Tapered Optical Fibre Sensors: Current Trends and Future Perspectives

Abstract

The development of reliable, affordable and efficient sensors is a key step in providing tools for efficient monitoring of critical environmental parameters. This review focuses on the use of tapered optical fibres as an environmental sensing platform. Tapered fibres allow access to the evanescent wave of the propagating mode, which can be exploited to facilitate chemical sensing by spectroscopic evaluation of the medium surrounding the optical fibre, by measurement of the refractive index of the medium, or by coupling to other waveguides formed of chemically sensitive materials. In addition, the reduced diameter of the tapered section of the optical fibre can offer benefits when measuring physical parameters such as strain and temperature. A review of the basic sensing platforms implemented using tapered optical fibres and their application for development of fibre-optic physical, chemical and bio-sensors is presented.

Magnetic array-templated method for fabrication of polymer nanoporous films

“…Delay lines in molecular sequencing and ion-exchange channels are examples from other areas [1]. Transparent nature of the films offers their application in optical detectors utilising fluorescent marking or near-field detection methods [23,24]. The ability to produce arrays of well-separated nanopores suggests that these membranes could be used for parallel processing in high-speed sequencing [25] of large molecules and bio-species.…”

Optical Fibre Long-Period Grating Sensors Operating at and around the Phase Matching Turning Point

“…1shows the resonant wavelength is dependent on the effective refractive indices of the core and cladding mode of the fibre. This central resonant wavelength and the sensitivity of an LPG is affected by the order of the coupled cladding mode; choosing the grating period, the type [23] and composition of the fibre [19], and any external perturbations can alter the coupled mode.…”

“…By increasing the refractive index, the dual bands appear and eventually split as shown in Figure 8. A mesoporous coating consisting of silica nanospheres was able to improve the refractive index sensitivity of a 100 μm period LPG operating near turning point, with a maximum sensitivity of 1927 ± 59 nm/RIU, as well as increase the detection range of the LPG [19]. The refractive index sensitivity of the first electric arc induced LPG at turning point was increased from 400 to 700 nm/RIU to 887-2146 nm/RIU by operating close to the turning point and by coating a thin film overlay of silicon nitride [20].…”

“…These sensors have the potential to measure concentrations of chemicals or for detecting gaseous species. These thin films can improve the sensing ability of the fibre and allow them to have different responses to different stimuli, such as concentrations of chemicals in the surrounding environment [19,66,67]. Functional materials can also be used to enhance the sensitivity for detection of a particular analyte.…”

“…Approaches employed to improve the sensing capability of LPGs have included methods such as tapering [12] and etching [13]; however this can weaken the structure of the fibre and requires more delicate handling or complicated packaging. These sensors have been successfully used for measuring parameters such as temperature [14][15][16], strain [14][15][16] and refractive index (RI) [17][18][19][20]. The properties of LPGs at PMTP can be tailored further by adding a functional nanoscale coating for chemical and gas sensing [21].…”