Ultra-Low Timing Jitter of Quantum Dash Semiconductor Comb Lasers With Self-Injection Feedback Locking

We compare the timing jitter of a mode-locked InAs/InP quantum dash (QD) coherent comb laser (CCL) with and without an external cavity self-injection feedback locking (SIFL) system. The jitter is determined through a measurement of the first harmonic of the RF power spectrum of the laser output detected using a fast photodiode. A significant reduction in timing jitter is observed in the laser with the external cavity SIFL. A pulse to pulse root-mean-square time jitter of 1.56 fs is achieved for the laser with the external cavity SIFL. This low timing jitter is a promising light source for the next generation high-speed coherent networking systems and all-optical signal processing. We demonstrate results of a double polarization 16-QAM data format transmission system at a symbol rate of 25 GBd using more than 30 individual channels of the QD CCL. An error vector magnitude of 5.8% and bit error rate of 3.0 × 10
^-9
were obtained. And, 6.0 Tb/s (16QAM 30 × 25 Gbd PDM) coherent transmission is achieved.