Environmental Sensors and Subsystems

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Micro OptoFluidic Ring Resonators for Micro Gas-Chromatograph Detectors
Kee Scholten, Xudong Fan, and Edward T. Zellers
A) SEM image of a µOFRR with 100 micron inner diameter B) Diagram illustrating the basic structure and operation of the µOFRR
A) SEM image of a µOFRR with 100 micron inner diameter B) Diagram illustrating the basic structure and operation of the µOFRR

This project concerns the development of a new generation of vapor sensitive micro-transducers; the microfabricated optofluidic ring resonator (µOFRR) is a whispering gallery mode resonator that integrates microfluidic and sensing functions into a single structure. The device is a cylindrical tube embedded in a Si frame, with a spherical expansion section to provide lateral confinement of optical modes. Fabrication entails defining a Si mold with deep reactive ion etching then growing the SiOx µOFRR via thermal oxidation. Devices with 50-200 µm diameters and 2 µm walls have been fabricated and characterized. In experiments, light from a coherent source was coupled into the cavity evanescently; monitoring output intensity while varying wavelength produced a series of characteristic “peaks” with quality factors exceeding 104, and measurements of the free spectral range confirmed that the resonant behavior mimics that of planar ring resonators. Recently, work has begun on a microfluidic device that incorporates 250 µm diameter µOFRRs with on-chip fluidics and structures for permanently anchoring of aligned fiber optic waveguides. This design will facilitate the use of these resonators as vapor sensors for micro gas chromatographic analysis systems. This work is supported by the National Science Foundation, the Department of Homeland Security, Science and Technology Directorate, and by the National Institute of Health, Microfluidics in Biomedical Sciences Training Program.

Updated 04/03/2012