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arXiv · 1707.01847

Demonstration of an efficient, photonic-based astronomical spectrograph on an 8-m telescope

N. Jovanovic·N. Cvetojevic·B. Norris·C. Betters·C. Schwab·J. Lozi·O. Guyon·S. Gross·F. Martinache·P. Tuthill·D. Doughty·Y. Minowa·N. Takato·J. Lawrence
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Abstract

We demonstrate for the first time an efficient, photonic-based astronomical spectrograph on the 8-m Subaru Telescope. An extreme adaptive optics system is combined with pupil apodiziation optics to efficiently inject light directly into a single-mode fiber, which feeds a compact cross-dispersed spectrograph based on array waveguide grating technology. The instrument currently offers a throughput of 5% from sky-to-detector which we outline could easily be upgraded to ~13% (assuming a coupling efficiency of 50%). The isolated spectrograph throughput from the single-mode fiber to detector was 42% at 1550 nm. The coupling efficiency into the single-mode fiber was limited by the achievable Strehl ratio on a given night. A coupling efficiency of 47% has been achieved with ~60% Strehl ratio on-sky to date. Improvements to the adaptive optics system will enable 90% Strehl ratio and a coupling of up to 67% eventually. This work demonstrates that the unique combination of advanced technologies enables the realization of a compact and highly efficient spectrograph, setting a precedent for future instrument design on very-large and extremely-large telescopes.

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N. Jovanovic, N. Cvetojevic, B. Norris, C. Betters, C. Schwab, J. Lozi, O. Guyon, S. Gross, F. Martinache, P. Tuthill, D. Doughty, Y. Minowa, N. Takato, J. Lawrence. 2017-08-26. Demonstration of an efficient, photonic-based astronomical spectrograph on an 8-m telescope. https://doi.org/10.1364/oe.25.017753

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