This paper describes the fundamentals of phase-only liquid crystal on silicon (LCOS) technology, which have not been previously discussed in detail. This technology is widely utilized in high efficiency applications for real-time holography and diffractive optics. The paper begins with a brief introduction on the developmental trajectory of phase-only LCOS technology, followed by the correct selection of liquid crystal (LC) materials and corresponding electro-optic effects in such devices. Attention is focused on the essential requirements of the physical aspects of the LC layer as well as the indispensable parameters for the response time of the device. Furthermore, the basic functionalities embedded in the complementary metal oxide semiconductor (CMOS) silicon backplane for phase-only LCOS devices are illustrated, including two typical addressing schemes. Finally, the application of phase-only LCOS devices in real-time holography will be introduced in association with the use of cutting-edge computer-generated holograms. The capabilities and applications of phase-only liquid crystal on silicon (LCOS) technology are reviewed by scientists in China and the United Kingdom. Zichen Zhang and co-workers from Tsinghua University in Beijing and the University of Cambridge describe how an electronically controlled liquid-crystal pixel array on a silicon backplane can be useful for manipulating the phase of coherent light. Such LCOS phase modulators have many potential applications, including real-time holography, head-up displays, wavelength-selective switches and reconfigurable optical add-drop multiplexers. Commercial devices currently offer array sizes of up to about 1-inch diagonal with pixel pitches in the range 6–20 μm. However, the technology is still immature; the liquid-crystal materials and silicon control backplane need to be optimized in order to realize the potential of such devices.

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Fundamentals of phase-only liquid crystal on silicon (LCOS) devices

An introduction to the technology of liquid crystal on silicon (LCOS) devices leads on to a discussion of the application areas which have been and are being opened up by the development of phase-only devices.

The Applications and Technology of Phase-Only Liquid Crystal on Silicon Devices

A useful filter for pattern recognition must strike a compromise between the conflicting requirements of in-class distortion tolerance and out-of-class discrimination. Such a filter will be bandpass in nature, the high-frequency response being attenuated to provide less sensitivity to in-class variations, while the low frequencies must be removed, since they compromise the discrimination ability of the filter. A convenient bandpass is the difference of Gaussian (DOG) function, which provides a close approximation to the Laplacian of Gaussian. We describe the effect of a preprocessing operation applied to a DOG filtered image. This operation is shown to result in greater tolerance to in-class variation while maintaining an excellent discrimination ability. Additionally, the introduction of nonlinearity is shown to provide greater robustness in the filter response to noise and background clutter in the input scene.

Application of nonlinearity to wavelet-transformed images to improve correlation filter performance

We discuss and implement a wavelet-modified maximum average
correlation height (MACH) filter for
0°-360° in-plane rotations in a hybrid digital-optical
correlator. Use of a wavelet transform improves the performance of the MACH filter by reducing the
number of filters that are required to identify a target rotated at any angle between
0° and 360° in-plane
rotations and enhances the autocorrelation peak intensity significantly. The output of a
hybrid digital-optical correlator contains two autocorrelation peaks and a strong dc. Using a chirp
function with the wavelet-modified MACH filter, the correlation signals are focused in three
different planes. Thus placing a peak-capturing CCD camera at a particular plane, only one
autocorrelation peak is recorded, discarding the strong dc and other autocorrelation peaks. A signal-to-noise
ratio has been calculated as a metric of goodness of the proposed wavelet-modified
MACH filter.

Wavelet-modified maximum average correlation height filter for rotation invariance that uses chirp encoding in a hybrid digital-optical correlator.

A signal processor that contains a programmable logic circuitry that is re-configurable in response to various parameters including, but not limited to, characteristics of a plurality of input data that is provided to the signal processor. The signal processor contains, among other things, a programmable logic configuration circuitry that provides a logic configuration to the programmable logic circuitry. In certain embodiments of the invention, the signal processor employs a wide word width to program the programmable logic circuitry, the wide word width is operable to configure an entirety of the programmable logic circuitry. The programmable logic configuration circuitry further contains a default configuration circuitry and an adaptive configuration circuitry. The default configuration circuitry contains a default logic configuration for the programmable logic circuitry. In other embodiments of the invention, the adaptive configuration circuitry generates an adaptive logic configuration for the programmable logic circuitry. The programmable logic circuitry is partitioned into a plurality of areas, each area within the plurality of areas is independently programmable.

Method and apparatus of selecting one of a plurality of predetermined configurations using only necessary bus widths based on power consumption analysis for programmable logic device

. A hybrid optical/digital configuration to implement a high- speed correlator is described. The input data is digitally Fourier trans-formed at video rates utilizing specialized digital signal processing chip sets and the computed spectral phase data passed to an electrically addressed phase modulating spatial light modulator (SLM). Successivetemplates, which are stored as angle multiplexed volume holograms ina photorefractive crystal, are reconstructed and optically correlated with the current input scene during an interval in which the SLM display is held stable. In this way, shift invariance, one of the major advantages of the correlation technique, is preserved. Of critical importance to thespeed of operation are the energy losses of the coherent wavefront through the system and the rate at which correlation plane data can beconverted to an electronic signal; both of these issues are consideredto estimate that at least a 3-kHz search rate is achievable from a 1000template memory with system components currently available.

High-speed hybrid optical/digital correlator system

A page-oriented, angle-multiplexed volume holographic optical-memory recording system has been constructed. This memory is addressed by the use of an acousto-optic deflector with a random-access time of 16 μs per page. This enables data transfer rates of 5.28 Gbits/s when pages of binary data are being stored. The reconstruction quality of images stored as memory pages is assessed with the quality achieved with the acousto-optic device compared with that achieved with the original recording optics.

High-speed, acousto-optically addressed optical memory

A reconfigurable hardware design permits very fast feature extraction from high frame rate video images. By implementing parallel pixel processing paths in programmable gate arrays, a wide range of image processing algorithms can be implemented in realtime.

https://ir.nctu.edu.tw:443/bitstream/11536/1105/1/A1996VF33600023.pdf

Parallel pixel processing using programmable gate arrays

A high-speed hybrid optical–digital correlator system was designed, constructed, modeled, and demonstrated experimentally. This correlator is capable of operation at approximately 3000 correlations/s. The input scene is digitized at a resolution of 512 × 512 pixels and the phase information of the two-dimensional fast Fourier transform calculated and displayed in the correlator filter plane at normal video frame rates. High-fidelity reference template images are stored in a phase-conjugating optical memory placed at the nominal input plane of the correlator and reconstructed with a high-speed acousto-optic scanner; this allows for cross correlation of the entire reference data set with the input scene within one frame period. A high-speed CCD camera is used to capture the correlation-plane image, and rapid correlation-plane processing is achieved with a parallel processing architecture.

Brian F. Scott

Papers

High-speed hybrid optical/digital correlator system

High-speed, acousto-optically addressed optical memory

Parallel pixel processing using programmable gate arrays

Experimental systems implementation of a hybrid optical-digital correlator.

A computer integrated business control system for an SME