Chemical Sensing with cavity-enhanced waveguide devices

22.08.2012, 11:15

Speaker: Dr Hans-Peter Loock (Dept. of Chemistry, Queen's University, Kingston, Canada)

Date: Wednesday August 22nd, 11:15 am

Organisation: MPL

Place: large seminar room / MPL

Title: Chemical Sensing with cavity-enhanced waveguide devices

Abstract: I will present a variety of waveguide-based devices that we and others developed for measurements of optical absorption, refractive index, pressure, and strain. The sensitivity of these optical sensing elements can be increased by placing them into an optical cavity. 

Examples for waveguide-based sensors and detectors are:

  • An absorption detector based on cavity ring-down (CRD) spectroscopy. Cavities of acceptable finesse can be made very simply and inexpensively from strands of optical waveguide, such as standard telecom single-mode fiber or multi-mode optical waveguides. Light can be trapped in these fiber cavities either by using fiber Bragg gratings or by connecting the two fiber ends to form a loop. Absorption detection of proteins, of pharmaceutical compounds and of single transparent microspheres in nanoliter volumes of liquid and at wavelengths between 1500 and 400 nm will be presented. Applications of fiber-loop cavity ring-down to microfluidic devices, HPLC and capillary electrophoresis will be discussed.

  • A silica microsphere is a high-Q cavity when its whispering gallery modes are excited. Phase-shift CRD can then be used to determine the real and imaginary part of the refractive index of a monolayer of adsorbent.

  • Photoacoustic spectroscopy can be conducted using fiber Bragg Gratings (FBGs) or fiber cavities as strain sensing elements. The same devices have also been used as “pick-ups” for musical instruments (the Photonic Guitar)

  • Finally, Silicon on Insulator (SOI) waveguide structures can be made sensitive to refractive index by coating them with functionalized materials. Coated Mach-Zehnder interferometers and ring-resonators have been used to determine the concentration of solvent vapours.