InGaAsP-on-Insulator Photonic Platforms: Process Development, Nonlinear Losses, and Frequency Comb Modeling

Abstract

Nonlinear integrated photonics has emerged as a key technology for advanced optical communication systems, enabling functionalities such as all optical signal processing, wavelength conversion, and frequency-comb generation. These capabilities depend on suitable material platforms that can support strong optical nonlinearity and efficient integration. Among the available material platforms, Indium Gallium Arsenide Phosphide (InGaAsP) offers a compelling combination of strong optical nonlinearity, high-speed optical response, and operation across the telecommunications wavelength bands. Furthermore, its ability to support both active and passive photonic functionalities makes it particularly suitable for monolithic photonic integration. However, optical performance in conventional C-band InGaAsP/InP structures remains inherently limited by nonlinear losses, dominated by two-photon absorption (TPA) and subsequent free-carrier effects (FCE).

To understand the impact of TPA and FCE-related losses in InGaAsP-based devices, in the first thesis project, we perform the lifetime measurement of TPA-generated free carriers prior to recombination. Pump-probe measurements conducted on fabricated InGaAsP/InP waveguides yielded free-carrier lifetimes of 0.24 ns and 0.46 ns upon exciting the fundamental TE and TM polarization of the waveguide, serving as a vital reference for future FC lifetime engineering.

Building on the obtained knowledge, the next thesis project investigates a novel InGaAsP-on-insulator (InGaAsP-OI) platform for nonlinear integrated photonics, focusing on its application to optical frequency-comb generation. We performed the first comprehensive theoretical analysis of InGaAsP-OI ring resonators while considering realistic nonlinear loss mechanisms - specifically TPA and FCE at the 1550 nm telecom C-band wavelength. Additionally, various strategies for tuning the free-carrier lifetime are evaluated alongside their impact on resonator performance.

We next undertake steps towards III-V semiconductors-on-insulator photonic integration platform development. In particular, we explore two material systems, including InGaAsP-OI and aluminum gallium arsenide (AlGaAs)-OI, developing the steps for their fabrication. The next thesis project describes our effort in wafer bonding of a III-V semiconductor layer to SiO2-on-silicon wafer and the consecutive III-V substrate-removal processes, outlining key technical challenges and experimental process development results.

Lastly, as a separate project, we developed a proximity-effect correction (PEC) scheme for artificial 2D nanostructures, termed metasurfaces. By relying on shape modification of individual structural elements of the metasurfaces and the electron-beam lithography parameter tuning, we achieved precise agreement between the target design and fabricated feature shapes and dimensions with a negligible measured resonance drift. The developed proximity effect correction method is applicable in university cleanroom facilities hosting low-voltage (low-kV) electron-beam lithography systems constrained by computational capacity.