Characterizing phase noise for beam steering devices

Date of Award

2014

Degree Name

M.S. in Electro-Optics

Department

Department of Electro-Optics and Photonics

Advisor/Chair

Advisor: Joseph W. Haus

Abstract

In this thesis we assemble a type of Mach-Zehnder interferometer to measure the complex signal after passage through a device under test placed in one arm. The signal's phase is extracted from the complex signal dataset and is analyzed to study the phase noise added due to the device. We are studying a liquid crystal beam steering system, which is a combination of two optical devices; the first is a variable liquid crystal half-waveplate and the second is a liquid crystal phase grating. The variable liquid crystal waveplate is the active element that has voltages applied to achieve a specific birefringence, whereas the liquid crystal phase grating is a passive device. For the beam steering devices of interest the liquid crystal phase grating is passive and therefore unlikely to impart appreciable amounts of phase noise, so the focus of this research was on the potential phase noise due to variable liquid crystal waveplate. The phase noise using the variable liquid crystal waveplate is measured in three operational states: a non-energized off state, an energized state having zero-phase change,and an energized state with voltage set for a half-wave phase change. We examine the phase spectrum |Φ(ƒ)|2, obtained from the frequency analysis of the temporal phase. A comparison is made between the phase noise spectrums in several cases: pre-device insertion to a post-device insertion of the variable liquid crystal waveplate for the three different states. We examine the signal spectrum over frequencies spanning the range from 1 Hz to 107 Hz and tentatively conclude that the active devices add little additional noise to the system. Further data is needed to solidify this conclusion given the data being analyzed is from one data capture, and the system required readjustment between captures, and we observe a drift of the noise floor.

Keywords

Spectral energy distribution Measurement, Liquid crystal devices, Signal processing, Optics, Military Studies, Technology, phase noise, beam steering, liquid crystal polarization gratings, mach zehnder, interferometry, polarization IQ

Rights Statement

Copyright © 2014, author

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