The light captured by the telescope enters from the left and propagates to
the right. The light path goes through seven key stages:
(1) The incoming light is captured by standard multi-mode imaging
fibers (MMFs). (2) The light is split according to wavelength using a beam
splitter (micro-dichroic). (3) The MMFs are each adiabatically tapered onto a parallel
array of single-mode fibers (SMFs) using
photonic lanterns (PLs, about 15 cm in length). (4) Ultra-broadband fiber Bragg gratings
(FBGs; about 20 cm in length) on each of the SMFs suppress the
unwanted OH sky lines in the near-infrared window (~1000-1800 nm). (5) Stacked phased array waveguides
(AWGs) integrated onto a chip, about 4 x 4 cm2 in size, serve as the
first dispersive stage. (6) The light on exit is reimaged
and cross-dispersed by integrated optics devices. (7) A large-format HgCdTe photon counting array transforms the
light into a digital signal that can be analyzed using standard
astronomical data analysis software packages.
Components #1 and #2 are off-the-shelf items available from the
industry. As shown in the above figures, examples of components #3-5
have already been fabricated, as part of an effort led by collaborator
J. Bland-Hawthorn from the University of Sydney. UMCP will take the
lead on components #6 and #7 and the overall integration of the
system. Component #6 will consist of stacked micro-cylinders+prisms
designed and manufactured in collaboration with a leading micro-optics
company (e.g., LIMO, Germany). Each micro-cylinder will focus the
output beam from each AWG and then the micro-prism will cross-disperse
the 3-7 spectral orders from each beam onto the detector on a scale of
less than 1 mm (~distance between AWGs). The main technical challenge
will be to achieve good curved and flat optical surfaces to preserve
the optical fidelity of the data and optimize use of the detector
while avoiding spectrum overlap. The stringent requirements imposed by
the faintness of our targets and the density of information from IPS
demands the use of large-format near-IR detectors (component #7) with
high quantum efficiency (80-90 percent), very low dark current (less
than 0.01 electron/pixel/sec), and readout noise (~1 electron). We
have held detailed feasibility discussions with Teledyne (formerly
Rockwell), the company closest in the world to achieving such
devices. The integration challenge will be to couple the various
components and enclose IPS in a microwave oven-size housing with no
loss of performance from light loss, image distortion, or
birefringence. The instrument will be configurable to any telescope
focus (e.g., Discovery Channel 4.2-meter Telescope in Arizona or
Gemini 8-meter telescopes in Hawaii and Chile, where both U.S. and
Australia are consortium members).