Search

Electrical current monitoring plays an important role in power transmission system, electric instruments, etc. The stability of the monitoring system is highly demanded. In this paper, a new interrogation scheme for a fiber Bragg grating (FBG) current sensor based on a dual-loop optoelectronic oscillator (OEO) with high stability, high precision and simple structure is proposed and experimentally demonstrated. The wavelength shift of the FBG, which is bonded on a magnetostrictive alloy-strip, is converted into the frequency shift of the microwave signal through the OEO system utilizing the wavelength to frequency mapping mechanism. Different from previous single-loop OEO schemes, a length of ∼1 km single mode fiber is used to form the second loop in the OEO-cavity, which can enhance the mode-selection ability and reduce the total gain requirement of the system. In addition, a fiber-ring-laser (FRL) cavity is adopted by integrating the sensing FBG-head as the wavelength-selective component to improve the quality of the optical carrier signal. The measured side-mode suppression ratio (SMSR) is up to 62.59 dB and the free spectral range (FSR) is five times larger than the single-loop structure, resulting in highly-enhanced stability and so the precision. Most importantly, the frequency fluctuation is as low as 0.277 ppm, which is the minimum to the best of our knowledge. Compensating methods for the influence of the temperature and the hysteresis are also discussed. The proposed scheme provides a feasible solution to promoting the development of OEO-based interrogation technology and its commercial applications. [ABSTRACT FROM AUTHOR]

In this work, a detailed study on volume and surface refractive index (RI) sensitivity of cladding modes for a fiber Bragg grating (FBG) based sensor is presented. Surface RI sensitivity of the cladding mode of FBGs has been illustrated and quantified with the concept of add-layer sensitivity for the first time to the best of our knowledge. A detailed investigation of mode transition of higher-order cladding modes has been revisited and important characteristics of the cladding modes are observed which could open a new designing path of fabrication and innovative way of the use of this family of optical fiber grating-based sensors. The effect of “mode transition” of higher-order cladding modes, higher operating wavelength for respective cladding mode and “mode stretching” effects are combined together to achieve higher volume and surface RI sensitivity of cladding mode of FBG. It has been shown numerically that with proper designing, sub-nanometer (∼0.04 nm) attachment of target analyte could be recognized by cladding mode of FBG which is quite promising for application in optical fiber grating bio-sensors. This critical designing method of FBG based surface refractometer would be very helpful in case of the fabrication of highly sensitive sensors for distinct biochemical applications. [ABSTRACT FROM AUTHOR]

Nowadays, the microwave photonics (MWP) concept has been evolved from laboratory tests to practical applications, and related techniques have been widely deployed in many fields including such as wireless communications, medicine, sensing, radars, electronic warfare, and space explorations. In this paper, we concentrate on the featured applications of MWP in the high-speed railways (HSRs), an emerging field and massive market, and an overview about our recent work is presented. The radio-over-fiber based wireless communications in high-mobility scenarios, photonic-assisted electromagnetic interference detection along HSR lines, and fiber sensing for safety protection of railways are investigated systematically in our group. Experiments are then performed to verify the basic functionalities of the three MWP-enabled systems mentioned above. In particular, field trials have been successfully implemented along two in-service HSR lines located in Southwest China, i.e., the Chengdu–Chongqing and the Chengdu–Mianyang–Leshan HSR lines. With these results and achievements, we can expect more MWP-enabled striking applications in the HSR field in near future. [ABSTRACT FROM AUTHOR]

Besides distinct features on RF/optical signal generation, optoelectronic oscillators (OEOs) have also been rapidly developed as emerging techniques towards sensing, measurement, and detection. In this paper, we start with the conceptual architecture and the analytical model of OEOs. Then, three operation principles behind sensing, measurement, and detection applications are categorized, including the variation on the time delay of loop, the passband reconfiguration of microwave photonic filter in loop, and the oscillation gain from injection locking, which clearly clarify the X-to-frequency mapping (X denotes target parameter or signal) for supporting practical solutions and approaches. Next, a comprehensive review to advances in OEO-based sensing, measurement, and detection applications is presented, including length change and distance measurement, refractive index estimation, load and strain sensing, temperature and acoustic sensing, optical clock recovery, and low-power RF signal detection. As a new application example, a novel approach for in-line position finding is proposed. When a long fiber Bragg grating inserted into OEO is locally heated to slightly broaden its reflection spectrum, the target position heated is mapped into the oscillating frequency shift, according to the first operation principle. A sensitivity of 254.66 kHz/cm is obtained for position finding in the experiment. Afterward, solutions for calibration and stabilization are briefly introduced, which enable us to improve the accuracy and reliability. Finally, features and future prospects on the sensing, measurement, and detection applications are discussed, such as compact and integrated OEOs. [ABSTRACT FROM AUTHOR]

A novel temperature-insensitive tilt sensor is proposed based on two fiber Bragg gratings (FBGs), which were embedded in a cylindrical cantilever-based pendulum in two orthogonal planes. Tilt-induced bending of the pendulum changes bandwidths and hence reflected optical powers of the two FBGs. Intensity-measurements of two-dimensional (2D) tilt angles can be realized without temperature dependence. Theoretical analysis and experimental verification have been carried out. Sensitivity of 42.97 nW/° with measurement accuracy of 0.27° has been achieved over a range up to ±15°. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:344-346, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27281 [ABSTRACT FROM AUTHOR]