  Recent advances in topological one-dimensional photonic crystal concepts have
enabled the development of robust light-emitting devices by incorporating a
topological interface state (TIS) at the cavity center. In this study, we
theoretically and experimentally demonstrate a one-dimensional TIS-extended
photonic crystal (1D-TISE-PC) structure. By integrating a linearly dispersive
zero-index one-dimensional photonic crystal structure with a four-phase shift
sampled grating, photons propagate along the cavity without phase differences,
enhancing the robustness to material variations and extending the TIS. Our
findings indicate that extending the TIS promotes a more uniform photon
distribution along the laser cavity and mitigates the spatial hole burning
(SHB) effect. We fabricated and characterized a 1550 nm sidewall 1D-TISE-PC
semiconductor laser, achieving stable single-mode operation across a wide
current range from 60 to 420 mA, with a side-mode suppression ratio of 50 dB.
The 1D-TISE-PC structure exhibited a linewidth narrowing effect to
approximately 150 kHz Lorentzian linewidth. Utilizing reconstruction
equivalent-chirp technology for the 4PS sampled grating enabled precise
wavelength control in 1D-TISE-PC laser arrays, achieving a wavelength spacing
of 0.796 nm +- 0.003 nm. We show that the TIS still exists in the TISE cavity
and topological protection is preserved. Its mode extension characteristics
mitigate the SHB so narrows the linewidth. We argue that the design simplicity
and improvement of the fabrication tolerance make this architecture suitable
for high-power and narrow-linewidth semiconductor lasers development.
