Investigation On Applications Of FBG In Sensing Technology

As a latest optoelectronic technology, fiber Bragg grating (FBG) has gone from theoretical research to large-scale practical applications, and is now finding its wide use in the field of optical fiber sensing and communication and other related market. Based on the Coupled Model Theory (CMT), the present paper focuses on a study of the FBG’s characteristics in case of slight disturbance on the core refractive index and makes a simulation analyse under the circumstance of slight linearly interference. The paper also analyzes the effects of FBG’s modulation amplitude on the performance of FBG and makes such simulations as uniform FBG/chirped FBG modulated by chirped amplitude, and the influence of the varied modulation amplitude on the FBG’s bandwidths. The demodulation technology of sensing network with distribution FBG is also researched. Sensors used for Solution concentration testing based on FBG are designed and makes related tests. The sensing technology of FBG with a cavity is analyzed theoretically and studied experimentally. After a review of the multiplexing technology of distribution sensing network, the paper proposes a quasi-distribution sensing network based on time division multiplexing (TDM) FBG, makes experimental studies and one based on spectrally coded multiplexing (SCM) FBG with a cavity. Some creative achivements have been achieved in this paper as follows. I. Investigation on sensors used for solution concentration testing based on FBGTwo kinds of sensors used for solution concentration testing are designed and fabricated with the phase shifted FBG and singlemode-multimode-FBG, and concentration sensing detection with four kinds of solutions is experimentally demonstrated. It is indicated that with the increase of resolution concentration, the phase-shifted label wavelength of the phased-shifted FBG shifts towards the long wavelength direction, and the sensor is more sensitive in the case of higher concentration. Higher order modes of the etched multimode fiber are more sensitive to the surrounding refractive index than that of the fundamental mode. Sensing detection of four kinds of solution is experimentally realized with the wavelength differences between high modes and the fundamental mode. And the higher order mode is more sensitive.II. Research on the sensing technology used FBG with a cavityThe spectral characteristics and sensing mechanism of the FBG with a cavity are investigated and simulated; Experimental Research is made on differential strain sensor system. It is shown that the differential strain sensor is more accurate in measurement with a standard error less than±18με, which is temperature insensitive. The sensing signal is demodulated by detecting component amplitude in Fourier domain, which is simple in the need of electrical demodulation equipment.Ⅲ. The application research of FBG in quasi distribution sensing network1. In order to effectively improve the capacity of grating multiplexing, proposed in the paper is a scheme of sensor network with quasi distribution FBG based on time division multiplexing (TDM) demodulation mode. The wavelength demodulation module connects one of the sensor channels in TDM mode, realizes the sensing demodulation end, using the sensing port select light link by the multiplying way to many sensing channel’s stop-go control, and demodulate the wavelengths of the FBG sensors. In the experiment system, repeat test with frequency of2.5Hz are taken based on the match FBG demodulation scheme. The multiple metering identical FBG cycle produces a demodulation precision of±0.06nm,which offered good measure stability. The results show that the scheme is feasible and prominent in extensible characteristic, which are helpful for designing high performance FBG sensor network.2. A scheme of quasi distribution FBG with a cavity sensor network based on spectrally coded multiplexing (SCM) is designed. The mechanism using SCM and the system structure of quasi distribution network are provided and experiment is also made and analyzed in the paper. The experiment results given a small error less than±8με. The demodulation system is simple in structure, in which all the sensor spectra can be overlapped. More importantly, the SCM does not take up the broadband resources, which means a substantial increase in the system’s multiplexing capacity by mixturing of SCM and wavelength division multiplexing (WDM). Due to its simplification in the signal treatment and economic feature, the sensing system is of highly practical significance and is expected to be widely used of in large-scaled quasi distribution moniting.