Laboratory evaluation of a pre-spectrograph wavelength splitter and pupil slicer for fiber optic based multi-object spectroscopy

Fiber optics based spectrographs have seen drastic improvements in multiplex capability; the number of simultaneously observable astronomical objects are expected to reach the tens of thousands. A large number of spectrographs are needed in order to accommodate this increasing target count. We present a design and laboratory evaluation of a prototype pre-spectrograph wavelength splitter and pupil slicer (WSPS) in order to nullify large wavelength splitters within multiwavelength channel spectrograph optics, and increase packaging efficiency of the single channel spectrographs. The WSPS is an optical assembly that interfaces to a subset of the incoming fiber optics (~100 per unit), splits the light into multiple wavelength channels (Blue, Green, Red, J, and H), and allows implementation of an arrayed output configuration to slice up the pupil. This assembly must achieve excellent light coupling and effectively suppress scattered light in order to distinguish faint from bright objects illuminating the same WSPS unit.