Experimental investigation of optical frequency combs performance through gain switched DFB laser with narrow pulse modulation signal

Abstract

It is small footprint, simplicity, and inexpensive that the direct modulation of a semiconductor laser to generate optical frequency combs (OFCs). However, their OFCs spectral characteristics are heavily dependent on the modulation signal waveform and the current parameters of the laser. It is essential that the research of more useful modulation signal and driving conditions to optimize the OFC performance. We evaluated the performance of the OFCs under gain-switched distributed feedback (DFB) lasers with several common modulation waveforms. It is showed that the relaxation oscillation frequency (ROF) was a restricted condition on the coherence of the OFC under the gain-switching (GS) mode when modulation frequency lower than ROF. We demonstrated that OFCs can be realized in a gain-switched DFB laser with a narrow pulse-width modulation signal under a lower modulation frequency than the ROF of the laser. The OFCs was realized with a comb spacing of 100 MHz, spectral width of 2 GHz, and carrier-to-noise ratio of 29.01 dB by a narrow pulse modulation signal with modulation frequency of 50 MHz at I_ON = 38.72 mA, I_OFF = 0.12 mA, pulse width of 1 ns. The performance of the OFCs under the narrow pulse and sinc modulation signals with different modulation frequency parameters and current driving conditions is further evaluated. This method of tuning the pulse modulation signals to achieve optimization of OFC performance has the advantages of simple operation, flexible settings, and inexpensive. This will have greater application value in high-resolution spectroscopy detection, especially a dual comb spectrum technology.