Beam combiner for the Asgard/BIFROST instrument

BIFROST will be a short-wavelength (lambda = 1.0 - 1.7 mu m) beam combiner for the VLT Interferometer, combining both high spatial (lambda/2B = 0.8 mas) and spectral (up to R = 25,000) resolution. It will be part of the Asgard Suite of visitor instruments. The new window of high spectral resolution, short wavelength observations brings with it new challenges. Here we outline the instrumental design of BIFROST, highlighting which beam combiner subsystems are required and why. This is followed by a comparison All-In-One (AIO) beam combination scheme and an Integrated Optics (IO) scheme with ABCD modulation both in terms of expected sensitivity and the practical implementation of each system.