A Review: Evolution and Diversity of Optical Fibre Plasmonic Sensors

Abstract

The purpose of this review is to bring to the attention of the wider research community how two quite different optical sensory techniques were integrated resulting in a sensor device of exceptional sensitivity with wide ranging capability. Both authors have collaborated over a 20 year period, each researching initially surface plasmon resonance (SPR) and optical fibre Bragg grating devices. Our individual research, funded in part by EPSRC and industry into these two areas, converged, resulting in a device that combined the ultra-sensitive working platform of SPR behavior with that of fibre Bragg grating development, which provided a simple method for SPR excitation. During this period, they developed a new approach to the fabrication of nano-structured metal coatings for plasmonic devices and demonstrated on fibre optic platform, which has created an ultra-sensitive optical sensing platform. Both authors believe that the convergence of these two areas will create opportunities in detection and sensing yet to be realised. Furthermore, giving the reader "sign-post" research articles to help to construct models to design sensors and to understand their experimental results.

Keywords: bio-sensors; gratings; optical fiber sensors; plasmonic nanostructures.

Figure 1

Basic schematic of generation of a surface plasmon resonance.

Figure 2

Conceptual illustration of the sensing volume and sensing coverage. (a) The full use of the evanescent wave of the surface plasmon to detection of bulk chemical changes in solution. (b) the partly use of the evanescent wave of the surface plasmon working in conjunction with recognition molecule adhered to the metal film for specific molecule detection

Figure 3

Conceptual representation of the dependence of the surface plasmon electric field on the distance from the metal surface of the sensor.

Figure 4

Typical calculated spectral shifts of the extinction of the LSP as a function of the spatial geometry and size of the nano-blocks, using the measured variation in the minor and major axes, for a Ge-SiO2-Au tri-layer with a surrounding index of 1.367. Along with showing the relative changes of shape for the nano-spheriods that generate the spectrums.

Figure 5

Typical Schematics of various fibre optical platforms used to produce surface plasmons. (a) Biconical tapered optical fibre surface plasmon resonance sensor. (b) Cladding removed fibre, the coating adhered directly to the core of the fibre. (c) An end-face reflection mirror/coating for the generation of the surface plasmons. (d,e) Conventional cylindrical optical fibre and D-shaped optical fibre, respectively, with a metal coating with the light coupled from a grating structure; tilted. (f) A low-dimensional nanostructured material/coating using a periodic strain field as the coupling mechanism for the light. (g) Photonic crystal fibre with the metal deposited on the inside of the holes of the fibre which support the surface plasmons.

Figure 6

Schematic of a biofunctionalised metal-coated optical fiber surface with the most commonly used strategies to attract specific analytes.