Offset-free all-fiber frequency comb with an acousto-optic modulator and two f-2f interferometers

We demonstrate an erbium-based offset-free frequency comb using a fiber-coupled acousto-optic modulator. The comb has two f-2f interferometers; one is for carrier-envelope offset beat detection, and the other is for frequency-shifted offset beat detection. The frequency was shifted by placing the acousto-optic modulator in front of an amplifier and a highly nonlinear fiber for spectral broadening. We confirmed that the offset frequency was stabilized at zero and measured it by shifting it from zero. The Allan deviations of the measured offset frequency were 0.10 and 0.18 Hz with a 1 s averaging time and using feedback and feed-forward stabilization, respectively. (C) 2017 The Japan Society of Applied Physics