L-band CYTOP Bragg gratings for ultrasound sensing

Abstract

Polymer optical fibre (POF) has been receiving increasing attention for sensing applications. The fundamental properties of POF such as PMMA deliver at least an order of magnitude in improvements over silica fibres, though practical difficulties create additional complexity. POF has the potential to deliver lower acoustic impedance, a reduced Young's Modulus and a higher acoustic sensitivity within the megahertz region. In contrast, existing piezo-electric transducers have an inherent narrow acoustic bandwidth and a proportionality to size that causes difficulties for applications such as endoscopy within the biomedical domain. POF generally suffers high attenuation per kilometre at telecommunications wavelengths, limiting fibre lengths to mere centimetres. However, CYTOP, a graded index perfluorinated polymer, is a commercially certified product allowing the use of telecoms region technology and tens of meters of fibre without exceeding acceptable losses. With an effective refractive index between 1.32 and 1.33, it is fundamentally better placed for applications using water or a similar media for acoustic coupling. We demonstrate ultrasonic detection at 5,10 and 15 MHz using a TFBG within a CYTOP fibre in the telecoms region and the latest knowledge in POF handling and connectorisation. This first step in the use of CYTOP demonstrates the viability of the sensor and paves the way towards further advances towards its eventual application.

CYTOP Fibre Bragg Grating Sensors for Harsh Radiation Environments

“…The CYTOP fibre was connectorised to silica SMF-28 fibre using the UV gel curing technique. Our variation of this technique typically delivers strong adhesion with minimal variance and low optical losses [23]. The resulting splice was separated from the FBG by over 20 cm of fibre to allow limited bending without affecting coupling conditions or pre-straining the FBG.…”

Polymer Optical Fiber Sensors in Healthcare Applications: A Comprehensive Review

“…Recently, pH sensors based on POFs were proposed, where the sensor is based on FBGs inscribed in POFs in different solutions, e.g., hydrogel [193] and aqueous solutions [194]. It is also worth mentioning many advances on photoacoustic effects and ultrasonic detection with POF sensor system that can lead to important advances in healthcare applications [45,195,196]. As a final important application, the thermal profiling assessment radiofrequency treatment was proposed in reference [197] using chirped FBGs inscribed in PMMA POFs, where the sensor high sensitivity enabled the thermal profile detection with millimeters resolution, which is important to assess the thermal ablation on the tissue during radiofrequency treatments.…”