Numerical Analysis of Phase Noise Characteristics of SGDBR Lasers

Detailed analyses of the phase noise characteristics of tunable sampled grating distributed Bragg reflector (SGDBR) lasers are presented in this paper. Based on the transmission line laser model, we derive the Langevin rate equations for the photon number and the electric-field phase in the cavity of SGDBR lasers. This model includes the spontaneous emission white noise in active section and the carrier shot noise in passive tuning sections, both of which contribute to the enhancement of the laser phase noise. Based on this model, the frequency modulation (FM) noise spectrum is calculated from the instantaneous laser phase fluctuation. The white noise linewidth and carrier shot noise linewidth are then calculated according to the FM noise spectrum. The linewidth tuning curves as a function of the currents in passive sections are simulated and the laser linewidth is strongly dependent on the tuning currents. Lower white noise linewidth is obtained when the longitudinal mode is located on the longer wavelength side of the total reflection-peak wavelength of the front and back gratings. However, the carrier shot noise linewidth increases with the increase of the injected current within each longitudinal mode. Finally, the impact of structural parameters on the linewidth is discussed.