Broadband phase noise suppression in a Yb-fiber frequency comb

We report a simple technique to suppress high-frequency phase noise of a Yb-based fiber optical frequency comb using an active intensity noise servo. Out-of-loop measurements of the phase noise using an optical heterodyne beat with a cw laser show suppression of phase noise by >= 7 dB out to Fourier frequencies of 100 kHz with a unity-gain crossing of similar to 700 kHz. These results are enabled by the strong correlation between the intensity and phase noise of the laser. Detailed measurements of intensity and phase noise spectra, as well as transfer functions, reveal that the dominant phase and intensity noise contribution above similar to 100 kHz is due to amplified spontaneous emission or other quantum noise sources. (C) 2011 Optical Society of America