SINGLE-MODE OPTICAL-FIBER RESONATOR AND APPLICATIONS TO SENSING (FIBER SENSOR, FIBER LASER, FIBER GYROSCOPE)

A new, potentially important fiber-optic device, the fiber resonator, is presented. A length of single-mode optical fiber is formed into a closed ring via a fiber directional coupler to constitute a low-loss, all-fiber ring cavity. The properties of this cavity resonator are similar to those of any resonant device where energy storage occurs at discrete excitation frequencies. The finesse of such a fiber cavity can approach 100.; A review of several recently developed single-mode fiber-optic components is given. These low-loss components are essential to the high performance of the all-single-mode fiber resonator. A theory of the resonator is derived which closely matches experimental performance. The resonator can be a building block upon which more complicated sensor systems can be constructed. Three such systems were built and are described in detail.; One system is sensitive fiber-optic interferometer in which any environmental perturbation affecting the phase of light in the fiber resonator, such as that caused by acoustic waves, can be detected. The sensitivity of this device is superior to that of other types of fiber sensors recently developed. Environmentally-induced periodic changes in the resonator optical path length as small as ten nuclear diameters are detectable.; The second system makes use of the small optical nonlinearities of the fused silica fiber material to produce an all-fiber ring laser. The high-amplitude optical fields within the resonator allow such nonlinear interactions to occur at low excitation powers. Stimulated Brillouin scattering provides gain and the resonator's low-loss optical feedback allows laser action to occur. The possibility of using this device as an active fiber-optic ring laser gyroscope is assessed.; The third system described is a passive fiber-optic ring resonator gyroscope. The Sagnac effect produces a rotationally-induced change in the resonant frequencies of the resonator which is measured with an external laser. This device presently is sensitive to rotations on the order of Earth's rotation rate, and much room for improvement theoretically is possible.; Finally, future applications of the fiber resonator are discussed. High-resolution optical spectrum analysis, optical filtering, and temperature sensing are among the possibilities.