Numerical and Experimental Analysis of Optical Frequency Comb Generation in Gain-Switched Semiconductor Lasers

Abstract

A numerical model has been implemented and used for the simulation of the optical frequency combs generated by gain-switching single mode laser diodes, either free-running or subjected to optical injection. The dynamical model consists of three rate-equations including stochastic noise terms. An exhaustive comparison between the simulated and the experimental temporal profiles and optical spectra, generated in a wide range of switching and optical injection conditions has been performed. The range of the explored conditions leads to a variety of scenarios including actual combs and broad incoherent spectra, and frequencies in the range of, and well below, the relaxation oscillation frequencies. The detailed maps generated provide guidelines for selecting suitable operation conditions for specific comb characteristics. The excellent quantitative agreement found in the entire range of the explored operation conditions supports the validity of the model for the analysis of the comb generation mechanisms. The model has been used for ascertaining the role of the frequency chirp in the evolution of the comb spectra and discussing the physics underlying the effects of the optical injection.

Experimental Investigation on Wideband Optical Frequency Comb Generation Based on a Gain-Switched 1550 nm Multi-Transverse Mode Vertical-Cavity Surface-Emitting Laser Subject to Dual Optical Injection

“…These phenomena indicate that under suitable modulation parameters, the comb spacing of OFC generated by the gain-switched SL can be tuned, which has been confirmed in Ref. [39]. In the following experiment, the modulation frequency is fixed at 2.5 GHz.…”

“…3(a2) and (b2)), the comb lines become indistinct, the timing jitter increases, and some pulses are not able to switch on. Under this case, the larger effect of spontaneous emission noise makes the frequency chirping more noisy and the comb lines in optical spectrum are lost, and meanwhile optical pulses switch-off to levels at which spontaneous emission noise dominates the evolution [39]. Moreover, the optical spectrum red-shift can be observed due to the heating effect resulted by the current modulation.…”

Gain-switched semiconductor lasers with pulsed excitation and optical injection for dual-comb spectroscopy

“…In parallel to the search for innovative applications, many efforts have been devoted to develop alternatives to mode-locked OFCs, with the aim of providing tunable, cost-efficient and field-deployable comb generators [9][10][11]. Among these comb platforms, OFCs generated from semiconductor lasers by gain-switching (GS) have attracted considerable attention in recent years [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. Besides benefiting from the usual advantages of semiconductor sources (high efficiency, low cost and small footprint), the comb generation by GS also offers low losses, flexible comb line spacing and, outstandingly, suitability for photonic integration [20].…”

“…In this scheme, the frequency and amplitude of the sinusoidal signal, as well as the bias value, constitute the set of parameters that determines the comb generation process. A systematic analysis of the effect of the switching conditions on the performance of the OFCs was reported in [26]. Briefly, for repetition frequencies of the order of the frequency of the laser relaxation oscillations (roughly ∼5-25 GHz), the GS mechanism produces a broad spectrum with well-defined spectral lines.…”

“…As demonstrated in [26], for repetition frequencies <1 GHz the range of driving conditions to generate broad and flat-topped OFCs under sinusoidal GS is dramatically reduced. In addition, the quality of the OFCs cannot be significantly improved by OI.…”