Characterization of Supported Cylinder-Planar Germanium Waveguide Sensors with Synchrotron Infrared Radiation

Jitraporn Vongsvivut, Jason Fernandez, Sanong Ekgasit, Mark S. Braiman

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Cylinder-planar Ge waveguides are being developed as evanescent-wave sensors for chemical microanalysis. The only non-planar surface is a cylinder section having a 300-mm radius of curvature. This confers a symmetric taper, allowing for direct coupling into and out of the waveguide's 1-mm 2 end faces while obtaining multiple reflections at the central <30-μm-thick sensing region. Ray-optic calculations indicate that the propagation angle at the central minimum has a strong nonlinear dependence on both angle and vertical position of the input ray. This results in rather inefficient coupling of input light into the off-axis modes that are most useful for evanescent-wave absorption spectroscopy. Mode-specific performance of the cylinder-planar waveguides has also been investigated experimentally. As compared to a blackbody source, the much greater brightness of synchrotron-generated infrared (IR) radiation allows a similar total energy throughput, but restricted to a smaller fraction of the allowed waveguide modes. However, such angle-selective excitation results in a strong oscillatory interference pattern in the transmission spectra. These spectral oscillations are the principal technical limitation on using synchrotron radiation to measure evanescent-wave absorption spectra with the thin waveguides.

Original languageEnglish (US)
Pages (from-to)143-151
Number of pages9
JournalApplied Spectroscopy
Issue number2
StatePublished - Feb 2004


  • Blackbody IR source
  • Evanescent wave absorption spectroscopy
  • Synchrotron IR radiation
  • Tapered waveguides
  • Throughput

ASJC Scopus subject areas

  • Instrumentation
  • Spectroscopy


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