Micro-machined optical fibre cantilever as sensor elements

Micro-fabricated cantilevers have been reported recently as miniaturized, rapid response, ultrasensitive sensors elements suitable for various chemical and bio-sensing applications. However, the alignment of the cantilever with the optical read-out system can be challenging and typically involves a bulky free-space optical detection system. We propose using cantilevers aligned to the core of an optical fibre during the fabrication process to address this issue. Focussed Ion Beam (FIB) machining has been demonstrated as capable of fabricating fibre-top cantilevers. Here we demonstrate techniques to design and fabricate micro-cantilevers using a combination of laser machining and FIB processing to fabricate sensing cantilevers onto the end of standard and multi-core fibres (MCF). In this way the cantilever can be aligned with the core of the fibre therefore offering stable and accurate means of optically addressing the cantilever. Use of MCF offers the potential for a single probe capable of making multiple measurements in a confined measurement volume, to determine multiple species of interest, or to provide background reference measurements for example. The optical cavity formed between the fibre and the cantilever is monitored using low-cost optical sources and fibre coupled spectrometers to demonstrate a practical measurement system. This can readily achieve <50nm resolution using analysis based upon recovering the free spectral range using the Fast Fourier Transform to calculate the final cavity length.