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Proceedings Paper

A compressive-sensing Fourier-transform on-chip Raman spectrometer
Author(s): Hugh Podmore; Alan Scott; Regina Lee
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Paper Abstract

We demonstrate a novel compressive sensing Fourier-transform spectrometer (FTS) for snapshot Raman spectroscopy in a compact format. The on-chip FTS consists of a set of planar-waveguide Mach-Zehnder interferometers (MZIs) arrayed on a photonic chip, effecting a discrete Fourier-transform of the input spectrum. Incoherence between the sampling domain (time), and the spectral domain (frequency) permits compressive sensing retrieval using undersampled interferograms for sparse spectra such as Raman emission. In our fabricated device we retain our chosen bandwidth and resolution while reducing the number of MZIs, e.g. the size of the interferogram, to 1/4th critical sampling. This architecture simultaneously reduces chip footprint and concentrates the interferogram in fewer pixels to improve the signal to noise ratio. Our device collects interferogram samples simultaneously, therefore a time-gated detector may be used to separate Raman peaks from sample fluorescence. A challenge for FTS waveguide spectrometers is to achieve multi-aperture high throughput broadband coupling to a large number of single-mode waveguides. A multi-aperture design allows one to increase the bandwidth and spectral resolution without sacrificing optical throughput. In this device, multi-aperture coupling is achieved using an array of microlenses bonded to the surface of the chip, and aligned with a grid of vertically illuminated waveguide apertures. The microlens array accepts a collimated beam with near 100% fill-factor, and the resulting spherical wavefronts are coupled into the single-mode waveguides using 45& mirrors etched into the waveguide layer via focused ion-beam (FIB). The interferogram from the waveguide outputs is imaged using a CCD, and inverted via l1-norm minimization to correctly retrieve a sparse input spectrum.

Paper Details

Date Published: 22 February 2018
PDF: 10 pages
Proc. SPIE 10539, Photonic Instrumentation Engineering V, 105390L (22 February 2018); doi: 10.1117/12.2288375
Show Author Affiliations
Hugh Podmore, York Univ. (Canada)
Honeywell Aerospace (Canada)
Alan Scott, Honeywell Aerospace (Canada)
Regina Lee, York Univ. (Canada)

Published in SPIE Proceedings Vol. 10539:
Photonic Instrumentation Engineering V
Yakov G. Soskind, Editor(s)

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