Spatial light modulators (SLMs) are the key components for real time electro-optical signal processing, computing, holographic optical memory storage, free space optical interconnect, information processing and data conversion systems. We have used our liquid crystal SLM technology to develop LC-SLMs for beam modulation in femto-second laser systems.
The wide range of electro-optical properties such as electrically adjustable optical activity, birefringence and scattering make liquid crystals (LC) suitable for defined alternation of amplitude, phase polarization and spectral composition. Optically and electrically addressable LC-SLM being the data input or light modulating devices result in arrangements which can be used for real-time image processing, holographic applications and optical computing systems. The range of SLM applications is dependent on such parameters as sensitivity, resolution capability, switching time, flatness and thermal-mechanical stability. The parameters of optical addressable a-Si:SLMs, MIS-SLMs, and CdS-SLMs with liquid crystals as light modulating layers and their technological dependence are in discussion.
Digital cameras are of increasing significance for professional applications in photo studios where fashion, portrait, product and catalog photographs or advertising photos of high quality have to be taken. The eyelike is a digital camera system which has been developed for such applications. It is capable of working online with high frame rates and images of full sensor size and it provides a resolution that can be varied between 2048 by 2048 and 6144 by 6144 pixel at a RGB color depth of 12 Bit per channel with an also variable exposure time of 1/60s to 1s. With an exposure time of 100 ms digitization takes approx. 2 seconds for an image of 2048 by 2048 pixels (12 Mbyte), 8 seconds for the image of 4096 by 4096 pixels (48 Mbyte) and 40 seconds for the image of 6144 by 6144 pixels (108 MByte). The eyelike can be used in various configurations. Used as a camera body most commercial lenses can be connected to the camera via existing lens adaptors. On the other hand the eyelike can be used as a back to most commercial 4' by 5' view cameras. This paper describes the eyelike camera concept with the essential system components. The article finishes with a description of the software, which is needed to bring the high quality of the camera to the user.
Optical computing and signal processing is a growing field of scientific research and now more and more entering into industrial applications. Therefore, fast switching spatial light modulators (SLMs) are needed for displaying and filtering processed information. In this paper we present a transmissive ferroelectric liquid crystal display (FLCD) with high performance which will be operated as an SLM in an optical pattern recognition system using incoherent optical spatial frequency analysis (OSFA). The layout and the manufacturing process of the display have been designed especially for the requirements of SLMs in optical systems. The matrix is consisting of a square matrix of 512 columns by 512 rows with a spatial resolution of 508 dpi. An additional black aperture diaphragm of 1 mm is introduced around the active area in the switching plane of the FLC. The display is passively addressed with a multiplex driving scheme using the intrinsic bistability of the FLC. Each pixel of the display represents a switchable half wave plate, resulting in binary amplitude or phase modulated pictures dependent on the polarizer settings. Using an FLC with a high spontaneous polarization and a high pretilt at the substrate surfaces, we obtain excellent contrast ratios of 100:1 and a very high switching speed based on a row address time of less than 7.5 microseconds allowing frame rates up to 500 pictures/sec.
The wide range of electro-optical properties such as electrically adjustable optical activity, birefringence and scattering make liquid crystals (LC) suitable for defined alteration of amplitude, phase polarization and spectral composition. The method of incoherent optical space frequency analysis (OSFA) on the basis of liquid crystal light modulators is shown. In an optically addressed image processing camera the objects, which have to become classified, are projected onto an LC-SLM. The reflective SLM gets read-out incoherently. As a 2D- radiator an electronically addressed 'transient-nematic' LC modulator is used. A photo- multiplier serves as detector. It is mathematically exactly proven that the measured intensities are corresponding to the surface integrals of the Fourier transform. In a microscope variant the principle gets translated into action by the way that a telescopic projection of a FLC matrix-display takes place over a condenser and micro-objective into the exit pupil plane. The change-over to incoherent OSFA allows a simple realization of a Fourier processor for detection of particle-size distribution. For this purpose a high speed nematic LC modulator with log-ring structure is incorporated into the aperture stop of the condenser. The coherent OSFA is used in evaluation of particle image velocimetry and laser speckle photographs. The autocorrelator with an optically addressable LC-SLM allows, due to the two 2D-Fourier transforms, a high speed and accuracy.
It is known that a transition from object to spatial-frequency domain with the aid of the Fourier transform may be a suitable solution for the problem of real-time pattern recognition of objects whose features cannot be determined exactly. The paper discusses the method of incoherent space frequency analysis with the aid of liquid-crystal light modulators. The hardware based on this technique can be simple and economical, and it overcomes a number of disadvantages of coherent-optical set-up. The parameters of LC modulators are discussed. These may be used to derive operational conditions, processing spreads, etc. of the optical processors involved. Selected examples illustrate suitable applications.