Experimental Demonstration of a Compact Variable Single-Mode Fiber Coupler Based on Microfiber

Single-mode fiber coupler with variable coupling ratio is a flexible tool for optical fiber applications. Here we demonstrate a microfiber based coupler with compact size and wide tuning range. The coupler consists of two identical single-mode microfibers that are fabricated via parallel pulling process. By adjusting the twisting angle between these microfibers, the coupling ratio varies from 3.15% to 98.5% due to the change of evanescent field interaction length. Numerical simulations are carried out and the results agree well with the experimental ones. The effects of diameter discrepancy between two microfibers and mode polarization are also studied experimentally and numerically.