Programmable complex field coupling to high-order guided modes of micro-structured fibres

We demonstrate a novel technique for generating tuneable complex field distributions for controllable coupling to high-order guided modes of micro-structured fibres. The optical Fourier transform of grating-based phase patterns, which are encoded on a computer-controlled spatial light modulator, generates complex field distributions for selective launching of a desired mode.

Both the amplitude and the phase of the programmable fields are modulated by straightforward and fast adjustments of simple pre-defined binary phase-only diffractive patterns. Experiments demonstrate tuneable coupling to the second-order guided modes of a commercially available index-guiding silica fibre with a triangular lattice air-hole micro-structure.