Methane-Based Photonic Microwave Oscillator With Stability Better Than 10−14 at 1-103 s Averaging Times

An improved version of the transportable photonic microwave oscillator based on the He-Ne/CH 4 optical frequency standard (OFS) ( \lambda = 3.39 ~\mu \text{m} ) and the femtosecond Er fiber laser optical-to-microwave frequency divider ( \lambda = 1.55 ~\mu \text{m} ) has been developed. Stable continuous operation of the generator was achieved for several days without operator intervention, and the relative Allan deviation below 1\times10 −14 was demonstrated for averaging times 1-10 3 s at output frequencies of 1.0 and 9.2 GHz. The choice of frequencies is determined by the implementation of the methane-based photonic microwave oscillator as an interrogation oscillator for Cs (Rb) fountain. The obtained relative frequency instability at averaging times of 1-200 s is lower than that of the best commercial H-masers. Compared to transportable photonic microwave oscillators based on an ultralow expansion Fabry-Perot (FP) cavity, the oscillator described in this article has an order of magnitude less drift and can be attractive for different tasks of coherent radio photonics where a relatively long-term accumulation of weak signals is required.