Analysis of optical fiber ring resonators using a collinear 3×3 fiber coupler

We present a detailed theoretical analysis of three different types of optical fiber ring resonators (Types 1-3) using a collinear (planar) 3×3 fiber coupler where three fibers inside the coupler lie in the same plane. Expressions for the circulating (resonant) and output intensities of these three types as well as the resonance conditions are obtained. The dependence of the output intensities and of performance parameters such as the finesse, contrast, and crosstalks on the major parameters of the fiber and the 3×3 fiber coupler is investigated. It is found that among six output intensities, two of them [I₁ (d) of Type I and I₃ (d) of Type 2] can reach full resonances, and that the Type 1 ring resonator is the best (followed by Type 3) for filter application, and Type 3 is the best for application as a densely spaced two channel wavelength-division multi/demultiplexer