By introducing an amplified spontaneous emission source as additional noise, two sets of experimental schemes are designed to measure noise figure characteristics of Erbium-Doped Fiber Amplifier employed in an analog optical system. The impacts of the signal power and the Signal to Noise Ratio on the Noise Figure are systematically measured. The qualitative conclusions are obtained that the decline of the input optical power and improvement of signal to noise ratio will lead a rising Noise Figure of Erbium-Doped Fiber Amplifier. These results will benefits the optimization of the analog optical amplifier by providing the proper working conditions of the Erbium-Doped Fiber Amplifier.
With the development of networking technology and optical fiber sensor network technology, the use of optical fiber system to construct a large-scale, long distance optical fiber sensing network has become a hotspot of research. Optimizing the system to reach very long sensing ranges actually requires launching high pump and probe powers into the sensing fiber to provide a sufficient signal-to-noise ratio (SNR) on the measurements at the far end of the fiber. However, increasing the input power above a critical level excites undesired nonlinear effects such as the modulation instability (MI) and the stimulated Raman scattering (SRS), which deplete the pump and reduce the maximum sensing range of the system. Compared to SRS, MI shows a lower critical power and thus determines the maximum sensing range of a fiber sensor, so MI becomes the most important factor to limit the sensing range. In order to understand the MI in the system with the DFRA, we design a lot of experiments to test which factors will affect it in the system with distributed fiber Raman amplifier (DFRA) in this paper. From the threshold expression of MI and a lot of experiments, we found that the input power, the state of polarization, the phase and so on, have a significant impact on the system. According to the result of the experiments, we can find the Raman gain affects the MI and find some useful information for suppressing the MI in the later.
A sensor system based on fiber Bragg grating (FBG) is presented which is to estimate the deflection of a lightweight flexible beam, including the tip position and the tip rotation angle. In this paper, the classical problem of the deflection of a lightweight flexible beam of linear elastic material is analysed. We present the differential equation governing the behavior of a physical system and show that this equation although straightforward in appearance, is in fact rather difficult to solve due to the presence of a non-linear term. We used epoxy glue to attach the FBG sensors to specific locations upper and lower surface of the beam in order to measure local strain measurements. A quasi-distributed FBG static strain sensor network is designed and established. The estimation results from FBG sensors are also compared to reference displacements from the ANSYS simulation results and the experimental results obtained in the laboratory in the static case. The errors of the estimation by FBG sensors are analysed for further error-correction and option-design. When the load weight is 20g, the precision is the highest, the position errors ex and ex are 0.19%, 0.14% respectively, the rotation error eθ, is 1.23%.
In this paper, a phase variation tracking method for the extrinsic Fabry-Perot interferometric (EFPI) voice sensing system is designed and experimentally demonstrated through a polarization-switched unit based on the combination of polarization-maintaining fiber Bragg grating (PMFBG). The measurements at two operation wavelengths are firstly achieved in one total-optical path, which eliminates the imbalance of optical power from the external disturbances, optical source fluctuation, different detecting response of photoelectric detector and different background noise. Two operation wavelengths reflected from a PMFBG for interference phase tracking are switched via an electro-optic modulator at a high switching speed of 10 kHz. Besides, an ellipse fitting-differential cross multiplication (EF-DCM) algorithm is proposed and illustrated for interrogating the variation of EFPI cavity gap length of the EFPI voice sensor effectively. Preliminary experimental results have proven that the polarization-switched system based on the EF-DCM algorithm could find potential applications in the fields of marine acoustic, medical science measurements, etc.
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