Design, fabrication, and characterization of an acoustically-induced distributed Bragg reflector (ADBR)

The purpose of this research is to investigate the feasibility of utilizing GHz-range surface acoustic waves (SAWs) to implement a tunable, distributed feedback (DFB) optical grating in an integrated-optic waveguide structure. The principle of distributed feedback for optical systems was first introduced in the early 1970's and provides the basis of operation of today's single-mode semiconductor lasers used in modern wavelength-division-multiplexing (WDM) optical communication systems. In these modern DFB and distributed Bragg reflector (DBR) semiconductor lasers, a periodic, etched, refractive index corrugation that satisfies the Bragg condition provides frequency-selective optical feedback which allows their single-mode operation. It was suggested in the early 1970's that a SAW could be used to provide a tunable DFB grating; however, this notion was dismissed at that time due to difficulty to fabricate the submicron interdigitated transducers (IDTs) require to launch GHz SAWs necessary to implement a working prototype. The work to be presented in this thesis will provide the first in-depth theoretical design and feasibility analysis and later fabrication and characterization of an acoustically-induced distributed Bragg reflector (ADBR). This study is divided as follows. Firstly, theoretical methods will be developed to evaluate the magnitude of the DFB coupling coefficient, kappa, for a variety of III-V semiconductor and proton-exchanged (PE) LiNbO3 ADBR structures that utilize GHz-range SAW devices. Jointly, an experimental feasibility analysis will be performed to determine if nanometer-scale SAW devices, which satisfy a low-order Bragg condition suitable to induce a DFB effect, can be fabricated via electron-beam lithography. Secondly, the design of an integrated-optic prototype ADBR device will be presented and a multilayer cleanroom fabrication process will be developed. Lastly, the electrical, optical, and acoustooptical characterization of prototype 3.5GHz PE:ZY-LiNbO3 ADBR devices will be carried out to investigate the strength of a SAW-induced DFB effect and the tunability of an ADBR device. Various fabrication and design techniques are listed which may enhance the ADBR kappa value, along with a list of other physical effects which may need to be considered in future analyses.