Honeycomb: A concept for a programmable integral field spectrograph

An unsolved problem in astronomical instrumentation is an imaging integral field spectrograph where the user has the freedom to specify arbitrarily complex, contiguous or disjoint regions over the focal plane, rather than a contiguous rectangular field. We present a new concept to solve this problem. Our device allows the user to format the field of view with fibre bundles packed into arbitrary patterns. The field of view is segmented by a large N×N microlens array (e.g. N=1000). This element divides the wavefront into small beams which pass through a metal plate drilled with a grid of holes in the same format as the microlens array. On the reverse side of the grid, hexagonal blocks comprising 67 input fibres are plugged into position on the grid with a pair of sliding "croupier" sticks. The fibred blocks transport the light to the spectrograph. The blocks are held magnetically and the plugging ensures accurate and repeatable registration with respect to the microlens array. The grid plate is micromachined with baffled holes in order to ensure photometric uniformity over the field of view.