The counterpropagating waves in a single traveling-wave cavity can be partially coupled by means of a small perturbation such as a notch. When it is side coupled to a waveguide, this single cavity yields a general second-order (Chebyshev) reflection response in the waveguide, which is useful for narrow-bandwidth reflecting applications. In a different application, the cavity amplifies small reflections induced by external perturbations, thus finding use in ultrafine sensing. Amplification factors as great as 10<sup>12</sup> are predicted for the highest-<i>Q</i> microsphere resonators. The analytic theory of these devices is presented.
© 1998 Optical Society of America
Brent E. Little, Sai T. Chu, and Hermann A. Haus, "Second-order filtering and sensing with partially coupled traveling waves in a single resonator," Opt. Lett. 23, 1570-1572 (1998)