Photoacoustic imaging in biomedicine and life sciences

Photo-acoustic imaging, also known as opto-acoustic imaging, has become a widely popular modality for biomedical applications. This hybrid technique possesses the advantages of high optical contrast and high ultrasonic resolution. Due to the distinct optical absorption properties of tissue compartments and main chromophores, photo-acoustics is able to non-invasively observe structural and functional variations within biological tissues including oxygenation and deoxygenation, blood vessels and spatial melanin distribution. The detection of acoustic waves produced by a pulsed laser source yields a high scaling range, from organ level photo-acoustic tomography to sub-cellular or even molecular imaging. This review discusses significant novel technical solutions utilising photo-acoustics and their applications in the fields of biomedicine and life sciences

L-band CYTOP Bragg gratings for ultrasound sensing

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

Fabry-Perot micro-structured polymer optical fibre sensors for opto-acoustic endoscopy

Opto-Acoustic Endoscopy (OAE) requires sensors with a high sensitivity and small physical dimensions in order to facilitate integration into an endoscope of less than 1mm in diameter. We present fibre Bragg grating (FBG) and Fabry- Perot intrinsic fibre sensors for ultrasound detection. We present a structure profile characterisation setup to analyse tune the fibre sensors in preparation for ultrasonic detection. We evaluate the suitability of the different structures and grating parameters for ultrasonic sensing. By analysing the prepared gratings, we enable the optimisation of the profile and a simplification of the detection regime for an optimal interferometric OAE configuration

Microstructured polymer optical fibre sensors for opto-acoustic endoscopy

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

Microstructured PMMA POF chirped Bragg gratings for strain sensing

[EN] We demonstrate a chirped microstructured polymer fiber Bragg grating based on taper technology for strain sensing application. The effective bandwidth of the grating is dependent on strain and remains practically constant with respect to temperature and humidity changes. We report a sensitivity of 0.90 pm/mu e for the central wavelength under stable temperature and humidity values. The 3-dB bandwidth of the grating has been measured under different temperature and humidity conditions.The authors acknowledge the financial support from FCT through the fellowship SFRH/BPD/109458/2015, program UID/EEA/50008/2013 by the National Funds through the Fundacao para a Ciencia e a Tecnologia/Ministerio da Educacao e Ciencia, and the European Regional Development Fund under the PT2020 Partnership Agreement. This work was also supported by the Research Excellence Award Programme GVA PROMETEO 2017/103 and the Science Foundation of Heilongjiang Province of China (2018026).Min, R.; Ortega Tamarit, B.; Broadway, C.; Hu, X.; Caucheteur, C.; Bang, O.; Antunes, P.... (2018). Microstructured PMMA POF chirped Bragg gratings for strain sensing. Optical Fiber Technology. 45:330-335. https://doi.org/10.1016/j.yofte.2018.08.016S3303354

A compact polymer optical fibre ultrasound detector

Polymer 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

Hot water-assisted fabrication of chirped polymer optical fiber Bragg gratings

© 2018 Optical Society of America. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibited"[EN] We obtained chirped gratings by performing hot water gradient thermal annealing of uniform poly (methylmethacrylate) (PMMA) microstructured polymer optical fiber Bragg gratings (POFBGs). The proposed method's simplicity is one of its main advantages because no special phase mask or additional etching are needed. It not only enables easy control tuning of the central wavelength and chirp characteristics, but it also leads to obtain flexible grating response, compared with tapered chirped POFBGs. Therefore, a flexible and low-cost chirped POFBG devices fabrication technique has been presented by using a single uniform phase mask. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing AgreementThis work was supported by Fundação para a Ciência e Tecnologia (FCT)/MEC through national funds, when applicable co-funded by FEDER PT2020 partnership agreement under the project UID/EEA/50008/2013 and the Research Excellence Award Programme GVA PROMETEO 2017/103 Future Microwave Photonics Technologies and applications, Science Foundation of Heilongjiang Province of China (F2018026). C. A. F. Marques also acknowledges the financial support from FCT through the fellowship SFRH/BPD/109458/2015.Min, R.; Ortega Tamarit, B.; Broadway, C.; Caucheteur, C.; Woyessa, G.; Bang, O.; Antunes, P.... (2018). Hot water-assisted fabrication of chirped polymer optical fiber Bragg gratings. Optics Express. 26(26):34655-34664. https://doi.org/10.1364/OE.26.034655S34655346642626Bonefacino, J., Tam, H.-Y., Glen, T. S., Cheng, X., Pun, C.-F. J., Wang, J., … Boles, S. T. (2017). 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Photoacoustic Imaging in Biomedicine and Life Sciences

Photo-acoustic imaging, also known as opto-acoustic imaging, has become a widely popular modality for biomedical applications. This hybrid technique possesses the advantages of high optical contrast and high ultrasonic resolution. Due to the distinct optical absorption properties of tissue compartments and main chromophores, photo-acoustics is able to non-invasively observe structural and functional variations within biological tissues including oxygenation and deoxygenation, blood vessels and spatial melanin distribution. The detection of acoustic waves produced by a pulsed laser source yields a high scaling range, from organ level photo-acoustic tomography to sub-cellular or even molecular imaging. This review discusses significant novel technical solutions utilising photo-acoustics and their applications in the fields of biomedicine and life sciences

Bragg Gratings Inscription in TS-Doped PMMA POF by Using 248-nm KrF Pulses

© 2018 IEEE. Personal use of this material is permitted. Permissíon from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertisíng or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.[EN] We demonstrate the Bragg gratings inscription in the 850-nm spectral region by using trans-4-stilbenemethanol-doped poly methyl methacrylate step-index optical fiber and a 248-nm krypton fluoride (KrF) excimer laser system. The gratings inscription only takes 0.4 s. A detailed study of the grating fabrication process using different pulse repetition rates is also reported. In addition, temperature, humidity, and strain sensitivities are measured to demonstrate the potentiality of these components for different sensing applications.The research leading to these results has received funding from the Fundacao para a Ciencia e Tecnologia (FCT)/MEC national funds and when applicable co-funded by FEDER-PT2020 Partnership Agreement under Project UID/EEA/50008/2013. This work was also supported in part by the Research Excellence Award Programme GVA Prometeo 2017/103 Future Microwave Photonics Technologies and Applications, and in part by the Fundamental Research Funds for the Heilongjiang Provincial Universities under Grant KJCXZD201703. The work of C. Marques was supported by FCT through the Fellowship SFRH/BPD/109458/2015.Min, R.; Ortega Tamarit, B.; Hu, X.; Broadway, C.; Caucheteur, C.; Pun, CJ.; Tam, H.... (2018). Bragg Gratings Inscription in TS-Doped PMMA POF by Using 248-nm KrF Pulses. IEEE Photonics Technology Letters. 30(18):1609-1612. https://doi.org/10.1109/LPT.2018.2863741S16091612301