An in-fiber integrated multifunctional mode converter

We propose a technique of designing a sandwich scheme of in-fiber integrated multifunctional mode converter which can be used to configure and match different mode fields between various specialty fibers and a conventional single-mode fiber with high mode transfer efficiency. In this technique, a double-clad fiber is introduced between the fibers, thus matching refractive index profiles could be implemented by thermal diffusion. Compared with previous mode converters, the proposed solution can be used not only as a Gaussian beam expander/compressor, but also as a mode converter to transfer a Gaussian mode to a ring mode, and as a fan-in/out adapter to convert one Gaussian mode to multiple Gaussian modes. This scheme is able to produce a stable and compact device which is more efficient in coupling and more flexible for new fiber lasers. In addition, the excellent performance of the proposed technique enables its usefulness of making other optical devices, such as optical coupler, optical connector, and optical interferometer.