Direct laser written multimode waveguides for astronomical applications

There is a high demand for multimode waveguides in astronomical instrumentation, as atmospheric turbulence distorts stellar wavefronts, broadening the point spread function in the telescope focal plane from the ideal diffraction limit, making coupling to single-mode fibres very lossy. With the aim of creating integrated photonic devices that are compatible with existing multimode fibre installations, we present a thorough characterisation of multimode optical waveguides created by the direct write technique. The waveguides reported are the largest to date (~40 µm core diameters) fabricated by the direct write technique and have numerical apertures of 0.2, which are both commensurate values with standard multimode fibres (50 µm and 0.2 respectively). However, waveguide ellipticity needs to be first overcome.