Fig. 4. Broadening and stabilizing the laser combs.
a Optical spectra of the locked combs via amplification and nonlinear spanning. Insets show the magnified structures. b Optoelectronic feedback on graphene with the TEC suppressing the power uncertainty from ±0.5 (free running) to ±0.01 dB (feedback stabilized). The statistics of 1000 points over 100 min show that the power variance decreases from 6.3 × 10−2 (free running) to 10−4 dBm2 (stabilized). c RF spectrum of the beat note before (grey) and after (red) stabilization, with a 3 Hz RBW. d Phase noise spectra. Locked on the RF synthesizer, S(f) is suppressed down to −120 dBc Hz−1, suggesting a timing jitter of 2.5 × 10−15 s. Here, the noise base is approximately −140 dB. e Allan deviation of the laser comb spacing. For long-term stability, the in situ feedback can provide four orders of optimization