Liquid Crystal Beam Research Articles

Development of Large Capacity and Low-Crosstalk Holographic Switches Using LCOS Spatial Light Modulators

The design of versatile, high-capacity 1 2 N photonic switches based on Ferroelectric Liquid Crystal (FLC) beam deflectors were investigated. Results obtained for a 1 2 14 switch prototype are presented. The extension to a larger capacity switch (1 2 32) is also investigated, with possible improvements in optical bandwidth, and inter-channel crosstalk.

In-Plane Liquid Crystal Beam Steering Devices with a Beam Separation Structure

In-plane liquid crystal beam steering devices with a beam separation structure have been investigated. The separation between ordinary and extraordinary beams could be realized by using a liquid crystal director inclined by 45° to an air-liquid crystal interface. Successful analog beam control of 8° is obtained under an application of in-plane electric field. Reflection and confinement phenomena are also obtained at the interface of the spatial distribution of the refractive index.

Angle-independent beam steering using a liquid crystal grating with multi-resistive electrodes

We report on the design and experimental evaluation of a liquid crystal beam deflector generating a blazed refractive index profile. By using multi-resistive electrodes, the wavefront of monochromatic light passing through the active areas of the array becomes spatially modulated in a continuous and linear manner. The special features of such a beam deflector are reduced number of electrodes and constant intensity of the deflected beam over the whole beam deflection range. Owing to the careful design and optimized fabrication process of the electrodes, the angular independence of steering efficiency has been successfully confirmed for the first time in a beam deflection experiment. The optical throughput of our beam deflector was enhanced by a novel Talbot array illuminator.

Measurement and modeling of the angular dispersion in liquid crystal broadband beam steering devices

Liquid crystal beam steering devices behave like blazed diffraction gratings: the design wavelength can be nicely diffracted into a single order. Unfortunately, the grating nature of these devices causes strong angular dispersion of the transmitted light when the incident beam contains a broad spectrum of wavelengths. We characterized the behavior of a liquid crystal beam steerer for broadband illumination. We report experimental measurements of the impulse response of the beam steering device as a function of illumination wavelength. We also compare our results to a theoretical analysis utilizing the beam-propagation method (BPM). We find that even a simple model of the phase profile gives good agreement with the experimental measurements.

Image restoration of dispersion-degraded images from a liquid-crystal beam steerer

Liquid-crystal arrays represents one of the first practical technologies capable of steering light by electronic control only. We use such a device to steer the field of view of a broadband imaging sensor. Unfortunately, dispersion degrades the image quality by smearing out details in the image and by introducing multiple diffraction orders (echoes) at the detector plane. We present a method to compensate for these unwanted effects and thus restore the broadband images obtained with the beam steerer. We use the beam-propagation method to find the wavelength-dependent impulse response, from which we determine the appropriate Wiener filter. When training data are available, we improve the filter with the adaptive least mean square algorithm. We present restored images that demonstrate the capabilities of this technique.

Nonmechanical microscanning using optical space-fed phased arrays

A method for microscanning in imaging sensors is developed that allows liquid-crystal beam steerers to be used as nonmechanical microscan devices. This submicroscanning method involves using the beam steerers to shift images on a focal-plane array by a fraction of the amount used in typical microscan methods. Interpolation techniques based on interlaced sampling are used to produce images free of aliasing out to twice the Nyquist frequency determined by the focal-plane array. Since a continuous phase ramp is produced by the liquid-crystal beam steerer, dispersion effects due to the gratinglike nature of the devices are avoided. Simulations for both one- and two-dimensional cases are presented, as well as experimental results using a 3- to 5-μm imaging sensor and a liquid-crystal beam steerer designed for operation at 1.064 μm.

Spatial light modulators

Near real-time reusable spatial light modulators for coherent optical data processing are reviewed. The PROM, liquid crystal, and electron beam addressed DKDP and oil film light valves appear to be the most promising devices for coherent optical data processing.