Real-time Spatial Light Modulators Research Articles

Enumeration of illumination and scanning modes from real-time spatial light modulators

Using a phase-only spatial light modulator (SLM) in a Fourier transform setup together with fast diffractive optics design algorithms provides a way to automatically generate complex and rapidly changing laser illumination patterns in the far-field. We propose a hierarchical software structure for the adaptive, on-line design of far-field illumination patterns. Using the on-line design system together with camera feedback of the illuminated scene would make it possible to detect and actively laser designate multiple objects in parallel. Possibilities for multispot, arbitrary trajectory scanning and also broad-area speckle-reduced illumination are demonstrated with experimentally measured diffraction pattern sequences from a 120 x 128 pixel phase-only SLM.

Amplitude-modulated JTC for improving correlation discrimination

In this paper, a new amplitude-modulated joint transform correlator (AMJTC) is proposed. Compared to the classical JTC and the nonlinear JTC by computer simulation, this correlator produces high auto-correlation peak intensity, compress the cross-correlation and sidelobe intensities, and can be implemented by real time spatial light modulators (SLMs).

Correlation Filters for Optical Pattern Recognition

Optical Pattern Recognition got its start when Vander Lugt proposed the frequency plane correlator to implement the matched spatial filtering. Since that time, correlators have been the subject of much research. While matched filter is theoretically optimum when the input signal (or image) is an exact replica of the reference signal, its performance degrades severely in practical situations where the input image may differ from the original due to distortions such as rotations and scale changes. Additional problems facing conventional correlators include: low light throughputs, lack of real time spatial light modulators and sensitivity to misalignment. Here, we review some of the significant developments in the area of optical correlation filter design that were aimed at solving some of these problems.

Index grating lifetime in photorefractive GaAs

The index grating lifetime in liquid encapsulated Czochralski-grown undoped semi-insulating GaAs was measured using a beam coupling technique. The largest lifetime measured was ~8 s under a read beam intensity of 0.7 mW/cm(2) with the grating periodicity being 0.63 microm. The measured value decreases to milliseconds as the read beam intensity and the grating periodicity increase to ~10 mW/cm(2) and 4 microm, respectively. This range of grating lifetime in this material is adequate for its use in real-time spatial light modulators, reconfigurable beam steering devices, and dynamic memory elements for optical computing. In addition, the results suggest that, the lifetime is sensitive to residual imperfections in the crystal.

Real-time joint spectral-spatial matched filtering

A technique for real-time joint spectral-spatial matched filtering is presented. The technique involves the real-time conversion of an input color image into a set of sampled monochromatic coherent images through the use of a tricolor grid and real-time spatial light modulator. These color-coded monochromatic images are then processed by a multi-channel, coherent matched filtering subsystem. The advantage of this technique over prior matched filtering methods is its ability to use both color and shape in recognizing objects.

Spatial light modulator based on a deformable oil laser

A passive real time spatial light modulator (SLM), using an oil layer as phase modulator of a radiation field, is described. Experiments with a SLM as incoherent to coherent image transformer were performed, revealing the limits in resolution and response speed.

Photoelectretic states in the real-time spatial light modulators (PROM-system)

Abstract In seeking an explanation of the mechanism for recording multivariate optical signals in PROM-type systems where the active layer is a photosensitive electro-optical material, we have beex studying the electro- optical properties, photorefractive and photoelectretic effects in Pb3MgNb2O9, BaxSz1−xNb2O6, Bi12SiO20, Bi12GeO20, SbSI, S2TiO3 with barrier and insulating contacts. We report the results of electro-optical investigations of these materials. We show that all these materials have internal field which can be 0bservedwhend.c. and pulsed d.c. electric fields are applied to them. This internal field can be destroyed by an external depolarization field or by illumination with light of appropriate wavelength (photorefractive effect). It is shown that these internal fields can be attrihuted to the existence of photoelectretic states. We have studied the creation and destruction of these photoelectretic states, the basic characteristics of these states, and have determinsd the Shotoelectretic charge. We have further studied the creation and destruction of these photoelectretic states 8s a function of wavelength, and applied field pulsing frequency, and find the analogous characteristic times for the photorefractive effect. On the basis of our results, we give recommendations for optimizing the operating conditions for a Real-Time Spatial Modulator using these crystals.

DKDP (Potassium Dideuterium Phosphate) Light Valves

The use of potassium dideuterium phosphate (DKDP) light valves for optical data processing is discussed. The operating principles and structure of optically and electron beam addressed DKDPs are compared, and specifications for both devices given. Optically addressed DKDPs are capable of higher resolution and contrast, but both systems represent viable real time spatial light modulators adaptable to optical processing. Examples of real time data processing performed by the DKDPs include: image addition and subtraction; reduction of noise introduced by scattered light in recording media; reconstruction of computer generated and acoustic holograms; reconstruction of synthetic aperture radar data; retrieval of three-dimensional information in X-ray diagnoses; radar signal processing and display; and optical pattern recognition and correlation of images, which has applications for missile guidance systems.