Phase and amplitude characterization of a 40-GHz self-pulsating DBR laser based on autocorrelation analysis

The authors propose a self-referenced method to measure the phase difference between optical beat notes in passively mode-locked self-pulsating (SP) distributed Bragg reflector (DBR) lasers with high-frequency repetition rate (> 10 GHz). The method is based on successive intensity autocorrelation analysis of groups of three adjacent longitudinal modes. Each group contains two beat notes at the repetition frequency, and a first-order Fourier analysis of the intensity autocorrelation signal allows the determination of the phase difference between the two beat notes. It can be used for a spectrum containing any number of modes by filtering successively three adjacent modes and measuring the related autocorrelation signal. The authors show that the pulse temporal profile can be reconstructed from the measurements of the optical spectrum and of the beat notes' phase differences. The authors applied this method to an SP DBR laser with a 40-GHz repetition rate.