Performance analysis of transmissive modified cladding optical fibre sensors

Optical fibre sensors with modified cladding have been a topic of great interest for decades. Thanks to the new techniques of fabricating nanostructured films, this interest has been renewed. Although there have been many increases in published experimental research, no comprehensive theoretical formulation of the structure is reported in the literature. In this study, a general theory for transmissive modified cladding optical fibre sensors is presented. The model is formulated based on the electromagnetic fields and optical power in the core and cladding of a step-index fibre. The model considers various parameters, especially the radius of the optical fibre core, modified cladding refractive index, and light wavelength. The sensitivity, response, and optical transmission of the sensor are analysed as a function of the parameters. The analyses show that optical transmission reduces dramatically when the modified cladding refractive index approaches the refractive index of the core of the fibre and results in higher sensor response and sensitivity. Increasing the core radius of the fibre will result in lower sensor response with higher sensitivity. Both parameters will increase for a light with a larger wavelength. The results are in good agreement with experimental evidence.