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Graphene, a novel form of the hexagonal honeycomb two-dimensional carbon-based structural material with a zero-band gap and ultra-high specific surface area, has unique optoelectronic capabilities, promising a suitable basis for its application in the field of optical fiber sensing. Graphene optical fiber sensing has also been a hotspot in cross-research in biology, materials, medicine, and micro-nano devices in recent years, owing to prospective benefits, such as high sensitivity, small size, and strong anti-electromagnetic interference capability and so on. Here, the progress of optical fiber biochemical sensors based on graphene is reviewed. The fabrication of graphene materials and the sensing mechanism of the graphene-based optical fiber sensor are described. The typical research works of graphene-based optical fiber biochemical sensor, such as long-period fiber grating, Bragg fiber grating, no-core fiber and photonic crystal fiber are introduced, respectively. Finally, prospects for graphene-based optical fiber biochemical sensing technology will also be covered, which will provide an important reference for the development of graphene-based optical fiber biochemical sensors. [ABSTRACT FROM AUTHOR]

Graphene, a novel form of the hexagonal honeycomb two-dimensional carbon-based structural material with a zero-band gap and ultra-high specific surface area, has unique optoelectronic capabilities, promising a suitable basis for its application in the field of optical fiber sensing. Graphene optical fiber sensing has also been a hotspot in cross-research in biology, materials, medicine, and micro-nano devices in recent years, owing to prospective benefits, such as high sensitivity, small size, and strong anti-electromagnetic interference capability and so on. Here, the progress of optical fiber biochemical sensors based on graphene is reviewed. The fabrication of graphene materials and the sensing mechanism of the graphene-based optical fiber sensor are described. The typical research works of graphene-based optical fiber biochemical sensor, such as long-period fiber grating, Bragg fiber grating, no-core fiber and photonic crystal fiber are introduced, respectively. Finally, prospects for graphene-based optical fiber biochemical sensing technology will also be covered, which will provide an important reference for the development of graphene-based optical fiber biochemical sensors.

Nonlinear ultrasonic technique that evaluates the growth of the barely visible fatigue crack in metal is difficult to be achieved by conventional optical fiber sensor because of the critical requirements for sensor sensitivity and bandwidth. In this paper, a high-performance optical fiber sensor using phase-shifted fiber Bragg grating and balanced demodulation system was applied to detect the fundamental and second harmonic Lamb waves propagating in an aluminum plate. After the nonlinearity was calculated from the modes of the Lamb waveform detected by the optical fiber sensor, its change due to the second harmonic generation shows an exponential trend in a fatigue test, which can be used to evaluate the crack growth with sufficient reliability. The experimental results from the optical fiber sensor were validated by comparing with results from the PZT sensor. This paper facilitates the development of optics-based nonlinear ultrasonic structural health monitoring for fatigue crack evaluation. [ABSTRACT FROM AUTHOR]

Several models have been employed for second-harmonic generation (SHG) in optical fibers. Their common drawback is the low conversion efficiency of SHG. When cladding modes had been studied as pump signals through tilted fiber grating coated by nonlinear layers, an efficiency of the order 0.14% was reached. In this paper, a detailed investigation is carried out to study SHG in absorbing optical fibers, where a new schematic is proposed by adding a thin metallic film between the fiber cladding and the nonlinear layer to excite some plasmonic modes. These modes possess enhanced field amplitudes within the nonlinear layer, leading to a higher SHG efficiency up to 22% and 4% in case of using silver and gold, respectively. Solutions of the dispersion relation, intermodal phase matching, coupling between core and cladding modes, and field distributions are fully studied. The grating parameters are optimized to reach the maximum possible efficiency. [ABSTRACT FROM AUTHOR]

A label-free biosensor based on graphene oxide (GO) and glucose oxidase (GOD) functionalized tilted fiber grating (TFG) with large tilted angle is proposed for low concentration glucose detection. Taking advantages of sufficient binding sites of the GO with oxygen-containing groups, the enzymes (GOD) are covalently immobilized onto GO-deposited TFG via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxyl succinimide cross-liner. Surface characterizations with optical microscopy, scanning electron microscopy, Raman and infrared spectroscopy provide detailed assessments and evidences about the homogeneity of GO deposition and the effectiveness of enzyme modification. Through the specific catalysis reaction of GOD on the glucose, a considerable refractive index change in local microenvironment around the TFG results in the resonant wavelength shifts of cladding modes. The detection results of the low-concentration glucose demonstrate that the resonant wavelength has a linear response to the glucose concentration in the range of 0–8 mM with a response coefficient of ∼0.24 nm/mM, showing an enhanced sensitivity and bio-selectivity compared with the pristine TFG. The miniaturized size and remote label-free sensing capacity of the proposed device permit a multitude of opportunities for single-point measurement in harsh conditions and hard-to-reach spaces, presenting a promising candidate for label-free glucose detection for disease diagnosis, pharmaceutical research and bioengineering applications. [ABSTRACT FROM AUTHOR]

In this study, an axial force sensor was developed and evaluated for a screw bolt using optical fiber grating (FBG: fiber Bragg grating). This sensor has high tolerance to electromagnetic noise. Furthermore, it has a characteristic long-distance signal transmission ability because it was made using optical fiber. This washer type sensor forms a circular projection because the stress distribution in the sensor is obtained only proportional to the axial force of the screw bolt. The axial force sensor was experimentally developed for an M10 screw bolt. According to test results, the reflection wavelength shift was proportional to the axial force, implying that this sensor has excellent characteristics.

Surface plasmon resonance (SPR) optical fiber biosensors can be used as a cost-effective and relatively simple-to-implement alternative to well established bulky prism configurations for high sensitivity biological sample measurements. The miniaturized size and remote operation ability offer them a multitude of opportunities for single-point sensing in hard-to-reach spaces, even possibly in vivo. The biosensor configuration reported in this work uses a tilted fiber Bragg grating (TFBG) in a commercial single mode fiber coated with a nanometer scale silver film. The key point is that by reducing the silver film thickness to around 20–30 nm (rather than 50 nm for optimal SPR excitation), different modes of the TFBG spectrum present very high but opposite sensitivities to refractive index (RI) changes around the TFBG. Experimental results obtained with the coated TFBG embedded inside a microfluidic channel show an amplitude sensitivity greater than 8000 dB/RIU (Refractive Index Unit) and a limit of detection of 10 −5 RIU. Using this device, the effect of different concentrations of protein in rat urine was clearly differentiated between healthy samples, nephropatic samples and samples from individuals under treatment, with a protein concentration sensitivity of 5.5 dB/(mg/ml) and a limit of detection of 1.5×10 −3 mg/ml. Those results show a clear relationship between protein outflow and variations in the RI of the urine samples between 1.3400 and 1.3408, pointing the way to the evaluation and development of new drugs for nephropathy treatments. The integration of TFBGs with microfluidic channels enables precise measurement control over samples with sub-microliter volumes and does not require accurate temperature control because of the elimination of the temperature cross-sensitivity inherent in TFBG devices. Integration of the TFBG with a hypodermic needle on the other hand would allow similar measurements in vivo. The proposed optical fiber/microfluidic plasmonic biosensor represents an appealing solution for rapid, low consumption and highly sensitive detection of analytes at low concentrations in medicine as well as in chemical and environmental monitoring. [ABSTRACT FROM AUTHOR]

A simple and compact sensor for simultaneous measurement of the tilt angle and temperature is presented. The sensor is composed of a fiber taper and a fiber Bragg grating. The tilt angle is measured by monitoring the tilt-induced loss of the taper. The grating is used for enhancing the tilt angle sensitivity as well as monitoring the wavelength shift induced by the temperature variation. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2248–2250, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22701 [ABSTRACT FROM AUTHOR]

We present a novel fiber grating measurement technique based on the direct modulation of a tunable laser source by an optical component analizer (COA). © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 14: 373–375, 1997. [ABSTRACT FROM AUTHOR]