Narrow Linewidth Laser Based on Extended Topological Interface States in 1D Photonic Crystals

Abstract Advances in 1D topological photonic crystals have enabled robust light‐emitting devices through a topological interface state at the cavity center. In this study, a 1D TIS‐extended photonic crystal (1D‐TISE‐PhC) structure both theoretically and experimentally is demonstrated. a linearly dispersive, zero‐index 1D photonic crystal is integrated with a four‐phase shift (4PS) sampled grating so that photons propagate through the cavity without phase differences, enhancing robustness and extending the TIS. This extension yields a more uniform photon distribution along the laser cavity and mitigates spatial hole burning. This is fabricated and characterized a 1550 nm 1D‐TISE‐PhC semiconductor laser, achieving stable single‐mode operation from 60 to 420 mA, with a side‐mode suppression ratio of 50 dB. The device exhibited a linewidth narrowing effect, with the narrowest Lorentzian linewidth of 126 kHz and a typical linewidth of 150 kHz, nearly an order of magnitude lower than conventional distributed feedback Bragg lasers. Using reconstruction equivalent‐chirp technology with the 4PS grating allowed precise wavelength control in laser arrays, with a spacing of 0.796 nm ± 0.003 nm. This results confirm that the TIS remains intact in the TISE cavity, preserving topological protection and demonstrating improved design simplicity and fabrication tolerance for high‐power, narrow‐linewidth semiconductor lasers.