Demonstration of displacement-measurement-sensitivity proportional to inverse group index of intra-cavity medium in a ring resonator

We show that an intra-cavity medium with dispersion modifies the sensitivity of the cavity resonance frequency to a change in its length by a factor inversely proportional to the group index, ng, in the medium. For a positive group index characteristic of the slow-light media, with a very large value of ng, this effect can help in constructing highly frequency-stable cavities for various potential applications without taking additional measures for mechanical stability. For a negative group index characteristic of the fast-light media, with ng close to a null value, this implies enhancement in sensitivity to change in cavity length. This enhancement in turn can be employed to increase the sensitivity of a ring laser gyroscope.