VCSEL-Based Optical Frequency Combs: Expansion of the Optical Span under Arbitrary Polarized Optical Injection

We report on a theoretical study of the optical frequency combs (OFCs) generated by Gain-Switching Vertical-Cavity Surface-Emitting Lasers (VCSELs) under arbitrary polarized optical injection (OI). Our results show that two orthogonally polarized sub-combs are obtained generating a wider overall optical comb for a certain angle between the linearly polarized optical injection and the direction of emission of the free-running VCSEL. This angle decreases as the injection strength increases. A characterization of the maximum expansion of the optical span of the overall comb has also been reported. Moreover, we have analysed the effect of the birefringence of the VCSEL in the expansion of the overall comb. We found that for VCSELs with large birefringence splitting, the maximum frequency enhancement is the optical span of the free-running comb, while for small birefringence splitting the maximum frequency enhancement is the birefringence splitting value.