Ciming Zhou

Optical fiber magnetic field sensors with TbDyFe magnetostrictive thin films as sensing materials

Different from usually-used bulk magnetostrictive materials, magnetostrictive TbDyFe thin films were firstly proposed as sensing materials for fiber-optic magnetic field sensing characterization. By magnetron sputtering process, TbDyFe thin films were deposited on etched side circle of a fiber Bragg Grating (FBG) as sensing element. There exists more than 45pm change of FBG wavelength when magnet field increase up to 50 mT. The response to magnetic field is reversible, and could be applicable for magnetic and current sensing.

Continuous-Wave Frequency-Shifted Interferometry Cavity Ring-Down Gas Sensing With Differential Optical Absorption

This paper proposes a novel frequency-shifted interferometry (FSI) fiber cavity ring-down (CRD) gas sensing with dual-wavelength differential optical absorption that requires no modulation to a continuous-wave source or without fast detection and switching electronics. The fiber cavity is constructed from standard fiber optical components that include a micro-optical gas cell. FSI-CRD experiments are carried out with two wavelengths at 1531.770 and 1532.000 nm. The technique is successfully carried out by measuring acetylene-nitrogen mixtures with acetylene concentrations varying from 0% to 1.0%. A resolution of 7.8125%/dB is obtained. A minimum detectable acetylene concentration of 105.25 ppm was achieved with a 48-mm gas cell. The results show a good linear relationship between acetylene concentration and absorption loss and are in good agreement with existing theories. Dual-wavelength differential optical absorption can enhance measurement precision efficiently and eliminate the influence of various external factors. The relative deviation of measured concentration is less than ±0.29%, measured at 1.0% acetylene concentration over 70 min.

Large-capacity multiplexing of near-identical weak fiber Bragg gratings using frequency-shifted interferometry

We demonstrate interrogation of a large-capacity sensor array with nearly identical weak fiber Bragg gratings (FBGs) based on frequency-shifted interferometry (FSI). In contrast to time-division multiplexing, FSI uses continuous-wave light and therefore requires no pulse modulation or high-speed detection/acquisition. FSI utilizes a frequency shifter in the Sagnac interferometer to encode sensor location information into the relative phase between the clock-wise and counter-clockwise propagating lightwaves. Sixty-five weak FBGs with reflectivities in the range of -31 ~-34 dB and with near identical peak reflection wavelengths around 1555 nm at room temperature were interrogated simultaneously. Temperature sensing was conducted and the average measurement accuracy of the peak wavelengths was ± 3.9 pm, corresponding to a temperature resolution of ± 0.4 °C. Our theoretical analysis taking into account of detector noise, fiber loss, and sensor cross-talk noise shows that there exists an optimal reflectivity that maximizes multiplexing capacity. The multiplexing capacity can reach 3000 with the corresponding sensing range of 30 km, when the peak reflectivity of each grating is -40 dB, the sensor separation 10 m and the source power 14 mW. Experimental results and theoretical analysis reveal that FSI has distinct cost and speed advantages in multiplexing large-scale FBG networks.

Large WDM FBG Sensor Network Based on Frequency-Shifted Interferometry

We combine wavelength-division multiplexing (WDM) and frequency shifted interferometry (FSI) to interrogate a large-scale ultra-weak fiber Bragg grating (FBG) array. Based on Sagnac interference, FSI can location resolve sensors without using pulses or fast detection, therefore considerably lowers the system cost. By combining FSI with WDM, higher spatial resolution can be achieved. We demonstrated simultaneous interrogation of 363 FBG sensors, grouped into 121 identical units of 3 FBGs of different central wavelengths and spaced two meters apart. Based on the performance of the 363 grating system, we show the potential for interrogating 3207 sensors with good signal-to-noise ratio. Stability test and temperature sensing were carried out, and the obtained temperature resolution was ± 0.4 ° C. The results indicate the proposed scheme can greatly enhance the multiplexing capacity and meet the requirements of large-scale optical fiber networks.

Fiber Bragg grating high-current sensor based on magnetic coupling

Current sensors always play a very important role in the power industry. For example, current sensors can provide the key information for measurement, control and relay protection. However, when the economic further develops and the level of current increases year by year, it is very difficult to meet the demand for current sensors based on conventional technology which is still the main stream. Novel current sensors always are pursued. A research focusing on the current sensor is the technology of fiber optic current sensor, because there is high resistance to electromagnetic interference in fiber optic sensors. Fiber Bragg grating (FBG) sensors have been applied in many fields and have gained great achievements. It is of great help to the current measurement if FBG current sensors are realized. In this paper, a novel FBG high-current sensor is developed based on magnetic coupling. The principle is described, such as the magnetic coupling, the structure of the sensor and the sensing data processing. Experiments are carried out, and the results show at least 60 pm wavelength shift with the change of 100A and 2563 pm wavelength shift when the current is 750A and a good repeatability. The results are in agreement with the principle and indicate that the proposed sensor is capable of measuring both dc and ac current.

Doppler Effect-Based Optical Fiber Vibration Sensor Using Frequency-Shifted Interferometry Demodulation

A novel optic-fiber vibration sensing system based on frequency-shifted interferometry (FSI) is proposed and demonstrated in this paper. The sensor is based on the phenomenon that the light frequency transmitted through a segment of bent fiber can be Doppler shifted by vibration. The Doppler frequency shift is measured using FSI demodulation. Compared to traditional fiber Bragg grating vibration sensor, the proposed sensor is easy to fabricate, of low cost and without directional dependency. The application of FSI demodulation allows for custom tailoring of measurement sensitivity, and has superior signal stability due to its same-path interference nature. The measured Doppler frequency shift using the FSI system agrees well with the calculated one, derived from strain measurements. The results show that the system has a high sensitivity and wide frequency range, limited only by the excitation apparatus used in the experiment.

In-line extreme ultraviolet polarizer with hybrid configuration

A novel hybrid Au-multilayer-Au in-line extreme ultraviolet (EUV) optical polarizer is presented in this paper. Different from all-Mo/Si multilayer EUV polarizer, this polarizer is based on the concept that Au surfaces work as reflecting elements for in-line optics routine, while polarization effect is realized by polarizing multilayer. Simulation shows that the proposed polarizer with 80 degrees-70 degrees-80 degrees angle configuration has about 30% of transmission and 12 eV of bandwidth half maximum, which enables more throughput and broader bandwidth than the all-multilayer one.

New trends and applications of optical fiber sensing technologies at the NEL-FOST

This paper reviews the recent development of optical fiber sensors at the National Engineering Laboratory for Optic Fiber Sensing Technologies (NEL-FOST) at Wuhan University of Technology. Integration of optical fiber with sensitive thin films will new possibilities for industry application, such as optical fiber hydrogen sensors based on Pt-doped WO3 coatings, fiber humidity sensors with porous oxide coating and high-temperature sapphire fiber sensors based on multilayer coating on fiber tip. Ultra-weak FBG array with thousand of FBGs with on-line draw tower technology will enable FBG sensing network with large capacity, also improved sensing performance and mechanical stability.

Fiber optic magnetic field sensor based on magnetic fluid and etched Hi-Bi fiber loop mirror

A novel magnetic field sensor consisting of magnetic fluid (MF) and etched highly birefringent fiber loop mirror (Hi-Bi FLM) is proposed in the paper. The sensor is based on the etched FLM interferometer by using the property of the controllable refractive index of MF under external magnetic field. The refractive index of MF is changed by a tunable magnetic field and the resonant dip wavelength produced by the FLM shifts correspondingly. The magnetic field intensity can be measured by detecting wavelength shift. High sensitivity of 11.31pm/Oe and a resolution of 0.1Oe are obtained for the proposed magnetic field sensor.

Research on fiber Bragg grating huge current sensing based on electromagnetic force

Current sensor is the core device for the electric energy measurement. Fiber Bragg grating (FBG) sensing technology has many applications with anti-electromagnetic interference, good insulation, high reliability, small size, distributed measurement. Fiber brag grating based current sensing becomes an important direction of research and exploration. The principle of fiber Bragg grating current sensor based on electromagnetic force has analyzed. The structure of fiber Bragg grating current sensor has designed. Huge current measurement has achieved with high-speed demodulation equipment. The demodulation range of fiber Bragg grating center wavelength is 2.7nm when DC (0-700A, step 100A, 50Hz) current were inflicted.