Shurong Lai

Positioning Method for Dual Mach-Zehnder Interferometric Submarine Cable Security System

Dual Mach-Zehnder interferometric fiber sensor is one of the appropriate solutions to the application of submarine cable security. While the seabed environment makes the vibration output a narrow bandwidth lowpass interference signal and these property makes the correlation based event positioning algorithm hard to design. A preprocessing method intends to increase signal power spectral range before correlation is proposed. A bandpass filter is imposed to enhance the effect of high frequency components, despite the filtered signal is different from the original one. A post-integration SNR threshold is calculated to determine the proper center frequency and bandwidth of the filter. Experiment results show a good accordance with theoretical prediction.

Performance improvement of PGC method by using lookup table for optical seismometer

A new demodulation method is proposed to eliminate the light intensity disturbance(LID) due to the Phase Generate Carrier( PGC) modulation method for the optical marine seismometer which is based on the fiber interferometer. A look up table by the use of a nonlinear function has been demonstrated. The experimental results show that the performance of the system has been improved with the harmonic suppression ratio(HSR) of the demodulation results increasing 30dB and the dynamic range of the system increasing 26dB, comparing with the Differential Cross-Multiplying(DCM) algorithm for the PGC method. The new method approaches a dynamic range of 130dB@100Hz with the HSR more than 50dB.

A novel method for simultaneous measurement of current and voltage using one low-birefringence fiber

Abstract A novel method for simultaneous measurement of current and voltage employing a single monomode low-birefringence (Lo-Bi) fiber is described. This uses the Faraday effect for detection of current and the Kerr effect for detection of voltage. The waveform of the output light intensity due to the Kerr effect has been detected and the Kerr constant was measured as 5.4×10−16 m/V−2 at 25°C. Theoretical analysis shows that the current component can be measured free from the influence of the voltage component and the two components can be easily separated.

A novel space structure for optical fibre process tomography

In this paper, a novel space structure and its mathematic analysis for optical fibre process tomography is presented which can be used to measure medium distributions and contents in a circular cross section of cylindrical space in the field of industry process monitoring and control. The structure comprises a centre-supporting pole and many extensible arms; an electrical motor is placed in the pole to control all arms stretching and retracting simultaneously. At the end of each arm a reflecting prism is employed to realize the transformation of the rays in the arm and the measured plane. Fibre cable and photoelectrical devices can be sealed in the arms or pole specially designed to withstand conditions such as high temperature and high pressure. A detailed analysis of all kinds of positioning accuracies indicates that it is feasible and practical to use the novel structure in engineering.

Fiber sensor for simultaneous measurement of current and voltage by single Lo-Bi fiber

A sensor using a single monomode low-birefringence (Lo-Bi) fiber for simultaneous measurement of current and voltage has been designed, which uses Faraday effect for detection of current and Kerr effect for detection of voltage. Theoretical analysis proved the current component can be measured free from the influence of the voltage component, and the two components can be easily separated. Experimental results demonstrate the feasibility of the Kerr effect of the Lo-Bi fiber for sensing voltage, which is the main point in this proposal.

Characteristics analysis of cascaded long-period gratings with nm-thick film coating

Cascaded long period grating with film coating is sensitive to the thickness and refractive index of the film material and the surrounding refractive index, so it can be used in the applications such as gas sensing, liquid concentration sensing and bio-sensing. In this paper, the characteristic of cascaded long period grating coating with higher refractive index nanostructured film overlay is investigated theoretically by using coupled-mode theory and transfer matrix method. The responses of interference fringe peak wavelength to the thickness and refractive index of the film and the surrounding refractive index are numerical calculated. The theoretical simulation results show that the minima wavelength of the interference fringes within the long period gratings attenuation bands are sensitive to the thickness and refractive index of the film coating and the refractive index of the surrounding environment. By choosing these parameters optimally, the sensitivity of the peak wavelength shift of the interference fringes can be enhanced. The theoretical analysis can provide guidance to the application of the nanostructured film coated cascaded long period grating sensor.

Strain measurement of steel structure using a novel FBG sensor packaged by titanium alloy slice

In recent years, Fiber Bragg grating (FBG) sensors become a focus in civil structure health monitoring because they have many advantages and show superior potential for health monitoring to ensure their structural integrity, durability and reliability. In this paper, fiber Bragg grating (FBG) sensors are used to monitoring the strain of steel structure. A designed novel titanium alloy slice is introduced to package the used FBG. A shallow rectangular groove is notched on the titanium alloy slice. Coated with a thin layer of epoxy, the FBG is fixed and protected on the groove. In order to eliminate to the temperature vibration effect on the wavelength shift of FBG sensors, a FBG temperature sensor is used for compensation. The traditional resistance strain gauges are also used to measure the strain for the comparison with the FBG sensors to validate the effectiveness. The strain of the flat steel at the elastic and yield stage of the steel are measured by monitoring the shift of center wavelength of FBG sensors and the change of the resistance strain gauges. The experimental results show that FBG sensors packaged by titanium alloy slice possess good stain sensing property and the strain sensitivity coefficients are 1.25pm/με. The shifts of center wavelengths of FBG are in good linear relationship with the tensile force and the strain measured by the resistance strain gauge. The linear correlation coefficients both reach 0.999.

An extrinsic Fabry-Perot interferometric optical fiber sensor system for hydrogen detection

An extrinsic Fabry-Perot interferometric (EFPI) optical fiber hydrogen sensor based on palladium silver (Pd-Ag) film is designed for hydrogen leakage detection. The sensing mechanism of such a sensor is based on the mechanical stress that is induced in the Pd-Ag film when it absorbs hydrogen. The sensor system which is portable and suitable for field detection is formed by a conventional coupler, a low-power LED operating at 850 nm, and a high resolution miniature spectrometer. To obtain the absolute length of the EFPI air gap, a cross-correlation signal processing method is introduced.The sensor is suitable for monitoring concentrations of hydrogen below the lower explosive limit.

A modified cross-correlation method for white-light optical fiber extrinsic Fabry-Perot interferometric hydrogen sensors

An extrinsic Fabry-Perot interferometric (EFPI) optical fiber hydrogen sensor based on palladium silver (Pd-Ag) film is designed for hydrogen leakage detection. A modified cross correlation signal processing method for an optical fiber EFPI hydrogen sensor is presented. As the applying of a special correlating factor which advises the effect on the fringe visibility of the gap length and wavelength, the cross correlation method has a high accuracy which is insensitive to light source power drift or changes in attenuation in the fiber, and the segment search method is employed to reduce computation and demodulating speed is fast. The Fabry-Perot gap length resolution of better than 0.2nm is achieved in a certain concentration of hydrogen.

Optimization design of the pressure phase sensitivity of the fiber-optic air-backed mandrel hydrophone

Pressure phase sensitivity is one of the most important performance indexes of the fiber-optic hydrophone. Maximizing the pressure phase sensitivity is a basic principle in the fiber-optic hydrophone design. In this work, the orthogonal experimental method has been used to optimize the design of the pressure phase sensitivity of the fiber-optic air-backed mandrel hydrophone. A general three-dimensional theoretical model is carried out, and nine fiber-optic hydrophones are fabricated for orthogonal experiment. Several factors which affect the sensitivity are analyzed in the experiments, and the results validate the theory. The optimized designs are also gained by the analysis of the results to maximize the pressure phase sensitivity.