Microstructured polymer optical fibre sensors for opto-acoustic endoscopy

Abstract

Opto-acoustic imaging is a growing field of research in recent years, providing functional imaging of physiological biomarkers, such as the oxygenation of haemoglobin. Piezo electric transducers are the industry standard detector for ultrasonics, but their limited bandwidth, susceptibility to electromagnetic interference and their inversely proportional sensitivity to size all affect the detector performance. Sensors based on polymer optical fibres (POF) are immune to electromagnetic interference, have lower acoustic impedance and a reduced Young's Modulus compared to silica fibres. Furthermore, POF enables the possibility of a wideband sensor and a size appropriate to endoscopy. Micro-structured POF (mPOF) used in an interferometric detector has been shown to be an order of magnitude more sensitive than silica fibre at 1 MHz and 3 times more sensitive at 10 MHz. We present the first opto-acoustic measurements obtained using a 4.7mm PMMA mPOF Bragg grating with a fibre diameter of 130 µm and present the lateral directivity pattern of a PMMA mPOF FBG ultrasound sensor over a frequency range of 1-50 MHz. We discuss the impact of the pattern with respect to the targeted application and draw conclusions on how to mitigate the problems encountered.

Thermal and chemical treatment of polymer optical fiber Bragg grating sensors for enhanced mechanical sensitivity

“…Polymer optical fiber (POF) sensors have received high attention recently due to their unique properties compared to the conventional silica optical fiber sensors [1].Advantages such as higher flexibility in bending, biocompatibility [2], higher failure strain [3], and higher fracture toughness are significant for many sensing applications. The lower Youngs modulus of POF [4] provides enhanced sensitivity when POF sensors are used for stress [5], pressure [6], and acoustic wave detection [7]. There are also some hydrophilic polymeric materials such as poly(methyl methacrylate) (PMMA) that can absorb water, enabling them to be applied for humidity detection applications [8].…”

An L-band ultrasonic probe using polymer optical fibre

“…To be considered for a wider variety of applications, the transition to Fibre Bragg Gratings (FBGs) took place to make probe formats possible and reduce the sensor size down to 1 centimetre in length. This transition produced results showing its sensing capability in part in the 850 nm wavelength region [7]. However, while many improvements have been demonstrated, the wavelength region is uncommon and significant sensitivity improvements need demonstrating before POF can be considered competitive against silica fibre sensors of the day.…”

Wavelength tuning of polymer optical fibre Bragg grating at longer wavelengths permanently

“…The main characteristics of POFs are high fracture toughness, high flexibility in bending, biocompatibility [2] and high failure strain [3]. POF sensors are preferred to be used in stress [4], pressure [5] and acoustic wave detection applications [6], due to their lower Young's modulus compared with silica based sensors, which provides an enhanced sensitivity on POF Bragg grating (POFBG) sensors. Furthermore, there is a wide range of applications in humidity monitoring, because of the hydrophilic nature of some polymeric materials, such as the poly(methyl methacrylate) (PMMA) [7].…”