Analysis of an end separation in single-mode fibers and a fiber Fabry-Perot resonator

Transmission characteristics of an end separation in two single-mode fibers and a Fabry-Perot resonator formed in the fiber are analyzed under Gaussian-beam approximation by using the method of planewave expansion. The interference effects between two fiber endfaces (or mirrors deposited on the fiber endface) and the angular divergence of the beam in the gap (or spacer) are incorporated in the present formulation. It is found that these transmission characteristics are strongly affected by the beam divergence even if the separation is several tens of micrometers and that the peak transmissivity of the Fabry-Perot resonator decreases as the reflectivity of mirrors increased. A simple improvement on the degradation of the peak transmissivity is also discussed.<>