Multiplexed refractive index-based sensing using optical fiber micro-cavities

摘要

Optical fibers are promising tools for performing biological and biomedical sensing due to their small cross section and potential for multiplexing. In particular, fabricating ultra-small sensing devices is of increasing interest for measuring biological material such as cells. A promising direction is the use of interferometric techniques combined with optical fiber post-processing. In this work we present recent progress in the development of Fabry-Perot micro-cavities written into optical fiber tapers using focused ion beam (FIB) milling. We first demonstrate that FIB milled optical fiber micro-cavities are sensitive enough to measure polyelectrolyte layer deposition. We then present new results on the fabrication and optical characterization of serially-multiplexed dual cavity micro-sensors. Two cavities were written serially along the fiber with two different cavity lengths, producing a total of four reflecting surfaces and thus six possible interferometric pairs/cavities. By using fast Fourier transform it is possible to obtain de-multiplexed measurements for each cavity. This will be particularly important for bioassays where positive and negative controls are required to be measured within close spatial proximity.