A single-mode optical fiber ring resonator using a planar 3×3 fiber coupler and a Sagnac loop

We present the first theoretical analysis of an optical fiber ring resonator using a planar 3×3 fiber directional coupler and a fiber Sagnac loop. In the planar 3×3 fiber directional coupler, the three fibers inside the coupler lie in the same plane. Expressions for the circulating (resonant) and the output fields of the fiber ring resonator are obtained. It is found that this fiber ring resonator has a special property where there are two or more main resonance peaks or dips inside a period 2π of the phase change of the fiber ring resonator. This ring resonator may have applications as a sensor with high-phase sensitivity and a densely spaced two-channel wavelength division multi/demultiplexer