Limitations of frequency stability transfer in the near infrared using a fiber-based ring cavity

We describe a fiber ring cavity for transferring frequency stability from a metrological optical reference at 1542 nm to tunable lasers covering 100 nm around 1.55 µm and show a stability transfer to the 10−15 level in relative value. The optical length of the ring is controlled by two actuators: a cylindrical piezoelectric tube (PZT) actuator on which a portion of the fiber is coiled and glued for fast corrections (vibrations) acting on the length of the fiber, and a Peltier module for slow corrections acting on its temperature. We characterize the stability transfer and analyze the limitations imposed by two critical effects in the setup: Brillouin backscattering and the polarization modulation generated by the electro-optic modulators (EOMs) used in the error signal detection scheme. We show that it is possible to reduce the impact of these limitations to a level below the detection threshold imposed by the servo noise. We also show that in the long term, the limitation to the stability transfer is a thermal sensitivity of –550 Hz/K/nm which could be reduced by active control of the ambient temperature.