We propose a compact stabilization system for erbium(Er)-fiber-laser-based frequency comb with wavelengths ranging from 1510 nm to 1610 nm, which is widely used in fiber-based optical communication. In this stabilization scheme, both the repetition rate and mode of the comb is directly stabilized to a Rb atomic resonator, based on the physical phenomenon of coherent population trapping (CPT) and saturated absorption resonance, respectively. The stabilized frequency comb provides the long-term instabilities of ∼3 × 10−12 for repetition rate and of ∼7 × 10−12 for each optical mode of comb and can meet the requirement of optical-comb-based communication.

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We developed a new radio frequency dissemination system based on an optical fiber link. A 1.55 μm mode-locked fiber laser was used as optical transmitter in the system. To actively reduce the phase fluctuation induced by the fiber length variations with high resolution, we proposed a novel compensation technique. In our technique, we directly control the phase of optical pulses generated by the laser to compensate the fluctuation. The phase-controlling method is based on both pump power modulation and cavity length adjusting. We performed the transfer in a 22-km outdoor fiber link, with a transfer stability of 3.7 × 10(-14) at 1 s and 6.6 × 10(-18) at 16000 s. The integrated timing jitter in 24 hours was reduced from 14 ps to 35 fs.

We demonstrate the direct frequency comb spectroscopy of Rb 5S→5D two-photon transitions directly excited by an optical frequency comb (OFC) in 1.5 μm fiber communication bands. A chain of comb spectral manipulation and quantum coherence control is implemented to enhance the efficiency of second harmonic OFC generation and eliminate the Doppler-broadening background. The direct frequency comb spectroscopy with clearly resolved transition lines is obtained. Our scheme provides a potential approach to realize the OFC at ~1.5 μm with high stability and accuracy.

We demonstrated a frequency standard based on a detuned coherent population beating phenomenon. In this phenomenon, the beat frequency of the radio frequency for laser modulation and the hyperfine splitting can be obtained by digital signal processing technology. After analyzing the spectrum of the beat frequency, the fluctuation information is obtained and applied to compensate for the frequency shift to generate the standard frequency by the digital synthesis method. Frequency instability of 2.6 × 1012 at 1000 s is observed in our preliminary experiment. By eliminating the phase-locking loop, the method will enable us to achieve a full-digital frequency standard with remarkable stability.