Relative Intensity Noise and Linewidth for Hybrid-Cavity Semiconductor Lasers

Low relative intensity noise (RIN) was demonstrated experimentally for hybrid square-rectangular lasers (HSRLs). In this paper, RIN of the HSRL is numerically simulated and the laser linewidth is investigated theoretically and experimentally. The non-zero delayed self-heterodyne method is utilized to measure the linewidth, and the laser linewidth of 2.9 MHz is obtained experimentally. A two-section single-mode rate equation model including Langevin noise sources is established to study the noise characteristics theoretically. The time-varying mode photon density and frequency are simulated, then the intensity and frequency noise (FN) spectra are calculated. With the rising of bias currents, RIN decreases and approaches the standard quantum limit. Large mode
Q
-factor, high bias current, and passive square microcavity are effective methods to reduce FN and linewidth of the HSRLs. By inducing a passive square microcavity, we can expect a low linewidth of 37 kHz for the hybrid-cavity laser with
Q
= 1.17 × 10
⁴
.