321 research outputs found
Temperature sensing performance of microsphere resonators
No full textIn recent years, many temperature sensing devices based on microsphere resonators
have emerged, attracting an increasing research interest. For the purpose of this review article,
microsphere resonators are divided according to their constituting materials, namely silicone,
silica, compound glass, and liquid droplet. Temperature monitoring relies mainly on the
thermo-optic/thermal expansion of the microspheres and on the fluorescence of the doped ions.
This article presents a comprehensive review of the current state of the art of microsphere based
temperature sensing and gives an indication of future directions
A simple Fabry-Perot pressure sensor fabricated on fiber optic tip
No full textIn this work, we demonstrate an extrinsic pressure sensor realized on single mode fiber tip by means of simple fabrication steps and with low-cost instrumentations. The sensing element consists in a Fabry-Perot cavity: one reflecting surface is the end of the optical fiber, precisely cut, and the other one is a metallic diaphragm. Under the action of the external pressure, the metallic diaphragm bends changing the optical cavity length and, consequently, the characteristics of the reflected signal. The holder structure, which allows the alignment of the fiber tip and reflecting diaphragm, consists in a commercial zirconia ferule with external diameter of Dex = 2.5 mm. Despite its simplicity and cost-effectiveness, the achieved results show performance comparable to more complex and expensive configurations. By using an aluminum plate as reflecting diaphragm. sensitivity ranging in the 70-130pm/mmHg is experimentally
Optical fiber sensors - based temperature distribution measurement in ex vivo radiofrequency ablation with submillimeter resolution
Get PDFRadiofrequency thermal ablation (RFTA) induces a high-temperature field in a biological tissue having steep spatial (up to 6 degrees C/mm) and temporal (up to 1 degrees C/s) gradients. Applied in cancer care, RFTA produces a localized heating, cytotoxic for tumor cells, and is able to treat tumors with sizes up to 3 to 5 cm in diameter. The online measurement of temperature distribution at the RFTA point of care has been previously carried out with miniature thermocouples and optical fiber sensors, which exhibit problems of size, alteration of RFTA pattern, hysteresis, and sensor density worse than 1 sensor/cm. In this work, we apply a distributed temperature sensor (DTS) with a submillimeter spatial resolution for the monitoring of RFTA in porcine liver tissue. The DTS demodulates the chaotic Rayleigh backscattering pattern with an interferometric setup to obtain the real-time temperature distribution. A measurement chamber has been set up with the fiber crossing the tissue along different diameters. Several experiments have been carried out measuring the space-time evolution of temperature during RFTA. The present work showcases the temperature monitoring in RFTA with an unprecedented spatial resolution and is exportable to in vivo measurement; the acquired data can be particularly useful for the validation of RFTA computational models. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)PUBLISHEDpeer-reviewe
Effect of Tm<sup>3+</sup> concentration on the emission wavelength shift in Tm<sup>3+</sup>-doped silica microsphere lasers
No full textIn this work, a Tm3-doped solgel silica microsphere lasing at 2.0 μm is reported. Microspheres with different Tm3 concentrations are fabricated by overlaying different Tm3 concentration solgel solutions on the surface of a pure silica microsphere resonator and then annealing the sample with a CO2 laser. Based on a traditional fiber taper–microsphere coupling method, single and multimode microsphere lasing in the wavelength range 1.8–2.0 μm is observed if an 808 nm laser diode is used as a pump source. A relatively low threshold pumping power of 1.2 mW is achieved using this arrangement. This solgel method allows for an easy varying of the Tm3 doping concentration. The observed laser output shifts to longer wavelengths when the Tm3 doping concentration increases. This has been explained by the larger Tm absorption at shorter wavelengths. The ability to fabricate solgel co-doped silica glass microlasers represents a new generation of low threshold and compact infrared laser sources for use as miniaturized photonic components for a wide range of applications, including gas sensing and medical surgery.</p
Optical interleaver based on nested multiple knot microfiber resonators
No full textA novel design of nested optical fiber based multiple knot resonators is presented. The design consists of three knot resonators, two of which share a significant fraction of their optical path. The relationship between the knots’ diameter ratio and the transmission spectrum is investigated. The output spectrum is theoretically analyzed using transfer matrix analysis and the calculated results exhibit good agreement with experimental results. The free spectral range (FSR) is varied by simply fine-tuning the diameter of the small knot. The periodic spectrum of this optical microfiber based photonic device has a number of applications in the sensing and communications field, e.g., optical interleavers, frequency combs, filters, and fiber lasers. This Letter demonstrates that the variation of the output spectrum can be implemented simply by changing the knot sizes and coupling coefficients.peer-reviewe
Influence of laser phase noise on Brillouin optical time-domain analysis sensors
No full textThis paper presents a numerical study of the phase noise from the laser in Brillouin Optical Time-Domain analysis (BOTDA) sensors. Due to laser phase noise, the phase shift cumulated by pump and probe beams during interaction in a generic fiber position is a stochastic variable, with zero mean and variance increasing with pulse duration. For negligibly small pulse leakage, the induced noise is independent of fiber length; otherwise, it increases with fiber length as long as the laser coherence length is longer than fiber
Intra-tissue pressure measurement in ex vivo liver undergoing laser ablation with fiber-optic fabry-perot probe
Get PDFWe report the first-ever intra-tissue pressure measurement performed during 1064 nm laser ablation (LA) of an ex vivo porcine liver. Pressure detection has been performed with a biocompatible, all-glass, temperature-insensitive Extrinsic Fabry-Perot Interferometry (EFPI) miniature probe; the proposed methodology mimics in-vivo treatment. Four experiments have been performed, positioning the probe at different positions from the laser applicator tip (from 0.5 mm to 5 mm)
Fibre optic sensors for temperature and pressure monitoring in laser ablation: experiments on ex-vivo animal model
No full textSensitivity enhancement using annealed polymer optical fibre based sensors for pressure sensing applications
Get PDFThermal annealing can be used to induce a permanent negative Bragg wavelength shift for polymer fibre grating sensors and it was originally used for multiplexing purposes. Recently, researchers showed that annealing can also provide additional benefits, such as strain and humidity sensitivity enhancement and augmented temperature operational range. The annealing process can change both the optical and mechanical properties of the fibre. In this paper, the annealing effects on the stress and force sensitivities of PMMA fibre Bragg grating sensors are investigated. The incentive for that investigation was an unexpected behaviour observed in an array of sensors which were used for liquid level monitoring. One sensor exhibited much lower pressure sensitivity and that was the only one that was not annealed. To further investigate the phenomenon, additional sensors were photo-inscribed and characterised with regard their stress and force sensitivities. Then, the fibres were annealed by placing them in hot water, controlling with that way the humidity factor. After annealing, stress and force sensitivities were measured again. The results show that the annealing can improve the stress and force sensitivity of the devices. This can provide better performing sensors for use in stress, force and pressure sensing applications
Stainless steel component with compressed fiber Bragg grating for high temperature sensing applications
No full textA smart metal component having the potential for high temperature strain sensing capability is reported. The stainless steel (SS316) structure is made by selective laser melting (SLM). A fiber Bragg grating (FBG) is embedded in to a 3D printed U-groove by high temperature brazing using a silver based alloy, achieving an axial FBG compression of 13 millistrain at room temperature. Initial results shows that the test component can be used for up to 700°C for sensing applications
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