A compact polymer optical fibre ultrasound detector

Abstract

Keywords: Polymer Optical Fibre Sensors, Fibre Sensors, Polymer Optical Fibre, Endoscopy, Biomedical Applications , UltrasoundPolymer optical fibre (POF) is a relatively new and novel technology that presents an innovative approach for ultrasonic endoscopic applications. Currently, piezo electric transducers are the typical detectors of choice, albeit possessing a limited bandwidth due to their resonant nature and a sensitivity that decreases proportionally to their size. Optical fibres provide immunity from electromagnetic interference and POF in particular boasts more suitable physical characteristics than silica optical fibre. The most important of these are lower acoustic impedance, a reduced Young's Modulus and a higher acoustic sensitivity than single-mode silica fibre at both 1 MHz and 10 MHz. POF therefore offers an interesting alternative to existing technology. Intrinsic fibre structures such as Bragg gratings and Fabry-Perot cavities may be inscribed into the fibre core using UV lasers. These gratings are a modulation of the refractive index of the fibre core and provide the advantages of high reflectivity, customisable bandwidth and point detection. We present a compact in fibre ultrasonic point detector based upon a POF Bragg grating (POFBG) sensor. We demonstrate that the detector is capable of leaving a laboratory environment by using connectorised fibre sensors and make a case for endoscopic ultrasonic detection through use of a mounting structure that better mimics the environment of an endoscopic probe. We measure the effects of water immersion upon POFBGs and analyse the ultrasonic response for 1, 5 and 10 MHz.

Phase-Shifted Bragg Grating Inscription in PMMA Microstructured POF Using 248-nm UV Radiation

“…In 2015, Broadway et al showed the POF potential for endoscopic operation [35]. Recently, the same group presented for the firs time opto-acoustic measurements using a microstructured polymer optical fibe (mPOF) FBG with a 130 μm diameter fibe and presented the lateral directivity pattern of an ultrasound sensor over a frequency range of 1-50 MHz [36], [37]. These works showed that the acoustic sensitivity for POF is 13 times higher than for silica optical fibe .…”

“…These works showed that the acoustic sensitivity for POF is 13 times higher than for silica optical fibe . Furthermore, 3 times more sensitivity can be achieved using mPOF than with the other POFs and a potential transition from uniform POFBGs to Fabry-Perot cavities or phase-shifted POFBGs (PS-POFBGs) can expand the potential that POF has to offer in this fiel [36], [37]. The goal with that is to deliver a narrower spectral shape, which can potentially be used to achieve higher sensitivities.…”

L-band CYTOP Bragg gratings for ultrasound sensing

“…The growing body of progress on polymer is driven by the fundamental characteristics of said fibre, best expressed through the most characterized variety of PMMA. PMMA typically has an elastic limit of 10% and a Young's Modulus of 3.2GPa [2] with specific positive results with relation to acoustic sensitivity [3]. It is important to stress that all polymer fibres have varying characteristics that include both advantages and disadvantages and that for a given application, it is important to consider the entire range of polymers to identify which presents the best proposal overall.…”

“…These range from the fundamentals of temperature [4] and strain [4] to fuel level monitoring [5], dosimetry [6], ultrasound [2] and humidity [7]. To date, both PMMA and TOPAS, a cyclic olefin co-polymer, have been preliminarily examined for ultrasound detection, in interferometric [3] and later fibre Bragg grating (FBG) sensing modalities [8].…”

Intrinsic Fabry-Perot Sensors for Magnetic Field Detection

“…The wide variety of sensing configurations, materials, geometry and a typically small size can deliver sensitivity inversely proportional to its own dimensions has led to widespread research into applications from acoustics [9] to humidity [10].…”