Filter-driven four wave mixing dual-mode mode-locked laser based on an integrated nonlinear microring resonator

A potential solution for the demand for highly stable pulsed lasers at hundreds of GHz repetition rates is represented by passively mode locked fiber lasers. These lasers are composed of a band-limited amplifier, a dispersive element and a nonlinear element. When a high finesse resonant filter is added intracavity, they emit pulses with a repetition rate equal to the filter free spectral range (FSR) - a configuration known as dissipative four wave mixing (DFWM) [1,2]. The main cavity (MC) modes selected by the filter exchange energy by four wave mixing (FWM) and lock their mutual phase as a traveling pulse emerges. However, this approach leads to several unsolved instability problems [3], and so it has basically no impact in practical applications. By moving the nonlinear element inside the filter [4], we demonstrated stable pulsed emission at 200 GHz of repetition rate using a novel design we term Filter-Driven Four Wave Mixing (FD-FWM), that takes advantage of the high nonlinearity of an integrated micro-ring resonator [4] in a doped silica platform [5]. The stability arises as only one main cavity mode oscillates in each nonlinear resonator resonance. Here we present the first example of a stable operating regime for the FD-FWM scheme where two MC modes per resonator linewidth are allowed to oscillate [6]. This novel stable operating regime leads to the formation of two spectral 200GHz-comb replicas separated by the FSR of the external main cavity (FSR_C = 65MHz). The beating of the two combs generates a sinusoidal modulation of the 200GHz output pulse train at the radio-frequency (Fig 1a) of the main cavity FSR, a quantity that is readily detectable with photodiodes.