Fig. 3: Feedback insensitivity of the SIL laser.
From: 3D integration enables ultralow-noise isolator-free lasers in silicon photonics
a, Schematic illustration of the feedback influence for the laser working at the free-running state and self-injection locking state. Under self-injection-locking conditions, both the through port and the drop port are characterized. b, Experimental set-up for the feedback sensitivity characterization. c, Calculation of the dependence of the critical feedback level (the highest tolerable reflection) for regime I boundary (fr1) on the cavity-loaded device. The backscatter (R) from the ultrahigh-Q resonator also impacts the highest tolerable downstream reflections. d, The laser spectral lineshape evolution recorded with an ESA by self-heterodyning with an AOM for the free-running laser state (top), SIL through-port output (middle) and SIL drop-port output (bottom). Different feedback regimes are indicated and details of the regimes are covered in the Supplementary Information. e, Frequency noise of the drop port at the SIL condition under different on-chip feedback levels. The top panel shows the recorded laser spectral lineshape evolution under a maximum of −6.9 dB on-chip feedback. CIR, circulator.
