The Research Of Fiber Sensor Multiplexing Technologies For Network Capacity Expansion And Their Applications

Accompanied by the development of optical communication technology, optical fiber sensor (OFS) technology has been grown up since40years ago. The applications of OFS technology have been extended to cover all fields of the national economy. However, now the OFS technologies are still mainly confined to discrete sensing devices and single/multiple point sensor systems, which are increasingly unable to meet the requirements of miniaturization, integration and networking in the future applications, and also restrict the large-scale development of the optical fiber sensor industry. Thus, OFS multiplexing network is the inevitable trend of OFS technology. High-capacity OFS network can not only improve the practicality of the OFS technology, but also expand the new application areas of the OFS technology.Aiming at the multiplexing network technique of OFS, this thesis proposes two novel techniques for optical sensors access and network capacity expansion based on the multi-domain multiplexing schemes. The key issues including structure characteristics, network architecture, and multiplexing capacity of the OFS network are investigated and analyzed. By combining the multiplexing and networking techniques with specific sensing technologies, the OFS applications in the fields of security and electricity are accomplished, and also the feasibility and advancement of them are verified. Moreover, to further improve the practicality of the multiplexing techniques, several common basic technologies for OFS network are investigated. The main research achievements are as follows:Firstly, a hybrid frequency-division-multiplexing/wavelength-division-multiplexing (WDM/TDM) technology based on distributed optical fiber sensing technology for network capacity expansion is studied, as well as the architecture of hybrid multiplexing sensing passive optical network (HSPON) is designed. According to the characteristics of the network, an unbalanced Mach-Zehnder/Sagnac interferometric distributed sensing structure with self-feedback ability is proposed. By theoretical analysis and simulating calculation, the performances of this structure are analyzed in detail, and it is demonstrated that the polarization-induced signal fading can be eliminated. By adopting the WDM/TDM scheme,256sensors can be multiplexed in this network. A HSPON system with the capacity of120units as well as the whole sensing distance up to60km is designed and achieved, for perimeter intrusion detection. The6months application test demonstrates that the system has the advantages of quick response, high sensitivity, low false alarm rate, and high reliability, which are suitable for the application of perimeter security.Secondly, a hybrid frequency-division-multiplexing/wavelength-division-multiplexing (FDM/WDM) technology based on smart micro-structure fiber sensors for network capacity expansion is studied. A novel micro-structure fiber sensor based on a pair of weak FBGs with very short cavity length is proposed, and its structure feature, sensing characteristic and fabrication technique are analyzed. It can be demonstrated that the microstructure sensor has the capacity of simultaneous frequency and wavelength encoded, and has the same temperature and the strain sensitivity as the fiber Bragg grating. By incorporating the FDM/WDM scheme, the fiber sensing network system of simple structure and huge capacity more than one thousand is presented. Meanwhile, the data processing method based on Fast Fourier Transformation (FFT) and Finite Impulse Response (FIR) filter is employed for rapid addressing and signal extraction from the fused signal of multi-sensor. Considering the requirements of power circuit monitor, a temperature sensing system based on this OFS network configuration is established, and the experimental test demonstrates that the system is of good stability and excellent temperature sensitivity.Thirdly, based on the analysis of the common basic technology in fiber sensing network, several Circuit module for light source driving and optical signal receiving are designed and investigated including the driver circuit for continuous light source with high stability, the driver circuit for high-speed pulse modulated light source, the low noise optical power detection circuit and the weak optical signal detection circuit with high magnification. By employing these circuits as the basic unit modules, a STM32microprocessor based on ARM Cortex-M3architecture as the main control module, serial peripheral bus architecture, and a touch screen as the interactive interface. The test platform is built for verifying the feasibility of the high capacity OFS network.