Scattering noise in four kinds of lithium niobate crystals of the same doubly doping system (they are LiNbO₃:Fe:Mn, LiNbO₃:Ce:Mn, LiNbO₃:Ce:Cu and LiNbO₃:Fe:Cu) is observed during nonvolatile holographic recording. The results show that nonvolatile holographic recording can effectively suppress scattering noise and this kind of suppression effect is decided by the recombination coefficients of the dopants in the shallower and the deeper centers, respectively. It is concluded that small recombination coefficients of the shallower centers and large recombination coefficients of the deeper centers benefit the amplification of the signal grating and the suppression of the noise grating. In addition, the initial seed scattering noise also impacts the finally suppressed scattering noise and little initial seed scattering leads to low scattering noise after recording. In a conclusion, the performances of LiNbO₃:Ce:Cu is the best with high diffraction efficiency and low scattering noise. The theoretical simulations are performed for validation. It provides a fundamental method to the problem of scattering noise intrinsic into the nonvolatile holographic recording.

In this paper, we report investigations on chemical analyses and optical measurements of our PQ doped PMMA photopolymer material. We have analyzed chemical compositions of four different samples: PQ doped PMMA solid and PQ dissolved MMA liquid samples, with light exposed and unexposed conditions, respectively. The investigations provide us a good understanding about the photochemical behaviors of the PQ and the MMA molecules during optical recording. Then, a mechanism for holographic recording is proposed. This result has been applied to develop photopolymers doped with different dye molecules. With changing of dye molecules, we have made three enew PMMA-based photopolymers. Their holographic recording characteristics have been tested and discussed.

Optically homogeneous bismuth germanate Bi₄Ge₃O₁₂ single crystals doped with vanadium, cobalt and vanadium plus cobalt have been successfully grown by Czohralski technique with automatically diameter-weight control. The distribution coefficients for individual doping elements are determined. The effect of doping on the light-induced properties of BGO single crystals is studied. Optical absorption spectrum of annealed samples can be strongly modified under ultraviolet illumination. The photochromic effect is optically or thermally reversible from one state to another. Volt-amper charactersitcs show linear behavour and dark conductivity values are s ~ 10^-13 (Ω.cm)^-1. Holographic grating were successfully recorded in all investigated doped crystals at 514 nm.

Control of refractive index in amorphous silicon materials is investigated. Elementary waveguide structures were prepared on two micron thick amorphous silicon by photon lithographic patterning of a silver masking layer. Hydrogen was implanted at fluence of ~5×10¹⁷ cm² for three energies, 50, 100 and 175 KeV yielding a total does of ~1.5×10¹⁸ cm² consistent with a 10% increase in atoms due to the hydrogen addition. The optical properties of the implanted and non-implanted regions were probed as a function of low temperature annealing. The optical band gap shift to higher energy was consistent with hydrogen addition. Some darkening, absorption increase, were noted on the implanted regions. However, low temperature annealing is known to remove dangling bond damage in amorphous silicon. Prospects of utilizing these waveguides to probe light induced optical changes in amorphous silicon is described as well as the prospects of more advanced devices.

Periodicaly poled LiNbO₃ single crystals with antiparallel domain configurations have been successfully grown with a (010) oriented seed from a congruent melting composition with 4 mol % potassium addition using a modified Cz geometry. The experiments reported in this paper showed that the polarization antiparallel domain structure in lithium niobate crystals can be created during growth process by a direct poling technique with electric field of alternating polarity. PPLN strucutres with period length 20-100 μm were demonstrated by this method.

In this paper, some recent advances in long period gratings, including (1) widely tunable single resonant band long period gratings, (2) long period gratings fabricated in single crystal sapphire fibers, and (3) long period gratings fabricated in photonic crystal fibers are presented. The applications of these novel long period grating to next generation ultra high capacity optics communication networks, high temperature distributed fiber optic sensors, and highly sensitive biosensors are discussed. Quantitative analyses and preliminary experimental results are provided.

From the ultraviolet induced absorption, we have found a broad blue band and little involvement of Pr ions in ultraviolet illumination. Ultraviolet excited photoluminescence and the excitation spectra for visible emission were also measured in Pr:LiNbO₃. We estimated photovoltaic constant and photoconductivity by measuring photovoltaic current and voltage with different boundary conditions. With ultraviolet gated short-circuit holographic recording, we have measured enhanced sensitivity and diffraction efficiency.

Recently, new applications of holographic gratings have been proposed to extend the hologram application area to optical communications. These applications are pulling much attention because the traditional applications of holograms such as displays, optical information processing and optical memories are saturating in research. In this paper, we compare holographic filter and other competitive optical devices for optical communication applications. In relation with dense wavelength division multiplexing system, we may find new opportunities by integrating several properties inherent to the holographic gratings. The critical issues might be material performance characteristics for each application.

We demonstrate beam shaping in a hybrid acousto-optic device with adaptive electronic feedback. Cases of positive and negative feedback, and from the un-diffracted and diffracted orders are investigated. We also show the dependence of the final value of the induced grating strength in the acousto-optic cell on the feedback parameters.

The paper presents the analysis of applications and performance characteristics of one-crystal 2D acousto-optic deflectors used for optical signal switching in communication systems. It compares performance and prospects for acousto-optic deflectors made of different material and of different layouts. It shows that 2D light deflection requires higher uniformity of frequency responses of each acoustic channel. Prospects for a 2D deflector built using 'strong' elastic anisotropy in some crystals are estimated. In this case, acoustic beams can coincide, their wave normals being approximately orthogonal. It is shown that crystals with high acoustic velocities and moderate elastic anisotropy (like GaAs) look more promising than traditional for acousto-optics TeO₂ in tasks requiring high operation speed (low switching time).

Bragg-grating sensors fabricated within the same optical fiber are buried within multiple-ply carbon-epoxy planar and cylindrical structures. Effect of different orientation of fiber-sensors with respect to carbon fibers in the composite structure is investigated. This is done for both fabric and uni-tape material samples. Response of planar structures to axial and transverse strain up to 1 millistrain is investigated with distributed Bragg-grating sensors. Material properties like Young’s Modulus and Poisson ratio is measured. A comparison is made between response measured by sensors in different ply-layers and those bonded on the surface. The results from buried fiber-sensors do not completely agree with surface bonded conventional strain gauges. A plausible explanation is given for observed differences. The planar structures are subjected to impacts with energies up to 10 ft-lb. Effect of this impact on the material stiffness is also investigated with buried fiber-optic Bragg sensors. The strain response of such optical sensors is also measured for cylindrical carbon-epoxy composite structures. The sensors are buried within the walls of the cylinder as well as surface bonded in both the axial as well as hoop directions. The response of these fiber-optic sensors is investigated by pressurizing the cylinder up to its burst pressure of around 1500 psi. This is done at both room temperature as well as cryogenic temperatures. The recorded response is compared with that from a conventional strain gauge.

Enhanced spectra of an object in high-frequency components by a photorefractive BaTiO³ two-wave mixing are image on a phase-only filter of a reference object displayed by a liquid-crystal spatial phase modulator. Enhanced preprocessing of an object with phase-only filtering can be achieved a good discrimination ability. The experiments with the system are shown.

We propose remote-multiplexing methods of holograms. A multimode fiber bundle is used as a reference beam-guiding device. Coherent optical wave coupled into the fiber bundle propagates through the bundle and free-space at the output facet. The generated far-field pattern is a kind of random pattern and is used as a reference beam for hologram multiplexing. We model the random pattern by superposition and concatenation of the propagation modes of the multimode fiber and free-space. Based on this model, we analyze and optimize remote multiplexing methods of angle multiplexing, shift multiplexing, and wavelength multiplexing cases. The optimization comes from controlling the number of waveguiding multimode fibers and the transversal spatial spectral range of the fiber-coupled optical wave. The experimental results show the validity of our model. This method and model can be applied to general multimode wave-guide array for random pattern referencing and provide integrated optical system for holographic data storage system.

Fiber Bragg grating (FBG) is an important element in many applications including filters and dispersion compensators in fiber communication systems. With recently developed inverse scattering algorithm, FBGs with desired reflection spectrum and/or dispersion properties can now be designed. However, most of these designs require arbitrary grating amplitude and phase control. Previously, fabrication of such FBGs relies on the accurate control of the temporal variation of the intensity pattern using a piezo electric translation stage. The precision of this fabrication method is limited by the noise in the control voltage, which is usually larger than 1%. The distortion in piezo response also affects the performance. In this paper, we develop and demonstrate a novel writing technique for arbitrary FBG fabrication. Our technique is based on a translate-and-write configuration. The incorporation of a precisely controlled shutter allows the apodization and phase of the FBG to be continuously changed at each grating line. The shutter error mainly results from the control signal's timing jitter, which is normally lower than 0.1%. Using this writing technique, we demonstrate a Hamming apodized grating with 20mm length, -22 dB minimum transmission, and < -25 dB reflection side lobe suppression. Furthermore, phase-shift in a grating can be fabricated by a simple delay in the control signal. We also demonstrate FBGs with π, π/2, 3π/2 phase-shifts, respectively. Our experimental results are in excellent agreement with theoretical predictions. To show the capability to fabricate a FBG with arbitrary structure, we demonstrate a 35 mm long zero dispersion grating.

We propose a new holographic multiplexing technique in LiNbO₃ with 90° geometry. The advanced concept of polarization-multiplexed holographic memory is based on photorefractive effect and photovoltaic effect. The holographic gratings are constructed in the crystal using two writing beams with isotropic and anisotropic polarizaiton recording. Even mutually orthogonal polarized waves can be used in holographic storage. The polarization multiplexing technique can be accompanied with other multiplexing method in the holographic storage, and we can increase the storage capacity doubly.

In the holographic data storage system, a shifting diffuser is employed in the reference beam to realize dynamic speckle multiplexing, while another vibrating diffuser is placed in the object beam to realize speckle modulation. These two methods can enlarge the storage capacity with high signal-to-noise rate. Speckle multiplexing can suppress the crosstalk due to multiple longitudinal modes of the small DPL laser. And speckle modulation in volume holographic correlators can suppress the diffraction sidelobes of output correlation signal along both vertical and horizontal direction. Another advantage of the speckle multiplexing and the speckle modulation is that the angular selectivity and the correlation peak are not sensitive to the thickness of the hologram. Finally a demonstration platform of compact holographic storage and correlation recognition system is briefly introduced in this paper.

The paper considers holographic nanostructures, in particular segmented structures that are used for imaging in the near diffraction field. The e-beam technique is employed to fabricate this sort of hologram and other nanostructures. The future of the method is discussed as applied to the development of nanostructure components, including plasmon structures, artificial dielectric devices for use in optoelectronic data-processing systems.

In this paper, we present investigations on holographic data storage using photopolymer of poly(methyl methacrylate) (PMMA) doped with phenathrenequinone (PQ) molecules. From the system specifications we derive the material parameters that are required for a data storage system. We present a technique of material preparation for obtaining samples with good optical quality. Then we present material characteristics for holographic data storage, including M/#, sensitivity, and material shrinkage. Experimental demonstration on digital data storage is presented and bit error rate is discussed.

In this paper, we propose and examine mask design methods for fabricating optical devices containing multiple holographic gratings. As the conventional fiber Bragg grating fabrication, the mask is also required to achieve compactness and accuracy in this case. However, for the case where there needs multiplexing of several holographic gratings in the same volume of the recording medium, the mask should provide multi-order diffractions and control their relative diffraction efficiencies. We propose two methodologies for the required mask, cascaded phase mask and polymeric angularly multiplexed holographic mask. The cascaded phase mask is composed of the multi-order generating mask and the Bragg mask of two-order diffraction. The polymeric angularly multiplexed holographic mask is a kind of commonly referenced multiplexed holograms. The mask design and fabrication processes are examined. Multiple holographic grating recording in the photorefractive crystal with designed mask is discussed. In order to exclude cross diffraction order modulations, there needs to control the density of acceptors in photorefractive crystal case.

Optical ring-resonators could be used to synthesize filters with low crosstalk and flat passbands. Their application to DWDM interleaving has been proposed and investigated previously. However, a number of important factors related to this topic have not yet been considered and appropriately addressed. In this paper, we propose a novel scheme of a symmetrically parallel-coupled ring resonator array with coupling apodisation. We show that it can be used to construct a wavelength interleaver with remarkably improved performance. Various design factors have been considered. An optimization procedure was developed based on minimizing the channel crosstalk in the through and drop ports simultaneously by adjusting the ring-bus coupling coefficients. We show that apodisation in coupling could suppress channel crosstalk effectively, by choosing the optimal coupling coefficients. We also introduced the equalization of both the input and output coupling coefficients to minimise passband ripple. For a 50 - 100 GHz DWDM applications, four rings is found to be the best choice for array size. A four-ring filter achieves crosstalk -24 dB, insertion loss at resonance <1 dB, and good passband flatness (shape factor >0.6).

Using a combination of ion implantation and laser ablation techniques, a waveguide of ion implanted SiC:Ga:Ge was fabricated and was used as a CO₂ laser line selector. It was observed that the CO₂ laser produces a thermal grating which drives the optical selector with maximum efficiency of 40 MHz of laser offset between the 9P20 and 9P18 CO2 laser lines. Using an external electric field, the moving thermal grating produces a 45 MHz offset between the laser lines. This phenomenon will be explained using the Kukhtarev model. The threshold of the thermal damage for the waveguide and the device limiting will be presented.

An optical security holographic memory encrypted by a random phase key and decrypted by a holographic key (a holographic optical element; HOE) is presented and demonstrated. The security hologram is based on protecting the access to the memory from the unauthorized users by encoding the reference waves. The holographic decryption key is fabricated by storing the wavefront information of the set of reference beams. Each addressed reference beam is stored in the HOE through holographic multiplexing technique. The decryption process is achieved by using the reconstruction reference beam to access the secure data. This security hologram system is suitable for practical application since the decryption key can be controlled copied. As to our best knowledge, this is the first experimental impementation to replace a random phase mask key.

In this paper, a photorefractive crystal based all-optical architecture for implementing the fringe-adjusted joint transform correlation (JTC) technique is investigated. The photorefractive JTC technique is fast because it operates in the optical domain and it generates the correlation output in one step. Computer simulation results using real life image sequences are presented to verify the performance of the proposed technique for target detection and tracking purposes.

We present a novel interrogation method to measure wavelength shifts in fiber Bragg grating sensor array. A fiber laser tuned by an intracavity FP (Fabry-Perot) filter was used to interrogate Bragg wavelength variations. To solve the linearity, stability, and accuracy problems caused by the nonlinear response of FP filter, we calculated the wavelength variation of the fiber laser using quadrature signal processing with an unbalanced M/Z (Mach-Zehnder) interferometer and time-delayed sampling technique. The phase modulated interferometric signal is sampled with time delay, generating quadrature phase-delayed signals. By applying arctangent demodulation and phase unwrapping algorithm to the signals, accurate wavelength readout is performed. The calculated wavelengths are mapped to corresponding temporal reflection peaks from the sensor array, which enables more accurate fiber grating interrogation without the problems from the FP filter’s nonlinear response. The wavelength resolution of ~ 20 pm was obtained in our experimental setup, which could have been greatly enhanced with faster phase modulation.

We propose and demonstrate a new way to image a coherent pattern through a thick dynamic phase distorting medium using a photorefractive LiNbO₃ crystal. The method involves only one beam of light- the object light. Making use of photorefractive fanning effect, gratings are formed in the LiNbO₃ crystal through the interference between the fanning light and the image light. In this way, the undistorted image is recorded in the crystal. The intensity distribution of the image can then be reconstructed at any time later. An undistorted image can be obtained under the condition that the period of the fluctuation time in the medium is much shorter than the response time of the crystal. Since this method uses only one beam of light, its layout is simpler and thus it avoids some aberrations due to the constraint in the layout in other methods, such as the aberration due to oblique incident light.

We propose a volume-holographic filter to perform 3D object filtering. Theoretical analysis and the corresponding experiment of the shifting tolerance of the volume-holographic filter are demonstrated. We find that the shifting selectivity is different for different shifting directions, which include laterally horizontal, laterally vertical, and longitudinal directions. The simulation results show that the shifting selectivity depends on the scale of the object and the distance between obejct and the holographic filters.

Using two beam coupling geometry, high order copropagating and contrapropagating isotropic and copropagating anisotropic self-diffraction are demonstrated using photorefractive cerium doped barium titanate. At small incident angles, typically less than 0.015 radians, both codirectional isotropic self-diffraction (CODIS) and contradirectional isotropic self-diffraction (CONDIS) orders are generated simultaneously. At larger incident angles, typically approximately more than 0.2094 radians, only codirectional anisotropic-self diffraction (CODAS) orders are generated. Ongoing work on image auto/cross correlation results are also shown.

The dependence of nonvolatile holographic recording on Ce and Cu dopant composition ratios in doubly doped LiNbO₃ crystals is investigated experimentally. Three groups of congruent LiNbO₃:Ce:Cu crystals have been grown by the Czochralski method with the compositions of 0.085 wt % Ce₂O₃ and 0.011 wt % CuO, 0.045 wt % Ce₂O₃ and 0.045 wt % CuO, 0.011 wt % Ce₂O₃ and 0.085 wt % CuO, respectively. The recording results and the transmission spectra show that the absorption characteristics of the crystals to ultraviolet light have great impact on the finally fixed diffraction efficiency, and the larger the absorption to ultraviolet light, the higher the fixed diffraction efficiency. At the same time, the dependence of the absorption characteristics to ultraviolet light of the medium on both dopant composition ratios and oxidization/reduction annealing conditions is analyzed. As a result, the weakly oxidized crystal with composition of 0.011 wt % Ce₂O₃ and 0.085 wt % CuO has the highest fixed diffraction efficiency.

Grating spacing has great influence on grating formation via electron transport in the conduction band during holographic recording. Grating spacing dependence of two center holographic recording is investigated by writing nonvolatile holograms in doubly doped LiNbO₃ crystals. Several types of electron characteristic transport lengths are defined. The effects of electron characteristic transport lengths and oxidation-reduction state on the amplitude of nonvolatile holographic grating are numerically discussed within the range of grating spacing from 0.14μm to 10μm. It is found that the bulk photovoltaic effect is the dominant electron transport mechanism of doubly doped LiNbO₃ crystals, while the diffusion effect does have appreciable effect on the grating formation when grating spacing is smaller than 1μm. Theoretical analysis and experimental results confirm that the logarithm of the amplitude of nonvolatile holographic grating Log (δn) increases with increasing grating spacing Λ within region of small grating spacing (Λsmaller than 1μm) and further increasing of grating spacing won’t influence the values of Log (δn) greatly.

Photoelectronic processes in CdIn₂Te₄ are investigated by means of photoconductivity studies and by the thermal spectroscopy: the photoinduced current transient spectroscopy. The so-called four-gate method shows that we are in presence of a continuous or quasi-continuous distribution of levels in the energy bandgap. This occurs in the whole range of energy prospected: 0.1 to 0.7 eV. The analysis of the decay of the photocurrent transients at various temperatures allows to calculate the density of states and leads to the conclusion that the trap distribution inside the gap is formed by two parts: a continuous exponential trap distribution under the conduction band, until 0.35 eV, and a Gaussian distribution from 0.35 to 0.7 eV with a maximum at 0.55 eV, near the middle of the gap.

On the basis of vectorial coupled-wave theory, the diffraction of optical waves by finite bounded volume holographic grating is described, taking into account polarizations of the reference beam and the subject beam, variation of the average dielectric constant and the modulation depth. The deduced set of coupled-wave equations restricted in a bounded volume is solved numerically by means of the Runge-Kutta calculation. The intensity distributions of the transmitted and diffracted beams are strongly influenced by the modulation depth, the polarization of incidence and the variation of average dielectric constant. It is demonstrated that a high coupling coefficient volume holographic grating may considerably distort the shape of the output beams. We can optimize intensity distributions of the output beams and provide the way for further improvement.

The time-space dynamics of the recording and fixing of photorefractive holograms in doubly-doped LiNbO₃:Fe:Mn crystals are analyzed by jointly and numerically solving the set of time-differential two-center material equations and the set of space-differential coupled-wave equations. In the formulation, the absorption of both the recording light and the sensitizing light is included. The results for optimizing the holographic recording are similar to those obtained by the previous steady-state solving. In this paper, therefore, a special attention is paid on the time-space evolution of the intensity and phase distributions of the induced space-charge fields and the exciting interference pattern of the two beams for recording or the readout and diffracted beams for coherent erasing. It is interesting to find that during the time development of hologram there is a spatially changed direction of energy transferring between the two-coupled beams, which depends spatially on the relative phase difference between the induced space-charge field and the exciting interference pattern. The energy transferring direction will be reversed as the relative phase difference becomes opposite in the sign. As a result, the spatial figures of the isophase and the recording or recorded holographic fringes are depicted, which gives a full understanding for the formation of photorefractive hologram in LiNbO₃:Fe:Mn.

A new approach to design the binary phase holograms, which is of less computation time and equal efficiency compared with the genetic algorithm method is proposed. Synthesized holograms having diffraction efficiency of 75.8% and uniformity of 5.8% are proven in computer simulation and experimentally demonstrated.

In this paper, Gaussian apodization technique applied to a transmission volume hologram for holographic demultiplexer is proposed. The Gaussian apodized grating of 15 mm x 11 mmsize, 38 μm thickness and 3.2 mm horizontal standard deviation of the modulating index profile was fabricated. A 22-channel demultiplexer based on that grating has been optically demonstrated. The channel spacing, the interchannel cross-talk level and the channel uniformity of 0.8 nm, -30 dB and 1.5 dB, respectively, were obtained.

In this paper, electro-optic properties of 0.67Pb(Mg_1/3Nb_2/3)0₃-0.33PbTiO₃ (PMN-33%PT) single crystals under proper AC bias are reported. It is found that PMN-33%PT has an extremely large linear electro-optic coefficient, r₃₃ ~9800 pm/V under proper AC bias. Besides this huge electro-optic coefficient, PMN-33%PT crystals also have very good optical quality and the random scatterings caused by the multiple domains can be totally removed by the AC bias. Furthermore, unlike KTN, PMN-PT has a much higher phase transition temperature (~175°C), which is sufficiently away from the room temperature so that a good thermal stability can be achieved. The combinations of giant electro-optic coefficient, good optical quality, and high thermal stability may make PMN-33%PT the best electro-optic material among all electro-optic crystals developed so far, which could revolutionize applications of electro-optic crystals to telecommunications, medical imaging, et al. This research may also help to understand the mechanism underlying the ultrahigh performance of this new generation of single crystal materials (e.g., PZN-PT, PMN-PT) via the interaction between crystal internal structures and external AC electric field, which may stimulate further interest in the fundamental theory of ferroelectrices under changing electric field that could direct improving the quality of existing ferroelectric crystals and developing new ferroelectric crystals.

A unique, all-optic switch based on an innovatively designed planar lightwave circuit (PLC) is presented in this paper. The switching function is achieved by using ultra large birefringence of nematic liquid crystals (NLC) filled at the trench of waveguides. The trench at the crossing forms a waveguide mirror or a matching medium when extraordinary and ordinary refractive indices of NLC are employed, respectively. The major advantages of our unique design are: (1) the limitation that refractive index of liquid crystal must be less than that of waveguide material itself is eliminated so that conventional NCL material such as E7 can be used; (2) it is a self aligned fabrication process that alleviates the tight tolerance of later tilt error; (3) the design is thermally stable. The successful fabrication of this unqiue switch could result in an enabling element for the next generation all-optic networks.

Although multimode fiber has a large space-bandwidth product (roughly equal to the number of modes), transmitting spatial signals by using a fiber is rather difficult. Conventional sensing schemes for fiber chemical sensors are based on the intensity and/or spectroscopic absorption or emission of fiber evanescent field of multimode fiber. However, the transmission of spatial signal has not been exploited in the field of chemical sensing. In our research, a novel chemical sensing method that employs the spatial information of a multimode fiber was investigated. When a laser beam is launched into a multimode fiber, the exit light field produces a complicated speckle pattern caused by the modal interference of the fiber. It is difficult to recover the transmitted information from the speckle field. However, the fiber speckle field can be used for fiber sensing with an inner product method. Our analysis and experiments have shown that the fiber specklegram sensor is very sensitive to chemical environment change.

The application of ferroelectric crystals in light modulation has been of significant interests due to their exceptional electrical field sensitive optical properties or high electrooptic coefficients. Single crystal fibers of lithium niobate and strontium barium niobate grown by laser heated pedestal growth method are explored for optical pulse engineering (frequency shift, pulse compact, or pulse reshaping). The electrooptic behavior was investigated and compared in a microwave cavity of TE103 mode at 10GHz.