Fig. 2
From: Free-space transfer of comb-rooted optical frequencies over an 18 km open-air link
Comb-rooted optical frequency synthesis a The source comb is stabilized by controlling the repetition rate and the offset frequency. Multiple comb modes are selected out as optical carriers and amplified by injection locking to laser diodes (LD), while one comb mode is phase-locked directly to a high-finesse cavity. PD photodetector, C optical circulator, OC optical coupler, VCO voltage-controlled oscillator, AOM: acousto-optic modulator, PZT: piezo-electric transducer. WDM: wavelength division multiplexer. b Optical and RF beat spectra of the optical carriers selected from 1530.3 nm to 1564.4 nm, all showing a 1.5 Hz instrument-limited narrow linewidth. c Single side band (SSB) phase noise spectrum of the source comb after stabilization to the high-finesse cavity. d The source comb’s Allan deviation that is converted from the SSB phase noise spectrum
