Numerical Analysis of Waveguide Coupling Between Photonic Crystal Fiber and Single-Mode Fiber

A new evanescent-field-based coupler that achieves high coupling efficiency between a single-mode fiber (SMF) and a photonic crystal fiber (PCF) is proposed. The coupling equations are presented and a numerical solution is obtained in this letter. Optimization of the refractive index, the effective radius of PCF, and the coupling length can enhance the coupling efficiency. It is shown that a maximum coupling ratio of 93% can be achieved for a coupling length of 1.72 mm for commercially available SMFs and PCFs. The proposed PCF-SMF fiber coupler opens a path for the development of unique modalities for fiber-optic chemical sensors where the light ingress and egress paths can be via SMF, but the light interaction with analytes of interest occurs in the PCF where enhanced evanescent interactions can be obtained at the multiple air holes.