We propose a novel multiplexed holographic storage technique in a coaxial alignment based on dually modulated spatial
light modulator (SLM). In this paper, a spatial light modulator based on a high-resolution twisted nematic liquid crystal
display is used to record both reference and object beams. We have programmed the active region of the SLM, so that
some part will work in the phase modulation mode and some part will work in the amplitude modulation mode. In our
coaxial holography design, the central ring area is reserved for amplitude modulation of the object beam while the outer
rings/annuli will cater for various phase modulation of the reference beams for multiplexed storage. A number of objects
can then be stored/encoded in the same location of the hologram and later be reconstructed using the appropriate
reference beams. Three different methods of phase modulating the reference beam are investigated, viz. the diffraction of
blaze grating, the diffusion of random speckle and beam shaping. The coaxial multiplexing holographic data encoding
and reconstruction are carried out experimentally in a single-beam 4-f setup using He-Ne laser with a wavelength of
632.8nm. A 2-D holographic medium is used for recording and the reconstructed images are captured by a camera on the
image plane. From the results of simulation and experiment, it can be seen that all the images are reconstructed clearly
and separately, demonstrating the feasibility of our proposed novel technique of coaxial multiplexed storage/encoding.
We describe two novel modulation techniques for collinear holographic data encoding, employing a spatial light
modulator (SLM) based on twisted nematic LCD. In the Fourier transform holographic storage system, the reference
beam in the outside part and the object beam in the inside part are simultaneously modulated by one single SLM, with
different modulation techniques. In one of the modulation methods, the reference beam is phase modulated with a
circular blazed grating pattern, and then diffracted into the central part to interfere with the amplitude modulated object
beam. Multiple holograms can be recorded on the same location with reference beams of different grating period.
Another modulation method is to modulate both the reference beam and the object beam with pure phase modulation by
the SLM. The binary ones are encoded with random phase shift from 0 to 2π, while the binary zeroes are encoded with a
constant phase of 0. When the dc component of the spatial frequency generated by the binary zeroes is blocked, a
homogeneous hologram will be obtained, and the amplitude object will be reconstructed directly. In this paper, both of
the two modulation methods are performed theoretically and experimentally. From the experimental results, it can be
seen that the blazed-grating modulation technique gets a higher efficiency, while pure phase modulation method can
reconstruct the images with more uniform intensity. These techniques are demonstrated to be attractive for applications
in data storage and encryption systems.
We propose here a new and novel technique using the dual modulation modes of the spatial light modulator (SLM) in
a single-beam set-up, thus enabling a more compact and more shock-proof holographic image storage and retrieval
system when compared to a double-beam interference set-up system.
This paper introduces a new and simple concept of moire effect. A circular grating placed at Talbot planes can achieve
beam deflection measurement in real time. It is not only used for 2-D beam shift measurement at every point, but also
used to measure the angle and plane parallel degree of optical element and birefringence measurement of the optical
material.
This paper introduces a high-capacity storage device based on the holographic optical disc storage system and applied
field. It details a novel configuration of a single beam holographic storage system. Through coding the object light and
reference light in same optical beam with a spatial light modulator (SLM), we achieve the aim of interference storage.
The experimental results indicated this configuration can be used commercially. This system has the advantages of huge
memory capacity and high access speed, thus offering a very useful storage alternative in the internet areas of
communications and multimedia systems.
KEYWORDS: Signal to noise ratio, Holograms, Holography, 3D image reconstruction, Digital holography, Data storage, Spatial light modulators, Optical storage, Optical discs, Binary data
This paper describes an optical system model of Fourier holographic recording. Its numerical calculation is based on the Fraunhofer diffraction theory. According to Fourier optics principle, the spatial fundamental frequency will have a minimum value. It will limit the increase of the storage density. This paper shows the results of the simulative storage and the digital storage. When the digital storage used on the film optical disk system (for example, photopolymer medium), the storage density of Fourier hologram can be evaluated by bit error rate (BER) and signal noise rate (SNR).
An adjacent sequence iteration method for designing a diffractive element with function of controlling wavefront propagation is presented, and a binary optical element for focusing a diode laser beam in a long focal depth is designed with this method, fabricated by means of photolithography and ion-etching techniques. The simulation calculated with the designed element indicates that the design is successful, and the experiment results of long focal depth by testing the produced element are consistent with the design requirements.
This paper proposed a new encryption method using Computer Generated Fourier Hologram in frequency domain. When the main frequency spectrum, i.e. brand and an encrypted information frequency spectrum are mixed, it will not recognized and copied. We will use the methods of Dot Matrix (Digital) Hologram Modulation and the filter to get real signal. One new multi-modulated dot matrix hologram is introduced. It is encoded using several gratings. These gratings have different angles of inclination and different periods in same dot, to enable us in obtaining more information.
The relationship of Bragg-mismatch and recording angles of holographic photopolymer was deduced, the calculated and experimental results were compared. It showed that the theory tallied with the experiment well. The result indicates that the Bragg-mismatch depends on the recording angles strongly, this result is important to the design of high-density photopolymer holographic memory system.
ASM method is an effective method for disk-type photopolymer high-density holographic storage that has a limited medium thickness. In this paper, the effects of recording angles of ASM method disk-type photopolymer high-density holographic storage on the recording capacity and density are studied theoretically. The calculation and analysis show that the recording density and capacity depend on the recording angles critically whether the spherical wave beam or plane wave beam is used as the reference beam. The results show that no matter spherical wave or plane wave is used as the reference beam the recording density and capacity increases monotonously with the increase of θs when θR is fixed. When the recording angle between two recording beams is large, it has an optimal incidence angle of reference beam to get the maximum recording density and capacity. By using this optimal recording angle we can get 3 - 4 times improvmeent of recording density and capacity.
Green light sensitive acrylamide-based photopolymer system has been prepared. The photosensitive medium was composed of monomer, photoinitiator, charge transfer agents and polymeric film-forming binder. The best Eosin Y, TEA, BAA and AA's concentration were got by optimization of acrylamide-based photopolymers composition. And diffraction efficiency as high as 55% with energetic sensitivity of 60 mJ/cm2 has been obtained in the photosensitive films of 150 μm thickness. The principle of photopolymerization reaction was investigated in the paper, especially the function of charge transfer agents TEA and DPI were studied and we found that there existed a compensation effect between TEA and DPI in the polymerization process of photopolymer.
The next generation digital versatile disk (DVD) which uses blue laser will have a capacity of 13 Gbytes to 15 Gbytes. Compared with the current DVD, the wavelength will be shorter and the NA will be higher. But with the increase of NA and decrease of wavelength, the depth of focus (DOF) decreases rapidly, which makes it hard to track by the servo-system. In this paper, we propose to use an optimized three-portion phase-shifting apodizer to increase the depth of focus and at the same time minimize the spot size, which makes the DOF of next generation DVD comparable to current DVD. The simulation results show that an optical system with this apodizer also has a good defocusing characteristic.
It is known that for the converged laser beam, the axial intensity distribution corresponds to a Gaussian curve, that is, the intensity on the focal plane is the peak intensity. When it defocuses, the intensity would decrease rapidly. In some cases, optical data storage, for instance, we expect the intensity within a certain distance to be almost equal. In this paper, we propose to use a pure phase superresolution apodizer to optimize the axial intensity distribution of the converged laser beam and at the same time attain superresolution. The intensity point spread function remains almost identical within certain region and the depth of focus is extended.
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