Optical signal generation, stabilization, and manipulation in broadband silicon photonics

Abstract

Together with the increasing number of applications in vastly different parts of the electromagnetic spectrum, more versatile, stable, and capable light generation and manipulation techniques are required in integrated photonics. In this thesis, using CMOS fabrication capabilities, and a single layer back-end deposition process, CMOS-compatible lasers are developed using aluminum oxide as the host medium. First, a low temperature deposition process is detailed, and erbium-based lasers are demonstrated in the C-band. Then, thulium is studied and characterized as a dopant for applications at longer wavelengths. On-chip frequency stability issues are addressed by investigating the thermo-optic characteristics of various CMOS-compatible media. Negative thermo-optic coefficient of titanium dioxide is utilized to compensate for the all-positive thermal index shifts in the Si/SiN waveguide platform. An athermal resonator with resonances that exhibit ultra-low thermal shifts is created and used to stabilize a continuous-wave laser. Compared to a conventional SiN resonator, the athermal resonator is shown to significantly reduce the frequency noise of a locked laser. Switching to design-based solutions, the concept of spectrally-selective waveguides that can spatially confine the mode depending on the wavelength are demonstrated for the first time. The spectrally-selective waveguides are then used to design and demonstrate the first on-chip transmissive dichroic filter with the sharpest roll-offs to date. Finally, directional coupler based solutions are studied to address wavelength selectivity for octave-wide signals, and propose designs for ultra-wideband couplers.