All-fiber ring-cavity for frequency stability transfer at 155  μm

A compact setup for transferring the stability of a metrological frequency reference at 1.55 μm is described. One mode of a fiber-ring cavity is frequency-locked onto the reference. The stability transfer is achieved by locking an extended-cavity diode laser, tunable over 100 nm onto one cavity mode. Once locked, this tunable laser exhibits a relative frequency stability close to 10^-12 for integration times from 1 to 3000 s (minimum of 6·10^-13 at 10 s). We show that this stability limitation is due to the polarization fluctuations' sensitivity of the fiber optic components. Using a second cavity, the frequency stability transfer over 58 nm is demonstrated at a level of 4·10^-12. Associated with a local frequency reference and with an efficient acoustic and thermal insulation, this compact setup is intended for embedded metrological applications.