Loss-gain coupled ring resonator gyroscope

A new gyroscope architecture inspired by parity-time-symmetric optics is proposed and theoretically modeled. It consists of two ring resonators coupled together, one with loss and the other with gain, with a loss and gain selected such that the device does not lase. A narrow-linewidth laser is coupled into the loss ring to probe the coupled resonator’s rotation-dependent resonances, and a detector measures the rotation-induced change in the power transmitted by the device. Assuming that the small-signal gain is smaller than the loss, a common radius for the two rings of 5 cm, and imposing that the power in the gain medium never exceeds 10% of the saturation power to avoid gain saturation, we demonstrate that this structure has a sensitivity to rotation ~170 times larger than an optimized resonant fiber optic gyroscope of equal ring radius and loss. Such loss-gain coupled resonators are known to exhibit an exceptional point at a critical value of the coupling between resonators, at which point the device’s resonances become extremely sensitive to external perturbations such as a rotation. However, we demonstrate that the maximum rotation sensitivity of this paritytime- symmetric structure does not occur at the exceptional point. Instead, for the aforementioned parameter values and the imposition of a small circulating power, it is maximum when the inter-ring coupling is ~11% stronger than the exceptional-point coupling. This significant increase in rotation sensitivity is found to result to a much larger degree from a strong enhancement in the power circulating in the gain ring (although there is not a one-to-one correspondence), and to a much lower extent from an enhancement in the rotation-induced resonance-frequency shift.