Bridging the Optical and Microwave Frequencies with the Dual-frequency Faraday Laser

The dual-frequency Faraday laser, utilizing the two-peak transmission of a Faraday anomalous dispersion optical filter (FADOF), can achieve simultaneous lasing on two modes both determined by the atomic transition. The beating frequency between the two modes is close to the frequency interval between hyperfine energy levels of the atomic ground state. Since the frequency of the beat signal and output laser modes all depend on the cavity length, locking one of them can also improve the stability of the others. Therefore, by locking the beat frequency to a stable microwave frequency reference, the stability of the reference can be transferred to the laser frequencies; Similarly, locking one of the output laser frequencies will also transfer its stability to the beat frequency in the microwave regime. This can serve as a means to bridge the gap between the optical and microwave frequency regimes, and can have wide applications, such as absolute frequency measurement of a laser, or photonic microwave generation.