This paper compares the read/write holographic memory with silicon storage on issues of cost, density, size and speed. With a photorefractive crystal on top of a silicon interface, the holographic memory is of cost efficiency, volume compactness and fast data accessing. Key challenges to implement the competitive holographic memory are discussed.

Recent investigations in holographic mass memory systems have produced proof of concept demonstrations that have highlighted their potential for providing unprecedented capacity, data transfer rates and fast random access performance. The exploratory nature of most such investigations have been largely confined to benchtop experiments in which the practical constraints of packaging and environmental concerns have been ignored. We have embarked on an effort to demonstrate the holographic mass memory concept by developing a compact prototype system geared for avionics and similar applications which demand the following features (mostly interdependent factors): (1) solid state design (no moving parts), (2) fast data seek time, (3) robust with respect to environmental factors (temperature, vibration, shock). In this paper, we report on the development and demonstration of two systems, one with 100 Mbytes and the other with more than 1 Gbyte of storage capacity. Both systems feature solid state design with the addressing mechanism realized with acousto- optic deflectors that are capable of better than 50 microseconds data seek time. Since the basic designs for the two systems are similar, we describe only the larger system in detail. The operation of the smaller system has been demonstrated in various environments including hand-held operation and thermal/mechanical shock and a photograph of the smaller system is provided as well as actual digital data retrieved from the same system.

By reading data in an angular multiplexed holographic storage system at a wavelength other than the wavelength used for writing, the problem of unwanted erasure can be prevented. By compensating data prior to recording, the mismatch resulting from the difference in reading and writing wavelengths may be minimized. Such a compensation technique was experimentally investigated by recording differentially encoded data within an Fe doped sample of LiNbO₃ at a wavelength of 514 nm and recalling data using 488 nm. Our system demonstrated that the recording of compensated data allowed accurate readout with a raw bit error rate of .08%.

We present a comparison of different two-step holographic recording schemes based on their multiplexing performance using a unified framework. The difference between the different schemes is mainly due to the energy levels and sources of the traps. The influence of effective trap density and recording and sensitizing intensities are addressed. It is shown that for low light intensity operation, the performance of the doubly-doped crystals is superior due to the lack of dark depopulation of the shallow traps. Usage of such crystals also results in the suppression of the intensity threshold that exists for two-step recording in singly-doped crystals. The promising potentials for improvements in the two-step holographic recording in doubly-doped materials is also addressed.

In multi-hologram recording, a simple system to implement rotational, angular, and spatial multiplexing efficiently together is proposed and experimented. The methods of both rotational and angular multiplexing are obtained by controlling the reference beam directly by the use of a pair of wedge prisms, while the method of spatial multiplexing is obtained by shifting the recording medium. The proposed system structure makes it easy to realize a practical holographic memory system by simplifying the control of three complex mechanical motions that are necessary for the three multiplexing techniques.

We report on the holographic storage and recovery of multiple high capacity (800 X 600, 480 kbit) data pages in 250 micrometer and 500 micrometer thick photopolymer media. The data pages were recovered with raw bit error rates less than 5 X 10^-3, the level correctable by current error correction strategies. Our results demonstrate that photopolymer systems can be fabricated with the optical quality and low level of scatter required for digital data storage.

A multiple-angle liquid crystal blazed grating beam deflector has been developed. It consists of a stack of liquid crystal blazed gratings where each layer can deflect incident light with very high efficiency into one of two different directions depending on the driving condition. Four steering angles (10.8 degrees, 7.2 degrees, 3.6 degrees, 0 degrees) with about 70% diffraction efficiency are demonstrated with 15 V. The device's working principle, design considerations, fabrication process, and characterization results are described.

We investigated compositional volume grating formation in the Polaroid medium that utilizes the cationic-ring-opening photoinitiated polymerization process, and compared our conclusions with the current physical model describing polymer holographic recording. We identified the effects of diffusion and polymerization during illumination, as well as significant postexposure grating development. Holographic recording in this medium allows for final strong gratings with high recording sensitivity (S approximately 2 cm/mJ), that were not limited at the higher recording intensities (I less than or equal to 250 mW/cm²) corresponding to photon (exposure) limited recording. The results of the present analysis allow for more comprehensive physical description of grating formation in the photoinitiated CROP process, and evaluation of the polymer recording process in a nonvolatile holographic storage system.

Holographic storage has the potential to become a digital data storage technology with fast readout and high density. Computer users have come to expect, however, that data retrieved from their storage devices will be retrieved error- free (with a probability of error less than 10^-12). In both conventional storage devices and holographic data storage, achieving this degree of reliability involves a good understanding of the data channel and a combination of careful hardware engineering, signal processing, and coding. At the IBM Almaden Research Center, we have leveraged the expertise acquired with 1-dimensional, time-dependent data channels found in magnetic and optical data storage systems, to develop unique and highly effective signal processing and coding algorithms to optimize the performance of the 2-dimensional, space-dependent digital holographic data storage channel. Crucial to our efforts has been the high-performance holographic data storage platform we built in 1996. This tool has allowed us to characterize and perturb a real holographic data channel, and implement and evaluate new data-coding and signal processing algorithms. This rapid feedback loop between ideas, implementation, and results both aids in selecting fruitful approaches and yields deeper understanding of the underlying data channel. In this paper, we discuss the holographic digital data storage channel as divided into five parts: the optical path, pre-processing (how the data gets into the holograms), post-processing (manipulation of raw data just after optical detection), conversion into binary 0's and 1's, and error-correction (using added redundancy). Optimizing the channel involves maximizing the system performance (density, speed) while minimizing complexity (and thus cost) and maintaining the required degree of reliability.

This paper describes the implementation of error detection and correction logic in the optoelectronic cache memory prototype at the University of Pittsburgh. In this project, our goal is to integrate a 3-D optical memory directly into the memory hierarchy of a personal computer. As with any optical storage system, error correction is essential to maintaining acceptable system performance. We have implemented a fully pipelined, real time decoder for 60-bit Spectral Reed-Solomon code words. The decoder is implemented in reconfigurable logic, using a single Xilinx 4000-series FPGA per code word and is fully scalable using multiple FPGA's. The current implementation operates at 33 Mhz, and processes two code words in parallel per clock cycle for an aggregate data rate of 4 Gb/s. We present a brief overview of the project and of Spectral Reed-Solomon codes followed by a description of our implementation and performance data.

It is essential for parallel optical memory interfaces to incorporate processing that dynamically differentiates between databit values. These thresholding points will vary as a result of system noise -- due to contrast fluctuations, variations in data page composition, reference beam misalignment, etc. To maintain reasonable data integrity it is necessary to select the threshold close to its optimal level. In this paper, a neural network (NN) approach is proposed as a fast method of determining the threshold to meet the required transfer rate. The multi-layered perceptron network can be incorporated as part of a smart photodetector array (SPA). Other methods have suggested performing the operation by means of histogram or by use of statistical information. These approaches fail in that they unnecessarily switch to a 1-D paradigm. In this serial domain, global thresholding is pointless since sequence detection could be applied. The discussed approach is a parallel solution with less overhead than multi-rail encoding. As part of this method, a small set of values are designated as threshold determination data bits; these are interleaved with the information data bits and are used as inputs to the NN. The approach has been tested using both simulated data as well as data obtained from a volume holographic memory system. Results show convergence of the training and an ability to generalize upon untrained data for binary and multi-level gray scale datapage images. Methodologies are discussed for improving the performance by a proper training set selection.

Data communication aggreagate bandwidth now doubles every 100 days. This transmitted data has origins and destinations, as well as way-stations. At terabit per second channel bandwidth, new optical memory technology may enhance the capability to launch, buffer, and collect multiplexed data streams in the optical domain. Candidate technologies include soliton fiber- loop and coherent transient memories.

We present a preliminary investigation of introducing multi- phase clock signals into optoelectronic integrated circuits that we use to interface optical memories and electronic computers. The potential advantage of multiphase clocking is the enabling of faster pipelining and parallelism on the chip. Our study suggests that we could gain significant performance improvement for special applications such as database processing.

The simple and compact optical design of the recently proposed smart pixels with smart illumination (SPSI) concept allows an integrated emitter and detector array to dynamically and efficiently illuminate and sense remote objects with enhanced functionality. Each pixel can control its associated photodetector(s) illumination level or modulation characteristics through electronic feedback from the pixel's photodetector(s) to its emitter. Features include intensity compression and background subtraction on every pixel. The SPSI concept has several potential applications in sensor array technology including edge detection; focus and tracking sensors; dynamic spotlight tracking systems; tracking of objects in manufacturing; and ranging. The features of SPSI can be exploited in the writing and reading interfaces of page-oriented optical memory systems. The simple optical design coupled with the electrically integrated array of emitters and detectors allows for simultaneous sensing of all elements of a two dimensional array, with each pixel adjusting to maximize its sensitivity. The opto-electronic feedback in each pixel allows for adjustment for variation in reflectivity (or emission) across a memory material and maximization of each photodetectors' dynamic range. Differential sensing capabilities allow for precise detection of dual rail digital or analog signals. Pixel-by-pixel background subtraction can reduce the effects of scattering and crosstalk between pixels. The dynamic spatial structure of the illumination could play an integral role in adaptive error correction and encryption algorithms.

We describe three-dimensional error correcting codes for encoding data to be stored in volumetric optical memories. Data are stored and retrieved in multiple pages where each page is a two-dimensional information bit array. This three- dimensional encoding, also called z-encoding, provides error detection and correction regarding error events which may span multiple pages. We discuss codes that can provide the same level of error protection to all the information bits in a page and codes that support unequal error protection such that selected groups of information bits are provided different levels of protection. The bit error rate performance of these codes is analyzed and simulated. For raw bit error rates ranging from 10^-5 to 10^-4, these codes provide corrected bit error rates ranging from 10^-14 to 10^-12, respectively. The codes can be implemented in a bit-serial and bit-parallel fashion.

The Structured Query Language (SQL) is the de facto standard for commercial database management systems. Optoelectronic database accelerator architectures must be able to support the complex arithmetic functionality of SQL to be accepted in the marketplace. We propose an optoelectronic architecture which directly supports SQL by combining an optically loaded RAM with conventional electronic circuity.

We have observed excitation of spin echoes and spin free induction decay (FID) by electromagnetically induced transparency (EIT) in an optically dense solid sample. The experiments are done in a double-lambda system of 605.7 nm 3H4 - 1D2 transition of Pr3+:Y2SiO5, where the 10.2 MHz ground state spin coherence is excited by low-power resonant Raman pulses. It has been shown that the spin coherence, including spin echo, is equivalent to the transparent state of EIT, and therefore a high efficiency is expected for such resonant Raman-excited spin echo. The observed efficiency of spin echo is as high as 75% of the FID signal at 5K. A background-free detection scheme is used based on EIT and enhanced nondegenerate four-wave mixing. The technique is applied in the frequency-selective time-domain optical data storage, that utilizes the spin as well as the optical inhomogeneous spectral widths. The data storage scheme is analogous to the stimulated spin echo with resonant Raman excitation of the spin coherence. We verify that the write window is determined by the spin T₂ which is much longer than the optical T₂, especially at higher temperature. We find that the spin dephasing time T₂ is almost constant at approximately 500 microseconds in the range of 2 to approximately 6 K, whereas the optical T₂ decreases rapidly, by a factor of approximately 50, above 4 K. These results will be useful in the development of high capacity time-domain optical data storage operating at higher temperature.

In photon-echo-based optical data storage and data processing the photon echo output intensity generally is about 0.1 - 1% of the input intensity. Many devices, such as processors would require that the photon echo output is used as an input to a new photon echo process. To obtain a sufficient signal-to- noise it would be necessary to first amplify the photon echo output signal. In this paper Pr-doped ZBLAN fibers are used to amplify the photon echo signals generated in Pr-doped Y₂SiO₅ at 606 nm. The fiber amplifier is pumped by the 476 nm output from an Ar-ion laser. Mirror-less lasing due to reflection at the fiber ends is eliminated by cleaving the fiber ends at an angle. The upper limit of the gain in a fiber is set by the core refractive index and the fiber numerical aperture. By changing from a fiber with numerical aperture of 0.4 to one with 0.15, the gain obtained at 606 nm is increased from 45 to 330.

It was envisaged that spectral holeburning based optical memory will provide orders of magnitude improvement in storage densities. The progress has basically been hampered by the lack of materials with proper performance characteristics. In the past two decades, novel atomic scale processes involved in holeburning have been investigated in detail in order to improve the performance of existing materials and to engineer new ones. On the other hand, significant advances have been made in optical storage techniques to use the materials available. And now, new materials that can approach the specifications of a memory device using different techniques for the storage are either available or are just over the horizon. This paper reviews the status of different classes of spectral holeburning materials suitable for memory devices.

The optical properties of four Tm³⁺ chelates, specifically (beta) -diketone tris chelates of thulium, in a poly(methyl methacrylate) matrix are presented. Samples under investigation were the Tm³⁺ complexes formed using thulium chloride (TmCl₃ (DOT) 6H₂O) with thenoyltrifluoroacetylacetone (TTFA), 1,1,1-trifluoro-2,4- pentanedione (TFD), 1-phenyl-1,3-butanedione (PBD), and 1,3- diphenyl-1,3-propanedione (DBM) ligands. These materials are interesting from the point of view of potential applications for optical hole-burning frequency and time-domain storage and processing. Optical absorption, steady state and time-resolved photoluminescence, and spectral hole-burning at the transition between ³H₆(1) and ³H₄(1) crystal-field levels were studied at temperatures between 1.4 and 300 K.

We have found that highly efficient waveform recall is possible in coherent transient systems in which the storage is optically thick. Coherent transients may be used in a variety of information storage and processing applications with advantages over traditional electronic methods. However, it is believed that a serious problem in application of photon echoes in practical systems is the relatively low efficiency of the process. We show in our numerical studies that waveform recall efficiencies greater than unity can be achieved in absorbing media with appropriate choice of absorption length and brief pulse area, even for very weak data pulses. We also present our preliminary experimental results in Barium vapor in which efficiencies of 50% were obtained for both the stimulated and two-pulse photon echoes.

This paper will explore the use of the protein, bacteriorhodopsin, as the photoactive recording medium in an optical three-dimensional memory. Although this protein has been used previously as the photoactive medium in a number of three-dimensional architectures (e.g., holographic and two- photon), a sequential one-photon volumetric architecture employing a photochemical branching reaction characteristic of the protein is currently showing the most promise. This unique branching reaction allows for long-term data storage by the protein, and rigorously excludes unwanted photochemistry. During the past two years, two prototypes have been constructed, and the preliminary results look promising. The use of chemical modification and genetic engineering of the protein has improved data reliability by roughly five-fold, but reliability remains an issue. Some of the key problems will be discussed. In addition, the use of gray-scale and polarization multiplexing to increase the storage capacity will be examined.

Photochromic films made from bacteriorhodopsin (BR) possess many desirable characteristics for a candidate holographic optical data storage medium. These properties include optical erasability, high spatial resolution, adequate diffraction efficiency, flexible film formats, durability, an optimal recording/readout wavelength of about 680 - 690 nm, and potentially inexpensive cost. In this paper, we experimentally study the raw bit-error-rate (BER) achievable with BR films made from the genetic variant known as D85N. Experimental data is collected for digital bit patterns fabricated as chrome-on- glass masks, at two different spatial resolutions. The results show that films fabricated from D85N have good potential for use in holographic data storage systems, but that further effort must be devoted to the film fabrication process in order to minimize optical nonuniformity and scattering losses.

A three-laser-beam technique is developed to study the transient diffraction efficiency of M-state dynamic phase holograms in a D96N mutant bacteriorohodopsin film (BR). A CW beam from 532 nm doubled Nd:YAD laser is used to pump BR molecules from B-state to photoexcited M-state. Then the M- state absorption laser 413-nm wavelength from a Krypton Ion laser is used to write holographic gratings in the excited M- state. The writing process also depletes M-molar concentrations. This process offers the advantages of better modulation and faster response. The reading is done with a 680 nm laser, which is far away from the absorption bands to ensure a negligible erasing effect on the gratings written in the film, resulting a pure phase hologram with high efficiency. A maximized transient peak diffraction efficiency approaches a saturated value when the ratio of write to pump intensity is approximately unity.

The possibility of reducing information loss in holographic memory systems in which different wavelengths are used for data recording and reconstruction has been investigated. We suggest replacing a thick recording medium which provides selective reconstruction of the holographic data with a multilayer recording structure. It has been shown that such a structure has the selectivity which significantly exceeds the selectivity of a single layer. At the same time it permits compensation for the Bragg mismatch along the thickness of the recording medium when 2-wavelength reconstruction is implemented. We consider various methods for such compensation and the possibility of their realizations.

We have experimentally discovered that the Signal-to-Noise Ratio (SNR) of holograms initially remains constant as the number of holograms stored increases and drops significantly only after a large number of holograms are recorded. This suggests that in a large-scale memory, the limiting noise source is not crosstalk between holograms but holographic noise due to the prolonged exposure of the signal beam. We have carried out experiments to investigate the formation and influence of the inter-pixel grating noise and shown that it is a very important form of holographic noise. We also proposed and demonstrated the use of random-phase modulation in the signal to suppress the inter-pixel grating noise.

The performance of holographic storage in photopolymer recording media gets limited by compositional volume grating distortions, arising primarily due to postrecording anisotropic medium dimension changes. We evaluate the polymer grating distortions, and the corresponding diffraction efficiency fluctuations, as noise in the holographic digital system. The analysis suggests the importance of the distortion induced grating strength fluctuations relative to optical scattering from the system performance, and encoding, characteristics at different grating distortion regimes.

The noise characteristics of the photon echo memory have been investigated. The photon echo memory has the ability to store many bits of information in a diffraction-limited spot, thereby dramatically increasing the storage density. The temporal Fourier transform of the input data sequence is written into the inhomogeneous absorption profile of the recording medium. Data are encoded by means of temporal modulation onto the waveform of a finite duration data beam. Individual bits are not localized to a specific spectral channel; instead, they are stored throughout a region of spectral-addressing space, In order to store and recall the input data accurately, the Fourier transform of the input data sequence must be narrower than the inhomogeneous bandwidth. In the photon echo memory mechanism, there are several factors affecting the system bit error rate such as finite-width write/read pulses, echo efficiency, shot noise, thermal noise, etc. The accuracy of the echo output depends on those system factors. In this paper we formulate a simple model of the photon echo system, and by analyzing this model we derive the relationship between the characteristics of the echo output signal and several factors such as the bandwidth of the system, echo efficiency, atom excited state population fluctuations, shot noise, and thermal noise.

The photoactive protein, bacteriorhodopsin (BR), may be used as the recording medium in optical three-dimensional memories. Experiments with a sequential, one-photon read/write scheme have shown promising results. In this scheme a planar laser beam activates a narrow slice of the medium, so that the bit patterns of the slice can be read independently of the rest of the memory. This gives rise to a paged memory architecture with approximately 100 Megabytes/page. Experimental images taken of the activated pages show bit patterns subject to degradation, which may be attributed to intensity variations within the activation beam. These intensity gradients are believed to be the result of refraction within the memory page. Writing a bit in the memory changes the index of refraction within the activated memory volume illuminated by the write beam. Bit error rates are directly related to the proportion of 0s and 1s written into the memory page, with minimum error rates recorded at a 50/50 ratio. In addition to experiments with prototype BR memories, we report on a computer model for the activation phase of the memory read cycle. This model may be used to study various schemes for placing the bits within a memory page and ensuring that the distribution of 0s and 1s is uniform.

Spectral hole burning (SHB) allows to extend conventional spatial-domain optical data storage and coherent processing into the dimensions of frequency and time. To achieve ultrafast performance, on the time scale of 10^-12 - 10^-13s, we use organic dye-doped polymer materials at liquid-helium temperature. These materials enable SHB recording and coherent transient responses with a broad optical band width of 5 - 10 THz. We discuss applications of organic SHB systems for associative recall of time-and-space domain events, spectral programming of pulse trains, Stark switching of holograms, THz-bit-rate multiplication, cross- spectral processing and photon gated recording of erasure resistant coherent transients.

We demonstrate a simple method for controlling the nonlinear oscillations by only using a semiconductor laser and photo detectors. The nonlinearity necessary for exhibiting period- doubling bifurcations and chaotic phenomenon was realized by appropriately superposing the threshold characteristics of semiconductor lasers on the saturation characteristics of photodiodes in their electric current vs. light intensity properties. An electro-optical NDFS (nonlinear delayed feedback system) has been composed by making use of this nonlinearity. A low-pass filter was inserted into this NDFS as an electric feedback element, which gave variety to the behavior of the nonlinear oscillations. With this system, multi-stable oscillations and chaotic transitions with various patterns have been observed. In this scheme, an optical dynamical memory function has been demonstrated to perform binary data writing. In addition, we have applied an external light input to the NDFS, for example, some sinusoidal wave modulations with acoustic frequencies. If the external input light effects to the oscillation waveform are to be reproducibly derived, new application to a waveform recognition system and cryptography will be expected.

We present the case of photoionization-induced persistent spectral holeburning in rare earth doped II-VI compounds for high density memory storage. Experimental data on photon-gated holeburning has been presented for different sulfide hosts (MgS, CaS: RE²⁺ and RE³⁺). With the proper choice of the host electronic band structure, the optically active rare earth ion and its electronic transitions involved in the holeburning process, we have observed the highest number of persistent holes ever burned in a single electronic transition. Efficient photon-gated holeburning in the 4f⁷ (⁸S_7/2) - 4f⁶5d¹ transition of Eu²⁺ is a result of photoionization of Eu²⁺ to Eu³⁺. These holes have a width of less than 5 GHz, have no detectable erasing effects after thousands of reading cycles, survive thermal cycling up to the room temperature and have infinite lifetime at low temperature (2 K). Although self- gated holeburning is observed with reading laser at higher powers, the photon budget for reading these holes is so small that thousands of reading cycles can be performed without significantly affecting the optical signal. We discuss the unique features of these systems that make them the most promising candidates to date for the holeburning based optical memories.

A review on the development of photoluminescent organic recording media is presented. Particular emphasis has been placed on positive photoluminescent materials for irreversible and reversible recording of optical information. The results of the study of light-sensitive systems based on irreversible and reversible photochemical transformations or organic molecules are discussed. The fundamental characteristics for made photoluminescent polymeric materials based on these photochemical systems and perspectives of their application as recording media, especially in the modern photography and 3D- optical memory devices, are given adequate consideration.

Real-time, wide band information storage and signal processing devices are critical to many computing and communication systems. Optical spatial-spectral holography has the potential to perform real-time storage and continuous signal processing at data rates up to a terahertz, with storage/pattern densities on the order of a terabit per centimeter squared, and with data block sizes/time-bandwidth products well over 10000. These attributes, coupled with spatial selectivity and the ability to process amplitude, phase and frequency modulated signals makes spatial-spectral holography an extremely versatile technology. Applications include time-, frequency-, or code-division multiplexed routing, pattern recognition; multi-dimensional cache memory; high density, high bandwidth database memory, associative memory, and look- up tables; temporal encryption and decryption for secure communications; interior memory for optical networks; real- time address decoder; all optical passive routing of data; header and data stripper and isolator for network packets; true time delays for phase arrays with simultaneous tracking of multiple targets; and dynamic pulse shaping and distortion compensation.

An experimental study to ascertain the combinative action of zinc chloride and triethanolamine (TEA) on improving photosensitivity of red-sensitized dichromated gelatin (RSDCG) has been carried out. Firstly, the exposure properties of home-made RSDCG were studied experimentally. Then, zinc chloride, a kind of Louis' acid, was added into the RSDCG to observe its catalytic effect on photo-cross-linking of gelatin molecules in RSDCG. After that, TEA, as a kind of external electron donor in RSDCG photo-chemical reaction, was introduced into RSDCG to make its photosensitivity higher in this study. Finally, the combinative effect of zinc chloride and TEA on the photosensitivity in RSDCG holograms was studied. The results show: (1) Zinc chloride and TEA have obvious combinative effect on improving the photosensitivity of RSDCG. (2) The curve of diffraction efficiency of RSDCG holographic transmission grating versus exposure energy is bell-shaped. (3) The maximum diffraction efficiency of the grating can reach as high as 83% corresponding to the exposure energy about 200 mJ/cm².

In this paper, a novel type of red sensitive photo-polymer system for optical storage, here called RSPP, is presented. First of all, the components in RSPP, for example, photo- sensitizer, photo-initiator, monomer, copolymer, combiner, stabilizer, hardener, and fabrication and processing technique of RSPP are given. Then, the absorption spectrum of RSPP material is measured. And the result shows the material is only sensitive to read light, whose absorption peak is at 662 nm and half-width of the absorption is about 100 nm. After that, the property of exposure in RSPP is studied. It is found that RSPP holographic plate has several advantages over the optical storage (holographic optical storage) material previously reported. First, this RSPP is fit to record both transmission holograms and reflection holograms. Second, the holograms recorded in RSPP plate can be processed both in dry and in wet processes due to its strong real-time effect. The performance parameters of the ESPP are following: (1) The photosensitivity is about 2 mJ/cm² at 630 nm; (2) The resolution of the material is more than 4000 pp/mm; (3) The saturation refractive index modulation is 0.0034 and 0.0141 for real time and wet processing respectively. In the study of the exposure in RSPP holographic plate, some other phenomena concerning real time effect in RSPP, such as, light- amplification and modulation of single light beam effect, are found. The mechanism of these phenomena is discussed.