Planar waveguides can be written with a UV-laser into photosensitised silica to produce a wide range of optical devices. Careful modulation of two interfering beams allows Bragg gratings to be directly written into the channel. These Bragg gratings are inherently sensitive to temperature and strain, however etching away the surface exposes the mode within the grating to its surroundings. The corresponding observed shift in Bragg wavelength can be used to detect changes in this environment . It has been previously reported  that the sensitivity of such a refractometer can be enhanced by over an order of magnitude through use of a high-index overlayer of tantalum pentoxide. This enhanced sensor has shown the potential to detect a single molecular monolayer upon the sensor surface . This sensitivity was confirmed through the successful attachment and detection of a single molecular monolayer of a fluorescein-based organic dye to the sensor surface .
© 2011 Optical Society of AmericaPDF Article
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