Long-term digital frequency-stabilized laser source for large-scale passive laser gyroscopes

Abstract

We report on the development of a digitally controlled long-term frequency stabilized ultrastable laser source, which serves as an injection laser to stabilize the perimeter of a 3 m × 3 m heterolithic passive resonant gyroscope. We operate the gyroscope at two different cavity modes to reduce back-scattering coupling disturbance for gyroscope locking. This scheme increases the requirement for the injection laser frequency stability since we are using the wavelength of the laser as the length standard for the heterolithic gyroscope structure. The laser source is digitally locked to an ultrastable high-finesse Fabry-Perot cavity and a femtosecond optical frequency comb referenced to an active hydrogen maser simultaneously. The fractional frequency stability of the locked laser is better than 1.2 × 10−14 for averaging times from 0.1 s to 10 000 s. The short-term frequency stability is limited by the stability of the Fabry-Perot cavity, and the long-term frequency stability is limited by the stability of the frequency comb. The digital locking system enables the laser to run autonomously for weeks and can quickly relock itself within seconds to ensure continuous running of the gyroscope. The digital frequency stabilization technique can also fulfill the requirements of space gravitational waves detection and the next generation space gravity recovery mission.

Noise Analysis of a Passive Resonant Laser Gyroscope

“…We hope to suppress it to the shot-noise level in the frequency region of to . For the FSR jitter, an active control scheme of the cavity length is required with a goal for the cavity length fluctuation to drop below [ 31 ]. The additional noise contribution from the beam combiner must be reduced by a more compact design and better environmental isolation.…”

“…In order to measure the conversion factor of the actuator K , a modulation method similar as the one used in the measurement of is implemented. When a modulation signal is fed to the laser driver, we record the frequency response of the laser by beating the diode laser with an ultra-stable reference laser [ 31 , 32 ]. Since there are two actuators inside the laser head, we measure the coefficients independently for the current and PZT.…”

“…The second contribution is caused by the change of the FSR [ 15 ], which depends on the longitudinal mode index m and can be expressed as . We obtain the cavity length fluctuation noise by beating the gyro laser with the ultra-stable laser as a reference when the primary servo loop is closed [ 31 ]. Since the noise of the ultra-stable laser is negligible, the beat signal fluctuations represent the variation in cavity length.…”

Vibration Property of a Cryogenic Optical Resonator within a Pulse-Tube Cryostat

“…We lock a 1064 nm continuous wave semiconductor laser to the cavity using the Pound–Drever–Hall (PDH) method [ 21 ]. We evaluate the laser frequency stability by beating the laser with another reference ultrastable laser locked to a room temperature cavity [ 22 , 23 , 24 ], as shown in Figure 3 a. The frequency stability of the reference laser is at 1 s averaging time.…”

“…A normal 6 cm sapphire cavity without a vibration-immune design was installed on the cryogenic plate of the cryostat. We locked a 1064 nm laser to the cavity using the Pound–Drever–Hall (PDH) method, and the laser frequency stability was evaluated by beating this laser with another ultrastable reference laser [ 21 , 22 , 23 , 24 ]. We obtained the vibrational sensitivity of the cryogenic cavity through different frequencies of vibrational modulation with three voice coil motors driving the cryostat in three perpendicular directions.…”