Theoretical investigation of nonvolatile holographic storage in doubly doped lithium niobate crystals

We have studied theoretically the inherent mechanisms of nonvolatile holographic storage in doubly doped LiNbO3 crystals. The photochromic effect of doubly doped LiNbO3 crystals is discussed, and the criterion for this effect is obtained through the photochromism-bleach factor a = S(21)gamma(1)/S(11)gamma(2) that we define. The two-center recording and fixing processes are analytically discussed with extended Kukhtarev equations, and analytical expressions for recorded and fixed steady-state space-charge fields as well as temporal behavior during the fixing process are obtained. The effects of microphysical quantities, the macrophotochromic effect on fixing efficiency, and recorded and fixed steady-state space-charge fields, are discussed analytically and numerically. (C) 2002 Optical Society of America.

Effect of wavelength of sensitizing light on holographic storage properties in LiNbO3 : Fe : Ni crystal

By sensitizing with 514 nm green light, 488 nm blue light and 390 nm ultraviolet light, respectively, recording with 633 nm red light, effect of wavelength of sensitizing light on holographic storage properties in LiNbO3:Fe:Ni crystal is investigated in detail. It is shown that by shortening the wavelength of sensitizing light gradually, nonvolatile holographic recording properties of oxidized LiNbO3:Fe:Ni crystal is optimized gradually, 390 nm ultraviolet light is the best as the sensitizing light. Considering the absorption of sensitizing light, to obtain the best performance in two-center holographic recording we must choose a sensitizing wavelength that is long enough to prevent unwanted absorptions (band-to-band, etc.) and short enough to result in efficient sensitization from the deep traps. So in practice a trade-off is always needed. Explanation is presented theoretically. (c) 2005 Elsevier GmbH. All rights reserved.

Vectorial solution of Kukhtarev equations for doubly doped crystals and optimal choice of recording directions in nonvolatile holographic storage

Vectorial Kukhtarev equations modified for the nonvolatile holographic recording in doubly doped crystals are analyzed, in which the bulk photovoltaic effect and the external electrical field are both considered. On the basis of small modulation approximation, both the analytic solution to the space-charge field with time in the recording phase and in the readout phase are deduced. The analytic solutions can be easily simplified to adapt the one-center model, and they have the same analytic expressions given those when the grating vector is along the optical axis. Based on the vectorial analyses of the band transport model an optimal recording direction is given to maximize the refractive index change in doubly doped LiNbO3:Fe: Mn crystals. (c) 2007 Optical Society of America.

Optical setup and analysis of disk-type photopolymer high-density holographic storage

A relatively simple scheme for disk-type photopolymer high-density holographic storage based on angular and spatial multiplexing is described. The effects of the optical setup on the recording capacity and density are studied. Calculations and analysis show that this scheme is more effective than a scheme based on the spatioangular multiplexing for disk-type photopolymer high-density holographic storage, which has a limited medium thickness. Also an optimal beam recording angle exists to achieve maximum recording capacity and density. (C) 2002 Society of Photo-Optical Instrumentation Engineers.

Riboflavin sensitized photopolymer materials for holographic storage

Riboflavin is employed as the photosensitizer of a novel photopolyrner material for holographic recording, This material has a broad absorption spectrum range (More than 200nm) due to the addition of this dye. The experimental results show that our material has high diffraction efficiency and large refractive index modulation. The maximum diffraction efficiency of the photopolymer is about 56%. The digital data pages are stored in this medium and the reconstructed data page has a good fidelity, with the bit-error-ratio of about 1.8 X 10(-4). it is found that the photopolymer material is suitable for high-density volume holographic digital storage.

Experimental study on polarization holographic storage in genetic mutant BR-D96N film

Recording with both parallel and orthogonal linearly polarized lights, polarization holographic storage in genetic mutant BR-D96N film is reported with both transmission type geometry and reflection type geometry. Polarization properties of diffraction light and scattering light are discussed for two different cases, parallel polarization recording and orthogonal polarization recording. It shows that, compared with recording with parallel polarization lights, orthogonal polarization holography can separate the diffraction light from the scattering noise, therefore improving the signal-to-noise ratio. It also shows that, compared with reconstruction with reference light, reconstruction with phase conjugated wave of the reference light can improve the signal-to-noise ratio of the reconstructed diffraction image, and also the wave-front aberration of the object light introduced by irregular phase object in the optical pass-way can also be corrected effectively, which ensures that the reconstructed diffraction image has a better fidelity. The preliminary angle-multiplexed volume holographic storage multiplexed by transmission type geometry and reflection type geometry is demonstrated in the BR-D96N film. Experiment shows that there is no cross-talk between the two pages of images except for some scattering noises.

Polarization holographic high-density optical data storage in bacteriorhodopsin film

Optical films containing the genetic variant bacteriorhodopsin BR-D96N were experimentally studied in view of their properties as media for holographic storage. Different polarization recording schemes were tested and compared. The influence of the polarization states of the recording and readout waves on the retrieved diffractive image's intensity and its signal-to-noise ratio were analyzed. The experimental results showed that, compared with the other tested polarization relations during holographic recording, the discrimination between the polarization states of diffracted and scattered light is optimized with orthogonal circular polarization of the recording beams, and thus a high signal-to-noise ratio and a high diffraction efficiency are obtained. Using a He-Ne laser (633 nm, 3 mW) for recording and readout, a spatial light modulator as a data input element, and a 2D-CCD sensor for data capture in a Fourier-transform holographic setup, a storage density of 2 x 10(8) bits/cm(2) was obtained on a 60 x 42 mu m(2) area in the BR-D96N film. The readout of encoded binary data was possible with a zero-error rate at the tested storage density. (c) 2005 Optical Society of America.

High-density holographic recording parameters under different wavelength of a two dyes-sensitized photopolymer

The high-density holographic recording parameters of a novel two dyes-sensitized photopolymer under different exposure wavelengths are studied. The results show that the maximum diffraction efficiency, exposure sensitivity, maximum refraction index modulation, dynamic range, and the exposure time constant increases with the increase of the exposure wavelength. The analysis indicates that the scattering has an important role in the forming of the holographic grating. (c) 2005 Elsevier GmbH. All rights reserved.

A wideband sensitive holographic photopolymer

A novel wideband sensitive dry holographic photopolymer sensitized by rose bengal (RB) and methylene blue (MB) is fabricated, the holographic storage characteristics of which are investigated under different exposure wavelengths. The result shows that the sensitive spectral band exceeds 200 nm in visible light range, the maximum diffraction efficiency under different exposure wavelengths is more than 40% and decreases with the decrease of exposure wavelength, the exposure sensitivity is not change with the exposure wavelength. This photopolymer is appropriate for wavelength multiplexing or multi-wavelength recording in digital holographic storage.

A new photopolymerizable holographic recording material based on acrylamide and N-hydroxymethyl acrylamide

A new polyvinylalcohol-based photopolymeric holographic recording material has been developed. The recording is obtained by the copolymerization of acrylamide and N-hydroxymethyl acrylamide. Diffraction efficiencies near 50% are obtained with energetic exposure of 80mJ/cm(2). N-hydroxymethyl acrylamide can improve the optical quality of the film. With the increase of the concentration of N-hydroxymethyl acrylamide, the flatness of the film increases, scattering reduces and the straight image is clearer with a small distortion. The postexposure effect on the grating is also studied. The diffraction efficiency of grating increases further during postexposure, gradient of monomer exists after exposure.

A new metal ion doped panchromatic photopolymer for holographic applications

This thesis has discussed the development of a new metal ion doped panchromatic photopolymer for various holographic applications. High-quality panchromatic holographic recording material with high diffraction efficiency, high photosensitivity and high spatial resolution is one of the key factors for the successful recording of true colour holograms. The capability of the developed material for multicolour holography can be investigated.In the present work, multiplexing studies were carried out using He-Ne laser (632.8 nm). Multiplexing can be done using low wavelength lasers like Ar+ ion (488 nm) and frequency doubled Nd: YAG (532 nm) lasers, so as to increase the storage capacity. The photopolymer film studied had a thickness of only 130 Cm. Films with high thickness (~500 Cm) is highly essential for competitive holographic memories . Hence films with high thickness can be fabricated and efforts can be made to record more holograms or gratings in the material.In the present study, attempts were made to record data page in silver doped MBPVA/AA photopolymer film. Image of a checkerboard pattern was recorded in the film, which could be reconstructed with good image fidelity. Efforts can be made to determine the bit error rate (BER) which provides a quantitative measure of the image quality of the reconstructed image . Multiple holographic data pages can also be recorded in the material making use of different multiplexing techniques.Holographic optical elements (HOEs) are widely used in optical sensors, optical information processing, fibre optics, optical scanners and solar concentrators . The suitability of the developed film for recording holographic optical elements like lenses, beam splitters and filters can be studied.The suitability of a reflection hologram recorded in acrylamide based photopolymer for visual indication of environmental humidity is reported . Studies can be done to optimize the film composition for recording of reflection holograms.An improvement in the spatial resolution of PVA/acrylamide based photopolymer by using a low molecular-weight poly (vinyl alcohol) binder was recently reported . Effect of the molecular weight of the binder matrix on the holographic properties of the developed photopolymer system can be investigated.Incorporation of nanoparticles into photopolymer system is reported to enhance the resolution and improve the dimensional stability of the system . Hence efforts can be made to incorporate silver nanoparticles into the photopolymer and its influence on the holographic properties can be studied.This thesis was a small venture towards the realization of a big goal, a competent holographic recording material with excellent properties for practical holographic applications. As a result of the present research, we could successfully develop an efficient panchromatic photopolymer system and could demonstrate its suitability for recording transmission holograms and holographic data page. The developed photopolymer system is expected to have significant applications in the fields of true-color display holography, wavelength multiplexing holographic storage, and holographic optical elements. Highly concentrated and determined effort has yet to be put forth for this expectation to become a reality.

LiNbO3：Fe：Ni晶体非挥发全息存储研究

采用三种不同的双光记录方案进行了LiNbO3：Fe：Ni晶体全息存储实验．详细研究了饱和衍射效率、固定衍射效率、动态范围和记录灵敏度，以及退火条件对记录的影响。结果表明，氧化LiNbO3：Fe：Ni晶体的饱和衍射效率、固定衍射效率和记录灵敏度比其他报道的双掺杂LiNbO3晶体高。结合掺杂能级图，理论分析了LiNbO3双掺杂晶体深陷阱中心能级的相对位置及其微观光学参量对全息记录性能的影响。LiNbO3：Fe：Ni晶体有望成为一种新的高效率非挥发全息存储材料。

Characteristics of recording and thermal fixing in lithium niobate

We present a theoretical model in which the band-transport equations and the coupled-wave equations are considered to study the two thermal-fixing methods (simultaneous fixing and postfixing) in Fe:LiNbO3. We found that, in simultaneous fixing, the existing ionic-grating affects the writing of the electronic grating by reduction of the coupling gain, and the grating envelope of the fixed-index grating is quite uniform inside the photorefractive crystal in comparison with the method of postfixing. The resulting diffraction efficiency of the fixed-volume grating is dependent mainly on the initial intensity modulation of the two writing beams. A set of experiments is also presented. (C) 1998 Optical Society of America.

Symmetry of the Talbot effect and its applications

The Talbot effect is one of the most basic optical phenomena that has received extensive investigations both because its new results provide us more understanding of the fundamental Fresnel diffraction and also because of its wide applications. We summarize our recent results on this subject. Symmetry of the Talbot effect, which was reported in Optics Communications in 1995, is now realized as the key to reveal other rules for explanation of the Talbot effect for array illumination. The regularly rearranged-neighboring-phase-differences (RRNPD) rule, a completely new set of analytic phase equations (Applied Optics, 1999), and the prime-number decomposing rule (Applied Optics, 2001) are the newly obtained results that reflect the symmetry of the Talbot effect in essence. We also reported our results on the applications of the Talbot effect. Talbot phase codes are the orthogonal codes that can be used for phase coding of holographic storage. A new optical scanner based on the phase codes for Talbot array illumination has unique advantages. Furthermore, a novel two-layered multifunctional computer-generated hologram based on the fractional Talbot effect was proposed and implemented (Optics Letters, 2003). We believe that these new results should bring us more new understanding of the Talbot effect and help us to design novel optical devices that should benefit practical applications. (C) 2004 Society of Photo-Optical Instrumentation Engineers.

LiNbO3：Cu：Ce非挥发全息记录掺杂组份比的优化

实验研究了掺杂组份比对LiNbO3：Cu：Ce晶体非挥发全息记录性能的影响。结果表明．在全息记录过程中，掺杂组份比通过改变晶体的紫外光吸收特性而引起全息记录性能的改变。增加LiNbO3：Cu：Ce晶体中Cu和Ce的掺杂组份比会导致晶体对紫外光吸收的增强，进而提高了全息记录灵敏度和固定衍射效率。在弱氧化处理的掺有CuO和Ce2O4的质量分数分别为0.085％和0．011％的LiNbO3：Ce：Cu晶体中．得到了最高的固定衍射效率ηf=32％和记录灵敏度S=0．022cm／J。