Fig. 1. Typical spectra of Ti:Sa MLL-based combs, Er-doped fiber laser-based combs, optical atomic clocks, and 1.5 μm fiber telecom band. Solid lines indicate the fundamental wavelength of optical atomic clocks; the dashed (dotted) lines represent 2× (4×) the wavelength of optical atomic clocks.

Fig. 2. (a) Experimental schematic for the detection of the beat note between the Ti:Sa MLL-based comb and a 1550 nm c.w. laser. It also shows the optical spectrum of the Ti:Sa MLL-based comb (solid lines) and the newly generated comb based on FWM (brown dashed lines). (b) Beat note of fb1550 separately detected at 1550 nm (green), 780 nm (red), and 590 nm (blue) in an RBW of 300 kHz. The abscissas of the spectra are intentionally shifted to be clearly seen. (c) SNR of fb1550 in an RBW of 300 kHz detected at different wavelengths when the polarization of the PCF input light is fixed.

Fig. 3. (a) Experimental diagram for optical frequency division from a cavity-stabilized laser at 578 to 1550 nm and its out-of-loop measurement. (b) Electrical diagram to obtain the error signal of Δ for phase-locking the 1550 nm c.w. laser to the cavity-stabilized laser at 578 nm. The frequency noise from the comb is subtracted with the transfer oscillator scheme. (c) Simplified diagram for testing the noise in coherence transfer from the cavity-stabilized laser at 578 nm to the 1550 nm c.w. laser. We use a multichannel optical frequency division based on a single comb to characterize an out-of-loop measurement. We use different methods to obtain the beat notes between the 1550 nm lasers and the comb. (d) Fractional frequency instability of the phase-locked Δ (in-loop, black squares) and the beat note (fb) between the two 1550 nm c.w. lasers (out-of-loop, blue dots).