Proposal for an ultra-high sensitivity and fast ring laser gyroscope using mode-locked optical frequency Combs

We propose an ultra-high sensitivity and fast angular velocity sensor as a new application of the optical frequency combs. By using the Sagnac interferometer, the time shift of the ultra-short pulse laser, corresponding to the optical path shift, occurs under a certain angular velocity. This time shift can be detected as the heterodyne beat of the optical frequency. The system we propose is composed of two optical frequency combs—one for reference and the other for sensing—and a stabilized laser. The relationship between the repetition frequency f_rep and the optical path L (= c / f_rep) is expressed by

Δf_rep / f_rep = ΔL / L. … (1)

ΔL is caused by the Sagnac effect, and the equation (1) is given by

Δf_rep = 2AΩ(f_rep / c)², … (2)

where A is the area of the Sagnac interferometer, c is the speed of light, Ω is the angular velocity. By the heterodyne detection of the beat signal with the stabilized laser, the difference in each beat frequency Δf_beat is given by

Δf_beat = 2NAΩ(f_rep / c)², … (3)

where N is an integer mode number. The mode-locked optical frequency combs enable high stability of optical frequencies on the order of μHz, the calculated angular velocity is expected to be on the order of prad/s (nano-degrees per hour). This has the potential to detect extremely small angular velocities with high sensitivity, without the need for a dither. Furthermore, the beat frequency is controlled at approximately 100 MHz, indicating the potential for the realization of a high-speed ring laser gyroscope.