ABSTRACT
A simple and robust technique to generate an optical comb is based on a Gain Switched Laser (GSL), which is usually realized by directly modulating a Distributed-Feedback (DFB) semiconductor laser. However, unfortunately the large temporal jitter, which reduces the phase correlation and the comb tone to the background Noise Ratio (TNR) of the optical comb, is also generated across the direct modulation technique. To acquire as large as possible TNR of the discernible optical comb at different modulation frequencies, the modulation ratio of the DFB laser, which is defined as the ratio between the operating current of the RF modulation signal and the bias current of the DFB laser, influences on the TNR and bandwidth of the discernible optical comb is studied in this paper. The experiment results show that there is a trade-off between the TNR and the bandwidth along with the modulation ratio changes, and to generate the discernible optical comb, the modulation ratio should be gradually increased or decreased as the modulation frequency gradually increases or decreases. By optimizing the modulation ratio, the discernible optical comb with a TNR larger than 30 dB is achieved at different modulation frequencies in experiment.
