Holographic gratings with asymmetric structure are widely used to couple light into and out of waveguides due to
their high diffraction efficiencies and planar packaging. In this paper, a holographic grating coupler based on the
photopolymer has been designed and experimentally demonstrated at wavelength of 405nm. To achieve the high
diffraction efficiencies in the structure, we investigated the optical properties of the coupler according to the
exposure energy at the 405nm wavelength. In the holographic recording for the asymmetrical geometry, we
researched the optical characteristics of the Dupont photopolymer HRF150-38 as the correction of the Bragg angles
shift because of shrinkage factor and the diffraction efficiency. The performance and the optical characteristics of
the coupler using volume holographic grating will discussed in detail.
Tir- and mono functional monomers were dispersed in a solution of polysulfone in organic solvent containing a photo initiator and other additives. New photopolymer film was prepared by dispersing acrylic monomer in a polysulfone matrix. The Polysulfone was adopted as a binder since it affords transparent thick films with low dimensional changes during holographic recording. Optical property of the photopolymer showed high diffraction efficiency (>90%) under an optimized optical condition at 532nm laser. The angular selectivity for angular multiplexing page oriented holographic memories (POHMs), the maximum diffraction efficiency of the material during holographic recording, the diffraction efficiency of the films as a function of an incident angle of two beams, exposure energy for saturation of the holographic material and application for holographic data storage will be discussed.
Holographic transmission gratings with 0o;-Bragg angle are widely used to couple light into and out of waveguides due to their high diffraction efficiencies and planar packaging. In this paper, a holographic grating coupler based on the photopolymer has been designed and experimentally demonstrated. To achieve the high diffraction efficiencies, we investigate the optical properties of the coupler according to the exposure energy at the 405 nm wavelength. For the asymmetrical geometry with 72othe correction of the Bragg angles shift of about 0.95o; and 3.45o;, which are induced by the 7.86% shrinkage factor, is successfully demonstrated. The performance and the optical characteristics of the coupler using volume holographic grating are discussed in detail.
We propose the fast accessible data storage system using the double side hologram reconstruction scheme which can simultaneously read out holograms using both the forward and phase conjugate reference beams. In this system, digital pages are recorded in the usual manner but are reconstructed in two CCD cameras by the double side hologram reconstruction. As a result, we achieved the speed of two times faster than the conventional readout and the estimated raw BER were 3.09×10-18 (left image) and 4.76×10-16 (right image), respectively.
In this paper, we present a scheme of recording apodized grating using an additional laser beam polarized orthogonally to two recording beams. The additional beam has a function to control beam intensity modulation of the recording beams and, therefore, changes the saturated modulation amplitude of the grating. An investigation of the diffraction efficiency depending on the intensity modulation is implemented in DuPont’s HRF-150-38 photopolymer. As results of the experiment, holographic apodized gratings with uniform, inverse Gaussian, and triangular profiles are fabricated successfully in this material.
Fabricating holographic apodized gratings is often impeded by nonlinear property of materials, which makes the resultant profile out of expectation. In this paper, the new scheme to fabricate Gaussian apodized grating is proposed. Instead of fixed Gaussian recording beams, recording beam profiles that can compensate the nonlinear sensitivity of the material at low recording intensities are created by a gray level spatial light modulator (SLM). DuPont’s HRF-150-38 photopolymer is chosen because of its stability and ease to use. As the first result of the experiment, a Gaussian grating of 2.7±0.02mm standard deviation is recorded at 0.3mW/cm2 recording intensity after exposure of 300 seconds.
Organic-inorganic nanocomposite films were prepared by dispersing an aromatic methacrylic monomer and a photo-initiator in organic-inorganic hybrid sol-gel matrices. The film properties could be controlled by optimizing the content of an organically modified silica precursor (TSPEG) in the sol-gel matrices. The photopolymer film modified with the organic chain (TSPEG) showed high diffraction efficiency (>90%) under an optimized condition. In addition, we implement a digital holographic security system that combines the electrical biometrics technology with fully digital holographic storage using an organic-inorganic hybrid type photopolymer film.
We analyze the thermal properties of the DuPont HRF150-38 photopolymer for digital holographic card manufacture. In case of recording after heating, the diffraction efficiency of the hologram is more than 70% at 100°C but is decreased exponentially at temperatures over 100°C. It is observed in the recording before heating that the diffraction efficiency of the hologram fixed by a UV light is increased to approximately 10% at 100°C, but the hologram are erased at temperatures over 120°C.
KEYWORDS: 3D image reconstruction, Digital holography, Holograms, Holography, Phase conjugation, Data storage, Digital imaging, Stereoscopic cameras, Image storage, Digital recording
We propose the double-side dual hologram reconstruction scheme which can simultaneously read out holograms using both the forward and phase conjugate reference beams, and demonstrate stereo image recording and playback by the holographic memory system. This system is composed of a stereoscopic camera obtained stereo image pairs, holographic data storage where stereo images are recorded in the usual manner but read out by double-side dual reconstruction, and a stereo monitor that use polarized light techniques. As a result, stereo digital pages, which are reconstructed by the proposed double-side dual reconstruction method, can be obtained with very low cross talk noise, and the estimated raw BER of retrieved holograms were approximately 3.59×10-4 (left image) and 5.0×10-4 (right image), respectively.
KEYWORDS: Holograms, Digital holography, Crystals, Data processing, Image processing, Binary data, Holography, 3D image reconstruction, Digital imaging, Holographic materials
In this paper, to reduce the Bragg-mismatch problem of the dual-wavelength method, we record the hologram in the Dupont's photopolymer of thickness L=38μm and use a digital image data which has 78×104 bit/page. Also, to compensate the image magnification problem, a pair of cylinder lens consisting of 4F system behind the F2 lens and proposed data matrix image processing technique is used. As a result, the raw BER through Gaussian fitting after extracting binary data is around 3.09×10-6.
In this paper, we demonstrate the holographic smart card system using digital holographic memory technique that uses reference beam encrypted by the random phase mask to prevent unauthorized users from accessing the stored digital page. The input data that include document data, a picture of face, and a fingerprint for identification is encoded digitally and then coupled with the reference beam modulated by a random phase mask. Therefore, this proposed system can execute recording in the order of MB~GB and readout all personal information from just one card without any additional database system. Also, recorded digital holograms can't be reconstructed without a phase key and can't be copied by using computers, scanners, or photography.
The independent characteristic of the angular selectivity for the writing conditions was presented in photorefractive grating. In general, the incident angle of writing beam and the interaction length determine the angular selectivity of the grating. When the focused probe beam is incident on the grating, we obtain a new relation that the angular selectivity of the photorefractive grating depends on the probe beam incident conditions and is independent of the writing conditions such as writing beam incident angle, wavelength, and interaction length. These characteristics are experimentally investigated as a function of the following parameters; writing beam incident angle, probe beam width and lens focal length. In the experimental results, it has demonstrated that the control parameters are not the incident angles of writing beam but the probe beam width and focal length of the convex lens. Another property of this configuration is to have same value within large angular range that is also determined by the readout conditions.
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