All-in-fiber SESAM based comb oscillator with an intra-cavity electro-optic modulator for coherent high bandwidth stabilization.

We demonstrate the stabilization of an all-in-fiber polarization maintaining semi-conductor saturable absorber mirror (SESAM) mode locked frequency comb oscillator with an intra-cavity waveguide electro-optic phase modulator (EOM) to a narrow linewidth HeNe laser over 46 hours. The high feedback bandwidth of the EOM allows a coherent optical lock with an in-loop integrated phase noise of 1.12 rad (integrated from 10 Hz to 3 MHz) from the carrier signal. No piezo fiber stretcher was required to guarantee long-term stabilization, preventing mechanical degradation of the optical fibers and enabling a long lifetime of the oscillator. As an application a hybrid stabilization scheme is presented, where a comb tooth is phase locked to a longitudinal mode of the large ring laser "G" located at the Geodatic Observatory Wettzell. The hybrid stabilization scheme describes the optical lock of the frequency comb to the G laser and the simultaneous compensation of the ring laser frequency drift by comparing the comb repetition rate against an active H-maser reference. In this context the ring laser reached a fractional Allan deviation of 5 · 10-16 at an integration time of 16384 s.

Closed-loop locking of an optical frequency comb to a large ring laser.

We report on the frequency locking of a 16 m2 ring laser to a single tooth of an optical frequency comb referenced to a hydrogen maser, obtaining a frequency stability of 1 kHz over several days. In common mode operation, where the counterpropagating laser beams run on the same longitudinal mode index, a sensitivity to rotation of 3×10(-9) relative to Earth's rotation is obtained. To test a proposal to bypass time-varying backscatter-induced readout errors in large ring laser gyroscopes, we have operated the laser on adjacent longitudinal cavity modes. The Sagnac frequency due to Earth's rotation obtained in this fashion was strongly influenced by atmospheric pressure changes because the counterpropagating beams within the cavity are affected differently by geometric cavity fluctuations.

Long-term frequency stabilization of a 16 m(2) ring laser gyroscope.

A 16 m(2) helium-neon-based ring laser gyroscope has been frequency stabilized to within 60 kHz over a period of three months. This is achieved using the beat frequency of the ring laser and an iodine-stabilized reference laser as a feedback signal on a pressure vessel enclosing the entire laser, under servo control. We demonstrate that we can compensate for, and thereby negate the influence of, atmospheric pressure variations, which are considerable sources of long-term instability.

How to detect the Chandler and the annual wobble of the Earth with a large ring laser gyroscope.

We demonstrate a 16 m(2) helium-neon ring laser gyroscope with sufficient sensitivity and stability to directly detect the Chandler wobble of the rotating Earth. The successful detection of both the Chandler and the annual wobble is verified by comparing the time series of the ring laser measurements against the "C04 series" of Earth rotation data from the International Earth Rotation and Reference System Service.