1,721,114 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
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
Sensitivity enhancement using annealed polymer optical fibre based sensors for pressure sensing applications
Full text linkThermal 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
3D printed sensing patches with embedded polymer optical fibre Bragg gratings
Full text linkThe first demonstration of a polymer optical fibre Bragg grating (POFBG) embedded in a 3-D printed structure is reported. Its cyclic strain performance and temperature characteristics are examined and discussed. The sensing patch has a repeatable strain sensitivity of 0.38 pm/μepsilon. Its temperature behaviour is unstable, with temperature sensitivity values varying between 30-40 pm/°C
Fibre optic chemical sensor based on graphene oxide-coated long period grating
Full text linkIn this work, a graphene oxide-coated long period fibre grating (GO-LPG) is proposed for chemical sensing application. Graphene oxide (GO) has been deposited on the surface of long period grating to form a sensing layer which significantly enhances the interaction between LPG propagating light and the surrounding-medium. The sensing mechanism of GO-LPG relies on the change of grating resonance intensity against surrounding-medium refractive index (SRI). The proposed GO-LPG has been used to measure the concentrations of sugar aqueous solutions. The refractive index sensitivities with 99.5 dB/RIU in low refractive index region (1.33-1.35) and 320.6 dB/RIU in high index region (1.42-1.44) have been achieved, showing an enhancement by a factor of 3.2 and 6.8 for low and high index regions, respectively. The proposed GO-LPG can be further extended to the development of optical biochemical sensor with advantages of high sensitivity, real-time and label-free sensing
High temperature stability testing of Ge-doped and F-doped Fabry-Perot fibre optical sensors
No full textWe present high temperature (similar to 1100 degrees C) stability tests of, Ge-doped and F-doped, optical fibre sensors. Our analysis includes the variation in their behaviours within high temperature environments and how the dopant diffusion affects their long term stability.</p
Ex vivo investigation of tissue optical properties using an optical fibre sensor
No full textBiomedical research has become a strong growing sector in recent years. Moreover the
interdisciplinary background involves novel possibilities and measurement techniques. Light
propagation in turbid media like human tissue is a central aspect to many medical and
biomedical applications. This is a very complex process and depends on parameters, which are
called optical properties. The spatial distribution of light is determined by those optical
properties. A major difficulty in this field can be explained by the forward and inverse problem.
There are several theories and approximations that are used to describe the propagation of light
in scattering media. Those approaches are often applied to get qualitative results that can be
helpful in fields like laser surgery, photodynamic therapy and diagnostic purposes. This thesis
presents the development of an optical fibre based system that uses diffuse reflectance data to
determine the optical properties of tissue. The optical properties obtained are intended to be
used as indicators in the characterization of burn wounds. Since the absorption of light by tissue
has a minimum in the therapeutic window, which is situated in the visible to near-infrared region
(600-1000 nm), this wavelength region is of special interest in reflectance measurements. The
development of the sensor includes designing a sensor head with an appropriate geometry,
electronics providing light sources and detecting the reflectance as well as the creation of a
procedure to determine the optical properties from the detected reflectances.
To solve the inverse problem and extract the tissue optical properties from the recorded
reflectances a neural network was trained with Monte Carlo simulation data. The neural network
has been improved several times until an appropriate range of optical properties was achieved.
The RMS error obtained within the range of absorption of the training data set (0.05 – 4.5 cm-1)
was 1.26 and 2.2 % for the absorption and scattering coefficient, respectively. For an extended
range of absorption (0.001 – 5.5 cm-1) the RMS error slightly increases to 2.4 and 4 % for the
absorption and scattering coefficient, respectively.
Measurement series performed with the calibrated sensor include in vivo measurements on
human test subjects with different skin colour and ex vivo measurements on healthy and burned
skin of pigs. The results obtained agree very well with values from the literature. This method of
optical property determination is in vivo and offers instantaneous results
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
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