Investigation of a periodically segmented waveguide Fabry-Pe/spl acute/rot interferometer for use as a chemical/biosensor

We present a periodically segmented waveguide Fabry-Pe/spl acute/rot interferometer (PSW-FPI) intended to be used for tagless real-time chemical/ biological sensing through bulk-material interaction. The differential sensor detects changes in the refractive index (RI) of a sample regardless of its absolute RI value. Experiments with a series of sucrose solutions of various concentrations are compared with theoretical results, and a very good match is found between the two. The theoretical sensitivity limit for a 50-dB-signal-to-noise-ratio (SNR) measurement system is estimated as /spl delta/n=3/spl middot/10/sup -7/. For a 29-dB-SNR measurement system, a measured sensitivity limit of /spl delta/n=4/spl middot/10/sup -5/ is comparable with the previously reported sensitivities of label-free real-time optical biosensors (2/spl middot/10/sup -5/-5/spl middot/10/sup -5/). However, the total required sensing length (720 /spl mu/m) of our PSW-FPI sensor is much shorter than that of the previously reported devices (9-20 mm).     

Analysis of bulk material sensing using a periodically segmented waveguide Mach-Zehnder interferometer for biosensing

Analysis of a periodically segmented Mach-Zehnder interferometer (MZI), intended for use as a biosensor, was performed using a "modular block" algorithm. The theoretical sensitivity limit increases with the number of cycles but is limited by cumulative attenuation. The periodically segmented MZI was found to exhibit better sensitivity than alternative methods under the same working conditions. However, devices with a high number of cycles (>350) were found to be impractical due to high attenuation losses. A 48-cycle periodically segmented waveguide MZI, with a predicted sensitivity limit of /spl delta/n/sub min//spl sim/3.96*10/sup -5/, requires a shorter sensing length (0.24 mm) than that of alternative devices with similar sensitivity.