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.
We present an all-optically stabilized, erbium-doped mode-locked fiber laser with an optically pumped ytterbium-doped fiber. The mode-locked fiber laser has two frequency-control actuators that are pump laser powers for erbium-doped and ytterbium-doped fibers. We investigate the frequency-control characteristics of the mode-locked laser and find that the fixed points for the two actuators are sufficiently apart from each other, realizing the simultaneous phase locking of the repetition and carrier envelope offset frequencies. We describe a long-term frequency measurement of an acetylene-stabilized laser at 1542 nm using an all-optically stabilized frequency comb.
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