Small size, wide spectral bandwidth, and highly multiplexed detector readout are required to develop powerful multi-beam spectrometers for high-redshift observations. Currently available spectrometers at these frequencies are large and bulky. The grating sizes for these spectrometers are prohibitive. This fundamental size issue is a key limitation for space-based spectrometers for astrophysics applications.

A novel, moderate-resolving-power (R-700), ultra-compact spectrographon- a-chip for millimeter and submillimeter wavelengths is the solution. Its very small size, wide spectral bandwidth, and highly multiplexed detector readout will enable construction of powerful multi-beam spectrometers for high-redshift observations. The octavebandwidth, background-limited performance of this spectrometer is comparable to that of a diffraction grating, but in a photolithographically developed thin-film package. This novel photolithographic on-chip spectrometer camera is compact, delivering 200 to 500 km/s spectral resolution over an octave bandwidth for hundreds of pixels in the telescope’s field of view.

The spectrometer employs a filter bank consisting of planar, lithographed, superconducting transmission line resonators. Each millimeterwave resonator is weakly coupled to both the feedline and to the inductive portion of a lumped-element microwave kinetic inductance detector (MKID). Incoming millimeter-wave radiation breaks Cooper pairs in the MKID, modifying its kinetic inductance and resonant frequency, allowing for frequency-multiplexed readout. This is realized using thin-film lithographic structures on a silicon wafer, with titanium nitride MKID resonators.

The ultra-compact superconducting spectrometer approach offers the potential for hundreds of individual spectrometers integrated into a 2D focal plane for future ground- and space-based astrophysics instruments.

This work was done by Goutam Chattopadhyay, Jonas Zmuidzinas, Charles M. Bradford, Henry G. Leduc, Peter K. Day, Loren Swenson, Steven Hailey-Dunsheath, Roger C. O’Brient, Stephen Padin, Erik D. Shirokoff, and Christopher McKenney of Caltech; Theodore Reck of ORAU; Jose V. Siles of Fulbright/JPL; Peter Barry, Simon Doyle, and Philip Mauskopf of Cardiff University; Nuria Llombart of Universidad Complutense de Madrid; Attila Kovacs of the University of Minnesota; and Dan P. Marrone of the University of Arizona for NASA’s Jet Propulsion Laboratory. NPO-48592

This Brief includes a Technical Support Package (TSP).
Ultra-Compact, Superconducting Spectrometer-on-a-Chip at Submillimeter Wavelengths

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This article first appeared in the January, 2013 issue of Photonics Tech Briefs Magazine.

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