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.