Revealing the nonlinear dynamics of VCSEL-based frequency combs induced by optical injection

Optical injection (OI) into VCSELs is a powerful tool to control VCSEL behavior and light emission. Previous studies by Doumbia et al. 2021 have shown that OI of a 3-line optical frequency comb (OFC) into a VCSEL allows tailoring the properties of the OFCs emitted in the VCSEL output light. Our efforts extend beyond the previous findings, as for the first time, we study the polarization-resolved nonlinear dynamics maps found in a VCSEL subject to two different types of orthogonal OI, namely continuous-wave (CW) injection and the injection of a 3-line gain-switched (GS) OFC. Our results reveal that, within a significant parameter region (encompassing frequency detuning and injected power), the VCSEL's nonlinear behaviors induced by the OI of a GS-OFC are mainly determined by two factors: (1) the frequencies of the nonlinear dynamics of the VCSEL under CW OI, and (2) the polarization switching curves obtained under both types of OI. Therefore, (1) and (2) provide guidelines to understand the OFCs obtained at the output of the VCSEL. When injecting a 3-line OFC with 2 GHz frequency comb spacing, we demonstrate OFCs with approximately 50 GHz width at the output of the VCSEL, similar to the experimental results of Doumbia et al. 2021. We also identify the nonlinear dynamics that underpin these results.