Optical parametric amplification in orientation-patterned GaAs waveguides

Date of Award

2016

Degree Name

M.S. in Electro-Optics

Department

Department of Electro-Optics and Photonics

Advisor/Chair

Advisor: Rita D. Peterson

Abstract

Creating tunable coherent infrared (IR) radiation sources is of high importance to the military and academia alike. There are plenty of lasers that emit radiation in the IR spectrum, however they have narrow line widths and lack the tuning to cover the entire region. Nonlinear optics provides a way to convert one frequency to another and with the help of advanced techniques like quasi-phasematching (QPM), we are able to grow crystals that provide tunable IR sources. Quasi-phasematching periodically changes the sign of the nonlinearity of a crystal, which allows energy to transfer from the pump field to signal and idler fields as long as the three interacting fields conserve energy and momentum. The nonlinear medium used in this experiment is orientation patterned gallium arsenide (OPGaAs), specifically an OPGaAs waveguide created with layers of GaAs and aluminum gallium arsenide (AlGaAs). A Q-switched 2.05µm Tm,Ho:YLF laser pumped a separate bulk OPGaAs crystal within a resonator creating an optical parametric oscillator (OPO), and the signal output from the OPO is recombined with the pump laser then amplified within the OPGaAs waveguide. Eight different OPGaAs waveguide samples with various lengths and QPM periods were tested in order to amplify the signal in this experiment. Signal gain up to 56.6% was observed, and the waveguide periods that showed gain matched the periods we predicted through modeling. In addition to producing nonlinear IR sources, this thesis explored laser induced damage thresholds on GaAs. High intensities are required to drive nonlinear processes, and the output from a nonlinear device can be increased if the damage threshold of the sample can be increased. Usually anti-reflection (AR) coatings damage before the crystal, and because of this TelAztec Inc. (Burlington, MA) has created new AR “motheye” treatments that improve performance. Four sets of motheye treated GaAs wafers were damage tested. The treatments did not significantly increase the laser induced damage threshold, but the damage threshold of bare untreated material was unusually low. In both cases, the damage is likely due to subsurface cracking that occurred during sample cutting and was not removed in the polishing step.

Keywords

Optical parametric oscillators, Gallium arsenide, Wave guides, Infrared radiation, Optics, Engineering, OPGaAs, Nonlinear, Waveguide, Quasi-phasematching, Signal, Idler

Rights Statement

Copyright © 2016, author

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