TDM interrogation of intensity-modulated USFBGs network based on multichannel lasers

Abstract

We report a large-scale multi-channel fiber sensing network, where ultra-short FBGs (USFBGs) instead of conventional narrow-band ultra-weak FBGs are used as the sensors. In the time division multiplexing scheme of the network, each grating response is resolved as three adjacent discrete peaks. The central wavelengths of USFBGs are tracked with the differential detection, which is achieved by calculating the peak-to-peak ratio of two maximum peaks. Compared with previous large-scale hybrid multiplexing sensing networks (e.g., WDM/TDM) which typically have relatively low interrogation speed and very high complexity, the proposed system can achieve interrogation of all channel sensors through very fast and simple intensity measurements with a broad dynamic range. A proof-of-concept experiment with twenty USFBGs, at two wavelength channels, was performed and a fast static strain measurements were demonstrated, with a high average sensitivity of ~0.54dB/µƐ and wide dynamic range of over ~3000µƐ. The channel to channel switching time was 10ms and total network interrogation time was 50ms.

Recent developments in fibre optic shape sensing

“…This has limited TDM application in FOSSs. Further development of short pulse lasers, high quality weak FBGs inscription and combined techniques promises a great future for TDM application in FOSSs over next few years [75,76].…”

“…There have recently been more work on developing novel techniques to combine advantages of multiple multiplexing techniques in one combo-measurement system to enable measurement of thousands of FBGs at the same time [75,76,82]. These are, however, not in commercial stage yet.…”

Code Division Multiplexing Applied to FBG Sensing Networks: FBG Sensors Designed as Discrete Prolate Spheroidal Sequences (DPSS-FBG Sensors)

“…Finally, taking inverse Fourier transformation to work in time domain the detected photo current will be proportional to (4).…”

“…Time Domain Multiplexing (TDM) has been widely used as an alternative to this problem [3] but, in general, it compromises the acquisition rate of the system and demands high speed switching circuits, recent approaches use weak FBGs to achieve large-scale sensing systems. Weak FBG sensors should be interrogated either with TDM [4] or frequency shifted interferometry [5] approaches exhibit crosstalk limitations due to the shadowing effect between near-identical FBGs [6]. Nowadays, tailored FBG sensors can be manufactured in a routine way.…”

Dual Wavelength Differential Detection of Fiber Bragg Grating Sensors with a Pulsed DFB Laser

“…Recently, another technique to probe the state of an FBG sensor has been proposed and demonstrated [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ]. It relies on measuring the reflectivity of the grating at two, or sometimes more, fixed wavelengths, all located within the spectrum of the FBG.…”