Grating couplers for dual-channel thin-film waveguide sensors produced by transmission photolithography
Grating-coupled, thin-film integrated optical waveguide (IOW) structures were fabricated using standard transmission photolithography and employed in a fluoro-affinity assay for the trace detection of analyte. Using a ruled chrome-on-quartz mask with a 0.7 μ repeat, gratings of three etch depths - 0.6, 0.8, and 1.0 μm - were ion milled into 0.5-mm-thick quartz substrates. Silicon oxynitride (SiON) guiding films (1.5 μm) were deposited on the etched substrates by plasma-enhanced chemical vapor deposition (PECVD). Coupling efficiencies for the first diffracted grating orders into the zero-order IOW-guided modes were evaluated at 632.8 nm. The deepest gratings coupled the most light; however, their efficiency was less than half that of prisms. Binding isotherms for fluorescently labeled avidin (Cy5-Av) binding to a biotinylated bovine serum albumin (BSA) adlayer were generated from both prism- and grating-coupled SiON sensor data. Both techniques discriminated the binding of avidin from a 10-15 M solution; however run-to-run (intraassay) and between-sensor (interassay) variability reduced reliability of the measurements. © 1997 Society of Photo-Optical Instru-mentation Engineers.
Plowman, TE; Peters, CR; Monty Reichert, W
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