Optical frequency standard of continuous wave for fiber communication based on optical comb

Abstract

An approach is reported to acquire an optical frequency standard based on precise frequency locking between optical frequency comb and continuous wave. A stabilized erbium-fiber-based frequency comb is created by locking to the two-photon absorption resonance of rubidium atoms. An Erbium-doped distributed-feedback narrow linewidth lasers is presented with an actively stabilized all fiber Mach–Zehnder interferometer. With this structure, many lines of the optical frequency comb can make a contribution to the error signal. The signal-to-noise ratio (SNR) is enhanced compared to traditional way which utilizes only one comb line. An acousto-optic modulator (AOM) is used to compensate the noise in fiber which is induced by environment. The relative frequency offset instability is 2 × 10−13 at 1 s and 6 × 10−15 at 1000 s. This stabilized system can be wisely used in optical communication at 1550 nm. The main advantage of this structure is the ability for long distance frequency transmission. Without dispersion, the stability and the robustness of the transmission is greater than the scheme only with the frequency comb. We transferred the signals along 10km optical fiber link with it. The relative frequency stability loss of the frequency signal is 1.1 × 10−15 at 1 s and reaches 7.6 × 10−19 at 1000 s.