Passive optical gyroscope with double homodyne readout

We present a passive, resonant, single-frequency gyroscope design that utilizes polarization modes of an optical cavity to readout rotation and generate a laser frequency discriminant. This design is notable for its simplicity, requiring no modulation electronics or frequency counters. We extract both the cavity length signal and rotation signal from two copropagating beams with orthogonal polarizations. This readout scheme can be applied to an optical cavity whose polarization eigenmodes experience different phase shifts such as fiber rings, whispering gallery mode resonators, and folded free-space cavities. We apply this technique to the passive free-space gyroscope and achieve a bias stability of 0.03°/h and a sensitivity of 5×10^-8  rad/s/Hz above 1 Hz, with a cavity of area 400  cm² and finesse of 10⁴.