features in spectra of reflectance and third-harmonic generation of the finite one-dimensional photonic crystals based of the porous silicon, which caused by "surface" modes of an electromagnetic field, similarly to surface states of semiconductors and dielectrics. Semiconductor surface states correspond to electronic wave which total reflect from potential barrier crystal-vacuum as well as crystal lattice due to Brag interference. Therefore the electrons can propagate only along the crystal surface. Similar effect can observed in electromagnetic spectrum of photonic crystals. Although ordinary photonic crystals have not potential barrier crystal-vacuum for photons but they have modified density of modes at the surface. The surface waves existed at the interface of two optically different media can be observed using attenuated total reflectance configuration whereas the change of density of modes gives a sensitive tool to observe optical properties in the surface region. For observation optical features associated to surface states of photonic crystal we have to create the photonic crystal with few layers - finite photonic crystal. Also we can observe changes of electromagnetic density of modes by using third-harmonic generation spectroscopy. Dependence of resonances of third-harmonic generation on number of layers in the structure was observed. Increase of Q-factor of photonic crystals lead to wash out optical features of surface modes in a linear spectrum, whereas the nonlinear optics remains sensitive to eigenmodes.

In this work, we present an analysis of harmonic frequency transmission filters based on one-dimensional photonic crystals using a Fourier transform approach. This approach relates the photonic crystal transmittance with the Fourier transform of the logarithmic derivate of their refraction index profile. We compare this Fourier approach with the exact transmission calculated by means of the transfer matrix method. We study the accuracy of different functions proposed in the literature that relate the Fourier transform of the index profile with the transmittance. This Fourier approach provides a more intuitive understanding of the transmission properties of one-dimensional photonic crystals. We experimentally demonstrate these properties by using coaxial cables of different impedances. This kind of electrical system is easier to perform experimentally and reproduces, in the radiofrequency range, the properties of one-dimensional photonic crystals.

We study the photonic band gap formation in 2D photonic crystals comprising rods covered with a thin interfacial layer. The dielectric constant of the interfacial layer is different from that of the rods and background material. The rod together with the surrounding interfacial layer can therefore be treated as a single rod having a core and cladding regions. We study how the thickness and the dielectric constant of the cladding material affect the properties of photonic gaps in 2D photonic lattices. Specifically, we consider triangular and honeycomb lattices consisting of air rods drilled in silicon matrix and silicon rods in air, respectively. Photonic band simulations of such structures are presented performed using both finite-difference time-domain and plane-wave expansion methods. We show that the physical properties of the cladding layer strongly influence the photonic gap parameters. In particular, the existence of dielectric cladding reduces the absolute PBG in case of air rods drilled in a dielectric host, but may lead to larger absolute gaps in case of dielectric rods embedded in air. We also discuss the practical technological feasibility of these structures and their experimental realization.

Fluid-solid interfacial phenomena are a subject of much interest. In the adsorption phenomena, the adsorbent experiences the action of the molecular forces inducing strains. In this paper, we experimentally investigate adsorption phenomena in porous silicon microcavities by spontaneous Raman scattering. Polarised Raman spectra are measured in a backscattering configuration using a diode laser at 404 nm. We observe a reversible blue shift of the Raman spectra exposing a porous silicon multilayer to air saturated with vapor of pentane or iso-propanol. We ascribe the shift of the Raman spectra to the strain in porous silicon due to the adsorption in the pore walls.

We present in this work the effects of the rapid thermal annealing on the optical properties of InGaAsN single quantum wells grown on two different kind of misoriented GaAs (111)B substrates: 1° toward [-211] and 2° toward [2-1-1]. An increase of more than one order of magnitude of the photoluminescence emission is shown, as well as a shift towards higher energies of peak emission of the quantum well. This blueshift was found to be greater for the samples grown on the 2° misoriented substrates than for the first misorientation. These samples were grown by molecular beam epitaxy simultaneously, to assure tha same growth conditions for both samples. Different annealing temperatures were used to find the optimum optical properties for the InGaAsN quantum wells on GaAs (111)B. A comparison of the electrical characteristics of p-i-n diodes processed using as grown and annealed samples is presented. Finally, the application of the RTA optimization to InGaAsN laser devices grown on GaAs (111)B is presented.

An electro-optically tunable erbium-doped fiber ring laser with a side mode suppression ratio of ~ 51.2 dB and a 0.062 nm linewidth is demonstrated. Wavelength tuning is achieved with a hybrid liquid crystal Solc structure used as an intracavity tunable filter. The laser wavelength is tuned over 28.6 nm with a tuning rate of 2.38 nm/V.

A lot of progress have been recently realized concerning the laser performances at 1.3 μm. However, extending the emission of (Ga,In)(N,As) lasers above 1.3 μm with good performances is still challenging, since it is reported that the threshold current density significantly increases. In order to extend the lasing wavelength above 1.3 μm, while keeping good laser characteristics, we have optimized the growth of (Ga,In)(N,As)/GaAs quantum wells (QWs) grown by molecular beam epitaxy in view of realizing laser structures. During the growth of a laser structure the QW is "self"-annealed due to the growth of the upper AlGaAs cladding layer at high temperature. It is important to know the effect of this self-annealing on the QW optical properties. For that purpose, we have realized in situ thermal annealing on QWs grown at different temperatures and with different nitrogen composition. Separate confinement hetero-structure laser diodes with a single In_0.4Ga_0.6As_1-xN_x (x=0.015, 0.021 and 0.033)/GaAs QW have been grown, combining a low growth temperature and a high in situ annealing temperature. The broad area devices have a room temperature threshold current density of 1500 A/cm² and emit around 1.34 μm just above threshold. Furthermore, increasing the nitrogen composition extends the lasing operation up to 1.44 μm with a threshold of 1755 A/cm² and even to 1.52μm with a 4060A/cm² threshold.

The ladder method for solving the linearized Boltzmann equation is developed to deal with a non-parabolic conduction band. This is applied to find the low field Hall mobility of electrons in bulk GaN_xAs_1-x using the band-anticrossing (BAC) model, which predicts highly non-parabolic energy dispersion relations. Polar optical, acoustic phonon, piezoelectric, ionized impurity, neutral impurity and nitrogen scattering are incorporated. In finding an exact solution to the linearized Boltzmann equation, we avoid the unrealistic assumption of a relaxation time for inelastic scattering via polar optical phonons. Nitrogen scattering is found to limit the electron mobility to values of the order 1000 cm²V^-1s^-1, in accordance with relaxation time approximation calculations but still an order of magnitude higher than measured values for dilute nitrides. We conclude that the non-parabolicity of the conduction band alone can not account for these low mobilities.

Flat panel display technology constitutes the fastest growing segment of the semiconductor industry. Presently, the majority of display related research is focused on the application of electrooptic effects due to the ease and efficiency of molecular reorientation with an applied voltage. One such area of study is the surface stabilized ferroelectric liquid crystal (SSFLC) display, which has many advantages over conventional cathode ray tubes as well as other types of liquid crystal displays. Antiferroelectric liquid crystal (AFLC) displays have unique electrooptical properties such as tristate switching behaviour, fast response, intrinsic analogue grey scale and a wide viewing angle that lead these materials in very attractive candidates for their potential use in high-resolution flat panel displays and microdisplays for computers and TV. To become a competitive display technology, they should work at video frequency and give full colour and a significant number of the grey levels. These features depend on the AFLC material used in the display device as well as the addressing schemes employed. We present a new programmable driver for addressing passive matrix AFLC displays based on a microcontroller system. This prototype was built with commercial electronic subsystems and it is able to range voltage levels for the row selection of ±40V and has a minimum time resolution of 5 microseconds to shape the frame complete (selection pulse, bias, well and reset slots). The driver can address a 16x160 pixels AFLC display. A grey scale will showed in a preliminary 4x4 pixels AFLC display by using this prototype.

This paper presents a novel light modulator based on the technologies of liquid crystal diffractive optical elements (LCDOE) for a recordable optical pickup head with switching capability on single-beam data writing and multiple-beam data retrieving. The method of Dammann's phase grating was adopted on the LCDOE pattern design for generating seven diffracted orders. The diffraction pattern was etched on transparent conducting glass substrate to act as the electrodes of the modulator and the LCDOE was made by the fabrication processes of liquid crystal devices. The experimental results show that the multiple-beam LCDOE has the function of generating seven diffracted beams with equal light intensities while applying a voltage to the device. By adjusting the amplitude of the voltage, that accordingly changes the difference between the refractive indices of the ordinary and the extra-ordinary rays, the diffraction efficiency can be properly optimized. The switching capability is controllable by turning the voltage on or off. Besides, the polarization-selective effect is verified and an advanced multiple-beam pickup design in integrated type is also proposed.

The use of Light Emitting Diodes (LED) offers a multitude of advantages over conventional illuminating displays in various fields (traffic, publicity, screens for public events and so on). Each pixel of these displays is normally formed by a collection of different color LED's. These "clusters" of LED are used to correctly reproduce colors. In this paper we developed a color performance characterization method. The input is the light emitting spectrums of LED's and their uncertainties derived through the control of manufacturing processes.

Edge emitting photonic crystal (PhC) laser are the keystone opening the way to highly integrated planar photonic circuits. Most of the geometries investigated to date rely on the use of the hexagonal lattice which offers a fully opened photonic band gap. However, it was recently demonstrated that the square lattice based W1 waveguide geometry can provide single mode lasing across the gain whole spectral window (over 150 nm demonstrated under optical pumping). This rather unique property is of high interest for designing high yield, integrated, single mode lasers arrays. In this paper, we show that lasing occurs due to 2nd order DFB effect. Based on 2 and 3 dimensional FDTD computations, we show that the spectral selectivity of the square lattice arises from in plane and out of plane diffraction. We study the tunability options provided by this geometry using FDTD models. We show that whilst C-WDM is compatible with simple design schemes using lattice period variations, WDM and DWDM specifications require the use of a rectangular deformation of the lattice.

Tilted short-period fibre gratings (SPFG) couple the LP01 core mode to contra-directional core and cladding modes and can be used as optical fibre sensors and devices, mainly in reflection. Tilted long-period fibre gratings (LPFG) couple LP01 core mode to co-directional cladding and core modes and can be used as optical fibre sensors and devices in transmission. In this work we present the study and design of two optical devices based on both tilted SPFG and LPFG for mode conversion. The first proposed device is composed by a tilted LPFG and a tilted SPFG, both of them inscribed in the core of a few-modes fibre. Moreover it is used an optical circulator, which guides the light reflected in the second grating to the output. This optical fibre structure could be used in optical filtering and sensing due to the high sensitivity to the intrinsic or extrinsic perturbations of the spectral response in transmission and in reflection of the tilted LPFG and SPFG, respectively. By means of a proper structure it is possible to design an optical filter with two peaks due to different effects and to measure three different parameters. The another proposed device is composed by a LPFG and a 45-degrees tilted SPFG and based on a polarization mode conversion for filtering and sensing applications.

A simple method to extract the far-infrared dielectric parameters of a homogeneous material from terahertz signals is explored in this paper. Provided with a reference, sample-probing terahertz signal and a known sample thickness, the method can determine the underlying complex refractive index of the sample within a few iterations based on the technique of fixed-point iteration. The iterative process is guaranteed to converge and gives the correct parameters when the material thickness exceeds 200 μm at a frequency of 0.1 THz or 20 μm at a frequency of 1.0 THz.

In this work, 4x4 organic light emitting diode passive matrices based on new poli(2,7-fluorene phenylidene) (PFP) derivatives have been developed. The fabrication process has involved spin-cast heterostructures that improve charge carrier injection, processing of devices by means of photolithography, together with metallic contact evaporation. Electroluminescent diodes using different polymer derivatives as active layer, and different geometries, have been fabricated and compared. Electrical characterization was carried out in terms of pulsed current-voltage (I-V) measurements. Dependence of the threshold voltage on active material and structural parameters is obtained from the I-V curves, yielding values from 10 V to 25 V. Electroluminescence spectra recorded from the new PFP based devices, as well as commercial polymers, are in good agreement with similar devices found in literature. Finally, experimental data have been fitted using a theoretical model considering several injection and transport mechanisms, including thermionic, reverse, tunnelling, ohmic and space charge limited currents.

The potential of 1.3um GaInNAs SQW laser diodes for high speed operation is experimentally investigated in this paper, computing the differential gain, dg/dn, at a temperature range suitable for most network applications (293K-348K) and the small signal modulation bandwidth. The investigation begins with a basic characterization calculating the T0, with a value of 56K in a range of temperatures of 293K-318K. The lasing wavelength at 293K is found to be 1250nm with a linear temperature dependence of 0.377nm/K. Secondly, the paper presents a detailed study of the modulation bandwidth of the device, obtaining a value of 6.06Ghz for the maximum modulation bandwidth at 293K. In a range of temperatures of 293K-318K, the modulation bandwidth is found to decrease only slightly with the temperature with a slope of 0.0088Ghz/K. Finally, the paper explains the temperature behaviour obtained for the modulation bandwidth studying the temperature dependence of the differential gain, dg/dn. For this evaluation, the value of the differential gain with the current (how the peak gain changes with the sub-threshold bias current applied to the sample), dg/dI, is obtained using the Hakki-Paoli method. Using impedance measurements, a relation between the carrier density, n, and the bias current applied to the laser, I, has been obtained. With this relation, we obtained the differential current with the carrier density, dI/dn. Then, we calculated the differential gain dg/dn = dg/dI * dI/dn. To conclude we saw how the differential gain, dg/dn, has been found to have similar temperature behaviour as the small signal modulation bandwidth.

A low temperature MEMS process integrated with an infrared detector technology has been developed. The integrated microsystem is capable of electrically selecting narrow wavelength bands in the range from 1.6 to 2.5 μm within the short-wavelength infrared (SWIR) region of the electromagnetic spectrum. The integrated fabrication process is compatible with two-dimensional infrared focal plane array technology. The demonstration prototypes consist of both HgCdTe SWIR photoconductive as well as high density vertically integrated photodiode (HDVIP®) detectors, two distributed Bragg mirrors formed of Ge-SiO-Ge, an air-gap optical cavity, and a silicon nitride membrane for structural support. The tuning spectrum from fabricated MEMS filters on photoconductive detectors indicates a wide tuning range and high percentage transmission. Tuning is achieved with a voltage of only 7.5 V, and the FWHM ranged from 95-105 nm over a tuning range of 2.2 μm to 1.85 μm. The same MEMS filters, though unreleased, and with the sacrificial layer within the optical cavity, have been fabricated on planarised SWIR HDVIP® photodiodes with FWHM of less than 60 nm centred at a wavelength of approximately 1.8 μm. Finite element modelling of various geometries for the silicon nitride membrane will also be presented. The modelling is used to optimize the filter geometry in terms of fill factor, mirror displacement versus applied voltage, and membrane bowing.

In this work, an optoelectronic device that provides the absolute position of a measurement element with respect to a pattern scale upon switch-on is presented. That means that there is not a need to perform any kind of transversal displacement after the startup of the system. The optoelectronic device is based on the process of light propagation passing through a slit. A light source with a definite size guarantees the relation of distances between the different elements that constitute our system and allows getting a particular optical intensity profile that can be measured by an electronic post-processing device providing the absolute location of the system with a resolution of 1 micron. The accuracy of this measuring device is restricted to the same limitations of any incremental position optical encoder.

An all optical autofocus has been designed and tested for tight line width control in a high NA laser photoplotter system. The laser system is based in a GaN semiconductor laser with power 30 mW and wavelength 405 nm. The advantage of using this laser, despite the relatively long wavenlength, is compactness and easy for high frequency modulation. The autofocus system is based in a secondary 635 nm GaAlAs laser without need for wavelength, neither power stabilization. The two beams are delivered coaxially through the focusing lens by means of a dichroic beamsplitter. Focusing lens need no correction for chromatic aberration, as this is compensed by appropriate autofocus beam divergence. After reflection in the sample, the autofocus beam is separated from the returning writing beam and then guided to a collimation sensor, in which defocus of about 1/20 of the Rayleigh range of the writing beam can be detected and compensated by an analogue PID electronic control. Stable linewidth within 5% is achieved with different numerical aperture focusing lenses.

The coupling between waveguides via cavities fabricated in 2D photonic crystals is investigated within a numerical framework. We demonstrate that the symmetry of the modes plays an important role in light propagation through waveguides coupled by cavities. Two different situations are addressed: the structures are defined varying the geometrical parameters and varying the dielectric constant ε. In both situations we show that if the symmetry of the waveguide mode does not correspond to that of the localized mode of the cavity the coupling is negligible.