Wavelength-versatile GaSb Light Emitters for Hybrid Photonics Integrated Circuits

Photonics integration is experiencing a growing interest as an enabling technology for many photonics applications. In particular, the development of photonic integrated circuits (PICs) operating within a 2 – 3 µm wavelength region has recently emerged as a solution for developing compact optical sensors. This leads to new requirements in terms of functionality and triggers new development of optoelectronics components tailored for mid-IR photonics integration. To this end, this thesis is focused on the development of spectrally broadband light emission chips for the 2 – 3 µm wavelength and their integration with PICs. In particular, the work aims at using PIC-based functionality for wavelength filtering and tuning. The light-emitting chips utilize gallium antimonide (GaSb) type-I material systems targeting high gain, broad emission, and efficient coupling to silicon photonics platforms. These chips are based on the operation principle of light amplification in semiconductor media and function as i) superluminescent diode (SLD), generating a broad spectrum that can be sliced on demand, or ii) reflective semiconductor optical amplifier (RSOA), which is used in an external cavity laser with tunable wavelength. The SLDs used in this thesis incorporate a cavity suppression (CS) element that enables high injection current and high output power while maintaining spectral broadness. The RSOAs have been designed for enabling low coupling losses with PIC.

The choice of the PIC platform is based on the broad transparency window in 2 – 3 µm wavelength. Therefore, micron-scale thick waveguide silicon-on-insulator (SOI) and a relatively thinner silicon nitride-on-insulator (SNOI) PIC platforms are chosen for hybrid integration. The hybrid integration between the GaSb chip and PIC is achieved by end-fire coupling, targeting low coupling loss and simplicity of the integration process. The low-loss PIC components were designed and customized for hybrid lasers at 2 µm wavelength.

As a first result, a high output power single-pass SLD enabled by CS element with about 60 mW output power at around 2 µm is demonstrated. The output power is doubled by implementing double-pass architecture emitting a record of 120 mW output power and 1.8 mW/nm power spectral density. Then the efforts were directed to demonstrate SLDs with mW level output power operating at around 2.5 – 2.6 µm. These SLDs represent the state-of-the-art performance for this operation wavelengths and exhibited a good beam quality that is paramount for the efficient coupling with PICs. Furthermore, an on-chip GaSb/SOI distributed Bragg reflector laser emitting 6 mW output power at around 2 µm was demonstrated using the flip- chip mounting technique. Finally, a compact GaSb/SNOI hybrid Vernier laser emitting about 15 mW at around 2 µm and exhibiting a very broad tuning range between 1937 nm to 2026 nm is demonstrated. All these demonstrations form a new toolbox for GaSb, SOI, and SNOI components that are validated for operating in PIC-based architectures with functionality at 2 µm and beyond. These developments are instrumental for the advancement of mid-IR integrated photonics and its penetration to high-impact applications in sensing and spectroscopy.