Optical Frequency Comb Expansion Using Mutually Injection-Locked Gain-Switched Lasers

We propose a novel scheme for the expansion and comb densification of gain-switched optical frequency combs (GS-OFC). The technique entails mutual injection locking of two gain-switched lasers with a common master to generate a wider bandwidth OFC. Subsequently, the OFC is further expanded and/or densified using a phase modulator with optimum drive conditions. We experimentally demonstrate the generation of an OFC with 45 highly correlated lines separated by 6.25 GHz with an expansion factor similar to 3. In addition, operating in comb densification mode, the channel spacing of the OFC is tuned from 6.25 GHz to 390.625 MHz. Finally, a detailed characterization of the lines, across the entire expanded comb, is reported highlighting the excellent spectral purity with linewidths of similar to 40 kHz, a relative intensity noise better than -152 dB/Hz, and a high degree of phase correlation between the comb lines. The proposed method is simple, highly flexible and the architecture is suitable for photonic integration, all of which make such an OFC extremely attractive for the employment in a multitude of applications.

Automated summary

The proposed scheme utilizes mutual injection locking of two gain-switched lasers to generate a wider bandwidth optical frequency comb, which can be further expanded and densified using a phase modulator. Experimental results showed the generation of highly correlated lines with adjustable channel spacing. The method is simple, flexible, suitable for photonic integration, making it attractive for various applications.