Gain Switched Frequency Comb Enhancement Using Monolithically Integrated Mutually Coupled Lasers

A tunable comb source is demonstrated through gain switching a three sectioned photonic integrated circuit (PIC). The PIC consists of two mutually coupled lasers, integrated on an InP epistructure. One of these lasers is a tunable, two-section, single mode laser and its tunability is demonstrated by varying the bias current across the two sections, producing distinct wavelengths with a tunable range of 1535-1560 nm. The second laser is a simple Fabry-Pérot cavity laser which can be phase-locked with the single mode laser. Frequency combs were produced by phase-locking the two lasers and then gain switching the Fabry-Pérot laser by applying a high power radio frequency (RF) signal. In this letter we explore the effects that the biasing symmetry between the two coupled lasers has on the resulting gain switched comb. We demonstrate that a mutually coupled system results in enhanced gain switched frequency combs with a broader bandwidth and higher power compared to the asymmetrically biased coupling.