We have proposed and demonstrated a vertically coupled microring resonator filter as an Add/Drop wavelength filter. The ultra-compact ring resonantor can be realized by the ultra-high index contrast waveguide (=34%) consisting of glass core (n=1.80) and air cladding and the vertically coupled configuration, where a microring resonator with a few tens micron radius is stacked on the crossing point of cross-grid bus waveguides. The cross-grid topology of busline waveguides and very small ring radius enables a dense integration of filter circuit. To achieve the 3D integration, we developed a novel fabrication process of flat-top waveguide using a so-called lift-off process and the SOG (Spin-On-Glass), and successfully obtained a very smooth and flat surface of lower waveguide with a step height less than 0.01μm. In addition, to manipulate the center wavelength after fabrication, we developed two trimming methods; one is the use of UV-sensitive polymer for the over-cladding, and the other is the direct UV irradiation to the ring ocre made of Ta₂O₅-SiO₂ compound glass. Utilizing the former method, the channel spacing of filter array was precisely controlled within 0.5nm, which can not be achieved by the control of ring radius.

The fabrication and the optical properties of sol-gel high quality DBRs and microcavities are described and the emission of the europium ions included in the cavity observed. The microcavities are constituted of an SiO₂ half wave Eu³⁺ doped active layer inserted between two sol-gel Bragg reflectors. These reflectors are formed by a stack of alternated quarter wave films of SiO₂ and TiO₂. Films were deposited by a dip coating method. To fabricate high quality Bragg mirrors, a large number of layers has to be stacked, but sol gel thin layers develop internal stresses during the drying and firing processes, leading to defects and cracks into the stacked films. The study of the stresses in the layers shows that a short 900°C layer annealing solves this problem and the number of stacked layers can be greater than 60 without cracks. A microcavity with 7 doublets Bragg mirrors has been fabricated using this process. Eu³⁺ luminescence modification due to the cavity effect, intensity enhancement and modification of the lineshape, has been observed, showing a cavity quality factor of 1200. The reflectivity factor of the associated Bragg mirrors reaches 99.8% for seven alternated SiO₂/TiO₂ layers.

Photonic crystal angle elements fabricated in silicon-on-insulator (SOI) are reported. These elements are modelled using three-dimensional finite difference time domain (FDTD) method. Photonic crystals have a two-dimensional trigonal lattice structure with cylindrical air columns. The period of the crystal is approximately 420 nm and the cylinder diameter is about 330 nm. Defect creation is performed by removing air columns from certain lattice sites. The SOI-layer is one micron thick and it also defines the column height. The FDTD modelling results imply that photonic crystal angle elements with lower height do not exhibit proper light transmission at the telecommunications wavelength window, 1550 nm. FDTD modelling results give higher transmission for TE-polarised light than for TM-polarisation. For better light coupling a taper element with widened waveguide end is designed.

A new kind of Erbium doped heavy fluoride glass Er:ZBLALiP has been studied. Microspheres were fabricated with this fluoride glass. Whispering Gallery Mode laser spectra around 1550 nm were analyzed for different sphere diameters and Erbium concentrations (from 0.01% to 0.2% by mole) under pumping by a fiber taper at 1480 nm. Red-shift effect on the frequencies of both fluorescence and laser spectra is experimentally observed when the pump power is increased, originating from thermal effects. A spectroscopic technique based on the green upconversion fluorescence is used to compute a loading effective temperature for the Er:ZBLALiP microsphere and this further allows us to calibrate the properties of the microsphere laser in terms of the thermal expansion as well as the variation of the refractive index.

A family of narrow linewidth integrated optical distributed Bragg reflector- (DBR-), distributed feedback- (DFB-), and DBR-/DFB-coupled cavity lasers with Er-doped LiNbO₃ single-mode waveguide is reviewed. They have one or two photorefractive gratings in Fe-doped waveguide sections. Two types of DBR-lasers have been developed. The first type has a cavity consisting of one Bragg-grating in a Ti:Fe:LiNbO₃ waveguide, a gain section with Ti:Er:LiNbO₃ waveguide, and a multi-layer dielectric mirror deposited on one polished end face. The second DBR-cavity consists of two gratings in Ti:Fe:LiNbO₃ on both sides of the Er-doped waveguide. Their power characteristics and spectral properties were investigated. Single-frequency operation could be achieved in the latter case at various wavelengths in the Er-band (1530nm <λ< 1575nm) with up to 1.12mW output power. A DFB-laser with two lowest-order modes has been demonstrated with a photorefractive grating in a Ti:Fe:Er:LiNbO₃ waveguide; it is combined with an integrated optical amplifier on the same substrate. Moreover, an attractive DBR/DFB coupled cavity laser has been developed and investigated. Its cavity consists of a photorefractive Bragg grating in the Ti:Fe:Er:LiNbO₃ waveguide section close to one end face of the sample, a Ti:Er:LiNbO₃ gain section and a broadband dielectric multi-layer mirror of high reflectivity on the other end face.

Er³⁺/Yb³⁺-codoped 92SiO₂-8TiO₂ planar waveguides, with 1.2 mol% Er and molar ratio Er/Yb of 2, were fabricated by rf-sputtering technique. The active films were deposited on silica-on-silicon and v-SiO2 substrates. The parameters of preparation were chosen in order to optimize the waveguides for operation in the NIR region with particular attention to the minimization of the losses. The thickness of the waveguides and the refractive index at 632.8 and 543.5 nm were measured by an m-line apparatus. The losses, for the TE₀ mode, were evaluated at 632.8 and 1300 nm. The structural properties were investigated with several techniques such as Secondary Ion Mass Spectrometry, Energy Dispersive Spectroscopy and Raman Spectroscopy. All waveguides were single-mode at 1550 nm. An attenuation coefficient of 0.5 dB/cm at 632.8 nm and 0.1 dB/cm at 1300 nm were measured. The emission of ⁴I_13/2 → ⁴I_15/2 of Er³⁺ ion transition with a 40 nm bandwidth was observed upon excitation at 981 and 514.5 nm in the TE₀ mode. Back energy transfer from Er³⁺ to Yb³⁺ was demonstrated. Photoluminescence excitation spectroscopy was used to obtain information about the effective excitation efficiency of Er³⁺ ions by co-doping with Yb³⁺ ions.

We report on a novel high density ECR plasma deposition system based on matrix-distributed configuration specifically designed for large area applications. System is capable of depositing uniform high quality silica films with rate of up to 10 nm/s onto 300 mm wafers. Films are grown from silane and oxygen, while nitrogen is used for doping. Optical properties of the layers have been assessed by UV-visible ellipsometry while their chemical composition have been evaluated by ERDA and RBS techniques. FTIR spectroscopy was used to evaluate quality of the films for application in communications. Preliminary data show that films are perfectly stoichiometric and contain hydrogen in amount between 1 and 4 per cent, depending on experimental conditions. We have also deposited films doped with nitrogen doping and were able to control precisely refractive index of the material with simple gas flow regulation and in-situ kinetic ellipsometry measurements.

A new chemical nanotechnological route for the preparation of fully densified doped SiO₂ coatings with thicknesses in the low µm-range on Si- and SiO₂-wafers has been developed. Beside pure SiO₂ coatings, that might be useful as a buffer layer on silicon, silicate layers with increased refractive index are needed for planar waveguide application. Therefore, a synthesis for the preparation of nano particulate sols was developed, thus allowing the incorporation of dopands like Al₂O₃, PbO and Er₂O₃ for passive and active layers. Alumina was incorporated for the improvement of the Erbium solubility in active components. The coating sols consist of an organic binder, dissolved in a suspension of nanoscaled silica particles (10 nm in diameter) and dopands and were applied on Si- and SiO₂-wafers by spin coating. After removal of the binder at 500 °C, investigated by IR-spectroscopy, highly porous (nD = 1.23) but transparent doped silica layers were obtained. The densification of the layers was examined by measuring the refractive index by ellipsometry as a function of the densification temperature. Completely densified layers with thicknesses between 1.7 µm (doped SiO₂) and 6.5 µm (doped SiO₂) were obtained at temperatures between 1000 °C (doped SiO₂) and 1100 °C) (pure SiO₂). The layer thickness and unevenness was determined by interferometric measurements. The optical loss of Al₂O₃ and PbO doped layers was measured by prism coupling, the Er₂O₃ doped layers with Er³⁺ concentrations of up to 2.5 mole % show fluorescence around 1500 nm with a fluorescence lifetime of about 3.6 ms.

Widely tunable lasers are promising sources for future high-capacity dense wavelength divison multiplexing and photonic switching systems. These devices can be used for sparing in the cold standby mode, restoring in hot standby restoring, rerouting wavelength rerouting or conversion, or fast switching in all-optical networks. Tunable lasers need to demonstrate some featuers such as wide tunability range, optical output power of 10 dBm or more, cost and structure similar to those of commercial DFB lasers. High performance devices would require low laser chirp, high modulation speed, small size and very high reliability. For system applications, requirements on the tunable laser reliability are very stringent. Reliability studies and appropriate related testing procedures are necessary to define stability of tunable lasers and their expected lifetime. In this paper we propose some reliabilty test 'strategies' useful for qualification of tunable lasers with reference to some critical issues of the main technologies used to achieve the tunability feature.

Full optical characterization of planar nonlinear waveguides is of major importance for the assessment of reliable fabrication processes of integrated all-optical devices. A high accuracy in the design of the waveguide parameters fixing the refractive index profile (typically optical depth and index change) and in the knowledge of their wavelength dependence are mandatory for the realization of nonlinear integrated optical devices that meet phase matching conditions and achieve highly efficient interactions. Conventional characterization techniques, such as m-lines spectroscopy, do not always fulfil the accuracy requirements especially in the case of very thin waveguides. Moreover additional preliminary determination of the refractive index of the substrate is often required. In our laboratory we developed different non-conventional optical characterization techniques to overcome the main problems related to nonlinear waveguides and, in particular, to proton-exchanged (PE) waveguides in lithium niobate or lithium tantalate that are the most commonly used waveguides for all-optical devices. Different methods will be presented. In most cases, both radiation and guided modes are exploited in the characterization process. The new techniques proposed allowed a full optical characterization of the ordinary and extraordinary refractive indices of the substrates and index profiles of the exchanged layers for single-mode and multimode PE waveguides and the determination of the Sellmeier dispersion curves. Experimental results on typical waveguides will be presented. A new method, based on prism coupling, for the measurement of waveguide losses will also be discussed.

In response to demand for higher volumes and greater product capability, integrated optoelectronic device processing is rapidly increasing in complexity, benefiting from techniques developed for conventional silicon integrated circuit processing. The needs for high product yield and low manufacturing cost are also similar to the silicon wafer processing industry. This paper discusses the design and use of an automated inspection instrument called the Optical Surface Analyzer (OSA) to evaluate two critical production issues in optoelectronic device manufacturing: (1) film thickness uniformity, and (2) defectivity at various process steps. The OSA measurement instrument is better suited to photonics process development than most equipment developed for conventional silicon wafer processing in two important ways: it can handle both transparent and opaque substrates (unlike most inspection and metrology tools), and it is a full-wafer inspection method that captures defects and film variations over the entire substrate surface (unlike most film thickness measurement tools). Measurement examples will be provided in the paper for a variety of films and substrates used for optoelectronics manufacturing.

Fabrication characterization and operation stability of Zn-indiffused integrated optical devices in lithium niobate are described. Two examples of the operation of active waveguides fabricated by this technique are presented: laser operation of Nd³⁺ doped channel waveguides, and blue light generation by Quasi Phase Matching (QPM) using periodically structured substrates. In both cases n_e-polarized high power denstiy CW-optical beams are involved and stable room temperature operation is sustained.

We realized one and two dimensional periodic ferroelectric domain structures obtained by an electric-field poling process applied to 500μm thick Lithium Niobate crystal samples patterned by means of interference lithography. The fringe pattern is realized using a Michelson interferometric set-up and a He-Cd laser. We report on the appearance of high density and micrometer-sized single dot domains aligned along the direction of the interference fringes, as consequence of overpoling procedures. These structures are similar to those induced by back-switching. The effect seems to be originating by inverted domains’ merging under the photoresist fringe pattern after spreading. We investigate the possibility to obtain a highly regular and homogeneous dot-structure which can find application for photonic crystals technology and nonlinear optics.

We present a broadband DBR recorded with violet light (441.6 nm) by use of a holographic technique into Tiindiffused channel LiNbO₃ waveguides, which were doped by proton-assisted copper exchange, giving unique possibility to reach an extremely high modulation of refractive index (≥5x10^-4) within photorefractive grating. In a first approach we obtain a reflectivity of 17 % and bandwidth (FWHM) of 1.2 nm for IR light with center wavelength 1534.3 nm. Finally, we present the experimental data on specific spectral response of an asymmetric Fabry-Perot interferometer formed by broadband DBR and air-waveguide interface.

The conditions of HNbO₃ precipitation on the lithium niobate single-crystal and titanium diffused lithium niobate were studied. It has been shown, that the maximum of HNbO₃ precipitation corresponds to the highest humidity of atmosphere at the annealing temperatures of 800-850°C for 5-10h. Moreover, the application of humid atmosphere during the annealing of LN at 600-850°C does not ensure in full measure the lack of LiNb₃O₈ precipitation.

The topmost surface of crystal after all stages of proton-exchanged Ti-indiffused LiNbO₃ waveguide preparation was studied using atomic force microscopy and high energy electron diffraction. The formation of the flat terraces with minimal height step ~0.24 nm as a result of high temperature annealing has been detected. The global changing of crystal surface morphology induced by Ti diffusing was observed. Ion exchange has no influence upon surface microrelief. No new phase formation on the surface was detected. The stability of refractive index was investigated.

We report the achievement of buried single-mode waveguides in special Boro-Aluminum-Silicate glass. The waveguides are characterized by very low propogation loss (<.01dB/cm) and negligible birefringence. The optical mode at the input and output ports is essentially identical to the mode of a standard single-mode optical fiber. We fabricated and tested several devices and report here 1×8 and 1×16 powers spitters and an interleaver defined for a 100GHz DWDM network. Due to the low birefringence of the waveguides, the TE and TM responses of the device are undistinguishable by customary characterization equipment. In addition we report a technique for permanent trimming of the otpical circuit by localized heating. This unique advantage of ion-exchange technology, allowed us the adjustment of devices' parameters at post-fabrication stage. As an example, the trimming of a 2×2 directional coupler manifested here in the control of coupling coefficient value over a wide range (0.04-1.5). The process control was such that a target value of 0.5 for the coefficient was accurately attained. The same process enabled us the tuning of the interleaver to the ITU grid within 10pm accuracy.

A nonlinear integrated optical device, presenting an intrinsic bistable behaviour by means of the Kerr effect produced by counterpropagating beams, is presented. The proposed feedback mechanism, which preserves the spatial shape of the beams, is based on the transverse modal coupling of the beams to optical fibers through integrated multilenses. An optimum waveguiding design is presented to allow both the fabrication of this device by hybrid integration on glass and show the results of bistability.

Transmission phase gratings have been designed and fabricated in glass samples via implantation of helium and nitrogen ions of energies in the 500 keV - 1.6 MeV range, through photoresist masks. Both mono- and multienergy implantations have been applied. Diffraction efficiencies of the gratings as function of the energy and dose of the ion implantation were measured.The phase profiles of the lines of the gratings have also been measured directly via interference and phase contrast-microscopy and scanning electron microscopy. Diffraction efficiencies up to 20 % have been obtained.

A survey of the most common silicon-on-insulator (SOI) substrates and waveguide structures, as well as an evaluation of their applicability in optical telecommunication at the 1550 nm wavelength is presented. The design, fabrication and characterization of straight and bent SOI waveguides, as well as a thermo-optical SOI switch are described. The propagation loss of the realized SOI waveguides is below 0.25 dB/cm and thermo-optical switching is demonstrated at 10 kHz. The effect of cladding material on top SOI ridge waveguides on the polarization properties of straight and bent waveguides, as well as on directional couplers, is discussed. Both polarization independent and polarization maintaining waveguides are demonstrated. Finally, a basic principle of multi-step SOI waveguides is proposed. As examples of the potential in multi-step processing, efficient coupling between different rectangular, ridge and photonic crystal waveguides, ultra-small bends, waveguide mirrors, and extremely short multi-mode interference couplers are described.

Silicon oxynitride (SiON)- technology has been widely accepted for realizing integrated optical devices for application in optical telecommunication. Some of the severe requirements put in this field to devices and hence to technology are more relaxed in sensing applications, but other ones pop up in this area. These differences are explained from the general requirements put on the performance of integrated optical sensors performance and they are analyzed with respect to their consequences for applying SiON technology. Data about the technology are given. Application of the technology is illustrated on some chemo-optical sensors, a Mach-Zehnder interferometer, a polarimeter and a bend sensor, which have been developed in the MESA+-institute.

Fast pulse-generating laser sources at 10 GHz are commercially available. For future communications system applications of these light sources at 40 GHz, we developed a passive, fully integrated optical 10 to 40 GHz time-domain multiplexer. This device is very compact (16×5 mm²) and robust, whereby its miniaturization and robustness are based on the high-index-contrast silicon-oxynitride (SiON) waveguide technology used. This 4X multiplexer consists of two cascaded asymmetric Mach-Zehnder structures. Thereby a total of three directional couplers and two delay lines of 50 ps and 25 ps, respectively, are cascaded. Because of the high SiO2-SiON index contrast of 3.8 % it was possible to realize a multiplexer device with bending radii of less than 1.0 mm in an ultra-compact double-folded design. The slightly unbalanced attenuation in the delay lines was pre-compensated by the directional coupler design, i.e. by detuning from 50 % : 50 % coupling ratio. We demonstrated experimentally that with a fundamentally mode-locked 10 GHz Er:Yb:glass laser source at the design wavelength of 1535 nm our 4X multiplexer produces a 40 GHz pulse train with < 0.22 dB pulse-to-pulse power variation and < 350 fs timing jitter. Although the current device is designed for 40 GHz, its principle can be applied to 160 GHz or higher, provided that suitable pulse sources are available.

In the last decade, the advances in the MEMS technology lead to the integration of optical structures with MEMS. This association between MEMS technologies and integrated optical structures may provide complex functionality such as sensing, modulation or switching. Optical MEMS integrated on silicon are very attractive in terms of potential for cheap mass production and compatibility with CMOS technologies. In this paper we present the technology of SiON waveguide fabrication including aspects of PECVD and micromachining. PECVD process optimisation in order to increase the waveguide performances is presented. Finally the integrated opto-mechanical sensing structures are discussed.

This paper presents novel approaches on fabrication technology for micromachined spatial light modulators that are based on thin deformable viscoelastic layers. These layers are formed between two chips. The bottom chip contains an array of interdigitated electrode structures, where each structure represents one pixel. The top chip contains the mechanical layers which are transferred to the elastic layers by means of bulk etching techniques. This results in a high quality reflective surface with a 100% optical fill factor over the active region. Flexibility in choice of coatings gives the devices the potential to operate in specific spectral ranges with high load handling capability. The top chip is coated with a 50nm nitride layer onto which a 80nm aluminum layer is deposited. After curing of the intermediate viscoelastic layer, the entire device is placed in an elastomer holder and the bulk silicon is etched away in a 33wt% KOH solution. Devices were fabricated with electrode sizes in the range of 10 to 100μm and a 5μm thick viscoelastic layer. Experiments have shown far-field scattering as a result of 300V potential difference applied between the electrode. Biasing the membrane will lower this potential requirement to make integrated electronics possible. Applications can be found in high-end projection displays, optical lithography and optical communication networks.

In the past the optical component market has been mainly driven by performances. Today, as the number of competitors has drastically increased, the system integrators have a wide range of possible suppliers and solutions giving them the possibility to be more focused on cost and also on footprint reduction. So, if performances are still essential, low cost and Small Form Factor issues are becoming more and more crucial in selecting components. Another evolution in the market is the current request of the optical system companies to simplify the supply chain in order to reduce the assembling and testing steps at system level. This corresponds to a growing demand in providing subassemblies, modules or hybrid integrated components: that means also Integration will be an issue in which all the optical component companies will compete to gain market shares. As we can see looking several examples offered by electronic market, to combine low cost and SFF is a very challenging task but Integration can help in achieving both features. In this work we present how these issues could be approached giving examples of some advanced solutions applied to LiNbO₃ modulators. In particular we describe the progress made on automation, new materials and low cost fabrication methods for the parts. We also introduce an approach in integrating optical and electrical functionality on LiNbO₃ modulators including RF driver, bias control loop, attenuator and photodiode integrated in a single device.

One of the main problems in modeling guided wave devices in silica is the determination of the proper input parameters to the model. In this paper, we propose a method to determine five critical parameters: the depth, the length, the refractive index, the loss, and the thermo-optic coefficient of the silica waveguide. The finite difference method is used for the calculation of the optical modes in waveguides with a step index profile. The Beam Propagation Method (BPM) is used to analyze the test structures of the test-chip. The test set includes a planar waveguide, a symmetric Mach-Zehnder structure, an asymmetric Mach-Zehnder structure, and a series of planar waveguides with different lengths. This test-set is designed based on 1um Optical Integrated Circuit (OIC) technology.

We report a beam deflection technique that exploits electric-field controlled deflection and total internal reflection at the interface between two anti-parallel domains realized in a single crystal lithium niobate wafer. The LiNbO₃ z-cut sample was 500-μm-thick and was photolithographically patterned and poled by means of an applied electric field, in order to realize two adjacent regions of opposite domain orientation. The boundary between these domains should be very regular and free from residual stress, but in practice, a small residual index difference exists at the interface. An electric filed Ez applied across the interface region, produces equal in magnitude, but opposite in sign, refractive index variations between the adjacent anti-parallel domains. For sufficiently large index variation, and for grazing incidence geometry, that is when the incidence angle is between 87° and 89°, we obtain a high efficient beam deflection. Furthermore, if the incidence angle approaches the limit angle, which is about 89°, the Total Internal Reflection (TIR) occurs, producing an abrupt beam switch from transmission to reflection, characterized with a theoretical 100% switching contrast. However, the residual interface stress generates significant Fresnel reflection from this interface at high grazing angles, limiting the switching contrast ratio achievable at 20 dB. We present data obtained for wavelengths of 632.8 nm and 4.5 μm; at the latter wavelength we demonstrated the possibility to perform amplitude modulation faster than mechanical chopping, in a spectral region where no Pockels cells are available.

Multifunctional integrated optical chip (MIOC) for fiber optical gyroscope with linear digital output is developed. The technology is based on recently proposed High-Temperature Proton Exchange method. MIOC is used for industrial closed-loop fiber optic gyro.

Reflection second-harmonic generation (SHG) from the polished waveguide end face is used to investigate the second-order nonlinear optical properties of different types of PE LiNbO₃ and LiTaO₃ waveguides in different H_xLi_1-xNbO₃ and H_xLi_1-xTaO₃ phases: as-exchanged and annealed proton-exchanged (APE) waveguides, high-temperature proton-exchanged (HTPE) waveguides, as well as reverse proton exchanged (RPE) waveguides. A detailed correlation is done between the nonlinear properties, the processing conditions, crystal structure parameters, the refractive index changes and the optical losses of the waveguides. The intensity of reflected SH signal, strongly reduced after the initial proton exchange in both LiNbO₃ and LiTaO₃, is found to be restored and even increased after annealing. However, this apparent increase of the nonlinearity is accompanied by high scattering and a strong degradation of the quality of the SHG reflected beam in the region of initial step-like PE waveguides. The recently proposed HTPE technique has been shown to produce high-quality alpha-phase PE LiNbO₃ or PE LiTaO₃ waveguides with essentially undegraded nonlinear optical properties. It has been also shown that the nonlinear properties of annealed proton exchanged LiNbO₃ and LiTaO₃ waveguides can be effectively recovered by the reverse proton exchange technique.

Coupling efficiency in a directional coupler is influenced by the change of refractive index of substrate. It can be modulated by applying electric field and changing the coupling constant in an electro optic substrate. In this work a Ypropagating Ti:LiNbO₃ channel waveguide fabricated in a Z-cut LiNbO₃ substrate is simulated. Then, two waveguides with an enough separation gap are considered. Solving Maxwell’s equations and applying boundary conditions yields new eigenmodes of this structure. Using these new eigenmodes, coupling constant is obtained. For obtaining eigenmodes of coupled system, a recently reported variational approach has been used. Then, performance of the sensor was studied by applying electric field. It changes refractive indices in this structure, which gives new eigenmodes and new coupling constants. Simulation results show variations in coupling constant with the change of electric field; these changes of output optical power level can be used to measure the applied electric field.

Optical measurement of voltage because of its excellent advantages is studied by several research groups. In this paper, two optically voltage measurement method based on periodic structure have been introduced. First one is based on Bragg reflection effect. The coefficient of reflection from a periodic layered medium depends on properties of periodic structure. In this work a periodic structure on LiNbO₃ substrate was considered and under a high voltage electric field perpendicular to surface of layers, refractive indices of substrate have been changed. Performance of reflection versus applied electric field was calculated. Second method was based on Guided-mode resonance effect. Guided mode resonance effects in waveguide grating structures results in sharp variations in the intensity of the observable propagation waves. When a waveguide grating structure is illuminated with an incident light beam, part of the beam is directly transmitted and part is diffracted and trapped in waveguide layer. The trapped light is then rediffracted and it can interfere destructively with the transmitted or reflected light and show transmission or reflection anomalies. This phenomenon is sensitive to constitutive parameters of structure; therefore, it can be used in order to electro-optic voltage measurement.

In this paper tuneable optical filters based on liquid crystal Fabry-Perot interferometers (LCFPI) are presented. Liquid crystal (LC) devices are lightweight and suitable for compact arrays with a large number of pixels, as shown in high resolution flat panel displays. The fabricated filters offer a high finesse (119) and a wide tuning range. The devices are coupled to standard single mode fibers by fiber collimators. For all filters the layer structure of a standard passive LC display is used, adding only two reflective layers. Dielectric mirrors (R = 0.98) are used to achieve high finesse and low insertion losses (-4.8 dB). The cost can be further reduced by using thin gold layers, acting as electrodes and mirrors (R = 0.9) at the same time. The finesse of the Gold-FPIs is about 30 and the measured insertion loss is -10 dB. Additionally, a twisted nematic (TN) structure is investigated. Using this orientation, the polarization dependence of the device is reduced with increasing tuning voltage.

In computer architecture bandwidth and memory latency represent a major bottleneck. One possibility for solving these problems is the use of optical interconnections with their inherent capability for large fanin and fanout, low skew, etc. Today the possibilities to produce integrated chips with optical and electronic connections are advanced and the barrier for their adoption in computer systems gets smaller. The European Union project 'High-Speed Opto-Electronic Memory Systems' (HOLMS) aims at demonstrating the feasibility of an optical bus system for CPU memory access. The bus system is based on planar integrated free-space optics (PIFSO) in combination with fibre and PCB integrated waveguide optics. The goal is to demonstrate a novel architecture of low latency memory access. Here, we will discuss the task of the free-space optics. The assignment of the PIFSO is to perform all fanin and fanout operations for the interconnection between CPU and memory. Longer distances like connections between CPU and memory will be broadcasted by waveguides in the PCB; and fibres are used to combine two PCBs to a multiprocessor system. The first task consists of the design and the realization of the interface between the PIFSO and the PCB integrated waveguides. Besides the optical coupling, it is the main aspect to find an optical solution that allows large mechanical tolerances in the packaging of the different parts of the system. The large number of optical lines and their fanout and fanin are a challenge for design and construction, too. Design issues will be discussed and first experimental results will be presented.

The present work relates to the design, the fabrication and the spectroscopic characterisation of an efficient grating polarising structure which uses a quasi extra-cavity resonant grating in association with a multilayer to dictate the polarisation emitted by a semiconductor pumped solid-state Nd:YAG laser at 1.064 μm wavelength.

Optical waveguides in LiF crystals by high energy He⁺ ion-beam irradiation have been obtained. F₂ and F₃⁺ produced color centers increase refractive index of LiF crystals, allowing the formation of waveguides, and show strong photoluminescence activity in the green-red optical band. Details of the fabrication process and preliminary characterization data are reported.

In this work we present the study of step-index channel directional couplers which can be fabricated on a buffer planar guide in a such a way that they can be properly designed to support separable modal fields, though the index profile is non separable. The main advantage of this approach is the great simplicity in the analysis, design and fabrication of the directional couplers, or other different integrated strucutures, since it is possible to apply, for instance, the effective index method obtaining a quasi-exact solution for the modal fields. Analytical and numerical results will be presented to confirm that an accurate design of the operation properties of the directional coupler can be achieved.

The objective of this study was to find the relationship between process parameters and responses in deep silica etching for hybrid integration. The process parameters were the wafer temperature, oxygen addition, clamp material and process pressure. The responses to these parameters were sidewall roughness, profile of etched waveguide, the morphology of etched surface and critical dimension change. When the process parameters were varied, the change in responses could be interpreted by analyzing sidewall polymer thickness and selectivity. Polymer thickness and selectivity also have positive correlation. To investigate which parameter is dominant in determining the coupling efficiency between waveguide end facet and active device in application for hybrid integration, the propagation loss of waveguide with or without deep trenches were measured and analyzed.

In this paper, we report characterization of insertion losses, mode profiles and intensity distributions in channel LiNbO3 optical waveguide fabricated by High-Temperature Proton Exchange (HTPE). Optimal fabrication parameters were chosen in accordance with results obtained for test samples of a planar waveguide. A target wavelength of our optimization procedure was 810 - 840 nm, as fabrication of phase modulator used in sensor is developed. The guided mode intensity has been mapped by scanning near-field optical microscopy with a sub-wavelength resolution (<100 nm), simultaneously with observation of the topography of the scanned area (100 μm x 100 μm). These measurements offer important information about loss mechanisms in our waveguides.

Ferroelectric domain micro structuring of bulk Lithium Niobate is very useful for optoelectronic applications such as non-linear optics employing Quasi-Phase-Matching for efficient harmonic and parametric conversion processes or for the fabrication route for production of novel MEMS devices, like micro-cantilever beams. Quasi-Phase-Matching based applications require periodically reversed ferroelectric structures with periods of the order of micrometers. Precise control of the surface quality and of the domain structure of the micro structured materials is required such as in the case of optical MEMS applications. We here report on the application of Digital Holography as metrological tool for the inspection and characterization of the domain structures in bulk Lithium Niobate samples. This technique allows reconstructing both the intensity and the phase of the microstructures under test and it allows determining quantitatively the phase distribution. Several examples of application of the Digital Holography technique for the numerical reconstruction of the micro-topography of domain structure are presented and discussed.

Laser crystal integration using a neodymium-doped yttrium vanadate (or orthovanadate) laser crystal, and non-doped yttrium vanadate crystals that function as cold fingers has been demonstrated. In our bonding technique of YVO₄ crystals, a newly developed dry etching process was adopted in the preparation for contact of mechanically polished surfaces. In the successive heat treatment process, temperature optimization was essential to get rid of precipitation of vanadic acid caused by the thermo-chemical reaction in a vacuum furnace. The bonded surface of 5 mm × 6 mm was studied via optical characteristics and magnified inspection. In addition, we also compared the integrated crystal with a normal one in laser output power pumped by a CW laser diode. From these experiments, it was clear that the integrated Nd:YVO₄ laser crystal, securing the well-improved thermal conductivity, can increase laser output power nearly twice that of the conventional single crystal which was cracked in high power laser pumping due to its intrinsic poor thermal conductivity.

In this work we present theoretical and experimental results of influence of electric field on reorientational nonlinearity in homeotropic oriented nematics. In the analyzed configuration the light beam passing through the liquid crystalline layer induces the reorientation, which is observed in far-field diffraction pattern changes as a result of self-modulation effect. The created phase mask inside the nematic cell can be used in optical switching or to control the propagating direction of optical signals passing through the liquid crystalline cell. Both electric and optical field control the observed phase pattern dynamics. The response time in reorientational phenomena is large and its determination and reducing is very important issue for applications. Obtained results are in good agreement with theoretical prediction.

This paper highlights photonic crystal Mach-Zehnder structures that use W1 channel waveguide in 2D hexagonal photonic crystal structures and have channel orientation along GammaK directions. The FDTD software, Fullwave, from RSoft has been used to simulate photonic crystal channel waveguides, Y-junction and bend in order to design a complete Mach-Zehnder interferometer structure in epitaxial II-V semiconductor material for operation at 1550nm. It is our near-future aim to use these Mach-Zehnder structures as the basis for thermo-optic switching devices. Electro-Beam lithography (EBL) and reactive ion etching (dry-etching) processes have been used to fabricate these devices

The design of some 1D waveguiding photonic bandgap (PBG) devices and Fiber Bragg Gratings (FBG) for microstrain based sensing applications has been carried out by a model based on the Bloch-Floquet theorem. A lwo loss, very narrow passband GaAs PBG filter for the operating wavelength λ = 1.55 μm, having an air bridge configuration, was designed and simulated. Moreover, a resonant Si on glass PBG device has been designed to obtain the resonance condition at λ= 1.55 μm. Finally, a FBG-based microstrain sensor design has been carried out, having an array of 32 FBG. A complete analysis of the propagation characteristics, electromagnetic field harmonics and total field distribution, transmission and reflection coefficients, guided and raidated power, and total losses, enabled the optimization of the design in a very short CPU time.