Mr. Longtao Yang Profile

Longtao Yang

at Guilin Univ of Electronic Technology

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Publications (3)

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Proceedings Article | 1 November 2021 Paper

Mode-conversion in few-mode fibers based on PC-FWM

Longtao Yang, Jiamin Li, Cong Chen, Zhenhua Xu, Zujun Qin, Jianyuan Li

Proceedings Volume 12057, 120572C (2021) https://doi.org/10.1117/12.2605857

KEYWORDS: Optical fibers, Phase matching, Signal processing, Refractive index, Phase conjugation

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Four-wave mixing (FWM) in few-mode fibers (FMFs) has been extensively investigated to develop mode-related alloptical signal processing, such as wavelength conversion, parametric amplification and mode conversion. Compared to the FWM processes in single-mode fibers, intermodal FWM in FMFs shows more flexible phase-matching condition by tailoring the modal dispersion of each optical mode. Generally, there are two mainly different types of FWM processes, namely, Bragg scattering (BS) and phase conjugation (PC). In this paper, we focus our interest on the PC-FWM in both graded-index (GI) and step-index (SI) FMFs to probe mode conversion. In the PC-FWM, the energy transfers from pump modes to both signal and idler waves. From the point of phase matching, the modal dispersions of the two FMFs is firstly optimized by genetic algorithm (GA) to design optimal core radius and core-cladding refractive difference. We then investigate the effect of the small deviations of these two parameters from their optimal values upon the phase mismatch. Numerical results show that both SI and GI fibers are able to convert the LP₀₁ mode to the LP₀₂ mode with the phase matching condition of the SI fiber being more sensitive to the changes of fiber parameters. In addition, we analyze the dependence of mode conversion performance (bandwidth and efficiency) on fiber length and pump level. It is shown that the 3dB-bandwidth increases with the pump power in the PC-FWM, which can be attributed to the nonlinear phase shift induced by the high pump power compensate for the linear phase mismatch.

Proceedings Article | 28 February 2021 Paper

φ-OTDR vibration detection based on dual-channel sensing of a two-mode fiber

Longtao Yang, Jiangjiang Gao, Zujun Qin

Proceedings Volume 11781, 117810H (2021) https://doi.org/10.1117/12.2591333

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Generally, phase-sensitive optical time-domain reflectometer (φ-OTDR) adopts a single-channel sensing structure, which makes it vulnerable to random interferences and increases the probability of vibration misjudgment in practical applications. In this paper, a dual-channel φ-OTDR based on a two-mode fiber (LP₀₁ mode and LP₁₁ mode) is constructed, and a simple demodulation algorithm is designed accordingly to locate pencil-break vibrations. The purpose of using dual-channel scheme is that the probability of false detection, simultaneously happened in double channels at the same position and at the same time, would be greatly reduced. In signal processing, both the conventional amplitude differential accumulation algorithm (DAA) and the standard variance algorithm (SVA) are employed to process the Rayleigh scattering traces of LP₀₁ and LP₁₁ channels to detect the pencil-break. The results show that the DAA is highly dependent on the parameters of the algorithm and not suitable to be directly used in practical. Due to the strong randomness of Rayleigh scattering, it is found that the pencil break cannot be detected just by the SVA. Thus, a simple method of producing two decision signals is proposed for vibration detection by combining the DAA and SVA, in which the DAA signals of one channel are crossmultiplied with the SVA signals in another channel. The results show that this method shows reliable performance of locating the pencil-break.

Proceedings Article | 8 January 2021 Paper

Identifying vehicle vibrations on a highway based on multipath information fusion in φ-OTDR systems

Jiangjiang Gao, Zujun Qin, Longtao Yang, Cong Chen, Feng Hu, Wangchun Zhu, Wentao Zhang, Xianming Xiong

Proceedings Volume 11607, 1160703 (2021) https://doi.org/10.1117/12.2583550

Read Abstract +

In practical application, it is found that single-path phase-sensitive optical time-domain reflectometers (φ-OTDR) is susceptible to noise and random interference, which increases the probability of missing detection over external perturbations by conventional amplitude demodulation. In the work, a dual-channel system based on two fibers extracted from an armored four-core cable is investigated to enhance the robustness of the φ-OTDR. In signal demodulation, by combining the conventional differential accumulation algorithm (DAA) and standard deviation algorithm (SVA) a multipath information fusion algorithm (MIFA) is accordingly proposed to conclude whether the vibration signal is present. The MIFA-based dual-channel φ-OTDR is experimentally demonstrated on a highway of 9 km to position a running vehicle, indicating a considerable performance improvement of vibration identification compared to the DAA and SVA.

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