Spectral Characteristics of an InP-Based Semiconductor Laser With Fully Coupled Straight-Ridge and Racetrack Waveguides

Integrated semiconductor lasers are important for optical communications, gas sensing, biomedicine, and related fields. Conventional devices are commonly fabricated by dry etching, where sidewall roughness and surface defects may affect scattering and waveguide losses. In this work, we propose and fabricate an InP-based semiconductor laser with a fully coupled straight-ridge/racetrack waveguide structure using wet chemical etching. Under p-side-up continuous-wave (CW) operation and without facet coatings, the device exhibits a threshold current of 230 mA and a single-facet output power above 17 mW. At an injection current of 230 mA, single-longitudinal-mode lasing is obtained at a center wavelength of 1655.2 nm with a 3-dB linewidth of 0.12 nm. When the injection current is increased to 1520 mA, the spectrum shows comb-like characteristics within a broadband envelope of approximately 1670–1696 nm, with an average adjacent peak spacing of 0.22 nm in the pronounced multi-peak region. To the best of our knowledge, this is the first report of a derived satellite-peak spectral feature in an InP-based fully coupled straight-ridge/racetrack integrated semiconductor laser fabricated by wet chemical etching. These results show that the fully coupled structure enables current-dependent spectral evolution and produces equally spaced comb-like spectral features, providing experimental evidence and a useful reference for future studies of integrated semiconductor light sources.