Highly sensitive displacement sensor based on composite interference established within a balloon-shaped bent multimode fiber structure

A novel optical fiber displacement sensor based on composite interference established within a balloon-shaped bent multimode (BSBM) fiber structure is described and experimentally demonstrated. The BSBM fiber structure is realized by bending a straight single-mode–multimode–single-mode (SMS) fiber structure into a balloon shape using a length of capillary tube to fix the shape of the structure. Owing to the bend in the multimode waveguide, the original undistorted multimode interference pattern is changed, and an extra Mach–Zehnder interferometer is effectively introduced within the multimode fiber (MMF) section at a suitable bending radius. This established composite interference greatly improves the displacement sensing performance of the SMS fiber structure. A maximum displacement sensitivity of 0.51 dB/μm over the displacement range of 0–100 μm at the operating wavelength of 1564.7 nm is achieved experimentally. Based on its easy fabrication process, low cost, and high measurement sensitivity, the sensor of this investigation could be a realistic candidate in the high-accuracy displacement measurement field

Disrupted Lipid Metabolism in Multiple Sclerosis: A Role for Liver X Receptors?

Multiple sclerosis (MS) is a chronic neurological disease driven by autoimmune, inflammatory and neurodegenerative processes leading to neuronal demyelination and subsequent degeneration. Systemic lipid metabolism is disturbed in people with MS, and lipid metabolic pathways are crucial to the protective process of remyelination. The lipid-activated transcription factors liver X receptors (LXRs) are important integrators of lipid metabolism and immunity. Consequently, there is a strong interest in targeting these receptors in a number of metabolic and inflammatory diseases, including MS. We have reviewed the evidence for involvement of LXR-driven lipid metabolism in the dysfunction of peripheral and brain-resident immune cells in MS, focusing on human studies, both the relapsing remitting and progressive phases of the disease are discussed. Finally, we discuss the therapeutic potential of modulating the activity of these receptors with existing pharmacological agents and highlight important areas of future research

A High-Temperature Humidity Sensor Based on a Singlemode-Side Polished Multimode-Singlemode Fiber Structure

A relative humidity (RH) sensor based on a simple singlemode-side polished multimode-singlemode (SSPMS) fiber hybrid structure is investigated, which is capable of working over a relatively high-temperature range, at which many RH sensors based on moisture sensitive material coatings cannot operate. The beam propagation method is used to analyze the light transmission characteristics within the side polished multimode fiber (SPMMF) structure. Experimental results show that the SPMMF surface roughness has a significant influence on the sensor\u27s humidity sensing performance, as a result of the adsorption and desorption of water molecules along the side polished surface. A higher surface roughness results in an increased RH sensitivity. It is concluded that the SSPMS fiber structure based RH sensor can achieve around 0.069 dB/%RH within the humidity range of 30%RH–90%RH for a temperature range of 70 °C to 90 °C. In addition, the temperature cross-sensitivity has been investigated experimentally. The developed fiber optic sensor in this investigation provides a simple and effective approach for RH measurement in a variety of production applications

An investigation of 3.5 μm emission in Er3+-doped fluorozirconate glasses under 638 nm laser excitation

Intense 3.5 μm mid-infrared emission has been achieved in Er3+-doped ZBYA glasses, which is ascribed to the Er3+: 4F9/2→4I9/2 transition. Based on the absorption spectrum of Er3+ ions, a 638 nm laser was utilized to directly pump the upper level (Er3+: 4F9/2) to achieve 3.5 μm emission with enhanced quantum efficiency. Spectroscopic parameters were predicted by Judd-Ofelt theory. The maximum emission cross-section of the Er3+-doped ZBYA glass was estimated to be 5.5×10-22 cm2 at 3496 nm. Additionally, the fluorescence spectra and energy level lifetimes of ZBYA glass samples with different Er3+ ions doping concentrations were also measured. The theoretical and experimental results confirm the potential of Er3+-doped ZBYA glasses for use in the development of 3.5 μm mid-infrared fiber lasers

Strain Sensor Based on Grourd-Shaped Single-mode-multimode-single-mode Hybrid Optical Fibre Structure

A fibre-optic strain sensor based on a gourd-shaped joint multimode fibre (MMF) sandwiched between two single-mode fibres (SMFs) is described both theoretically and experimentally. The cladding layers of the two MMFs are reshaped to form a hemisphere using an electrical arc method and spliced together, yielding the required gourd shape. The gourd-shaped section forms a Fabry-Perot cavity between the ends of two adjacent but noncontacting multimode fibres’ core. The effectiveness of the multimode interference based on the Fabry-Perot interferometer (FPI) formed within the multimode inter-fibre section is greatly improved resulting in an experimentally determined strain sensitivity of −2.60 pm/με over the range 0—1000 με. The sensing characteristics for temperature and humidity of this optical fibre strain sensor are also investigated

High-Sensitivity Vector Bend Sensor Based on a Fiber Directional Coupler Inscribed by a Femtosecond Laser

In this Letter, we demonstrate a high-sensitivity vector bend sensor based on a fiber directional coupler. The fiber directional coupler is composed of two parallel waveguides inscribed within a no-core fiber (NCF) by a femtosecond laser. Since the two written waveguides have closely matched refractive indices and geometries, the transmission spectrum of the fiber directional coupler possesses periodic resonant dips. Such a fiber directional coupler exhibits a good bending-dependent spectral shift response due to its asymmetric structure. Experimental results show that bending sensitivities of -97.11 nm/m-1 and 58.22 nm/m-1 are achieved for the 0° and 180° orientations in the curvature range of 0-0.62 m-1, respectively. In addition, the proposed fiber directional coupler is shown to be insensitive to external humidity changes, thus improving its suitability in high-accuracy bending measurements

Simultaneous measurement of displacement and temperature based on two cascaded balloon-like bent fibre structures

A low-cost optical fibre sensor based on two cascaded balloon-like bent fibre (BBF) structures for simultaneous displacement and temperature measurement is reported. The sensor is fabricated by cascading two balloon-like bent single-mode fibres (SMFs) which with different bending radii, generating two separate interference dips within a limited wavelength range. The wavelength of the two interference dips exhibits different responses to external displacement and temperature variations, hence simultaneous measurement of displacement and temperature is realized. Experimental results show that the proposed optical fibre sensor achieves a displacement sensitivity of −318.8 pm/μm and a temperature sensitivity of 47.4 pm/°C. Taking advantage of its low-cost, ease of fabrication, and experimentally determined high sensitivity, the sensor in this investigation can be potentially applied in both displacement and temperature measurement fields

High Sensitivity Temperature Sensor Based on Singlemode-no-Core- Singlemode Fibre Structure and Alcohol

A high sensitivity temperature sensor based on a singlemode-no-core-singlemode (SNCS) fibre structure and surrounded with alcohol within a silica capillary is described. In this investigation, no-core fibre (NCF) is used as the multimode waveguide and alcohol is chosen as the temperature sensitive medium. By packaging the alcohol solution with a short length of NCF enclosed within a silica capillary, the surrounding temperature can be detected by monitoring the variations of transmission loss at a specific wavelength. The theoretical analysis predicts this temperature sensor can provide high sensitivity, and the experimental results support this. The maximum temperature sensitivity of the sample is 0.49 dB/oC with a potential temperature resolution of 0.02 oC at the operating wavelength of 1545.9 nm. In addition, the repeatability and response time of the sensor of this investigation are investigated experimentally