Selective higher order fiber mode excitation using a monolithic setup of a phase plate at a fiber facet

TL;DR

This paper demonstrates a monolithic phase plate setup at a fiber facet for selective higher order mode excitation, achieving high purity and efficiency compared to free-space methods, supported by experiments and simulations.

Contribution

It introduces a monolithic phase plate approach for high-purity higher order mode excitation in optical fibers, improving efficiency over traditional free-space setups.

Findings

Achieves >99% mode purity in higher order modes.

Monolithic setup is twice as energy-efficient as free-space phase plates.

Experimental results agree well with numerical simulations.

Abstract

Controlling the modal content coupled into an optical fiber can be desireable in many situations, e.g. for adjusting the sensitivity of the guided field distribution to external perturbations. For this purpose we used a monolithic setup of a phase plate at a fiber inpute facet to excite selectivly higher order modes, which theoretically can provide a mode purity of more than 99%. We investigated the capabilities of this approach by complete modal decomposition of the fiber output signals, considering the achievable mode purity with respect to several possible imperfections of the setup. The experiments are compared with detailed numerical simulations and show a high agreement. Additionally a comparison with a well known setup with free space phase plates was undertaken. This showed the monolithic setup to be energetically twice as efficient.