Efficient ultra-broadband low-resolution astrophotonic spectrographs
Abstract
Broadband low-resolution near-infrared spectrographs in a compact form are crucial for ground- and space-based astronomy and other fields of sensing. Astronomical spectroscopy poses stringent requirements including high efficiency, broad band operation (> 300 nm), and in some cases, polarization insensitivity. We present and compare experimental results from the design, fabrication, and characterization of broadband (1200 - 1650 nm) arrayed waveguide grating (AWG) spectrographs built using the two most promising low-loss platforms - Si3N4 (rectangular waveguides) and doped-SiO2 (square waveguides). These AWGs have a resolving power (λ/Δλ) of ∼200, free spectral range of ∼ 200-350 nm, and a small footprint of ∼ 50-100 mm2. The peak overall (fiber-chip-fiber) efficiency of the doped-SiO2 AWG was ∼ 79% (1 dB), and it exhibited a negligible polarization-dependent shift compared to the channel spacing. For Si3N4 AWGs, the peak overall efficiency in TE mode was ∼ 50% (3 dB), and the main loss component was found to be fiber-to-chip coupling losses. These broadband AWGs are key to enabling compact integrations such as multi-object spectrographs or dispersion back-ends for other astrophotonic devices such as photonic lanterns or nulling interferometers.
Copyright and License
© 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement.
Acknowledgement
Support for P. Gatkine was provided by NASA through the NASA Hubble Fellowship Grant HST-HF2-51478.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, incorporated under NASA Contract NAS5-26555. This work was supported by the Wilf Family Discovery Fund in Space and Planetary Science, funded by the Wilf Family Foundation, as well as the support from Keck Institute for Space Studies at Caltech. Some of this research was carried out at Caltech and the Jet Propulsion Laboratory and funded through the President’s and Director’s Research & Development Fund program. This work was supported by NASA through the Center Innovation Fund. The authors would like to thank the staff at Lionix for the development of some of the photonic chips presented herein.
Funding
Keck Institute for Space Studies; Wilf Family Foundation; Wilf Family Discovery Fund in Space and Planetary Science; Jet Propulsion Laboratory (Center Innovation Fund, PDRDF); National Aeronautics and Space Administration (HST-HF2-51478.001-A, NAS5-26555).
Data Availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
Conflict of Interest
The authors declare no conflicts of interest.
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Additional details
- Keck Institute for Space Studies
- Wilf Family Foundation
- Wilf Family Discovery Fund in Space and Planetary Science
- Jet Propulsion Laboratory
- Caltech/JPL President and Director's Research and Development Fund
- National Aeronautics and Space Administration
- NASA Hubble Fellowship HST-HF2-51478.001-A
- National Aeronautics and Space Administration
- NAS5-26555
- Caltech groups
- Astronomy Department, Keck Institute for Space Studies