Current Issue : October-December Volume : 2023 Issue Number : 4 Articles : 5 Articles
Determination of the poloidal magnetic field distribution in tokamaks is of prime importance for the successful operation of tokamaks. In this paper, we propose a polarization-sensitive reflectometry-based optical fiber sensor for measuring the spatial distribution of the poloidal magnetic field in tokamaks. The measurement method exploits the Rayleigh backscattering and Faraday magneto-optic effect in optical fibers. The former is an intrinsic property of optical fibers and enables distributed polarization measurements, while the latter arises in the presence of a magnetic field parallel to the optical fiber axis and rotates the polarization state of the light. When an optical fiber is looped around a toroidal section of the vacuum vessel, the local polarization rotation of the light is proportional to the local poloidal magnetic field in the tokamak. The proposed method is discussed theoretically and experimentally using the results from JET. The obtained magnetic field measurement shows a good agreement with that of the internal discrete coils. A potential solution to recover the magnetic field data from the noise-affected region of the optical measurement is proposed and is demonstrated through simulations using the JET magnetic field configuration....
This paper presents a novel improvement in the optical path structure of a three-wavelength symmetric demodulation method applied to extrinsic Fabry–Perot interferometer (EFPI) fiber optic acoustic sensors. The traditional approach of using couplers to construct the phase difference in the symmetric demodulation method is replaced with a new approach that combines the symmetric demodulation algorithm with wavelength division multiplexing (WDM) technology. This improvement addresses the issue of a suboptimal coupler split ratio and phase difference, which can affect the accuracy and performance of the symmetric demodulation method. In an anechoic chamber test environment, the symmetric demodulation algorithm implemented with the WDM optical path structure achieved a signal-to-noise ratio (SNR) of 75.5 dB (1 kHz), a sensitivity of 1104.9 mV/Pa (1 kHz), and a linear fitting coefficient of 0.9946. In contrast, the symmetric demodulation algorithm implemented with the traditional coupler-based optical path structure achieved an SNR of 65.1 dB (1 kHz), a sensitivity of 891.75 mV/Pa (1 kHz), and a linear fitting coefficient of 0.9905. The test results clearly indicate that the improved optical path structure based on WDM technology outperforms the traditional coupler-based optical path structure in terms of sensitivity, SNR, and linearity...
Fiber laser sources operating near 2300 nm in the atmospheric transparency window are interesting for different applications, such as remote sensing, lidars, and others. The use of Tm-doped fiber lasers based on tellurite fibers is highly promising. We propose and theoretically study a highly efficient diode-pumped Tm-doped zinc-tellurite fiber laser operating at two cascade radiative transitions at 1960 nm and 2300 nm, with additional energy transfer between these laser waves due to the Raman interaction. We demonstrate numerically that a dramatic increase in the slope efficiency up to 57% for the laser wave at 2300 nm, exceeding the Stokes limit by 22% relative to the pump at 793 nm, can be obtained with optimized parameters thanks to Raman energy transfer from the laser wave at 1960 nm to the wave at 2300 nm....
Recent results of research of passive and active optical waveguides made of high-purity chalcogenide glasses for middle infrared fiberoptic evanescent wave spectroscopy of liquid and gaseous substances are presented. On the basis of selenide and telluride glass fibers, novel types of highly sensitive fiber probes are developed. On the basis of Pr(3+)- and Tb(3+)-doped Ga(In)-Ge-As- Se and Ga-Ge-Sb-Se glass fibers, the 4.2–6 μm wavelength radiation sources are created for all-fiber sensor systems. Successful testing of chalcogenide glass fiber sensors for the analysis of some liquid and gaseous mixtures was carried out....
The signal-to-noise ratio (SNR) is a crucial parameter for assessing audio transmission quality and fiber optic acoustic sensors. This study presents a model for predicting the SNR of a fiber optic F-P acoustic sensing system using the Fabry–Perot (F-P) cavity length modulation principle, considering noise and line loss in the optical path. To validate the model, we constructed an F-P acoustic sensor system and measured the SNR in a semi-anechoic room. Additionally, we used MATLAB to simulate the SNR model and compared the results with experimental data. The model accurately predicted the SNR of the fiber optic F-P acoustic sensor system. Our results offer valuable guidance and theoretical support for optimizing system performance....
Loading....