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

Abstract

Optical fibres have been exploited as sensors for many years and they provide a versatile platform with a small form factor. Long-period gratings (LPGs) operating at and around the phase matching turning point (PMTP) possess some of the highest sensitivities to external perturbations in the family of LPG-based sensor devices. This type of optical fibre grating has been demonstrated as a sensor for use in a wide range of applications. In this review chapter, an overview of PMTP LPGs is presented and the key developments, findings and applications are highlighted. The fabrication considerations and sensor limitations are also discussed.

Highly Sensitive Optical Fibre Bragg Grating Contact Pressure Sensor Embedded in a Polymer Layer: Modelling and Experimental Validation

“…Optical fibre sensors offer attractive solutions to a number of measurement challenges faced in healthcare (Correia et al, 2018). Different optical fibre sensing approaches can be applied to physical measurements such as fibre long period grating (Rana et al, 2022;Wong et al, 2019), fibre in-line interferometer (Wu, 2021;Chen, 2020) and fibre Sagnac loop (Culshaw, 2006;Shao, 2019). Amongst these, fibre Bragg gratings (FBGs) offer an attractive solution for healthcare as they offer the opportunity to multiplex multiple sensors (up to 40) on the same optical fibre.…”

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“…With a large grating period, the LPFG is relatively easier to manufacture than FBG. As shown in Fig 2 .5, the fundamental forward-propagation core mode couples with one or more forward-propagation cladding modes [68]. There is no backpropagation in LPFGs, and attenuation dips could only be observed in the transmission spectra.…”

“…Unlike conventional FBG, the coupling modes of LPFG involve only the forwardpropagation core mode and cladding modes. The resonance wavelengths of the LPFG can be expressed as [67,68]:…”