Coupled-ring exceptional-point gyroscopes

We will discuss and contrast the predicted performance of two types of exceptional-point (EP) gyro, the objective being to elucidate the role of the EP in enhancing rotation sensing. The first is a PT-symmetric coupled-ring resonator where a ring with gain is coupled to a lossy ring. The loss is chosen to be large enough to operate the device below lasing threshold. A probe laser is coupled into the gain ring to interrogate the device’s resonances by measuring changes in the laser power transmitted through the gyro. At its EP, a 300-fold sensitivity enhancement is predicted over the benchmark single-ring gyro. This enhancement increases to 2400-fold by detuning from the EP. The second gyro has the same topology except that both rings are lossy (no gain). In this second gyro, simulations show that the EP-enhanced Sagnac splitting remains fully present, but the sensitivity enhancement vanishes. A comprehensive noise study also shows that no enhancement in the signal-to-noise ratio is predicted in either limit of shot noise or detector noise. We therefore attribute the enormous sensitivity enhancement achieved by the first gyroscope to the gain, rather than the enhanced splitting from the EP. This general conclusion abounds in the direction of a number of recent publications on EP gyros that incorporate a gain medium and are operated above threshold, yet provide no net enhancement due to the EP.