Beating the classical limit: A diffraction-limited spectrograph for an arbitrary input beam

• Main Authors: Betters, Christopher H, Leon-Saval, Sergio G, Robertson, J. Gordon, Bland-Hawthorn, Joss
• Format: Journal Article
• Language: English
• Published: 17-10-2013
• Subjects: Physics - Instrumentation and Methods for Astrophysics
• DOI: 10.48550/arxiv.1310.4833

Optics Express, Vol. 21, Issue 22, pp. 26103-26112 (2013) We demonstrate a new approach to classical fiber-fed spectroscopy. Our method
is to use a photonic lantern that converts an arbitrary (e.g. incoherent) input
beam into N diffraction-limited outputs. For the highest throughput, the number
of outputs must be matched to the total number of unpolarized spatial modes on
input. This approach has many advantages: (i) after the lantern, the instrument
is constructed from 'commercial off the shelf' components; (ii) the instrument
is the minimum size and mass configuration at a fixed resolving power and
spectral order (~shoebox sized in this case); (iii) the throughput is better
than 60% (slit to detector, including detector QE of ~80%); (iv) the scattered
light at the detector can be less than 0.1% (total power). Our first
implementation operates over 1545-1555 nm (limited by the detector, a
640$\times$512 array with 20$\mu$m pitch) with a spectral resolution of 0.055nm
(R~30,000) using a 1$\times$7 (1 multi-mode input to 7 single-mode outputs)
photonic lantern. This approach is a first step towards a fully integrated,
multimode photonic microspectrograph.