Expanded Optical Frequency Comb Generation Using a Gain Switched Self-Seeded Passive Feedback Laser

In this paper, an expanded optical frequency comb (OFC) using a gain-switched self-seeded passive feedback laser (PFL), is presented. The device consists of two sections comprising an active distributed feedback (DFB) section and a passive integrated feedback (IFB) section, providing an on-chip injection to the active DFB section. Optimising the feedback from the IFB section results in an expansion of the number of generated OFC lines. As each comb line can be used as a distinct data carrier, the ability to boost the number of tones results in an increase in the overall data rate that can be transmitted using a single OFC. The paper presents a characterisation of important parameters of the laser, such as phase noise and linewidth, both in continuous wave (CW) and gain-switched mode operations. The effect of varying the phase shift of the feedback signal, through varying the bias applied to the IFB section, is also examined. The results show that by optimising the feedback signal, an expanded OFC can be generated.