Precision closed-loop control of optical beam steering

Alfred Dale Ducharme; Geert J. Wijntjes; Constantine T. Markos; Glenn D. Boreman

doi:10.1117/12.305499

20 April 1998 Precision closed-loop control of optical beam steering

Alfred Dale Ducharme, Geert J. Wijntjes, Constantine T. Markos, Glenn D. Boreman

Proceedings Volume 3292, Spatial Light Modulators; (1998) https://doi.org/10.1117/12.305499
Event: Optoelectronics and High-Power Lasers and Applications, 1998, San Jose, CA, United States

Abstract

Unlike in the microwave domain, where open loop phase control is adequate, a phased array antenna working at optical frequencies will require precise closed loop control of each element pixel to realize a well defined high brightness far-field antenna pattern. We describe and present experimental data for a design that permits precision, to < (lambda) /100, phase control with a high bandwidth that compensates for temperature, mechanical effects, delay times of each phase shift element, and non- linear response. Experimentally, the output of a phase measurement system is used in an electronic feedback loop to dynamically linearize an inherently non-linear liquid crystal. The experiment consisted of a spatial heterodyne, temporal homodyne, fiber optic Mach-Zehnder interferometer to recover phase of a single nematic liquid crystal element. The resulting phase measurement, represented as an analog voltage, is used in a feedback loop to correct for the non- linear drive voltage-to-phase retardance response of the liquid crystal. A demonstration of this technique using several periodic drive waveforms at frequencies of 10-100 Hz was performed. Data are presented showing a phase retardance resolution of < 1 nm which enabled a significant improvement in the linearity of the liquid crystal response.

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Alfred Dale Ducharme, Geert J. Wijntjes, Constantine T. Markos, and Glenn D. Boreman "Precision closed-loop control of optical beam steering", Proc. SPIE 3292, Spatial Light Modulators, (20 April 1998); https://doi.org/10.1117/12.305499

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KEYWORDS

Liquid crystals

Phased array optics

Phase measurement

Modulators

Antennas

Beam steering

Sensors

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