An Ultrastable and Calibration‐Free Arbitrary Tunable External Cavity Laser

ABSTRACT Tunable lasers are key components for reconfigurable large‐scale photonic systems, yet many integrated designs suffer from wavelength instability and require complex calibration. Here, we demonstrate an ultrastable and calibration‐free arbitrary tunable external cavity laser (ECL) based on hybrid integration of a reflective semiconductor optical amplifier with a silicon photonic integrated circuit. The silicon platform integrates an ultralow‐loss spiral waveguide, an arrayed waveguide grating, and an optical switch array. Wavelength selection is achieved via simple digital on–off control of the switches, eliminating analog tuning and calibration required in conventional cascaded‐resonator approaches. Experimental results show that the laser produces 20 discrete wavelengths with a uniform spacing of 1.6 nm over a tuning range from approximately 1560 to 1590 nm. The device achieves side‐mode suppression ratios exceeding 44 dB, intrinsic linewidths of 7.88–10.3 kHz, arbitrary wavelength‐switching times of below 34.7 µs, and a maximum output power of 14.8 mW. The system also demonstrates excellent stability, with negligible wavelength and power variations across different switch heating powers and after 10,000 switching cycles. These results indicate that the proposed ECL offers a scalable and practical light source for next‐generation wavelength‐division multiplexed optical interconnects and rapidly reconfigurable optical networks.