An on-chip astrophotonic spectrograph with a resolving power of 12,000

Abstract

With the upcoming extremely large telescopes (ELTs), the volume, mass, and cost of the associated spectrographs will scale with the telescope diameter. Astrophotonics offers a unique solution to this problem in the form of single-mode fiber-fed diffraction-limited spectrographs on a chip. These highly miniaturized chips offer great flexibility in terms of coherent manipulation of photons. Such photonic spectrographs are well-suited to disperse the light from directly imaged planets (post-coronagraph, collected using a single-mode fiber) to characterize exoplanet atmospheres. Here we present the results from a proof-of-concept high-resolution astrophotonic spectrograph using the arrayed waveguide gratings (AWG) architecture. This chip uses the low-loss SiN platform (SiN core, SiO${}_2$ cladding) with square waveguides (800 nm $\times$ 800 nm). The AWG has a measured resolving power ($\lambda /\delta \lambda$) of $\sim$ 12,000 and a free spectral range (FSR) of 2.8 nm. While the FSR is small, the chip operates over a broad band (1200 $-$ 1700 nm). The peak on-chip throughput (excluding the coupling efficiency) is $\sim$40\% (- 4 dB) and the overall throughput (including the coupling loss) is $\sim$ 11\% (- 9.6 dB) in the TE mode. Thanks to the high-confinement waveguide geometry, the chip is highly miniaturized with a size of only 7.4 mm $\times$ 2 mm. This demonstration highlights the utility of SiN platform for astrophotonics, particularly, the capability of commercial SiN foundries to fabricate ultra-small, high-resolution, high-throughput AWG spectrographs on a chip suitable for both ground- and space-based telescopes.

10 pages, 7 figures, Published in the proceedings of SPIE Optics + Photonics conference 2021

References in corpus (8)

• Arrayed Waveguide Grating Spectrometers for Astronomical Applications: New Results
• First on-sky demonstration of an integrated-photonic nulling-interferometer: The GLINT instrument
• First starlight spectrum captured using an integrated photonic micro-spectrograph
• Astrophotonic Spectrographs
• Instruments without optics: an integrated photonic spectrograph
• Demonstration of an efficient, photonic-based astronomical spectrograph on an 8-m telescope
• Potential of commercial SiN MPW platforms for developing mid/high-resolution integrated photonic spectrographs for astronomy
• Development of an integrated near-IR astrophotonic spectrograph

Cited by in corpus (2)

• On-sky demonstration at Palomar Observatory of the near-IR, high-resolution VIPA spectrometer
• Simulating the Study of Exoplanets Using Photonic Spectrographs