Direct UV-written broadband directional planarwaveguide couplers

Editore: Optical Society of Americ

Assessment of a Dual-Wavelength Compensation Technique for Displacement Sensors Using Plastic Optical Fibers

The paper analyzes the performance of a dual-wavelength technique devised to compensate power fluctuations in intensity-modulated plastic optical fiber sensors, which were specifically conceived for the measurement of displacements in industrial and civil applications. These sensors retrieve the displacement from the variation of the attenuation along the light path and use two signals at different wavelengths to compensate for the effects of parasitic quantities, such as temperature and strains along the fiber. The theoretical behavior of the compensation technique is presented, and the results of experiments carried out with different combinations of signal wavelengths and plastic fibers are reported. The experimental setup has proved that, by proper choice of the compensation signal wavelength, it is possible to monitor displacements in the range (0 to 10) mm, even for low received power and under severe perturbation conditions, thus significantly improving the long-term stability of the sensor

Mediterranean diet and nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is emerging as the most common chronic liver disease, and is characterized by a wide spectrum of fat-liver disorders that can result in severe liver disease and cirrhosis. Inflammation and oxidative stress are the major risk factors involved in the pathogenesis of NAFLD. Currently, there is no consensus concerning the pharmacological treatment of NAFLD. However, lifestyle interventions based on exercise and a balanced diet for quality and quantity, are considered the cornerstone of NAFLD management. Mediterranean diet (MD), rich in polyunsaturated fats, polyphenols, vitamins and carotenoids, with their anti-inflammatory and antioxidant effects, has been suggested to be effective in preventing cardiovascular risk factors. In adults, MD has also been demonstrated to be efficacious in reducing the risk of metabolic syndrome. However, few studies are available on the effects of the MD in both adult and pediatric subjects with NAFLD. Thus, the aims of the present narrative review are to analyze the current clinical evidence on the impact of MD in patients with NAFLD, and to summarize the main mechanisms of action of MD components on this condition

Two-Dimensional Displacement Sensor Based on Plastic Optical Fibers

An inexpensive fiber-based displacement sensor for two-dimensional crack monitoring is proposed and analyzed. The device is packaged as conventional crack monitoring gages based on sliding plates and exploits the dependence of the transmitted power between facing optical fibers with the displacement. The use of multi-core polymeric fibers with high numerical aperture allows a compact form factor and simplifies the sensor assembly. The position detection algorithm has been optimized through simulations; then experimental tests have shown a good agreement with simulations and have proved that even with simplified layout and artisanal realization the sensor can measure displacements in a square area of 3 mm by 3 mm with an uncertainty better than 0.05 m

Towards self-diagnosis composites: Detection of moisture diffusion through epoxy by embedded evanescent wave optical fibre sensors

This paper reports on an epoxy matrix for glass fibre reinforced polymers equipped with low cost optical fibre sensors for the early detection of water diffusion, with devised applications in the oil and gas industry. Novel evanescent wave optical fibre sensors were designed, fabricated and embedded in epoxy resin samples. The tips of the optical fibre sensors were coated with a silver layer to work in reflection, so that they could be used as probes. Accelerated diffusion tests were performed: the samples were exposed to simulated sea water at 80 °C for up to 148 hours. The water diffusion resulted in a remarkable change of the reflected signal from the sensors, a result that was then confirmed through gravimetric measurements and a theoretical prediction, according to Fick’s diffusion law. The results corroborate the feasibility of “sensitive” fibre reinforced polymers in harsh environments and that chemicals diffusion in these materials can be remotely and continuously monitored by means of the presented sensing system

Reflectance-based low-cost disposable optical fiber surface plasmon resonance probe with enhanced biochemical sensitivity

A reflectance-based surface plasmon resonance (SPR) fiber sensor with enhanced sensitivity for biochemical sensing is reported after comparing its result with the transmittance-based SPR optical fiber sensors. The fabricated SPR sensor contains a gold-coated multimode fiber with the implementation of a standard source-sensor-spectrometer interrogation system. As the refractive index of the liquid under test is increased, a redshift of the SPR is observed. The coupling of the source to the fiber sensor is optimized by investigating the effect of an intentional misalignment in transmission-based setup. When a fiber tip coated with the silver mirror and the bifurcated fiber bundle is used, an alignment-free disposable sensor probe is achieved. A comprehensive characterization of the proposed reflectance-based SPR probe is discussed. The maximum sensitivity of 3212.19  nm/refractive index unit (RIU) is obtained

Optical fiber flowmeter based on a single mode-multimode-single mode structure

Single mode-Multimode-Single mode (SMS) sensors have been attracted a relevant attention because of their simple manufacturing, their capability of sensing different quantities, and their enhanced sensitivity compared to the most common fiber optic sensor represented by Fiber Bragg Gratings (FBGs). Moreover, SMS sensors exhibit blue-shift sensitivity to strain, opposite to FBGs, making them suitable in applications where strain-temperature cross-sensitivity may be an issue. SMS sensors are made by splicing a short multimode, preferably a two mode or quasi two-mode, optical fiber jumper between single mode pigtails. The interference of the modes propagating at different phase velocities produces a spectral pattern that shifts with temperature, strain or any perturbation of the phase difference among the modes. In this paper we review the main features of SMSs as temperature sensors and we present a potential biomedical application in an all-fiber flowmeter based on the hot-wire principle: a fiber-coupled laser source at 980 nm is used as a controllable heating source of the SMS sensor that, when immersed in fluid flow, converts the temperature variation, caused by the heat removal, into a wavelength shift of the transmitted spectrum. Thermal characterization and proof-of-concept experiments show the feasibility and functionality of the sensor and provide an outlook on possible developments and potential applications