Fig. 2: Experimental setup.
a The microcomb source, a laser diode self-injection-locked to a photonic crystal ring resonator (PhCR) operating in the dissipative Kerr-soliton regime, is stabilised via two phase-lock loops feedback controlling the diode current Ip and heater current Ih respectively. OFC: reference optical frequency comb; ESA: electronic spectrum analyser; EOM: electro-optic modulator; BP: band-pass filter; PD: photodetector; LD: laser diode; PhCR: photonic crystal ring resonator; PID: proportional-integral-derivative controller. b Frequency diagram, depicting the self-injection-locked microcomb (blue), the reference 1 GHz oscillator (red) and the electro-optic (EO) modulation comb (grey). The frequencies fb, foff, and fol, corresponding to the repetition rate, offset, and out-of-loop beat notes, respectively, are extracted by the optical band-pass filters BP1-3 (green) as shown in the insets. c Optical spectrum of a self-injection-locked microcomb. The spectrum is well fitted by a sech2 envelope with a FWHM of 1.44 THz.
