Fig. 2: Spectral purity of the self-injection-locked laser.
From: Low-noise frequency-agile photonic integrated lasers for coherent ranging
a Experimental schemes of laser frequency noise measurements, using optical cross-correlation technique or heterodyne beat with the external cavity diode laser (ECDL) locked to a high-Q crystalline resonator using the Pound-Drever-Hall technique. b Schematic in the frequency domain of optical cross-correlation (C.C.) technique. c The Si3N4 photonic chips with an FSR of 9.87 GHz have an intrinsic loss of κ0/2π < 10 MHz, corresponding to a quality factor of Q0 > 20 × 106. The κ0/2π histogram of 1477 TE00 resonances from a 9.87 GHz FSR microresonator is shown. d Optical spectrum of the SIL DFB emission. e Single-sided PSD of frequency noise of the hybrid integrated laser system upon self-injection locking to microresonators with FSRs: 190.7 GHz (green), 9.87 GHz (red), 2.45 GHz (blue) and free running regime (grey). Dark colour traces correspond to optical cross-correlation data, light colour traces to the heterodyne beat method. The dotted red, green, blue lines indicate the calculated thermo-refractive noise limit for Si3N4 microresonators with different FSR. f The inset shows a comparison of frequency noise of SIL DFB with a commercial ECDL (Toptica CTL) and a commercial fibre laser (NKT Koheras Adjustik E15).
