Nonlinear Dynamics of Optical Frequency Combs Generated by Gain-Switched Semiconductor Lasers Subject to Optical Injection

We report on an experimental study of the nonlinear dynamics appearing when an optical frequency comb (OFC) generated by a gain-switched semiconductor laser is subject to optical injection. OFCs with a frequency spacing of $f_{\mathrm{m}}=5$ GHz were generated at two values of the modulation amplitude. For low injected power two combs with the same frequency spacing are observed, one due to the gain-switched laser and the other due to the modulated injected field. When the injected power is increased for a fixed value of the frequency detuning, a rich variety of nonlinear dynamics was found. Irregular behaviour, limit cycles or locked combs with a frequency spacing of $f_{\mathrm{m}}/N$ , with $N$ a positive integer up to 14 are obtained. A much more complex dynamics was found for the low modulation amplitude comb.