http://arxiv.org/abs/2006.13601
A generic fiber positioning strategy and a fabrication path are presented for microlens-fiber-coupled integral field units. It is assumed that microlens-produced micro-images are carried to the spectrograph input through step-index,multi-mode fiber, but our results apply to micro-pupil reimaging applications as well. Considered are the performance trades between the filling percentage of the fiber core with the micro-image versus throughput and observing efficiency.A merit function is defined as the product of the transmission efficiency and the etendue loss. For a hexagonal packing of spatial elements, the merit function has been found to be maximized to 94% of an ideal fiber IFU merit value (which has zero transmission loss and does not increase the etendue) with a microlens-fiber alignment (centering) tolerance of 1 um RMS. The maximum acceptable relative tilt between the fiber and the microlens face has been analyzed through optical modeling and found to be 0.3 degree RMS for input f-ratio slower than f/3.5 but it is much more relaxed for faster beams. Several options of fabricating fiber holders have been compared to identify cost-effective solutions that deliver the desired fiber positioning accuracy. Femto-second laser-drilling methods deliver holes arrayed on plates with a position and diameter accuracy of 1.5 um RMS, and with an aspect ratio of 1:10. A commercial vendor produces plates with thickness of 5 mm, but with similar (1 um RMS) positioning accuracy. Both of these techniques are found to be moderately expensive. A purely photo-lithographic technique performed at WCAM (a facility at the University of Wisconsin, Madison), in tandem with deep reactive ion etching, has been used to produce a repeatable recipe with 100% yield. Photo-lithography is more precise (0.5 um RMS) in terms of hole positioning and similar diameter accuracy (1 um RMS).
S. Chattopadhyay, M. Bershady, M. Wolf, et. al.
Thu, 25 Jun 20
46/78
Comments: 26 Pages, 18 Figures, 1 Table
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