Slope efficiency of integrated external cavity hybrid lasers: A general model and analysis

The integrated tunable external cavity diode laser (ECDL) plays an important role in many emerging applications, such as LiDAR, integrated free-space optical communication, integrated nonlinear optics, quantum information processing, and data center optical interconnects. Based on the III-V/silicon or III-V/silicon nitride hybrid integration, chipscale tunable ECDL could achieve a broad wavelength tuning range (>100nm) and very narrow linewidth (<10kHz) with the help of micro-ring resonators. However, most hybridly integrated ECDLs exhibit a low slope efficiency (<0.1W/A), which severely limits the laser performance. We have developed a general numerical model for the hybrid laser and investigated several methods to improve its slope efficiency. We show that the slope efficiency of the hybrid laser can be efficiently increased by controlling the external cavity phase, improving the coupling between the laser chip and passive chip, using optimized anti-reflection and high reflection coatings, and reducing the laser intrinsic loss. We have also experimentally built an arrayed waveguide grating (AWG) based hybrid laser and shown that the numerical simulation results match well with the experimental results.