An etalon stabilized 10-GHz comb source using a slab coupled waveguide amplifier

An optical comb source based on a slab-coupled optical waveguide amplifier (SCOWA) is presented. The laser is harmonically mode-locked at 10.287 GHz repetition rate and stabilized to an intra-cavity Fabry-Pérot etalon via Pound- Drever-Hall locking. The Fabry-Pérot etalon serves as a reference for the optical frequency of the comb-lines and suppresses the fiber cavity modes to allow only a single longitudinal mode-set to oscillate, generating a frequency comb spaced by the repetition rate. The pulse-to-pulse timing jitter and energy fluctuations are < 2 fs and < 0.03%, respectively (integrated from 1Hz to 100 MHz). Fundamental to this result is the incorporation of the SCOW amplifier as the gain medium and the use of an ultra-low noise sapphire-loaded cavity oscillator to mode-lock the laser. The SCOWA has higher saturation power than commercially available gain media, permitting higher intra-cavity power as well as available power at the output, increasing the power of the photodetected RF tones which increases their signal-to-noise ratio. A high visibility optical frequency comb is observed spanning ~3 nm (at -10 dB), with optical SNR > 60 dB for a cavity with no dispersion compensation. Initial results of a dispersion compensated cavity are presented. A spectral width of ~7.6 nm (-10 dB) was obtained for this case and the pulses can be compressed to near the transform limit at ~930 fs.