Multiwavelength Photonic Integrated Lasers with Emission at 2–3 µm

The general scope of the thesis was the development of tunable and multiwavelength semiconductor lasers operating within the 2–3 μm wavelength region, targeting applications in gas spectroscopy. The focus is on novel photonic integrated circuit (PIC) architectures including GaSb/GaInAsSb reflective semiconductor optical amplifiers (RSOAs) and wavelength conditioning elements realized using silicon on insulator (SOI) or silicon nitride on insulator (SNOI) technologies.

A tunable Vernier hybrid laser combining a 2.6 μm GaSb-based RSOA and a thermally tunable double ring resonator (RR) SOI PIC was demonstrated for the first time. The laser operated in pulsed mode with emission wavelength tunable over a range of 70 nm (2550–2620 nm), the longest wavelength emission for GaSb/SOI hybrid laser ever reported. Replacing the SOI PIC with a RR SNOI PIC enabled continuous wave (CW) operation with a maximum CW output power of 6.4 mW at the center wavelength, which is the highest CW output power recorded for PIC-based hybrid lasers at >2.1 μm wavelengths. The laser showed a tuning range of 170 nm (between 2474 nm and 2644 nm). This is the widest tuning range recorded for PIC-based hybrid lasers at >1.7 μm wavelengths.

Furthermore, hybrid integrated narrow linewidth distributed Bragg reflector (DBR) lasers with single and multiwavelength (MWLs) emission were demonstrated. The lasers utilized SNOI PIC-based DBRs with spiral-shaped waveguides and circular post-type grating next to the waveguide. For operation near 2 μm the DBR laser had a maximum power of 17.4 mW, which is the highest output power demonstrated for any PIC-based hybrid laser at this wavelength region. At 2.68 μm a maximum power of 7.1 mW was achieved, which is sufficient for sensing applications. A narrow linewidth emission below 50 kHz (measured over 7 ms) was demonstrated at both wavelengths. Finally, wavelength switchable operation between 2670 nm, 2629 nm, and 2594 nm was demonstrated for a hybrid MWL incorporating spiral gratings.

These first-of-a-kind demonstrations represent state-of-the-art performance for PIC-based hybrid lasers operating in the 2–3 μm wavelength region. They have the potential to revolutionize the realization of integrating PIC sensors for many applications, for example for the monitoring of environmental gases or biomarkers.