Fig. 2: On-chip laser directly self-injection locked to the co-integrated μFP cavity.
From: Harnessing micro-Fabry–Pérot reference cavities in photonic integrated circuits
a, Schematic of the on-chip circuit design enabling SIL to the co-integrated μFP cavity. b, Photograph of the DFB laser self-injection locked to the μFP cavity through an interface chip. c, Schematic of the experimental setup for noise measurement. The black lines indicate electrical control, and the red lines indicate optical circuits. PD, photodetector; ESA, electrical spectrum analyser; AOM, acousto-optical modulator. The output of the self-injection-locked laser either beats with another stable laser or performs self-heterodyne with an 800-m delay line for the ESA to measure the phase noise. d, Phase noise spectra for the self-injection-locked and free-running lasers. The phase noise of the free-running laser is measured using self-heterodyne. The faded curve indicates that the noise is limited by the measurement noise floor. e, RF beat-note spectrum of the self-injection-locked laser and a stable laser revels linewidth compression when locked. A zoomed-in view of (i) is shown in (ii). Free-running beat note is taken with 91-kHz RBW, and the locked beat note is taken with 3-kHz RBW. f, Allan deviation of the self-injection-locked laser measured from the frequency counter (FC) with and without linear drift removal.
