1 × N Fiber Optic Coupler Based on a Polyhedral Gradient-Index Lens

A 1 × N fiber coupler based on a single-polyhedral gradient-index lens (p-GRIN) is proposed. The entrance end of the p-GRIN has polyhedral convex cone shape with N surfaces and the exit end has a flat surface. When light from a single-core optical fiber illuminates the input end of the p-GRIN, N spatially separated light beams will be focalized at the output end and coupled, respectively, into N different fibers cores. With ray-tracing analysis, the coupling parameters design model was established. Calculation and simulation with ZEMAX showed that the output beam positions can be optimized by adjusting the input cone angle and the distance between the input fiber end and the cone tip. The light beam power distribution is simulated and mode field evolution is investigated. The results indicate that high coupling efficiency could be achieved with optimized parameters design. This method may be adapted for different types of optical fibers and provide a practical solution for light coupling between singleand multicore fibers.