Recent results on electro-optic visible multi-telescope beam combiner for next generation FIRST/SUBARU instruments: Hybrid and passive devices

摘要

FIRST (Fibered Imager foR a Single Telescope instrument) is an instrument that enables high contrast imaging and spectroscopy, thanks to a unique combination of sparse aperture masking, spatial filtering by single-mode waveguides and cross-dispersion in the visible. In order to increase the instrument's stability and sensitivity, we proposed a new series of photonic beam combiners. The idea is to achieve phase modulation inside an optical chip and get rid of external delay lines, and improve the transmission by using novel techniques that will allow for beam combination in 3D, avoiding planar X-crossings and large bending radii observed in planar integrated optics instruments, between first and last inputs to combine, when the inputs separation is large (i.e. in 9 telescopes beam combiners). In a previous paper [4] we presented first prototypes of beam combiners for FIRST/SUBARU 9T. Planar 2D concepts were studied, but transmission was low due to the high number of crossings and the sharp bending angles needed to achieve beam combination within the length of the wafer. In this paper we will present our recent results on improved designs concerning: A) A hybrid Lithium-Niobate active beam splitter and phase modulator (9T, 1×8), coupled to a passive glass beam combiner (72×36, by pairs). B) A full passive device (5T splitter+beam combiner) and C) a narrow 5T splitter + phase modulator based on lithium niobate, to reduce the bending losses and optimize the overall transmission once coupled to the passive combiner. A comparative analysis of different performances will be presented.