Current Issue : January - March Volume : 2018 Issue Number : 1 Articles : 5 Articles
In this work, a linear birefringence measurement method is proposed for an optical fiber\ncurrent sensor (OFCS). First, the optical configuration of the measurement system is presented.\nThen, the elimination method of the effect of the azimuth angles between the sensing fiber and the\ntwo polarizers is demonstrated. Moreover, the relationship of the linear birefringence, the Faraday\nrotation angle and the final output is determined. On these bases, the multi-valued problem on\nthe linear birefringence is simulated and its solution is illustrated when the linear birefringence is\nunknown. Finally, the experiments are conducted to prove the feasibility of the proposed method.\nWhen the numbers of turns of the sensing fiber in the OFCS are about 15, 19, 23, 27, 31, 35, and 39,\nthe measured linear birefringence obtained by the proposed method are about 1.3577, 1.8425, 2.0983,\n2.5914, 2.7891, 3.2003 and 3.5198 rad. Two typical methods provide the references for the proposed\nmethod. The proposed method is proven to be suitable for the linear birefringence measurement in\nthe full range without the limitation that the linear birefringence must be smaller than Ãâ?¬/2....
To help reduce the impact of geo-hazards, an innovative landslide early-warning\ntechnology based on an energy demodulation-based fiber optic sensing (FOS-LWfor short) technology,\nis introduced in this paper. FOS-LW measures the energy change in a sensing fiber at the segment of\nmicro-bending, which can be caused by landslide movements, and automatically raises an alarm as\nsoon as the measured signal intensity in the fiber reaches a pre-set threshold. Based on the sensing\nof micro-bending losses in the fiber optics, a two-event sensing algorithm has been developed for\nthe landslide early-warning. The feasibility of the FOS-LW technology is verified through laboratory\nsimulation and field tests. The result shows that FOS-LW has some unique featuresââ?¬â?such as\nthe graded alarm, real-time responses, remote monitoring, low cost and passive optical networkââ?¬â?and\ncan be applied in the early-warning of landslides....
Speckle noise, dynamic range of light intensity, and spurious reflections are major challenges when laser scanners are used for\n3D surface acquisition. In this work, a series of image processing operations, that is, Spatial Compound Imaging, High Dynamic\nRange Extension, Gray Level Transformation, and Most Similar Nearest Neighbor are proposed to overcome the challenges coming\nfrom the target surface. A prototype scanner for metallic surfaces is designed to explore combinations of these image processing\noperations.Themain goal is to find the combination of operations thatwill lead to the highest possible robustness and measurement\nprecision at the lowest possible computational load. Inspection of metallic tools where the surface of its edge must be measured at\nmicrometer precision is our test case. Precision of heightsmeasured without using the proposed image processing is firstly analyzed\nto be �±7.6 ...
We propose a novel denoising method based on empirical mode decomposition (EMD) to\nimprove the signal-to-noise ratio (SNR) for vibration sensing in phase-sensitive optical time domain\nreflectometry (Ãâ? -OTDR) systems. Raw Rayleigh backscattering traces are decomposed into a series of\nintrinsic mode functions (IMFs) and a residual component using an EMD algorithm. High frequency\nnoise is eliminated by removing several IMFs at the position without vibration selected by the Pearson\ncorrelation coefficient (PCC). When the pulse width is 50 ns, the SNR of location information for the\nvibration events of 100 Hz and 1.2 kHz is increased to as high as 42.52 dB and 39.58 dB, respectively,\nwith a 2 kmsensing fiber, which demonstrates the excellent performance of this new method....
An arbitrary pulse shape by compensating gain saturation in a solid-state Master oscillator\npower amplifier (MOPA) system made up of three Neodymium doped yttrium vanadate (Nd:YVO4)\namplifiers is demonstrated. By investigating the amplifier dynamics in detail, car-shaped pulse shapes\nwere obtained with compensated pulse distortion. Desired pulse shapes, such as multiple-step, square,\nparabolic, and Gaussian pulses, were achieved, with a high peak power level of 41.6 kW and a narrow\nlinewidth less than 0.06 nm. In addition, through second harmonic generation (SHG), a green laser\nwith different pulse shapes was obtained, with a maximum conversion efficiency of 42.6%....
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