Mass fabrication considerations of pre-spectrograph wavelength splitter and pupil slicer units for fiber optic based multi-object spectroscopy

Fiber optic-based multi-object spectrographs have been used for astronomical surveys since the 1980’s. Towards the end of the 1990s and the early 2000’s the multiplex capability grew to allow hundreds of astronomical targets to be observed simultaneously within the same telescope field of view. Additionally, recent instruments have been developed with higher target counts and with implementation on larger aperture telescopes. Design studies are currently in progress for more massively multiplexed spectrographs on telescopes with apertures of 10 to 20 meters with target counts approaching 20,000. The substantial number of spectrographs needed for these facilities are increasingly larger with correspondingly difficult and risky designs. We present fabrication considerations based on a prototyped pre-spectrograph wavelength splitter and pupil slicer (WSPS). 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 the implementation of an arrayed output configuration to slice up the pupil. The performance of the WSPS must achieve excellent light coupling of the incoming light to the output channels. A facility like the Maunakea Spectroscopic Explorer (MSE) requires several hundred high-precision units. Mass production and simplified/automatic alignment techniques are desired to minimize the human resources and time required for assembly. This evaluation includes consideration of materials and fabrication techniques (CNC machining, 3d printing, etc.).