<title>Spatial light modulator system for application as a dynamic diffractive element and in optical image processing</title>

Abstract

The importance of spatial light modulators (SLMs) in optical systems is increasing. This paper presents our work on an SLM system based on Sony LCD. We show the optimization of the LCD modulation behavior concerning the application as dynamical diffractive element, and the implementation of images and filter functions in optical correlators and pattem projection systems.Measurements of the coupled amplitude and phase modulation and the planarity of the display at different wavelengths lead to correction functions and several optimized operation modes, e.g. gray scale or binary amplitude modulation. The optimization in the amplitude mode leads either to high contrast images of reduced gray levels or to a mostly linearized full gray scale mode. A similar way leads to optimized modes for the phase modulation and to a realization Ofa total phase shift of 2it. The increase of the processing performance of phase-only filters in optical correlators is presented. Furthermore, diffraction efficiency (DE) measurements of Fourier holograms addressed to the SLM prove the optimization process, compared to the non-optimized and the theoretical DE-values. So, estimations can be made concerning the application ofthe SLM as dynamical diffractive element.

Investigation of spatial light modulators for their application in the reconstruction of coherent masks

“…So, computer generated holograms were addressed at video frame rates. We have reported the results in some earlier papers [5][6][7]. It became obvious the limiting parameters of the performance are mostly due to physical boundary conditions, such as pixel number and size, response time, transmission etc..…”

“…But of course, these displays are not especially developed for the purpose of realizing high-resolution phase modulating spatial light modulators. So, more or less accidentally the first liquid crystal devices, like the one we used the SONY LCX012BL series, showed due to the birefringence of the LC-material a comparable good phase modulation of 2π @ 532 nm [5]. Since that time quite a few research groups looking for the right display type for coherent or diffractive applications.…”

<title>Liquid crystal display as dynamic diffractive element</title>

“…So, we measured the performance of a 5 x 5 off-axis beam splitter calculated with 256 phase steps. The adapted gray level matrix, using the correction factors from the look up table [2], realized a ratio of signal to dc intensity of around 5:1. Whereas, the original calculated matrix showed only half of the dc intensity in the signal.…”

“…Properties of the system architecture The phase type of the diffraction grating, which optical thickness or refractive index changes regularly, and here especially the multi-phase level to have continuous phase distribution, produces high diffraction efficiency. An exclusive phase modulation is hard to achieve with nematic Liquid Crystal Displays (LCDs), mostly the amplitude and phase modulation is coupled [2,[6][7][8]]. …”

“…We already demonstrated the measurements done on the LC 1004 system from HoloEyeTM [2]. Using the obtained results concerning the modulation properties and using the design software DigiOpt for the calculation of diffractive structures we did more effort in the investigation of the SLM system as diffractive element.…”