Design and fabrication of a recycled carrier modulator
Date
2015
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Publisher
University of Delaware
Abstract
In this thesis, I outline several design and fabrication approaches that can be used to achieve a Distributed Bragg Gratings on a Lithium Niobate (LiNbO3) based substrate. These gratings function as wavelength selective mirrors and help create a Fabry-Perot resonator topology for recycling an optical carrier wave. First and foremost, the choice of material was made bearing in mind the implication it would have on the fabrication and operation of the device. Lithium Niobate was chosen given the fact that over the years it has been proven to be a more matured and well understood wave guiding technology with excellent mechanical and chemical stability. Grating materials were chosen bearing in mind the substrate material that was selected for the modulator. Factors such as material compatibility (adhesion), and ease of processing were carefully considered. Numerical simulations were conducted to determine the effects that the different grating materials have on the reflection and transmission of the optical signal. Factors such as refractive index, material thickness, loss, duty cycle and the quality of the grown material were shown to have effects on the reflection and transmission. Actual devices were then fabricated and tested. Due to the size of the grating (with a pitch of about 360 nm and smallest feature size of ~180 nm), electron beam lithography was clearly the most viable option for a high precision and repeatable process. Material growth was done using plasma enhance chemical vapor deposition (PECVD), and thermal (resistive and electron beam) evaporation. Pattern transfer was carried out with an inductively coupled plasma (ICP) etch. Every step of the fabrication was carried out in the nanofabrication facility here at the University of Delaware. In this thesis, I present the different results that were achieved with the different material systems used. Furthermore, I discuss possible future endeavors towards achieving a higher index contrast and incorporating electrode structures.