This PDF file contains the front matter associated with SPIE Proceedings Volume 6698, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Optical and electrical effects in semiconductors and ferroelectric crystals will be modeled. Standard photorefractive equations are supplemented by the equation of state for the polarization density following Devonshire-Ginsburg-Landau (DGL) approach. We have derived equations for pyroelectric and photogalvanic contribution to the holographic grating recording in ferroelectric materials. We will consider double-functional holographic interferometer, based on holographic pyroelectric current and optical beam coupling. Crystal electrostatic accelerators, based on charging of ferroelectric crystals by pyroelectric and photogalvanic effects are discussed in relation to generation of self-focused electron beam, X-rays and neutrons.

The quality of the fiber depends to a considerable extent on homogeneity, i.e., on the distribution of both special added and detrimental impurities. A non-uniform distribution of such impurities along the fiber length and cross-section leads to non-uniform spatial, electrical and optical properties of the crystal. Variations of the concentration of impurities are determined by the processes that take place during the fiber manufacturing. In order to eliminate non-uniformities, crystal growth experts have concentrated on the analysis of the mass transport, heat transfer, impurity distribution and shape of the crystal-melt interface. In order to evaluate the dopant distribution, a stationary numerical model-including incompressible fluid flow in the Boussinesq approximation, heat and mass transfer, and surface tension-driven flows due to the temperature gradient along the liquid free surface (meniscus)-is developed using the finite element method. A two-dimensional axissymmetric model is implemented with COMSOL Multiphysics 3.3 software, and the Nd impurity distribution dependence on the pulling rate v₀ and on the radius of the capillary channel R_cap in a LiNbO₃ fiber grown from the melt by the EFG method is determined. Using this dependence, the optimal v₀ and R_cap which assure the best impurity distribution are chosen.

In this paper, within the spectrum range from 351 nm to 799 nm, the different reductions of nucleation field induced by the focused continuous irradiation with different light intensity are achieved in congruent LiNbO₃ crystals. The reduction proportion increases exponentially with decreasing the irradiation wavelength, and decreases exponentially with increasing the irradiation wavelength. Basing on photo-excited effect, we propose a proper model to explain the mechanism of light-induced domain nucleation in congruent LiNbO₃ crystals.

Barium titanate crystals were grown by top seeded solution growth technique, nominally pure and also 0.05% and 1% Cr³⁺ impurity. We have conducted electron paramagnetic resonance (EPR) and photo-EPR studies at room temperature to investigate the role of Cr³⁺ impurity in photoinduced electron transfer. Nominally pure crystals contained Fe³⁺ as impurity, and its EPR is consistent with work reported by previous investigators. The Cr³⁺ doped crystals also contained Fe³⁺ impurities. It was observed that the site symmetry and the strength of the axial field parameter for Fe³⁺ complex were significantly different in Cr³⁺ doped crystals compared to nominally pure BaTiO₃. The EPR spectra of Cr³⁺ were distinguished using the hyperfine structure of odd isotope ⁵³Cr (I=3/2). By Photo-EPR technique we observe that in the presence of Cr³⁺, Fe³⁺ is not significantly photosensitive. In contrast Cr³⁺ exhibited higher photosensitivity in the presence of Fe³⁺. This was monitored by locking the magnetic field to 1/2↔1/2 transition of Cr³⁺, and recording intensity as a function of time, under insitu laser illumination. In lightly doped crystals the intensity of Cr³⁺ signal is sharply reduced immediately after switching the laser OFF showing non-exponential decay. In heavily doped crystals photo-EPR signal clearly shows that the fast decay of Cr³⁺ was followed by slow and steady build up of Cr³⁺ signal. The growth of Cr³⁺ signal was attributed to photoinduced decoupling of Cr³⁺ dimers. Thus, by doping BaTiO₃ with Cr³⁺ more efficient grating formation can be achieved and time dependent phenomena are observed.

Lead magnesium niobate-lead titanate, Pb(Mg, Nb)O₃-PbTiO₃ is a piezoelectric, ferroelectric crystal at room temperature with large electromechanical coefficient. The crystals were grown by PbO-B₂O₃ flux method. Typically the crystals were colorless and transparent, but a small fraction of them were Brown/reddish colored and show interesting photoluminescence (PL) properties. The PL studies were conducted under XeCl (308nm) excitation and under Argon Ion (Ar⁺) laser excitation. The excitation with 308nm gave broad PL centered at 500nm and intense emission at 710nm. The emission at 710nm in colorless crystals is very weak. The excitation with Ar⁺ laser coinciding with electronic absorption in brown samples gave rich and sharp PL particularly with 514.5 nm excitation. The PL with 514.5nm-Ar⁺ laserexcitation, consisted of intense anti stokes emission in addition to intense red and near infrared emission, is a result of photo-transfer optically stimulated luminescence (PT-OSL). This involved electron-hole recombination at photoinduced magnetic polaron site. The PL emissions and the centers identified are the followings: 718nm emission due to magnetic polaron and 360nm emission due to cooperative emission from two polarons, Fe-R line at 660nm due to Fe³⁺ coupled to a cation; 380nm and 399nm due to Pb²⁺ clusters and Nb⁵⁺ center; 630 and 860 nm due to 6p→6s transition of Pb³⁺ and 760nm due to isolated Fe³⁺ ions. Raman spectrum of brown samples revealed the presence of nano particles/wires of orthorhombic β PbO. The FTIR spectrum gives evidence of significant amount of hydroxyl impurity.

Photopolymer materials are practical materials for use as holographic recording media, as they are inexpensive and self-processing. By understanding the mechanisms present during recording in these materials their limitations for certain processes can be improved and a more efficient, environmentally stable material can be produced. In this paper we briefly review the application of photopolymer materials in the area of holographic data storage. In particular we discuss the recent development of the Non-local Polymerisation Driven Diffusion Model, (NPDD) including absorption and inhibition, and analysis of the photochemical effects present during the evolution of holographic grating formation. The inclusion of these effects allows a more accurate understanding of the photo-polymerisation process.

PbTe thin films were grown on BK7 glass and Si(100) substrates using femtosecond pulsed laser deposition at room temperature. The influence of the background pressure and the laser fluence on the structural and optical characteristics of the PbTe films was studied. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the surface and structural properties of the deposited PbTe thin films, respectively. Transmission spectroscopy measurements in the visible and infrared region (VIS-IR) were used to investigate the optical properties of the PbTe thin films.

A new optical device whose dynamic grating intensity can be electrically controlled at specific magnetic fields and wavelengths has been demonstrated. This device has a semiconductor/polymer multilayer structure formed by pulsed laser deposition at room temperature. The reflection intensity can be electrically controlled with a response time of less than 2 ms. The EPR spectrum of the multilayer determined the concentration of the free spin and the effect of the light on the growth and decay of the Fe which was doped in the polymeric thin film using the high pulse laser deposition technique.

Photo-acoustic spectroscopy (PAS) has been successfully applied to detect various gases and chemicals due to its high selectivity and sensitivity. However, the performance of the conventional acoustic sensors prohibits the application of PAS for harsh environment gas species real-time monitoring. By replacing conventional acoustic sensors, such as microphone and piezo-transducers, with a high-temperature Fiber Bragg Grating (FBG) vibration sensor, we developed a fiber-optic PAS sensing system that can be used in high-temperature and high-pressure harsh environments for gas species identification and concentration measurement. A resonant acoustic chamber is designed, and FBG vibration sensor is embedded in the molybdenum membrane. An OPO laser is used for spectrum scanning. Preliminary test on water vapor has been conducted, and the result is analyzed. This sensing technology can be adapted into harsh environments, such as Integrated Gasification Combined Cycle (IGCC) power plant, and provide on-line real-time monitoring of gases species, such as CO, H₂O, and O₂. Presently, our FBG-based vibration sensor can withstand the high temperature up to 800°C.

In this paper, we report the fabrication of higher-order-mode rejected fiber Bragg gratings (FBGs) in sapphire crystal fiber using infrared (IR) femtosecond laser illumination. The grating is tested in high temperature furnace up to 1600 degree Celsius. As sapphire fiber is only available as highly multimode fiber, a scheme to filter out higher order modes in favor for the fundamental mode is theoretically evaluated and experimentally demonstrated. The approach is to use an ultra thin sapphire crystal fiber (60 micron in diameter) to decrease the number of modes. The small diameter fiber also enables bending the fiber to certain radius which is carefully chosen to provide low loss for the fundamental mode LP01 and high loss for the other high-order modes. After bending, less-than-2-nm resonant peak bandwidth is achieved. The grating spectrum is improved, and higher resolution sensing measurement can be achieved. This mode filtering method is very easy to implement. Furthermore, the sapphire fiber is sealed with hi-purity alumina ceramic cement inside a flexible high temperature titanium tube, and the highly flexible titanium tube offers a robust packaging to sapphire fiber. Our high temperature sapphire grating sensor is very promising in extremely high temperature sensing application.

In this paper, we report laboratory test results of an LPG that can maintain a constant resonant peak depth over an enhanced tuning range when it is coated with an ITO electrode that has optimized thickness and refractive index. Without the ITO layer, LPG tuning ranges as large as 50 nm have been achieved when the ambient index is increased from 1.00 (air) to ~1.444 (index of the silica cladding), but the peak depth cannot be maintained. When a properly designed, high-index ITO overlay is coated onto the silica cladding, mode transition effects coincide with the LPG's intrinsic sensitivity to changes in the ambient index, resulting in a stable peak depth over an enhanced tuning range. The authors have experimentally demonstrated an LPG coated with ITO that can be tuned in excess of 150 nm with an ambient refractive index change of less than 0.01. To the best of the authors' knowledge, this is the highest sensitivity reported for an LPG to date. In addition to the tuning performance, the resonant peak remains within 1 dB of its maximum depth for at least 100 nm of the tuning range, which allows the tunable LPG to be used in real applications.

3D shape reconstruction using fringe projection or interference schemes has been extended studied. However, speckle noises could be introduced once a coherent light source is used. In this paper, we use the empirical mode decomposition (EMD) to remove speckles caused by such kind of coherent illumination. This makes it possible to accurately analyze fringes in the frequency domain and to accurately reconstruct a 3D image.

In this work we theoretically model continuous and pulse wave propagation using the underlying dispersion relations. We also derive the dispersion relations of the underlying wave equations based on the real and imaginary parts of the propagation constant which are related through Hilbert transformation to ensure causality. Also, in this paper we show that by using a model of photorefractive two wave coupling, we can derive the dispersion relation for pulsed propagation and coupling in a diffusion dominated photorefractive material. We note that the dispersion relation we have found in photorefractive material also obeys the Hilbert transform property. Finally, we show that the group velocity of light can be slowed down by means of phase coupling in the photorefractive two-wave mixing process.

We report the generation of white light comprising red, green, and blue spectral bands from a frequency-doubled fiber laser in submicron-sized cores of microstructured holey fibers. Picosecond pulses of green light are launched into a single suspended core of a silica holey fiber where energy is transferred by an efficient four-wave mixing process into a red and blue sideband whose wavelengths are fixed by birefringent phase matching due to a slight asymmetry of the structure arising during the fiber fabrication. Numerical models of the fiber structure and of the nonlinear processes confirm our interpretation. Finally, we discuss power scaling and limitations of this white light source.

When a new element base is created for information and telecommunication systems, the properties of the materials used must be well understood. In particular, a thorough investigation of the elastic and elasto-optical properties is required for materials used in optical telecommunication systems, optical display panels, acousto-electronic information devices, etc. For example, the elastic nonlinearity for various crystals must be known. If the materials under study are optically transparent, acousto-optics can be used to obtain such information. It is known that elastic nonlinearity is one of the most important factors distorting and limiting the performance of acousto-optic information systems. Due to such nonlinearity, the attenuation coefficient of acoustic waves increases; this effect can be strong in some materials and depends on the acoustic power density. Using the coupled-mode method, new solutions describe the spatial distributions of the acoustic wave amplitude, taking into account the initial power of the wave at the generation edge and assuming the square law of the nonlinearity. The current method approximates real distributions more accurately than previous solutions, and we have confirmed this experimentally. The experimental results of a specific nonlinearity in an acoustic resonator are shown. The higher harmonics sharply reduce their amplitudes after reflecting from the rear face of the sample, then the amplitudes steadily increase. The decrease in the amplitude of the higher harmonics is related to the decrease of the attenuation coefficient for the main acoustic mode. Using the measured data, an approximate synthesis has been made for the shape of the acoustic signal deformed by the elastic nonlinearity of the medium. Evaluations have been made for a 500 MHz longitudinal acoustic mode and an initial power level of 200 W/cm² at various traveling points of that wave in LiNbO₄ crystal.

In recent years, there has been significant interest in using surface enhanced Raman scattering (SERS) and optical fibers for chemical, biological, and environmental detections. The combination of SERS and optical fibers offers the advantages of the molecular specificity of Raman scattering, huge enhancement factor of SERS, and flexibility of optical fibers. In this paper, we report our work on the development of fiber biosensors based on SERS emphasizing on recent progress in the fabrication of photonic crystal fiber (PCF) SERS sensors for highly sensitive molecular detection. To increase the sensitivity, one needs to increase either the excitation laser power or the amount of analyte molecules in the active region of the sensor. The high excitation intensity is not desirable for biosensors due to the low damage threshold of live tissues or bio-molecules. In our investigation of various fiber configurations, hollow core (HC) PCFs show the greatest advantages over all other types of fiber probes because of the large contact area. The hollow core nature allows the analytes and SERS substrate to fill the inner surface of the air channels. In addition, by sealing the cladding holes of the HCPCF, only the central hole will be open and filled with liquid samples. As both the light and the sample are confined in the fiber core, the sensitivity is significantly improved. The newly developed liquid core PCF sensor was tested in the detection of rhodamine 6G (R6G), human insulin, and tryptophan with good sensitivity due to the enhanced interaction volume.

A novel technique using projected fringe profilometry with pulsed illuminations for finding the absolute shape of an object, which is vibrating with high frequency, is proposed. The proposed method can accurately describe the observed 3D shape at a sequence of time. Even though the tested object vibrates up to 10K-Hz, the proposed method can accurately describe the observed 3D shape at a specific time. Depth accuracy better than one part in ten thousandths of the field of view can be achieved even with excessive image noises. Furthermore, using the proposed method, the vibrating frequency and local displacement at each pixel can be accurately identified.

Broadband coherent anti-Stokes Raman scattering (CARS) microscopy promises non-invasive, high information content microscopic imaging for live cells and tissues. Generation of a broadband continuum with appropriate characteristics to be used for Stokes light has been a roadblock for bringing this promise to fruition. Here we present numerical and experimental work towards generation of a suitable Stokes light continuum from a femtosecond pulse laser. In the simulations, the pulse propagation along the fiber is governed by the generalized nonlinear Schroedinger equation, including linear effects from the group velocity dispersion and the nonlinear effects from self phase modulation, delayed Raman scattering process and self-steepening. The equations are integrated using a symmetrized split-step Fourier method. Optimal fiber-related simulation parameters used in the model, such as the nonlinear coefficient, dispersion coefficients and the fraction of the stimulated Raman scattering contribution etc, are systematically investigated and determined for the GeO₂ doped fiber.

Novel supercontinuum generation by launching ultra-short femtosecond laser pulses into single crystal sapphire fibers is demonstrated. Supercontinuum generation using sapphire fiber exhibits many advantages that include high transparency up to 5 micron, low material dispersion in the 0.8 micron to 5 micron spectral range, and an extremely high laser damage threshold (500 times higher than that of silica). Thus, supercontinuum spectrum with high power, super broadband, and spatial coherence can be realized by pumping single crystal sapphire fibers. By experimental comparison, we prove that sapphire fiber can provide a broader supercontinuum spectrum than that of bulk sapphire counterpart under the same exciting conditions. Since supercontinuum generation in single crystal sapphire fibers can radiate high power supercontinuum in the middle-IR regime, it will have a great impact on many applications, including sensing and broadband multi-spectrum free space communications.

A method using multiple fringe projections from different viewpoints for finding the absolute shape of an object is proposed. In this method, surfaces with large depth discontinuities can be identified without ambiguity. Shadowing caused by tilted fringe projection can be eliminated as well. The other advantages of the proposed measurement system are: (1) large depth-of-field in the projection system; (2) very low fringe distortion (even for a large field of view); and (3) robust performance to analyze dynamic objects.

A method to reconstruct a 3D profile using a projected fringe profilometry from a 2D image blurred by uniform linear motion is proposed. The proposed method offers following major advantages: (1) very low computation cost for the 3D reconstruction, (2) only one phase measurement needed for operation, and (3) robust performance to analyze dynamic objects.

Photorefractive crystals have been deeply studied for holographic data storage. A number of approaches have been studied to improve the storage properties of such materials. In particular, methods to make the photorefractive gratings nonvolatile, i.e., insensitive to erasure during readout and during storage in the dark, have been developed. Doubly doped lithium niobate crystals can realize nonvolatile holographic recording by a real time and all optical processing, which have become a topic of great current interest. Sensitive light with short wavelength, such as UV light, and recording light are simultaneously applied in the recording process, and only one recording beam is used in the fixing process. Previous researches of this kind of crystals are always based on 633nm red light or shorter wavelength recording light. Longer wavelength recording light are more applicable for a practical data storage system. In this paper, for the first time, near infrared nonvolatile holographic recording is realized in different kinds of doubly doped LiNbO₃:Fe crystals. In our experiments, the same sensitive light and recording lights at different wavelengths are adopted to compare the recording performance. The recording conditions are optimized to improve the near infrared recording characteristics. In near-infrared two-center holographic recording, the intensity dependence of recording sensitivity is found to be different with that by recording at 633nm, caused by small bulk photovoltaic coefficient of Fe traps, long response time and the simultaneous erasure of recorded hologram by sensitizing light.

The recording and readout characteristics in doubly-doped LiNbO₃ crystal with one-color scheme are investigated based on jointly solving material equations and coupled-wave equations. Asymmetry between grating buildup and readout process is found when electrons in deep centers can be excited by recording light; the grating is quasi-nonvolatile. The shorter recording wavelength, and dopant in deep centers with a closer energy level to Fe in LiNbO₃ crystal, can strengthen such asymmetry. The further investigation shows that two aspects induce the quasi-nonvolatile behavior in doubly-doped LiNbO₃ crystal, one is the beam coupling between incident and diffracted beams, the other is two grating form in both centers. This research provides a possible method to prolong the lifetime of grating in doubly-doped LiNbO₃ crystals.

A new type of photorefractive volume holographic lenses for converting a plane wave to a lateral-spread spherical wave with different wavelength has been suggested, which are recorded at 632.8nm wavelength and reconstructed at 800nm wavelength. Using the coupled-wave theory, the wave-front conversion by photorefractive volume holographic lenses between spherical and plane waves is studied. The off-Bragg parameter values of the holographic lenses in the reconstruction process are analyzed. The dependence of diffraction efficiencies on the focal length of recording spherical wave and the geometric sizes of the photorefractive holographic lenses are discussed in detail. In addition the intensity distributions of the diffracted beam are analyzed also.

Transmission properties of a novel optical waveguide structure based on Nafion polymer are investigated by the technique of the m-line spectroscopy at a wavelength of 632.8nm. The refractive index profiles for Nafion film for both TE and TM modes are found to be of quadratic nature with surface refractive indices values of 1.3408 and 1.3446 respectively. The attenuation loss of this polymeric waveguide is found to be 1.53 dBcm^-1

Recently, we proposed a new speckle-based hologram multiplexing recording technique. In this method, a multi-mode LiNbO3 single crystal fiber is employed to generate speckle patterns which are used as reference beams in hologram recording process. The speckle pattern generation can be precisely controlled by external E-field. Theoretically, this technique can generate thousands of decorrelated reference beams at given practical constraints. The system storage capacity has so far been estimated based on idealized settings. As it is well known that, besides the limitation set by the modulation mechanism capacity the storage density of a volume hologram memory system can be also restricted by many other factors. Among all factors, the crosstalk is a fundamental one that may ultimately put a tighter bound to system storage capacity. This paper is devoted to the theoretical analysis and numerical simulation of crosstalk in this proposed technique.

We present our studies on preparation of LiNbO₃ oriented stoichiometric thin films by sol-gel method. The technology of synthesis of precursor systems, containing Li and Nb, has been developed. Studies of structure, morphology, optical and physical properties were carried out. The lattice parameters have been determined and correspond to stoichiometric lithium niobate crystals. The crystallographic orientation of LiNbO₃ films corresponds to orientation of a sapphire substrate, i.e. on substrates with orientation (0001) the C axis of film is perpendicular to a substrate surface, and on (11^-₂0) substrate C axes lays in a plane of a substrate. The developed method allowed to obtain lithium niobate thin films with 300-700 nm thickness, transparent, with precise crystallographic orientation both on sapphire substrate and conductive ZnO films.

Both n-type and p-type ZnO will be required for development of homojunction light-emitting diodes and laser diodes. It is easy to obtain strong n-type ZnO, but very difficult to create consistent, reliable, high-conductivity p-type material. Here we present our investigations of p-type ZnO thin film preparation by sol-gel method using single Li doping and Ga(Al)+N codoping technique. ZnO thin films with c-axis orientation have been prepared on glass substrates. Zn acetate dihydrate, gallium nitrate and acetamide were used as zinc, gallium and nitrogen precursors respectively. SEM, X-ray diffraction, electric conductivity and Hall effect measurements were carried out. The results show that p-type conducting ZnO films with hole concentrations as high as 5x10¹⁷ cm^-3 were obtained by this method.

Single-mode polarization splitter with a configuration of asymmetric Y-junction is proposed in two-dimensional (2D) honeycomb photonic crystal (PhC) of dielectric rods. Six dielectric rods with a radius of 0.12a (The radius of a regular rod is 0.25a.) are placed on the junction region to block transverse magnetic (TM) light and to pass transverse electric (TE) light by the bandgap effect, where a is the shortest distance between two regular rods. And one rod with a radius of 0.32a is employed to enhance the bending efficiency of TM light through a resonance effect. Device performance is simulated by the finite-difference time-domain method. At 1550 nm wavelength, polarization extinction ratio (PER) between the two output waveguides is larger than 20 dB for either TE or TM input. Polarization splitting as a function of wavelength is also studied in this paper.

The main aim of this paper is to analyze the propagation and attenuation in PIR fibers. The thermal change of these parameters for different mode structures will be done due to propagation of high optical power witch cases fiber heating.

Photopolymer materials are practical materials for use as holographic recording media, as they are inexpensive and selfprocessing. By understanding the mechanisms present during recording in these materials their limitations for certain processes can be improved and a more efficient, environmentally stable material can be produced. Understanding the photochemical and photo-physical processes present during the formation of holographic gratings in photopolymer materials is crucial in enabling further development of holographic applications such as data storage, metrology, free space optical components etc. In order to achieve this, it is necessary to develop material electromagnetic theory, which models these applications. In this paper we begin by experimentally estimating parameters associated with absorption due to dye in the photopolymer. This information is needed when using Non-local Photo-Polymerization-Driven Diffusion model (NPDD) to characterise such materials. Absorption also leads to the formation of non-uniform tapered grating structures. While the NPDD has been used to characterise materials recording slanted gratings problems have arisen in determining diffusion constants accurately. In order to deal with electromagnetic diffraction by the resulting non-uniform slanted grating structures we develop first order analytic expressions governing the replay of such gratings.

We synthesized a new magneto-optical nanoparticle material Bi_1.8Y _1.2Fe₄Ga₁O₁₂ (BYIGG) with substitution of gallium by iron. It was prepared using coprecipitation and annealing processes. High Energy ball-milling was used to mill the nanoparticle to tens of nanometer range. The thin-film coated shows improvement of transmittance because of the substitution. A simple model for scattering and Faraday Effect was used to calculate the transmittance and Faraday Rotation angle, which shows have a good match with the known experimental result.

The dynamic and static measurements of phase variation induced by domain inversion are performed in congruent lithium niobate crystal by the digital holographic interferometry. The existence of ridge-shape phase distribution adjacent to 180° domain wall is observed. During the domain wall motion, the phase variations are not uniform but have obvious relaxations. In the static measurement, the ridge elevation can vary linearly with the uniform electric field. The reasonable assumptions are proposed to explain these effects. The phase contrast across the crystal thickness induced by the internal field is also measured by the digital holographic interferometry just after the congruent lithium niobate crystal is partially poled. The direction of applied external field is antiparallel to that of internal field, and the measured phase contrast varies linearly with the applied external field. A new internal field is obtained by this method, and named effective internal field. The distinct discrepancy between effective and equivalent internal fields is observed. We attribute this effect to the new macroscopic representation of elastic dipole components of defect complex in the crystal.

We demonstrate a broad supercontinuum source by bridging two separate supercontinua that are pumped at two different IR wavelengths. Two separate supercontinua are overlapped to form a broadband supercontinuum source without spectrum discontinuity between two different pumping sources. The bridging effect of two separate supercontinua is successfully demonstrated by applying two pumping sources at 1460 nm and 1769 nm into a regular single mode fiber. Also, more than 1000 nm expansion possibility due to the bridging effect can be achieved by pumping at 1350 nm and 1963 nm.

The two-center holographic recording method is a very effective technique to realize nonvolatile photorefractive holographic storage in doubly-doped LiNbO3 crystals, but its main drawbacks are low fixing diffraction efficiency and low recording sensitivity. Commonly homogeneous readout light was used to fixing holographic grating, because the concentration of donor in shallower center had a nearly 180° phase difference to space-charge field at the end of recording phase, a negative photovoltaic field should be created and drive part of electrons come back to its origin position, finally low the fixing space-charge field. In this paper a new fixing method for two-center holographic recording was proposed, and the modulated light with the same optical phase to recording light is used to fix holographic. The new formed photovoltaic field has the same phase with recording light and counteracts with the negative photovoltaic field, finally heavily enhance the fixing space-charge field. Furthermore, the recording sensitivity can be markedly increased with higher intensity ratio of recording light to sensitizing light, at the cost of a little decreasing in fixing space-charge field.

Based on anisotropic diffraction of photorefractive LiNbO₃ crystal, we theoretically discuss an optical WDM scheme implemented by a single volume grating. Using only one grating recorded by two He-Ne laser beams at a specific wavenumber, we can realize wavelength demultiplexing around telecommunication wavelength. The possible wavelength range suitable for WDM is discussed, which is in the range from 1081nm to 1217nm. Our theoretical scheme can be used in the design of a practical WDM.

Multimode laser emission is observed in a polymer optical fiber doped with a mixture of rhodamine 6G and rhodamine B dyes. Tuning of laser emission is achieved by using the mixture of dyes due to the energy transfer occurring from donor molecule (rhodamine 6G) to acceptor molecule (rhodamine B). The dye doped polymethylmethacrylate (PMMA) based polymer optical fiber is pumped axially at one end of the fiber using 532nm pulsed laser beam from an Nd: YAG laser and the fluorescence emission is collected from the other end. At low pump energy levels, fluorescence emission is observed. When the energy is increased beyond a threshold value, laser emission occurs with a multimode structure. The optical feedback for the gain medium is provided by the cylindrical surface of the optical fiber which acts as a cavity. This fact is confirmed by the mode spacing dependence on the diameter of the fiber.

Acousto-optical tuning has been implemented for an α-Al₂O₃:Ti³⁺ laser pumped by a 30 W Cuvapor laser, which is a generator-amplifier system operating at 15,625 Hz, with a pulse duration of 50 nsec. The system can select an arbitrary laser wavelength in the IR range for approximately 64 μsec. Experimentally the transformed IR beam has been varied in the visible and UV range.

We have observed nanosecond electrical and optical pulsations from photorefractive lithium-niobate optical fibers using CW green and blue low-power lasers. Fourier spectra of the pulsations have a maximum at ~900 MHz with peaks separated by ~30MHz. We consider free-space and fiber supported illumination of the fiber crystal. Strong nonlinear enhanced backscattering with phase conjugation was observed from bulk crystals and crystal fibers along the C-axis. Model of transformation of CW laser irradiation of ferroelectric crystals into periodic nanosecond electrical and optical pulsations is suggested. This model includes combinations of photorefractive, pyroelectric, piezoelectric, and photogalvanic mechanisms of the holographic grating formation and crystal electrical charging. Possible applications of these short photo-induced electrical pulses for modulation of holographic beam coupling, pulsed electrolysis, electrophoresis, focused electron beams, X-ray and neutron generation, and hand-held micro X-ray devices for localized oncology imaging and treatment based on our advanced sensor work are discussed.