High-power, narrow-linewidth, thermally tuned multi-channel interference tunable laser based on butt-joint regrowth with accurate frequency tuning

We demonstrate a monolithically integrated thermally tuned multi-channel interference (MCI) laser with high power and narrow linewidth for next-generation coherent systems. By employing butt-joint regrowth for low-loss active–passive integration, the device achieves a facet output power of 120 mW with a minimum Lorentzian linewidth of 40 kHz. The laser exhibits a tuning range of more than 56 nm, SMSR larger than 49 dB, linewidth below 90 kHz, and fiber-coupled output power of up to 18.1 dBm. Air-gap suspended phase sections enable efficient thermal tuning with minimal power less than 55 mW per wavelength. Through precise common-phase tuning, we achieve a frequency error of less than ±0.05 GHz and excellent reliability with only ±30 pm drift through 5000 h of aging at 100°C. Moreover, we characterize the tuning speed of the thermally tuned MCI laser for the first time to our knowledge, and the response time is below 250 µs for steady-state frequency tuning of both 25 GHz and 6 THz. The presented MCI laser using butt-joint regrowth is specifically developed to meet the demands of 800 Gbit/s and beyond coherent communications.