A Coaxial Dual-Waveguide Fiber Coupler

We demonstrate a method to fabricate an in-fiber integrated multi-waveguide fiber coupler based on thermal diffusion technology to achieve stable and efficient coupling of a single-mode fiber to a multi-waveguide fiber. Simulation results show that the efficient coupling of a single-mode fiber and a multi-waveguide fiber can be realized by introducing double-clad fiber into single-mode fiber and multi-waveguide fiber. A coaxial dual-waveguide fiber coupler was fabricated based on thermal diffusion technology. The measurement results of the three-dimensional refractive index distribution of the coaxial dual-waveguide fiber coupler verified the feasibility of the thermal diffusion technology to fabricate the multi-waveguide fiber coupler. The insertion loss of the thermally diffused coaxial dual-waveguide fiber coupler was tested, and its performance was better than that of the fusion tapered coupler. The multi-waveguide fiber coupler fabricated by thermal diffusion technology allows for an all-fiber setup with coupling efficiency as high as 98%, achieves a relatively stable fundamental mode excitation in multi-waveguide fiber, requires minimal maintenance, and will accelerate the translation toward particle trapping, spectral detection, and optical communication.