Amplitude Spatial Light Modulator Research Articles

Holographic memory optical system based on computer-generated Fourier holograms

Holography is known to be a prospective tool for storing large amounts of digital information, providing long lasting safety and high speed data access. In this paper, we present a new approach to holographic memory system design. Our method is based on an application of discrete Fourier-transform calculations to encode two-dimensional binary data pages as computer-generated amplitude Fourier holograms (CGFHs). These CGFHs, represented as grayscale raster images, can be displayed with the use of a high resolution amplitude spatial light modulator (SLM) in an optical projection system and exposed on holographic medium with multiple reduction. The optical scheme required for the technical realization of this method appears significantly simpler compared with known holographic memory recording devices; moreover, it can be built using either coherent or incoherent light sources. Coding of data pages by precise pseudorandom phase masks during CGFH synthesis allows us to achieve about 3% of the recorded microholograms diffraction efficiency. The experimental results of CGFH projection recorded with a 20× reduction on photosensitive holographic medium and its reconstruction are presented.

Photopolymeric Multifunctional Dendrimer toward Holographic Applications

We present a photopolymeric multifunctional dendrimer for holographic applications. In this study, we described a synthesis of multiphotoreactive dendrimer and phase compatible polymer matrix as well as a numerical simulation of the dendrimer. This holographic photopolymer containing a nanosized photoreactive organic dendrimer could address the aggregation issue of conventional inorganic nanoparticle additives and allowed writing-induced shrinkage to be successfully reduced to the extent of acceptable values for 130 μm thick film. In this report, holographic performance including diffraction efficiency (DE), transmission, photosensitivity, modulation of refractive index, polarization sensitivity, and volume shrinkage has been discussed. The page-wise recording by using an amplitude spatial light modulator (SLM) was also demonstrated.

Robust interpenetrating network photopolymer containing hyper-branched photoreactive nanoparticle for holographic data storage

Herein we report an interpenetrating network (IPN) photopolymer containing an inorganic hyper-branched photoreactive polyhedral oligomeric silsesquioane (POSS) nanoparticle (NP) which can address the problem of light scattering induced by the aggregation of nanoparticles and can allow writing-induced shrinkage to be successfully reduced to the extent of negligible values for 500-μm-thick film. Holographic optical properties including diffraction efficiency (DE), sensitivity, and volume shrinkage are investigated as a function of POSS concentration. Angle multiplexing and page-wise recording are also demonstrated by using an amplitude spatial light modulator (SLM).

Binary encoded computer generated holograms for temporal phase shifting

The trend towards real-time optical applications predicates the need for real-time interferometry. For real-time interferometric applications, rapid processing of computer generated holograms is crucial as the intractability of rapid phase changes may compromise the input to the system. This paper introduces the design of a set of binary encoded computer generated holograms (CGHs) for real-time five-frame temporal phase shifting interferometry using a binary amplitude spatial light modulator. It is suitable for portable devices with constraints in computational power. The new set of binary encoded CGHs is used for measuring the phase of the generated electric field for a real-time selective launch in multimode fiber. The processing time for the new set of CGHs was reduced by up to 65% relative to the original encoding scheme. The results obtained from the new interferometric technique are in good agreement with the results obtained by phase shifting by means of a piezo-driven flat mirror.

LPCC filter realization in 4-F correlator of images with application of purely amplitude binary spatial modulation

In this paper the results of numeric modeling and experimental realization of correlation filter with linear phase coefficient (LPCC-filter) in scheme of optical coherent correlator of images are represented. Represented results prove the possibility of synthesized complex correlation filter realization as digitally synthesized hologram in scheme of optical correlator using modern fast-operating amplitude spatial light modulators (SLM) with limited dynamical range of the hologram transmission gradation levels representation.

Fourier Transform Optical Beamformer Employing Spatial Light Modulator

Optically controlled beam forming techniques are effective for phased-array antenna control. We have developed the Fourier transform optical beamformer (FT-OBF). The antenna radiation pattern inputted into an amplitude spatial light modulator (A-SLM) is optically Fourier transformed to a specific phase-front light beam equivalent to an antenna excitation in the FT-OBF. Optical signal processing, used the Fourier transform optics, is effective to large-scale, two-dimensional, and high-speed signal processing. To implement a flexible and finer antenna beam pattern control, we use an A-SLM as input image formation of the FT optics. And, to realize a small-size FT-OBF, we use symmetric triplet lenses with convex, concave and convex lens. The total optical system becomes below 1/5 length compared with the length using single lens. Finally, we evaluated the developed FT-OBF with the generated amplitude and phase distributions, which excitation signal of an array antenna. We measured an antenna radiation beam pattern, beam steering and beam width control, in the C-band. Measurement results agreed with theoretical calculated results. These results show the feasibility of the spatial light modulator based FT-OBF.

Phase-only Spatial Light Modulation by the Reverse Phase Contrast Method

A new approach to phase-only spatial light modulation is proposed in which a given amplitude pattern can be converted into a spatially identical binary phase pattern. A spatial filtering approach is applied to transform spatial amplitude modulation into spatial phase modulation using the Reverse Phase Contrast (RPC) method. The analytical method for achieving this is outlined and experimental results are shown for the generation of a binary phase-only distribution using an amplitude spatial light modulator and a phase-only spatial filter.

Implementation of high-resolution diffractive optical elements on coupled phase and amplitude spatial light modulators

We propose the optical implementation of diffractive optical elements onto electrically addressed liquid-crystal spatial light modulators. We compare the classic implementations onto amplitude-only or phase-only domains with the implementations onto coupled phase and amplitude (spiral) domains. We demonstrate that the coupling between amplitude and phase provides a trade-off between diffraction efficiency and the signal-to-noise ratio in the reconstruction. Furthermore, when investigating the influence of the maximum dephasing on phase domains and spiral domains through the use of optimal trade-off design, we show that phase-only domains with limited maximum dephasing can provide satisfactory performance. Finally, optical implementations are provided.

Multichannel single-output color pattern recognition by use of a joint-transform correlator

A novel method for performing color image recognition by the use of the coherent joint-transform correlator is introduced. The input plane of the proposed method is a spatial rearrangement of the separation into color channels of both the color input scene and the color target. This input plane is gray scaled and monochromatic, thus it can be displayed by the use of amplitude spatial light modulators to achieve real-time operation. The system provides a single output-plane result of the optical coherent addition of the separate channels' correlation outputs. At the output plane no electronic postprocessing is needed, and the detection decision is achieved simply by the application of threshold detection. Experimental results and computer simulations are presented to demonstrate the abilities of this system.

Experimental implementation of a joint transform correlator using synthetic discriminant functions

A joint transform correlator (JTC) was implemented in the Optical Science Department at CERT. In order to ensure a rotational invariance, the reference image is replaced by a synthetic discriminant function (SDF) image displayed on an amplitude spatial light modulator (SLM). Numerical simulations are performed and then compared to experiments. We show that the pseudo-inverse SDP (PI-SDF) gives accurate experimental results. The training ability of the PI-SDF allows it to recognize the reference object unambiguously, even if the input view does not explicitly belong to the training set. Then, we propose to replace our amplitude device with a ternary phase and amplitude device, in order to display positive and negative images: this allows us to display any kind of SDF filters, e.g. OT-SDF or MINACE-SDF, which reduce the side lobes, with a good resistance to noise.