Single-end hybrid Rayleigh Brillouin and Raman distributed fibre-optic sensing system

Backscattered lightwaves from an optical fibre are used to realise distributed fibre optic sensing (DFOS) systems for measuring various parameters. Rayleigh, Brillouin, and Raman backscattering provide different sensitivities to different measurands and have garnered the attention of researchers. A system combining the three principles above can effectively separate the measured strain and temperature completely as well as provide measurements of both dynamic and static parameters. However, the combined system is extremely complicated if the three systems are independent of each other. Hence, we propose a single-end hybrid DFOS system that uses two successive pulses to realise the Brillouin amplification of Rayleigh backscattering lightwaves for combining Rayleigh and Brillouin systems. A 3-bit pulse-coding method is employed to demodulate the Raman scattering of the two pulses to integrate Raman optical time-domain reflectometry into the hybrid system. Using this hybrid scheme, a simultaneous measurement of multiple parameters is realised, and a favourable measurement accuracy is achieved

Ultra-Long-Distance Hybrid BOTDA/Ф-OTDR

In the distributed optical fiber sensing (DOFS) domain, simultaneous measurement of vibration and temperature/strain based on Rayleigh scattering and Brillouin scattering in fiber could have wide applications. However, there are certain challenges for the case of ultra-long sensing range, including the interplay of different scattering mechanisms, the interaction of two types of sensing signals, and the competition of pump power. In this paper, a hybrid DOFS system, which can simultaneously measure temperature/strain and vibration over 150 km, is elaborately designed via integrating the Brillouin optical time-domain analyzer (BOTDA) and phase-sensitive optical time-domain reflectometry (Ф-OTDR). Distributed Raman and Brillouin amplifications, frequency division multiplexing (FDM), wavelength division multiplexing (WDM), and time division multiplexing (TDM) are delicately fused to accommodate ultra-long-distance BOTDA and Ф-OTDR. Consequently, the sensing range of the hybrid system is 150.62 km, and the spatial resolution of BOTDA and Ф-OTDR are 9 m and 30 m, respectively. The measurement uncertainty of the BOTDA is ± 0.82 MHz. To the best of our knowledge, this is the first time that such hybrid DOFS is realized with a hundred-kilometer length scale

Time Localization of Abrupt Changes in Cutting Process using Hilbert Huang Transform

Cutting process is extremely dynamical process influenced by different phenomena such as chip formation, dynamical responses and condition of machining system elements. Different phenomena in cutting zone have signatures in different frequency bands in signal acquired during process monitoring. The time localization of signal’s frequency content is very important. An emerging technique for simultaneous analysis of the signal in time and frequency domain that can be used for time localization of frequency is Hilbert Huang Transform (HHT). It is based on empirical mode decomposition (EMD) of the signal into intrinsic mode functions (IMFs) as simple oscillatory modes. IMFs obtained using EMD can be processed using Hilbert Transform and instantaneous frequency of the signal can be computed. This paper gives a methodology for time localization of cutting process stop during intermittent turning. Cutting process stop leads to abrupt changes in acquired signal correlated to certain frequency band. The frequency band related to abrupt changes is localized in time using HHT. The potentials and limitations of HHT application in machining process monitoring are shown