Tongyu Liu

Fiber methane gas sensor and its application in methane outburst prediction in coal mine

Fiber optic methane gas detecting system based on distributed feedback (DFB) laser wavelength scanning technique is demonstrated. Wavelength scan of methane absorption peak at 1665.9 nm is realized by saw tooth modulation of current which is injected to DFB laser. A reference methane gas cell is used to find the methane absorption peak around 1666 nm, and normalization is used to reduce the outside affection such as power drift, fiber loss. Concentration is got by arithmetic processing absorption coefficient of the methane gas. In-situ test is carried out in coalmine and long time precision of 0.05% is achieved. Some spot data of coal mine is introduced. By the system, methane outburst can be measured.

Novel gas sensor combined active fiber loop ring-down and dual wavelengths differential absorption method

A novel active fiber loop ring-down gas sensor combined with dual wavelengths differential absorption method is proposed. Two Distributed Feedback Laser Diodes (DFB LDs) with different wavelengths are employed. One LD whose wavelength covered with the absorption line of target gas is used for sensing. Another LD whose wavelength is centered outside the absorption line is used for reference. The gas absorption loss can be obtained by differencing the reference signal and sensing signal. Compared with traditional method of one wavelength employed, it can eliminate the influence of the cavity loss variety and photoelectric device drift in the system efficiently. An Erbium Doped Fiber Amplifier (EDFA) with Automatic Gain Control (AGC) is used to compensate the loss of the light in the ring-down cavity, which will increase the cavity round trips and improve the precision of gas detection. And two fiber Bragg gratings (FBGs) are employed to get rid of amplified spontaneous emission (ASE) spectrum noise as filters. The calibrating ethyne samples of different concentrations are measured with a 65 mm long gas cell in order to evaluate the effect of reference. The results show the relative deviation is found to be less than ± 0.4% of 0.1% ethyne when a certain additional loss from 0 to 1.2dB is introduced to the cavity and the relative deviation of measured concentration is less than ± 0.5% over 24 hours.

Research on a novel composite structure Er 3+ -doped DBR fiber laser with a π-phase shifted FBG

A simple composite cavity structure Er³⁺-doped fiber laser was proposed and demonstrated experimentally. The resonant cavity consists of a pair of uniform fiber Bragg gratings (FBGs) and a π-phase shifted FBG. By introducing the π-phase shifted FBG into the cavity as the selective wavelength component, it can increase the effective length of the laser cavity and suppress the multi-longitudinal modes simultaneously. The narrow linewidth of 900 Hz and low RIN of -95 dB/Hz were obtained. And the lasing wavelength was rather stable with the pump power changing. The SMRS was more than 67 dB. The results show that the proposed fiber laser has a good performance and considerable potential application for fiber sensor and optical communication.

Application of Distributed Optical Fiber Temperature Sensing System Based on Raman Scattering in Coal Mine Safety Monitoring

The principle and design of the distributed optical fiber temperature sensing system based on Raman scattering is presented in this paper. The spatial resolution is enhanced by reducing the pulse width of the light source and high speed progressive average etc. The distributed optical fiber sensor not only has the characteristics of resistance to electromagnetic interfere, against fire and so on, but also it can sense the change of temperature along the optical fiber by the form of continuous distance. Because of its ascendency and the augmented performance, This paper also introduces the example used in coal mine goaf temperature monitoring and data analysis.The principle and design of the distributed optical fiber temperature sensing system based on Raman scattering is presented in this paper. The spatial resolution is enhanced by reducing the pulse width of the light source and high speed progressive average etc. The distributed optical fiber sensor not only has the characteristics of resistance to electromagnetic interfere, against fire and so on, but also it can sense the change of temperature along the optical fiber by the form of continuous distance. Because of its ascendency and the augmented performance, This paper also introduces the example used in coal mine goaf temperature monitoring and data analysis.

Fiber optic vibration sensor based on over-coupled fused coupler

The theory and experiment results of fiber optic vibration sensor based on over-coupled fused coupler (OCFC) is described, 2 novel scheme to form single-end sensor is presented, i.e. OCFC sensor with a reflection mirror and OCFC fiber loop sensor, the transmission spectrum of these OCFC sensor when applied with different strains is investigated and interrogation system is developed, the output of these sensors when applied with vibration and shock is shown. We demonstrate that the OCFC fiber loop sensor is feasible to have practical use to measure vibration signal because the sensor is easy to be fabricated, it has good low and high frequency response and the interrogation system is simple, low cost.

A micro-seismic fiber Bragg grating (FBG) sensor system based on a distributed feedback laser

In this work a micro-seismic fiber Bragg grating (FBG) sensor system based on a narrow linewidth distributed feedback (DFB) laser is investigated. By automatic control of the temperature of the DFB laser, the wavelength of the laser can be locked in the −3 dB reflectivity spectrum of the FBG. So the FBG sensor system can be made immune to temperature. Using the reference channel, the measurement precision of the system is improved by wiping out the power noise of the DFB laser. Experiments on the sensor systems frequency character and linearity have been performed. Results show that this sensor has the smallest acceleration of 1 mm s−2.

Interrogation a Fiber Bragg Grating vibration sensor by narrow line width light

A method to interrogate fibre Bragg grating vibration sensor by narrow line width light is demonstrated; the interrogation scheme takes advantage of the intensity modulation of narrow spectral bandwidth light, such as distributed feedback laser, when a reflection or transmission spectrum curve of an FBG moves due to the strain which applied on the sensor. The sensors response to acceleration frequency and amplitude is measured by experiment. We also discussed the factors which have impacts on the sensitivity of the interrogation system.

A temperature self-adapting FBG vibrating sensor system

A temperature adaptive fiber Bragg grating (FBG) vibration sensor system of low frequency based on narrow line width distributed feedback (DFB) laser is investigated. By automatic controlling the temperature of the DFB laser, the wavelength of the DFB laser can be locked in -3dB reflectivity spectrum of FBG. So the system can realise the self adaptation of the temperature changes. Using the reference channel, the measurement precision of the system was improved by wiping off the power noise of the DFB laser. Experiments show that this sensor has the smallest acceleration of 1mm/s2 and the sensitivity of 6.2V/m/s2.

A low cost mutiplexed 1.331 μm spectroscopic remote methane sensor system

A remote multiplexed methane sensor system taking advantage of low cost 1.33 1&mgr;m SLD is demonstrated. it has long time stabilization, immunize from the influence of the temperature changing. Reference light is adopted in the system to reduce the affection of attenuation caused by long distance transmission of light in fiber and the drift of the SLD output power. Resolution of 0.01% (10-s time constant) is obtained by introducing intensity modulation and Lock-In-Amp.

Application of Distributed Optical Fiber Temperature System in Online Monitoring and Fault Diagnosis of Smart Grid

With the development of smart grid, The distributed optical fiber temperature monitoring system has more and more applications in power cable monitoring area. this paper presents the technology of distributed optical fiber temperature monitoring system running on the power cable, it use to real-time online monitoring for the power cable temperature and carrying capacity, and through carrying capacity analysis for fault diagnosis, this paper Introduced the theory, architecture design and function of the distributed optical fiber temperature sensing system based on the Raman scattering, the fiber-optic sensor as a new temperature sensor on power cable has its special characteristics and advantages, Finally by engineering example proved that this system to improve the intelligent power cable running safety, improve the reliability of power system is of great significance.