Design and characterization of hybrid tunable distributed Bragg reflector microring resonator lasers

Abstract

Compact, tunable, and high-performance mid-infrared laser sources are critical for developing portable, scalable, and cost-effective spectroscopic laser systems for trace gas sensing. These laser sources have direct applications in environmental, industrial, and health monitoring systems. However, developing compact hybrid-tunable lasers with high output power in the mid-infrared regime remains a significant challenge. To meet this demand, this thesis details the design and simulation of four hybrid lasers within 2.3 – 3 µm wavelength range and presents the experimental characterization of a 2.7 µm laser targeted for CO2 monitoring. The primary objective was to develop high-power, hybrid-tunable single-mode lasers utilizing photonic integrated circuits, targeting specific molecular absorption lines for environmental and industrial monitoring. The laser system is realized through the hybrid integration of a gallium antimonide-based Type-I quantum well reflective semiconductor optical amplifier with a passive silicon nitride waveguide photonic integrated circuit. A novel laser cavity was designed, incorporating a microring resonator with an integrated distributed Bragg reflector. The design was guided by a robust simulation workflow, and the hybrid assembly was characterized by butt-coupling technique, facilitated by a semi-automated alignment procedure, utilizing a custom Python application. The fabricated laser targeting a wavelength of 2702.5 nm was experimentally characterized, demonstrating excellent performance that validates the design methodology. The device exhibited single-mode emission at 2705.16 nm with a signal-to-noise ratio of 36 dB. A high continuous wave output power of 16.75 mW was achieved at room temperature with a threshold current of 135 mA. The achieved output power sets a new performance benchmark for hybrid integrated tunable lasers that significantly surpasses previously published devices in this spectral region. Furthermore, a thermal tuning range of 2.82 nm was demonstrated utilizing a resistive heater placed on top of the DBR-MRR circuit and a phase shifter. While continuous mode-hop free tuning was challenged by coupled-cavity effects and thermal crosstalk, it was ultimately achieved by implementing a three-parameter tuning scheme involving the phase shifter, the microring resonator heater, and the gain chip injection current. Collectively, these results validate a robust design and integration strategy for mid-infrared hybrid tunable lasers. The achieved performance further substantiates the platform's suitability for developing field-deployable, packaged laser systems capable of real-time environmental gas monitoring.