Polymer optical fibres (POF) have been present for similar length of time as silica fibres, though the more favourable attenuation of silica fibre led to greater attention being focused upon the former and not the latter. Many papers based on POF have already demonstrated that silica fibres are outmatched in terms of fundamental properties and a growing interest in polymers has been observed as a consequence. While individual polymers present weaknesses (often associated with commercial readiness), POF Bragg gratings (POFBGs) have already found applications in an ever growing number of domains that are becoming increasingly complex, due a steady increase in commercial readiness over the past few years.
Fibre Bragg gratings (FBGs) are a permanent and periodic (or quasiperiodic) refractive index modulation of the fiber core along the axis of propagation. FBGs are of interest for two main reasons, in the first place FBGs are point sensors that are immune to perturbations outside the immediate vicinity of the refractive index modulated section. Secondly, FBGs can be cascaded in a single optical fibre, permitting a single optical fibre to contain hundreds of sensors. This is only limited by the multiplexing capabilities of the associated interrogator and source components. A single fibre can monitor many separate parameters, with each FBG potentially tasked to a different element or variable.
Historically, the typical application of POFBGs are based on the fundamental parameters of strain, temperature and humidity. With the steadily increasing progress in POFBG fabrication, many of the barriers to addressing more advanced techniques are now resolved or significantly weakened. Connectorisation techniques and the quality and diversity of polymer fibres have all improved in recent years, reducing the fragility of POFBGs and improving their performance.
Looking beyond the core applications of strain, temperature and humidity, POFBGs can potentially deliver more than silica fibres for advanced applications including radiative environments and biomedical ultrasonics. These more advanced applications have not been previously explored with POFBGs due to practical and readiness related issues. Polymer fibres should be more sensitive relative to silica when it comes to radiation and many of the applications within radiative environments can also benefit from the unique properties of POF. Ultrasound is widely used for a range of diagnostic applications in the medical domain, from foetal ultrasound imaging to guiding invasive procedures. Optical fibres have the potential to be promising replacements for piezo electric transducers as detectors, delivering immunity to electromagnetic interference and unimpeded by a relationship between sensor size and sensitivity.
This work focusses on progressing the commercialisation of polymer fibres with respect to FBG sensing applications that are already under consideration for silica fibres, specifically for radiative environments and biomedical ultrasonics.