Phase Spatial Light Modulator Research Articles

Motionless multiresolution interferometry based on Talbot effect

We describe the principle of a motionless interferometer based on the Talbot effect. The test object is scanned by a convergent spherical beam with variable curvatures and lateral shifts. The wave- fronts are generated by a programmable off-axis Fresnel zone plate, implemented on a high resolution and high speed binary phase spatial light modulator. The aberrated field is then analyzed by passage through a fixed binary phase grating, detection by a sensor located in a fractional Talbot plane, and numerical phase retrieval from the Fourier analysis of the reconstructed intensity distribution. We describe the principle of the object multiresolution analysis. The system operation is then illustrated experimentally in a simple case exhibiting subwavelength resolution ca- pability. Finally, we give some orders of magnitude for the dynamic range that can be expected with such a system, as well as possible extension toward very high resolution measurements. © 1999 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(99)01212-X)

Reconfigurable two-dimensional diffractive phase element with the fractional Talbot effect

We investigate the technical feasibility of the optical implementation of a four-phase-level diffractive element with two {0, pi}-phase spatial light modulators in a fractional Talbot configuration. The space-bandwidth product of the spatial light modulators is seen as the main theoretical limitation of the proposed approach. We investigate the robustness of technological and geometrical parameters on the diffraction efficiency of the whole system. Ferroelectric liquid-crystal silicon backplane spatial light modulators are chosen because of their high reconfiguration rates and good electro-optics interface. Similarly, we assess the influence of liquid-crystal technical parameters on system performance.

Routing scheme, permutation properties, and optical implementation of a four-shuffle-exchange-based Omega network

The routing scheme and some permutation properties of a four-shuffle-exchange-based Omega network are discussed. The corresponding optical setup, which is composed of 2-D phase spatial light modulators and calcite plates, is proposed and demonstrated through mapping the inputs to a 2-D array. Instead of one shuffle-exchange followed by one switching operation as in ordinary Omega networks, in our presented system, the shuffle interconnection embraced in the switches is accomplished simply by varying the switching structure of each stage. For the proposed polarization-optical modules, the system is compact in structure, efficient in performance, and insensitive to the environment. (C) 1997 Society of Photo-Optical Instrumentation Engineers.

Joint transform correlator performing pure phase correlation for optical pattern recognition

Abstract A joint transform correlator, performing pure phase correlation by a phase spatial light modulator in the input to the second stage optical setup, is proposed. It can deliver excellent correlation performance in the presence of non-overlapping noise or additive noise. The proposed method extracts the interference fringe phase information from the joint power spectrum by simple subtraction and division operations; the extracted phase is then encoded onto a phase spatial light modulator to obtain the correlation results. To extract the fringe phasors, the proposed scheme uses an 50/50 beamsplitter and an λ/4 plate in the optical setup, and two CCDs to capture the joint power spectrum and the phase shifted joint power spectrum respectively. This system is found to be equivalent to correlation between only the Fourier phases of the reference and input images; however, there are practical difficulties in implementing this type of pure phase correlation using the VanderLugt architecture. Computer simulations show that the proposed joint transform correlator out-performs binary joint transform correlation, using the binarization methods of multilevel threshold function and adaptive windowing threshold, when the targets are embedded in either non-overlapping noise or scenes with additive noise; performance is maintained even when the target has a very low light contrast ratio in a severely noise corrupted input scene.

Joint transform correlator performing pure phase correlation for optical pattern recognition

Abstract A joint transform correlator, performing pure phase correlation by a phase spatial light modulator in the input to the second stage optical setup, is proposed. It can deliver excellent correlation performance in the presence of non-overlapping noise or additive noise. The proposed method extracts the interference fringe phase information from the joint power spectrum by simple subtraction and division operations; the extracted phase is then encoded onto a phase spatial light modulator to obtain the correlation results. To extract the fringe phasors, the proposed scheme uses an 50/50 beamsplitter and an λ/4 plate in the optical setup, and two CCDs to capture the joint power spectrum and the phase shifted joint power spectrum respectively. This system is found to be equivalent to correlation between only the Fourier phases of the reference and input images; however, there are practical difficulties in implementing this type of pure phase correlation using the VanderLugt architecture. Computer simul...

Optical two‐dimensional SW‐banyan network: optical implementation, routing control, and determination of permissible permutations

A 2-D SW-banyan network is introduced by properly folding the 1-D SW-banyan network, and its corresponding optical setup is proposed by means of polarizing beamsplitters and 2-D phase spatial light modulators. Then, based on the characteristics and the proposed optical setup, the control for the routing path between any source-destination pair is given, and the method to determine whether a given permutation is permissible or not is discussed. Because the proposed optical setup consists of only optical polarization elements, it is compact in structure, its corresponding energy loss and crosstalk are low, and its corresponding available number of channels is high. (C) 1996 Society of Photo-Optical Instrumentation Engineers.

Spatial light modulator phase depth determination from optical diffraction information

A noninterferometric technique is presented for determining the phase modulating characteristics of spatial light modulators. Examining the far-field diffraction pattern intensity distribution for specific input functions enables the phase modulation to be calculated. Results are compared with usual interferometric techniques for a liquid crystal based modulator.

Programmable wavefront generation using two binary phase spatial light modulators

A programmable wavefront generation system using two binary phase spatial light modulators is described. This a a spacevariant system with high diffraction efficiency. The amplitude and phase of a wavefront can be modulated with the system. It is experimentally implemented with two ferroelectric liquid crystal SLMs. A programmable optical crossbar interconnection system based on this scheme is also discussed. The properties of the system are analysed.

Dynamic asymmetric binary holograms using a ferroelectric liquid crystal spatial light modulator

The implementation of asymmetric binary phase holograms using a 128 × 128 ferroelectric spatial light modulator is describe. The symmetry is broken by providing a pseudo four-level phase system. A pixellated diffractive element is inserted in series with a binary phase spatial light modulator, generating enough phase freedom to break the symmetry. The diffractive element is constructed by etching photoresist spun onto an optically flat glass substrate. Experimental results are presented, with the symmetric order being suppressed by a minimum of 9.7 dB.

Reconfigurable optical interconnects by a combined computer-generated hologram and spatial light modulator method

A new method for implementing electrically addressed dynamic optical interconnects is presented. In this approach a phase spatial light modulator (SLM) is combined with a computer-generated hologram (CGH). The phase SLM is used to change the phase of the wave front that illuminates the CGH. Binary orthogonal phase codes are used to address the SLM. The CGH is designed with iterative discrete on-axis encoding so that different wave fronts direct light to different locations. High efficiency can be achieved because of the large number and the small dimensions of pixels in the CGH. The dynamic aspects result from the use of an SLM that may have a relatively small number of relatively large pixels. In this manner a high-efficiency programmable interconnect system with fast reconfiguration time based on current technology devices may be implemented. The CGH-SLM method yields connection efficiencies significantly higher than previous methods that are based on the use of thin optical elements. Simulation results indicate that for switch sizes in the range from 1 × 2 to 1 × 8, connection efficiencies of higher than 1/ √N (where N is the number of possible destinations) are feasible.

Effects and correction of magneto-optic spatial light modulator phase errors in an optical correlator

Here we study the optical phase errors introduced into an optical correlator by the input and filter plane magneto-optic spatial light modulators. We measure and characterize the magnitude of these phase errors, evaluate their effects on the correlation results, and present a means of correction by a design modification of the binary phase-only optical-filter function. The efficacy of the phase-correction technique is quantified and is found to restore the correlation characteristics to those obtained in the absence of errors, to a high degree. The phase errors of other correlator system elements are also discussed and treated in a similar fashion.

Dynamic holographic interconnects with analog weights in photorefractive crystals

A photorefractive interconnect system with coherently erasable synapses (PISCES) is described. Comparing holographic erasure by intensity and phase modulation of the writing beams, we find that the timeaverage technique is most amenable to system implementation. Calculations derived from a simple model of diffraction show that it is possible to find configurations that maximize the interconnection capacity. The PISCES includes Fresnel zone plates for spot array generation, amplitude and phase spatial light modulators based on liquid crystal technology, and detector arrays, in addition to the photorefractive crystal. Alternatives for each of these elements are described.

Optical tracking novelty filter

We demonstrate an optical filter that displays the time-dependent features of a scene. The heart of the device is an interferometer that is sensitive not to the difference between two optical paths lengths but to changes in the path-length difference. The interferometer arms share a phase-conjugating mirror. The phase conjugator ensures that, at steady state, the output of the interferometer is dark. The response of the interferometer to a step differential change in the optical lengths is a decaying exponential having a time constant governed by the time response of the phase conjugator. The interferometer may be used to monitor time- and space-dependent optical phase changes that are due, for example, to transparent fluid motion. With a modified liquid-crystal television used as a spatial light phase modulator in the interferometer, we detect time-dependent features of an image viewed by a video camera.