Narrow Linewidth Hybrid Integrated Laser Based on Distributed Feedback from Silicon Waveguide

We present a narrow linewidth hybrid integrated DFB diode laser by importing external distributed feedback from a silicon waveguide into the lasing cavity. Benefitting from the high refractive index and numerical aperture of the strip waveguide with a width of 1 µm, Rayleigh backscattering can be efficiently excited and collected, providing distributed feedback to the lasing cavity. Experimental results show that the Lorentzian linewidth of DFB laser diode measured by the self-delayed heterodyne interferometry is narrowed to 1.52 kHz, and the side-mode suppression ratio (SMSR) is improved to 74.71 dB. Meanwhile a white frequency noise of 24.44 Hz²/Hz at the offset frequency beyond 1 MHz is achieved, corresponding to an intrinsic linewidth of 76.74 Hz. This work provides a feasible pathway for the miniaturization of wavelength self-adaptive narrow linewidth laser based on distributed weak feedback.