This PDF file contains the front matter associated with SPIE Proceedings Volume 7056, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Photoinduced birefringence in the film made of our azobenzene copolymer was demonstrated using blue excitation laser beams and observed by a red probe laser beam. The birefringence values was obtained by polarimeter. The polarization state of the probe beam was changed by the photoinduced birefringent film when the polarization state is not agreed with the polarization state of the excitation laser beam. Then, a polarization component orthogonal to the polarization state of the incident probe beam was observed. Using the principle, an image pattern was recorded in the film using one-beam.

A stationary 2D axis-symmetric model able to evaluate the impurity distribution is developed by the finite element method for single-crystal sapphire fibers grown from the melt by the edge-defined film-fed growth (EFG) technique. The computations are carried out for two cases-one where the buoyancy is taken into account and the other where the buoyancy is neglected-using different vertical temperature gradients kg in the furnace. The dependence of the impurity distribution on kg and the Marangoni numbers Ma corresponding to the different surface tension gradients dγdT is analyzed. Computations reveal critical Marangoni numbers Ma_c determined by the fluid flow behavior, and that a smaller k_g assures the best homogeneity of the crystal over a wide range of d_γ/dT.

We present the results of the ab initio calculated electronic properties, first and second harmonic generation for the A^II B^IV N₂ (A^II=Be, Mg; B^IV =C, Si, Ge) compounds with chalcopyrite structure performed using the Linear Augmented Slater-Type Orbitals (LASTO) method. The second-order optical susceptibilities as functions of frequency for A^II B^IV N₂ are also presented. Specifically, we study the relation between the structural properties and the optical responses. Our electronic band structure and density of states (PDOS) analysis reveal that the underestimate bandgaps of these chalcopyrite AIIBIV N2 are wide enough (from 4eV to 6eV), direct transition and mainly located at Γ-point. Calcultion results show this new category wide-bandgap ternary nitrides has potential applications in optoelectronics.

Repetitive image reconstructions from a stratified reflection volume hologram have been shown, numerically and experimentally, that are coded by wavelength references satisfied by Bragg condition. Many holographic layers are recorded with red-sensitive photopolymers that are interleaved with slide glasses. The reflection comb responses have been measured by a wide-tunable laser diode that agree fairly with a rigorous coupled-wave analysis (RCWA).

Sapphire (single crystal aluminum oxide) is a material commonly used in optical, electronic and chemical applications due to its material properties. Sapphire is usually used for optical applications due to its ability to transmit from the Ultra Violet (UV) wavelengths into the mid Infra-red (IR) wavelengths. The transmission characteristics of the material is determined by various factors, however the impurities content seems to play a significant role. These impurities can either come from the growth process or from the starting raw material (commonly called crackle). We studied the effect of impurities of the starting raw material with specific interest in hydrogen's effect on the optical properties (absorption, transmission) of sapphire crystals grown by different growth techniques. We have characterized these growth techniques into two categories: A)Large Thermal Gradient Method: (Czochralski (Cz), Edge Defined Film Fed Growth (EFG) or Stepanov) B.) Low Thermal Gradient Methods (Kyropoulos, Heat Exchange Method (HEM)) We used the following starting raw materials ("crackle"): a. Vernuil crystals produced by different manufacturers b. High purity aluminum oxide powder c. High Purity Densified Alumina (EMT HPDAR) produced by EMT, Inc thru their proprietary patented technology. Through Nuclear Magnetic Resonance (NMR) analytical techniques, it was found that the hydrogen concentration is very high in Vernuil crystals or in aluminum oxide powder. Consequently, sapphire crystals grown using Vernuil starting material or aluminum oxide powder also have a very high Hydrogen content. Utilizing the same NMR analytical techniques, EMT HPDA^R starting material showed very low Hydrogen concentration. Thus, sapphire crystals grown from EMT HPDA^R starting material has a very low Hydrogen content. It was found that optical properties in sapphire crystals grown using EMT HPDA^R starting material are more uniform and have higher transmission than in sapphire crystals grown using as starting material aluminum oxide powder or Vernuil crystals.

In this paper, ultra low cross talk is achieved by using a resonant cavity at the intersection between two strip waveguides formed in a square lattice photonic crystal structure (PhC). Two PhC structures are studied: one consists of cylindrical rods and another consists of cubic rods. The Q-Factor of the cavity is changed by increasing the number of rods that form the cavity and by decreasing the spacing between the waveguide and the cavity. Our two dimensional simulation results show that the latter method resulted in cross talk reduction of more than 21 dB for both structures. The overall cross talk was -90.50 dB for the cylindrical rods structure and -105.0 dB for the cubic rods structure. The optimized PhC structures were fabricated on a silicon-on-insulator platform. The rods were buried in silicon oxide in order to maximize the photonic band gap and provide index guiding in the vertical direction.

In this work we present a method for creating an integrated optofluidic ring resonator (OFRR) laser system by embedding it in a low index polymer, polydimethylsiloxane (PDMS). Packaging the OFRR inside PDMS enhances portability, mechanical stability, and the ability to connect it to chip-based microfluidics. The OFRR retains high Q-factors even in the polymer (> 10⁶) and exhibits a low lasing threshold (<1 μJ/mm²). Additionally, the laser emission can be efficiently and directionally coupled out through an optical fiber or fiber prism in touch with the ring resonator. At 2.2 μJ/mm² pump intensity, the laser output from the fiber is 80 nW, corresponding to 50% power extraction efficiency. Our work will lead to novel design in lab-on-a-chip devices and micro total analysis systems for biological and chemical detection.

Single-beam phase conjugation (self-phase conjugation, or SPC) was observed in the ferroelectric crystal LiNbO₃:Fe using CW HeNe laser (wavelength 632 nm power 10-36 mW). Effective "out/in" reflection coefficient of phase conjugation (defined as the ratio the output phase-conjugated beam to the input laser beam measured before optical elements) was about 30%. For some crystals efficient phase conjugation was followed by the simultaneous generation of Fabry-Perot modes. Phase locking of two HeNe lasers and imaging of the amplitude objects with the help of self-phase conjugation was demonstrated. Appearances of additional beams (in transmission and reflection) have some analogy with the predicted behavior of the "negative-index materials".

Fiber SERS (surface enhanced Raman scattering) sensors have attracted significant interest in molecule sensing. In this paper, we briefly review our previous work on various configurations for fiber SERS probes, including side-polished fibers and various photonic crystal fibers (PCFs). In addition, we will report our recent experiments on a double substrate "sandwich" structure for fiber SERS probe. The approach is to coat one SERS substrate on the tip of a multimode fiber and mix the second substrate in solution with the target analyte molecules. Upon dipping the coated fiber probe into the solution, randomly formed structures of the two substrates will sandwich the analyte molecules in between. Our results show that the "sandwich" configuration exhibits significantly higher sensitivity than direct SERS detection.

A novel generation of sensors of strain, temperature, absolute and relative molecular concentration is reported. Such devices, based on 1-D photonic structures, rely on ultrastable laser sources, referenced to a fiber-based optical frequency comb synthesizer (OFCS). In particular, recent advances in the realization of two complementary laser sensors are presented. One is a spectroscopic facility which exploits frequency mixing in a periodically-poled LiNbO₃ crystal to generate highly coherent (a few hundred kHz linewidth) infrared radiation tunable in the 2.9-3.5 micron wavelength range. Such radiation can be coupled to high-finesse enhancement cavities to detect trace amounts of gases, including rare isotopes in natural abundance. The other system, making use of fiber Bragg grating components, provides strain and temperature sensing with extremely high sensitivities (about 100 fε, i.e. 10^-13 ΔL/L). Due to the remoteness guaranteed by the fiber coupling, these two systems can both be used in difficult environments and inserted in a multi-parametric network for real-time and continuous monitoring of large areas. Prospects for application in volcanic areas are also discussed.

The application of photonic crystals in biosensor applications has lead to the development of highly sensitive and selective sensor elements. The research efforts undertaken by this group have led to the development of a photonic crystal transducer that acts as a waveguide, nanofluidic flow channel, and resonant defect cavity. This sensor architecture shows promise for greatly enhancing the emission of naturally fluorescent or fluorescently-labeled biomolecules. Due to its transparency in the visible regime, GaN is a viable candidate for this photonic crystal biosensor application. This paper provides an overview of the sensor architecture as well as a discussion of one particular bottom-up approach to its fabrication. Molecular Beam Epitaxy (MBE) growth of heavily Mg doped GaN can result in inversion of the surface polarity from Ga-polar to N-polar GaN. This bottom-up approach includes patterning and etching of the Mg inversion layer, followed by re-growth of the opposite polarity to produce periodically poled GaN. Subsequent wet etching of N-polar regions then produces a GaN based photonic crystal structure. This process shows promise for achieving high aspect ratio, highly anisotropic nanostructures.

We report for the first time, a single mode, tunable, double-clad ytterbium-fiber (YDF) laser emitting in a wavelength range between 976 and 985 nm that operates using the re-imaging effect that occurs in multimode interference (MMI) devices. The system consists of an YDF with bare fiber cleaved ends. The forward end of this fiber is fusion spliced to a piece of 3 m of Samarium-doped- single-mode fiber with absorption measured at 980 nm of 0.3 dB/m, and at 1030 nm of 6 dB/m. The other end of the Sm⁺³ doped single-mode fiber is spliced to a 16.2 mm long multimode fiber (MMF) in order to induce the MMI self-imaging effect. From simulations, we found that, at this particular length, for the MMF, the light exiting will exhibit a maximum transmission for the 980 nm wavelength, while keeping a minimum for the 1030 nm wavelength. Near to the MMF facet, at a distance between 0 and 100 µm, we place a dichroic mirror which also helps in the selection of the wavelength emission. We calculated that 10 dB gain generated at 980 nm is enough to build up a laser since the total round-trip cavity losses are estimated to be 8.8 dB, whereas for the unwanted 1030nm get more than 60dB insertion loss in this setup. At the end, there is more than 1 dB for the effective gain at the preferred wavelength emission range which is enough to promote lasing at around 980 nm.

The paper presents theoretical and experimental investigations of the structure of the spatial distributions of strain amplitudes for an oscillating surface using an optical interferometer. A conventional Michelson interferometer and an interferometer containing an acousto-optic cell have been studied. It has been shown that the maximum possible sensitivity of the device is 0.001 Å, with the minimum strain amplitude reaching 0.001 Å. Practical advantages of the interferometer with an acousto-optical cell have been realized.

We derive mathematical criteria for a pair of guided modes which have the same parity, mutually parallel wave vectors along the guiding direction of the waveguide, but opposite directions of optical power flow in a negative-index slab waveguide using a graphical method. It is also proven that the so-called light trap mode corresponds to the degenerate mode of this pair. We also propose a waveguide structure in which guided light waves can be trapped via tunneling through thin metamaterial clad layers. This trap is temporary since the trapped light tunnels out completely after a short time.

In this paper, a novel all-fiber band pass filter based on a concatenated structure of multimode fiber, single-mode core mode blocker and a single-mode long period fiber grating was reported. It can simultaneously serves as a band pass filter and multimode-single-mode converter for interconnection between multimode fiber and single mode fiber network. The theoretical analysis, designing, fabrication and experiments result were presented.

Single-mode optical fibers for the mid-IR (λ=3-30μm) are needed for many applications such as IR fiber lasers and spatial filtering for nulling interferometry. In the past, we have already reported the design and fabrication of stepindex single mode fibers for the mid-IR. Index guiding photonic crystal fibers (IG-PCF) offer many advantages over step-index fibers, such as a wide spectral range, large mode area and low bending losses. So far, only limited success has been achieved in the development of such fibers, due to the lack of suitable materials that are transparent in this spectral range. We report here the design, fabrication and optical characterization of single-mode IG-PCFs for the mid-IR. Triangular and octagonal IG-PCFs were fabricated from silver halide polycrystalline materials which transmit well in the spectral range 2-20μm. The photonic crystal fibers were characterized by near-field and far-field measurements and they demonstrated a single-mode behavior with relatively low losses and a large mode area, in agreement with our simulations. As predicted from the simulations, the octagonal arrangement of the rods in the fiber resulted in a single mode fiber with lower losses, a better mode shape and a higher rejection of high order modes, in comparison to the triangular structure.

We continue a study of the equivalence particle principle applied to an optical spatial soliton which is a "narrow filament" that maintains its existence in a waveguide. Using this principle, expressions for acceleration, spatial frequency, spatial period and other variables for a spatial soliton can be derived from the solution of basic Nonlinear Schrödinger Equation. These results agree well with numerical simulations of the Modified Nonlinear Schrödinger Equation. If the expression of the acceleration is bounded in some cases this means the spatial soliton propagates with a swing effect. We go one step further in this theoretical study to investigate the effects of the swing effect with power law included in the Modified Nonlinear Schrödinger Equation.

A novel architecture of an optical filter for pulse compression in dense wavelength-division multiplexing (DWDM) systems is presented. We propose a comb filter for dispersion compensation within a transmission channel. A pair of chirped gratings with slanted grating lines is used. The effect of filtering is not based on resonances as used in Bragg gratings, but it is achieved by interferences of parts of the optical wave. Furthermore, the filter concept enables an amplification to compensate transmission losses. The filter parameters are adjusted by different phase shiftings of the grating lines. Their geometrical dimensions are equal for all grating lines. It will be shown, how different grating lengths and phase shiftings between the grating lines contribute to the transmission characteristic of the filter. We will give design rules for the chirp to develop appropriate filter functions for positive or negative dispersion values up to 1500 ps/nm while the linearity of the group delay is restricted to 6.5%. The performance of the structure will be presented by a filter designed for a DWDM-system with a channel distance of 0.4 nm.

An ultrafast light-activated magneto-optical modulator is demonstrated in this paper. This modulator is capable of 1 ns modulation speed and has a 1 mm clear aperture. The design of the modulator incorporates a photoconductive switch and enables a synchronized and jitter-free operation, which eliminates the need of any electrical or optical delay lines. These features make the current design very attractive in typical free-space pulse laser applications. To the authors' knowledge, this is so far the fastest MO modulator with such aperture size that has been reported.

Dual Band Wavelength Demultiplexer (DBWD) is designed to separate two telecommunication wavelengths, 1.31μm and 1.55 μm utilizing photonic crystals (PhC) in Silicon on Insulator (SOI). The waveguides formed in such PhC structures confine light horizontally by a photonic bandgap and vertically by total internal reflection. Plane Wave Expansion (PWE) method and Finite Difference Time Domain method are used to design and analyze the DBWD in Y type PhC. Numerical analysis indicates that the separation of two wavelengths with enhanced extinction ratio, transmittance and quality factor can be achieved, which confirms the superior performance of the proposed design of DBWD

We present a study of polarization rotation enhancement in birefringent magneto-optic photonic crystal waveguides and provide theoretical and experimental support for a novel type of photonic bandgap. The coupling between counter-propagating elliptically birefringent local normal modes of different order results in the formation of partially overlapping bandgaps and selective suppression of Bloch state propagation near the band edges. We use a bilayer unit cell stack model with an alternating system of birefringent states in adjacent layers. A magnetically tunable and large polarization rotation of the allowed Bloch modes near the band edges is computed theoretically and observed experimentally.

In this paper, the two different mechanisms of supercontinuum generation in single crystal sapphire fibers according to fiber lengths longer and shorter than dispersion length are theoretically and experimentally investigated. When the fiber length is shorter than the dispersion length, self-phase modulation is the dominant factor for supercontinuum broadening. A broad spectrum ranging from near-IR (1.2 μm) to the lower end of mid-IR (2.8 μm) is obtained. But, when the fiber length is longer than dispersion length, soliton-related dynamics with self-phase modulation is the dominant factor for supercontinuum. We further demonstrate that supercontinuum in a sapphire fiber can extend beyond the range of silica fibers by showing the spectrum from 2 μm to 3.2 μm. Also, we successfully apply the supercontinuum source generated from a sapphire fiber to IR spectroscopy. The spectra of pseudo-TNT chemical measured using our own supercontinuum source is in good agreement with those obtained by FTIR. Supercontinuum generation using a sapphire fiber, which has high damage threshold and broad transmission ranges can be used in many applications such as IR spectroscopy, broadband LADAR, remote sensing, and multi-spectrum free space communications.

A sensing configuration based on commercially available hollow-core photonic bandgap (PBG) fiber for the simultaneous optical detection of multiple gas samples is presented. Spectroscopic sensors based on microstructured fiber technology have been of recent interest. However, most designs have limited sensor response times due to long gas diffusion filling times for fiber lengths >1 m. Sensor response times that are shorter in duration unlike diffusion-limited filling times are reported. A length of PBG fiber with a 12.5 micron core diameter, an optical spectrum analyzer and a broadband light source were employed to operate in the transmission region where the absorption lines for sample gases, including acetylene and carbon dioxide, correspond to the near-IR region. A gas-filling time of 1 minute 30 seconds for acetylene to completely fill a ~2 meter length of PBG fiber at a pressure < 15 Psi was demonstrated. Reduced filling times that approach the sub-minute regime are possible, leading to shorter sensor response times. The sensitivity of the proposed system is also reported. Using the techniques presented, the detection of concentrations < 100 ppm for acetylene gas at pressures < 15 Psi is possible. The relatively low-loss PBG guidance mechanism (< 0.1 dB/m) confines light to the gas-filled region promoting long optical-field-interaction lengths (> 1 m) with small sample volumes (~μL) resulting in a compact, bend-insensitive rugged device with gas detecting sensitivities that have the potential to be higher than capillary based detectors.

Using 2D finite element modeling with the ability to solve the current continuity equations, carrier energy transport equation, Schrödinger and Poisson equations self-consistently, as well as the scalar wave equation for waveguiding devices, we have investigated the possible improvements of the device efficiencies by introducing transparent p-type contacts and multiple quantum shells (MQSs) in GaN / In_0.14Ga_0.86N / GaN / p-AlGaN / p-GaN core/multishell nanowires (CMS NWs). The addition of a transparent p-type current spreading contact was found to promote more uniform current injection into the CMS NWs, thus increasing the current injection efficiency. Despite the inclusion of a transparent ptype contact, the current density remained non-uniform and weighted towards the n-contact side of the NW. This asymmetry in the current density was found to be more important for higher injection current whereas it becomes much more uniform with decreasing injection current. Light generation with the transparent contact was found to become more uniformly distributed along the CMS NW, leading to more even light generation within the device in comparison to NWs without transparent p-type contacts. The replacement of single quantum shells (SQS) by MQSs in the active region of the nitride CMS NW-as has been used for conventional InGaN high brightness LEDs (HB-LEDs)-was found to be advantageous up to three quantum shells, increasing light generation from 80.47 to 94.04 W/m under a 4V bias.

Laser-induced domain inversion is a promising technique for domain engineering in LiNbO₃ and LiTaO₃. The ultraviolet-infrared laser induced domain inversions in MgO-doped congruent LiNbO₃ and near stoichiometric LiTaO₃ crystals are investigated for the first time here. Within the wavelength range from 351 to 799 nm, the different reductions of nucleation field induced by the focused continuous laser irradiation are systematically investigated in the MgO-doped congruent LiNbO₃ crystals. The investigation of ultrashort-pulse laser-induced domain inversion in MgO-doped congruent LiNbO₃ is performed with 800 nm wavelength irradiation. The focused continuous ultraviolet laser-induced ferroelectric domain inversion in the near stoichiometric LiTaO₃ is also investigated. The different physical explanations, based on space charge field and defect formation, are presented for the laser-induced domain inversion, and the solid experimental proofs are also presented. The results provide the solid experimental proofs and feasible schemes for the further investigation of laser-induced domain engineering in MgO-doped LiNbO₃ and near stoichiometric LiTaO₃ crystals. The important characteristics of domain inversion, including domain wall and internal field, in LiNbO₃ crystals are also investigated by the digital holographic interferometry with an improved reconstruction method, and some creative experimental results and conclusions are achieved.

Polarization data of a SM gyroscope coil may correlate to drift that provides a method to statically predict a performance range of a coil during manufacturing or at a minimum before integration into a FOG assembly. The Crossover Free (CF) coils described here are thermally symmetric and lack fiber crossovers. This design allows possible expansion of depolarized FOGs beyond the research environment. To that end a series of double sided CF gyroscope coils were manufactured and analyzed using a 4 channel fiber coupled polarimeter. In addition the coils were tested on a single axis rate table in a FOG testbed. A polarimeter was used to measure the output polarization state of the stand-alone coils and when integrated into an experimental FOG testbed. In addition Shupe data of the CF coils was taken to determine the thermal sensitivity of the coils. Coil geometry and construction, polarimetric and traditional drift data, and Shupe performance will be presented.

Due to the high-index contrast between the silicon core and silica cladding, the silicon waveguide allows strong optical confinement and large effective nonlinearity, which facilitates low cost chip scale demonstration of all-optical nonlinear functional devices at relatively low pump powers. One of the challenges in ultrafast science is the full characterization of optical pulses in real time. The time-wavelength mapping is proven to be a powerful technique for real time characterization of fast analog signals. Here we demonstrated a technique based on the cross-phase modulation (XPM) between the short pulse and the chirped supercontinuum (SC) pulse in the silicon chip to map fast varying optical signals into spectral domain. In the experiment, when 30 nm linearly chirped supercontinuum pulses generated in a 5 km dispersion-shifted fiber at the normal regime and 2.4 ps pulse are launched into a 1.7 cm silicon chip with 5 μm² modal area, a time-wavelength mapped pattern of the short pulses is observed on the optical spectrum analyzer. From the measured spectral mapping the actual 2.4ps temporal pulse profile is reconstructed in a computer. This phenomenon can be extended to full characterization of amplitude and phase information of short pulses. Due to time wavelength mapping this approach can also be used in real time amplitude and phase measurement of ultrafast optical signals with arbitrary temporal width. The high nonlinearity and negligible distortions due to walk off make silicon an ideal candidate for XPM based measurements.

This work presents a research in which a Twin Core Fiber (TCF) has been employed for designing a Mach- Zehnder interferometer and its behavior under the effect of thermal gradients has been regarded. From the coupled modes theory can be deduced that under the phase-matched condition-that is similar propagation constants in both cores of a TCF, the energy transported in the cores is the same, which is fundamental for developing this interferometer. This research required to design a thermal cavity and an automation circuit for applying thermal cycles to a segment of the TCF. The temperature was recorded by means of a thermocouple placed inside the thermal cavity and its signal was introduced into the computer where an instrumentation software (Lab View) designed for monitoring and controlling variables used this signal for controlling the on-off states of a power resistor and a refrigeration system for raising and lowering the temperature, respectively. It was observed that the optical power variations in a point of the interference pattern presented a weak dependence with the thermal cycles.

A key stage in production of the integrated optics devices is forming of microtopography on crystalline films. The current methods generally comprise two separate steps: producing of thin film and creation a topographical pattern on it. But the inherently large chemical stability of crystalline LiNbO₃ has effectively precluded the use of standard photolithographic patterning techniques. We present new approach based on the modified sol-gel technology using the photosensitive gel. In this case, the photolithography is used on the stage of dried gel whereupon the direct crystallization of patterned precursor film allows to create integrated optical element without subsequent etching of crystalline film. Presented method of patterned thin film preparation involves synthesis of photo-reactive complex of metal, which undergoes change under the UV light. This technology has allowed to obtain first samples of different types of waveguide devices.

Piezoelectric resonance contributions to the electrooptic coefficients in ferroelectric PZN-8PT single crystals were studied by a dynamic electrooptic measurement carried out using a continuous frequency scan over the range of frequency covering the sample's fundamental resonances. At certain frequencies relevant to piezoelectric resonance of a given mode, it is found that the E-field modulated optical transmission are greatly enhanced (> 2 orders of magnitude). Such enhancement is mode selective and scales with strain or the rate of change of dielectric permittivity. Instead of having linear dependence on the electric field, the piezoelectric resonance enhanced optical transmitted signal in this crystal shows a near linear response to the power of the modulating electric field.

The double threshold effect of ultraviolet laser-induced preferential domain nucleation in near stoichiometric LiTaO₃ is observed. The continuous ultraviolet laser beam (351 nm) is focused on the -z surface of the wafer, and the homogeneous electric field is applied simultaneously antiparallel to the direction of spontaneous polarization along the z axis. The double threshold effect includes both the primary and the secondary thresholds. The primary threshold is the minimum intensity to achieve the instantaneous preferential domain nucleation within the focus by the combined action of irradiation and electric fields. Below the dark nucleation field, the instantaneous preferential domain nucleation is achieved within the illuminated area when the intensity exceeds the primary threshold. The experiments prove that the domain inversion can be locally controlled by the laser irradiation. The secondary threshold is the minimum intensity to achieve the memory effect without any irradiation within the original focus. The memory effect of preferential nucleation is observed when the intensity is below the primary threshold and above the secondary threshold. The preferential domain nucleation of memory effect is investigated. The different physical explanations are presented for the instantaneous effect and memory effect. The space charge field created by the photoionization carriers is thought to be responsible for the instantaneous effect. The explanation based on the formation and transformation of extrinsic defect is presented for the memory effect.

In this paper, we experimentally verify that previously proposed idea of unequally spaced optical phased array can greatly reduce grating-lobes. As the verification purpose of our previous numerical design, a laser beam is passed through unequally-spaced slits, whose spacings are the same as the previous design. Interference patterns formed after both 4- and 8-channel slits clearly show that the grating-lobes can be greatly minimized. To realize the beam steering possible, optical waveguides array, which has unequally spaced design at the output ends is fabricated. The phase of each beam can be varied using fibers array wound around PZT tubes before each beam is coupled into the waveguides array. Interference patterns formed after the outputs of both 4- and 8-channel waveguides array show that the gratinglobes can be greatly reduced using unequally spaced optical phased array technique.

Because the efficiency of THz generation in air plasma is quite low, the residual power of input beam after THz radiation is generated in air plasma remains almost the same. A new method, multiple air plasmas, is proposed. The residual power can be used to induce other air plasmas and generate THz radiation again. The multiple air plasmas method provides a potential way for the development of the intense THz source. The preliminary experimental results confirm the theoretical prediction. The multiple air plasmas generated THz can be very useful for remote THz generation and standoff detection.

Crystal growth and spectroscopic characterization of Ni-doped MgGa₂O₄ belonging to inverse-spinel structure crystal family are described. Single crystals of this material were grown by floating zone method for the first time. Oxygen gas flow was essential to minimize evaporation of Ga₂O₃ during the floating zone crystal growth process. Bubble and inclusion-free crystals were obtained for the growth rate less than 5 mm/hour. Ni:MgGa₂O₄ single crystal was characterized by broadband fluorescence in 1100-1600 nm wavelength range and 1.6 msec room-temperature lifetime. It could be attributed to the transition of ³T₂(³F)→³A(²F) transition of the octahedrally coordinated Ni²⁺. The internal quantum efficiency of the near-infrared fluorescence was about 82 % for 1 mol% Ni-doped MgGa₂O₄ single crystal at room temperature. The new material is to be very promising for tunable laser applications covering the important optical communication, eye safe, 1100-1600 nm wavelength.

In this paper, superprism phenomena based on phase velocity has been studied. PCs composed of air holes of different shapes in a triangular lattice with constant filling fraction have been taken under study. The observation of superprism behavior has been made using angle sensitive and wavelength sensitive propagation of light. It has been found that the PC with hexagonal rod geometry yields the best behavior of the superprism in the case of angle sensitive propagation. For wavelength sensitive propagation PCs with hexagonal and circular air holes provide almost the same angular separation. Therefore we can conclude that the PC with the air-rod geometry of hexagon is the most suitable candidate for optical devices based on superprism phenomena.

High diffraction efficiency of each grating is desired to reduce light intensity loss when gratings are integrated to realize miniaturization for 3-D optical instruments in LiNbO₃ crystals. Based on jointly solving the two-center material equations, oscillating behavior of diffraction efficiency during recording and erasing process is investigated theoretically to realize maximized diffraction efficiency for integrated volume grating instruments in weak oxidized doubly-doped LiNbO₃:Fe:Mn crystals. Two nonvolatile gratings are integrated and nonvolatile diffraction efficiency for each grating exceeds 60%. These methods depend on the dopant elements and its concentrations, annealing (or oxidation-reduction) in doubly-doped LiNbO₃ crystals, and recording and sensitizing intensities and wavelengths. The experimental investigation will be performed to verify the calculated results.

The multimode interference (MMI) couplers, which operate at 1.55 microns in deep rib InGaAsP/ InP waveguide with large lateral confinement and tunable power splitting ratios, are of high interest in integrated optics. The gold contacts are applied on the top of waveguides where tuning is desired and the plasma effect will lead to negative refractive index change. The three-dimensional (3D) finite difference beam propagation method (FD-BPM) is used to model the tunable MMI couplers. The length of a 2×2 overlap-MMI is determined by FD-BPM, so the longitudinal position of tuning spots is obtained. The position of gold contacts with two types, the edge-pads or center-pad, are also determined. In our design, the length of MMI is 180 microns. If the width of pads is 50 micros and the refractive index is tuned from 0 to -0.027, the power ratio is tuned from50:50 to maximums 88.5:11.4. For deep rib structure, the effective index (EI) method can not be used to simplify the 3D waveguide to plane waveguide because its lower precision, and then the direct 3D FD-BPM simulation is necessary for the design of 3D MMI couplers.

SiO₂-based diffractive/refractive hybrid microlenses were fabricated by using femtosecond laser-induced nonlinear optical processes. Recently, hybrid devices have received much attention as important components for optical pickup systems and integrated sensors. SiO₂-based devices are particularly promising because of high transparency, physical and chemical stabilities. For these devices, microfabrication upon nonplanar substrates such as convex lenses, which is difficult for the semiconductor processes, is required. In this study, microFresnel lens patterns were directly written inside positive-tone resists upon convex microlenses of 240 μm diameters by using femtosecond laser-induced nonlinear absorption. The spot diameters are primarily determined at any position inside the resist by the region volume at which the nonlinear absorption occurs. Therefore, the precise patterns could be formed even upon the nonplanar substrates. After post-exposure-bake and development treatment, the patterns were transferred onto underlying lenses by CHF₃ plasma. Here, the etching depth was 1 μm. Consequently, SiO₂-based hybrid lenses with smooth surfaces were obtained. When He-Ne laser of 632.8 nm wavelength was coupled to this hybrid lens, the focal spot was 630 μm from the lens surfaces. This focal length agreed with theoretical value of 618 μm. More functional optical devices would be realized by improvement of fabrication processes.

Using split-step algorithm based on the fast Fourier transform and a fourth-order Runge-Kutta(R-K) method, we studied the second-harmonic generation(SHG) of high power laser with KDP crystal. The transverse walk-off effect, diffraction, the second-order and the third-order nonlinear effects of KDP crystal have been taken into consideration. Special attention has been paid to the influences of a kind of self-induced thermal effect. The phase mismatching quantity, the intensity distribution of output beam and the frequency conversion efficiency varying with the crystal temperature distribution have been analyzed. The calculated results indicate that self-induced thermal effects results in the temperature distribution in KDP crystal and the phase mismatching, then the phase mismatching leads to the decreasion of the conversion efficiency.

An optical system built with two Optune interferometers cascaded according to Vernier principle has attractive tunable band pass filtering properties for numerous applications. Several characteristics of Optune interferometer such as 0.2 dB insertion loss flatness across at least 90 nm interval, no tuning holes across 240 nm tuning range, quasi-periodic free spectral range and 1 dB insertion loss are key parameters to obtain a cascade with 0.1 nm band pass tunable across minimum 90 nm. Several properties of Optune interferometers are analyzed to build a cascade tunable across minimum 90 nm: the relationships between the free spectral ranges, bandwidths and tuning conditions. It is presented also a cascade prototype with two interferometers having 9.72 nm free spectral range and respectively 11.12 nm free spectral range. The cascade band pass is 0.1 nm tunable with 1 pm accuracy to any arbitrary wavelength across 150 nm free spectral range, without any tuning hole. It has 0.125 ms / 100 nm tuning speed, the insertion loss is less than 3 dB, 50 dB contrast, 0.5 dB flatness and 0.2 dB polarization dependent loss. A controller based on digital signal processor monitors the operation of the cascade to achieve optimum tuning performance.

We design air cladding tellurite (TeO₂), bismuth oxide (Bi₂O₃) based, and chalcogenide (As₂S₃) nanofibers, and calculate the chromatic dispersions. For each material, wavelength dependent propagation constants of the nanofiber are obtained from the exact solutions of the Maxwell's equations, and from the propagation constants the chromatic dispersion is calculated. We tailor the dispersion to zero at the communication wavelength, 1.5 μm, by proper selection of the core diameter of the nanofiber for all the above materials. We further explain the technique for flattening the zero dispersion in telecommunication window, using glass instead of air, as the cladding of the nanofiber structure. Using the glass cladding has the advantage of easy handling, specially, for the communication purposes. Further, the glass cladding causes larger effective index difference between various modes of the nanofiber, thus reducing the mode coupling. We present the numerical results of the dispersion flattening technique by assuming the borosilicate glass cladding to the chalcogenide As₂S₃ glass core nanofiber. With the borosilicate cladding the dispersion characteristics of the nanofiber change drastically and flattening of the zero dispersion is achieved at 1.408 μm wavelength, when the core diameter is 724 nm.

The phase-shifting errors mainly result from the imprecise movement of phase-shifter and the vibration of system. These geometric errors are classified into the positional inaccuracy and tilting of optics. And they can be represented as the longitudinal and transversal displacements of interferograms on the hologram plane. In this paper, we propose adaptive phase-shifting digital holography compensating these two displacements and this proposed method is based on genetic algorithm for finding optimized variables corresponding to real system. By computer simulations, the deteriorations in reconstruction image are modeled and the chromosomes are constituted. We find the fittest solution compensating the longitudinal and transversal displacements experimentally and present the reconstruction images by encoding the resultant holograms on a spatial light modulator.

We have observed generation of the electron beam by the pyroelectric crystal placed in the vacuum chamber. Different pyroelctric materials, Fe-doped LiNbO₃ and L-alanine doped TGS crystals, were tested. Crystals of L-alanine doped TGS (LATGS) were grown by evaporation of the solution with 10% initial concentration of L-alanine under T=45°C (somewhat below phase transition temperature T_C = 49.9°C). In this case crystallization proceeds immediately in the polar phase Heating/cooling cycles of the crystals in the vacuum (P~ 1-5 mTorr) produce uncompensated surface charges and strong electric field (~ 100kV/cm) on the polar crystal faces. These fringing fields ionize ambient gas and accelerate electrons to high energies (~100 KeV). For photosensitive LiNbO₃ crystal electrical charging and generation of electrons may be done by laser illumination, via photogalvanic effect. These generated electrons can be detected by the fluorescent ZnS screen or by the X-rays produced by placing copper plate in the electron beam. Model that explains and figures that depict the self-focusing of the electron beam is presented.

A 3D sensing method to describe an entire shape from many segmented measurements performed by projected fringe profilomety is presented. Unlike conventional algorithms, image registration is not required in this setup. Among all other integration schemes, this method is superior since it offers many major advantages, including: (1) very low computation cost for the data fusion, (2) reduced computational time, and (3) very high integration accuracy.

The speckle that is formed in coherent illumination confuses efforts to record an object's fine details. The confusion is particularly severe in optical metrology and microscopy. In this paper, a scheme using the empirical mode decomposition (EMD) to remove speckles is proposed. This makes it possible to accurately evaluate phases from a fringe pattern illuminated by a coherent light source.

We propose a projection scheme using a diffraction element for finding the absolute shape of an object with large depth discontinuities. Its application built into an endoscope to retrieve an object inside a body cavity is presented as well. Among all existing fringe projection schemes, this proposed method is notable for its compact design. Only one phase measurement is required. To inspect a dynamic object is desirable.

Recently magneto-optic spatial light modulators (MOSLMs) using magnetic garnet materials have advantages of high switching speed. However, these materials are difficult to be used in short wavelength range, so that it appears huge light absorption by magneto optic effect of transmittance mode (Faraday effect). This problem can be solved by using the materials of metal magnetic films for magneto optic effect of reflection mode (Kerr effect). We suggest the new method, which is the switching of pixels by heating the pixels with semiconductor laser until Curie temperature and changing the direction of the driving current at the same time, for developing high speed MOSLM in broadband using amorphous TbFe films. TbFe films were fabricated by RF sputtering using the Tb₂₁Fe₇₉target, and we have confirmed Kerr rotation (over 0.4 degree from 400nm to 800 in wavelength), the curie temperature (130 degree Celsius), and the switching of pixels of 16μm × 16_µm by heating the pixels with semiconductor laser and controlling magnetization from external bias magnetic field (15Oe) and driving current (20mA) of coil at 403, 532 and 633nm wavelength.

The subject of this project is the design; analysis, fabrication and characterisation of first order Bragg Grating optical filters in Silicon-on-Insulator (SOI) planar waveguides. It is envisaged that this work will result in the possibility of Bragg Grating filters for use in Silicon Photonics. It is the purpose of the work to create as far as is possible flat surface waveguides so as to facilitate Thermo-Optic tuning and also the incorporation into rib-waveguide Silicon Photonics. The spectral response of the shallow Bragg Gratings was modelled using Coupled Mode Theory (CMT) by way of RSoft Gratingmod ^TM. Also the effect of having a Bragg Grating with alternate layers of refractive index of 1.5 and 3.5 was simulated in order to verify that Silica and Silicon layered Bragg Gratings could be viable. A series of Bragg Gratings were patterned on 1.5 micron SOI at Philips in Eindhoven, Holland to investigate the variation of grating parameters with a) the period of the gratings b) the mark to space ratio of the gratings and c) the length of the region converted to Bragg Gratings (i.e. the number of grating period repetitions). One set of gratings were thermally oxidised at Philips in Eindhoven and another set were ion implanted with Oxygen ions at the Ion Beam Facility, University of Surrey, England. The gratings were tested and found to give transmission minima at approximately 1540 nanometres and both methods of creating flat surfaces were found to give similar minima. Atomic Force Microscopy was applied to the grating area of the as-implanted samples in the Advanced Technology Institute, University of Surrey, which were found to have surface undulations in the order of 60 nanometres.

In angle multiplexing, the angle between the reference light and the object light is slightly changed in different recordings. In reconstruction, only the reference beam with an accurate angular position can retrieve the corresponding object beam due to the characteristics of Bragg condition. Accordingly, a suitable angular separation of the reference beam should be decided for angle multiplexing. A larger angular separation will decrease the storage density, and a smaller angular separation will increase the cross-talk noise in small bi-angles. In general speaking, only one condition of full angle of lights is involved to calculate the angular separation with coupled-mode theory or with experiment. Thus the angular separation is fixed in the whole procedure of angle multiplexing. As a result, the angular separations of most multiplexed holograms are either larger or smaller. Only one hologram is multiplexed in the critical angular condition. In this paper, angle multiplexing with different angular separations were performed to quantitatively demonstrate the effect. The possible method to deal with the issue was also proposed.

The production of CuInGaSe₂ (CIGS) solar cell is based on vacuum processes, which requires a high manufacturing temperature and high cost. Our result show a simple method has been developed to prepare the silica substrates of CIGS solar cell. It's synthesized by sol-gel process from tetraethylorthosilicate (TEOS), methanol (CH₃OH) and pure water (both ion-exchange and distillation) in the presence of ammonia as catalyst. The preparation procedure was elaborated as the flexible sequence to control chemical composition and properties of the particles in sol-gel-derived silica substrate. The morphology, particle size, and size distribution of CIGS substrate were characterized with dynamic light scattering (DLS) and atomic force microscopy (AFM). The results of AFM morphology and statistic evidence we find an easy way, non-vacuum and low temperature processes, to successfully prepare the CIGS solar cell substrates with surface roughness below 3 nm. It is powerful the advance study in low cost solar cell.

Nonlinear optics in silicon has drawn substantial attention in the recent years. In this research, laser mode-locking and dual wavelength lasing are achieved in a fiber-ring-cavity using an Erbium-doped fiber amplifier (EDFA) as a gain medium and a 1.7cm long silicon-on-insular waveguide as pulse compressor, a mode-locker and a Raman gain media. We show that the transient behavior of two photon absorption (TPA) and TPA induced free carrier absorption can be used for pulse compression and laser modelocking in the silicon waveguide inside the laser cavity. The proposed technique takes advantage of spontaneous generation of free carriers and the slow recombination time, >17ns, to attenuate the trailing edge of the time varying signals passing through the waveguide. When a 5μm² model area silicon waveguide is placed inside a fiber ring cavity consisting of an EDFA as a gain media and ~50ps modelocked laser pulses are generated at 1540nm. We also observe that the generated short pulses also induce stimulated Raman scattering at 1675nm in the same silicon waveguide. We show that engineering the laser cavity facilitates laser modelocking and dual wavelength laser oscillation at 1540nm and 1675nm. Experimentally we obtain <100ps modelocked pulses at both wavelengths. The average pump threshold power of the Raman laser is measured to be 3.75mW and the Stokes average output power is measured to be 3 μW.

We present a discussion on how an area-encoded fringe pattern is applied to describe the 3D shape of complex objects that have spatially isolated surfaces or large depth continuities. Compared with conventional fringe projection techniques, the proposed scheme is relatively reliable and robust to identify the fringe order. Only one phase measurement is required. This makes it possible to analyze dynamic objects.

Temperature and strain sensing of critical aircraft engine components is a critical health and prognostics tool for future engine programs. Real-time feedback of key temperature and strain measurements can be used to provide better estimates to ground crews of engine component life, thus minimizing engine downtime and maximizing the effectiveness of planned inspections. One method for monitoring distributed stress and temperature throughout an engine is through the use of Fiber Bragg Grating (FBG) sensors. With just a single sensor line, both temperature and strain can be monitored simultaneously and in a distributed fashion. Unfortunately, FBG sensors bonded to a host structure are susceptible to both thermal strains and mechanically-loaded strains simultaneously, and without intelligent sensor design, the two signals are indistinguishable from each other. In the present work, a sensing array design is proposed and demonstrated to provide a means for separating thermal and mechanically-loaded strain signals by using two FBG sensors in close proximity to each other. Experimental results are provided using a structural beam element to demonstrate the feasibility of the proposed approach for decoupling the temperature and strain effect from fiber Bragg grating sensors.

A design of polarization beam splitter based on negative refraction in photonic crystal is proposed. The proposed structure is formed by a hexagonal lattice of embedded air holes in silicon materials and is based on 2-D photonic band structure and equi-frequency contour calculations where negative refraction is considered to be function of incident angle and thickness of slab. The designed structure exhibits oppositely signed (negative and positive) refraction for TE and TM polarization at telecom wavelength windows. The wavelength response of the designed PBS is obtained for both polarizations.

By using two optical fibers and a capillary it is possible to measure the refractive index of liquids. Light leaving a fiber is sent transversally to a capillary that behaves as a cylindrical lens when liquids are inserted in it. Focused light is collected by a second fiber and sent to a detector.

The SIM-Planetquest (Space Interferometry Mission), currently under development at the Jet Propulsion Laboratory, consists of two 6-meter baseline interferometers on a flexible truss. SIM's science goals require 1μas accuracy in its astrometric measurements[1]. To achieve this level of accuracy for detecting planets SIM built the Spectrum Calibration Development Unit (SCDU) testbed. The testbed requires a white light point source with broadband spectrum. Before each long test the spectrum on the camera must be calibrated. To achieve this task a laser light visible to camera was coupled to the white light source. The light system needed pointing stability of better than 4 micro-radians and a minimum optical power level at the fringe tracking camera. Due to stability requirement of the experiment, the setup, including the point source is in a vacuum chamber. To get a broadband spectrum point source inside the vacuum chamber white light from a multimode fiber was combined with laser light in free space to a photonics crystal fiber (PCF). The output is a single mode, broadband, and Gaussian beam. This paper explains the details of such a design and shows some of the results.