We present a novel amplified space-time coding technique which combines cyclic-Simplex and Simplex binary codes to overcome the main limitations of conventional coding for OTDR based ultra-long distance distributed temperature sensing applications. The decoding process is performed in two successive steps, addressing the main issue related to the computational complexity of conventional codes, which increases quadratically with the code lenght, seriously affecting their performance when dealing with extremely long code-words. A link control technique is also proposed to suppress gain transients induced by the EDFA dynamics, avoiding performance degradation due to nonlinear effects and codewords distortion. The proposed scheme provides significant coding gain enhancement and stable operations below the stimulated Raman scattering threshold, pushing the performance of Raman based distributed temperature sensors close to their physical limit using commercial off-the-shelf components.
In this paper we present an overview of the current efforts towards integration of Fiber Bragg Grating (FBG) sensor interrogators. Different photonic integration platforms will be discussed, including monolithic planar lightwave circuit technology, silicon on insulator (SOI), indium phosphide (InP) and gallium arsenide (GaAs) material platforms. Also various possible techniques for wavelength metering and methods for FBG multiplexing will be discussed and compared in terms of resolution, dynamic performance, multiplexing capabilities and reliability. The use of linear filters, array waveguide gratings (AWG) as multiple linear filters and AWG based centroid signal processing techniques will be addressed as well as interrogation techniques based on tunable micro-ring resonators and Mach-Zehnder interferometers (MZI) for phase sensitive detection. The paper will also discuss the challenges and perspectives of photonic integration to address the increasing requirements of several industrial applications.
We experimentally demonstrate the feasibility of Fiber Bragg Grating sensors interrogation using integrated unbalanced Mach-Zehnder Interferometers (MZI) and phase sensitive detection in silicon-on-insulator (SOI) platform. The Phase- Generated Carrier (PGC) demodulation technique is used to detect phase changes, avoiding signal fading. Signal processing allows us to extract the wavelength shift from the signal patterns, allowing accurate dynamic FBG interrogation. High resolution and low cost chips with multiple interrogators and photodetectors on board can be realized by exploiting the advantages of large scale fabrication capabilities of well-established silicon based industrial infrastructures. Simultaneous dynamic reading of a large number of FBG sensors can lead to large volume market applications of the technology in several strategic industrial fields. The performance of the proposed integrated FBG interrogator is validated by comparing with a commercial FBG readout based on a spectrometer and used as a reference.
In this paper we present a validation of distributed Raman temperature sensing (RDTS) at the CERN high energy accelerator mixed field radiation test facility (CHARM), newly developed in order to qualify electronics for the challenging radiation environment of accelerators and connected high energy physics experiments. By investigating the effect of wavelength dependent radiation induced absorption (RIA) on the Raman Stokes and anti-Stokes light components in radiation tolerant Ge-doped multi-mode (MM) graded-index optical fibers, we demonstrate that Raman DTS used in loop configuration is robust to harsh environments in which the fiber is exposed to a mixed radiation field. The temperature profiles measured on commercial Ge-doped optical fibers is fully reliable and therefore, can be used to correct the RIA temperature dependence in distributed radiation sensing systems based on P-doped optical fibers.
In this paper, we experimentally demonstrate a hybrid distributed acoustic and temperature sensor (DATS) based on
Raman and coherent Rayleigh scattering processes in a standard singlemode fiber. A single commercial off-the-shelf
DFB laser and a common receiver block are used to implement a highly integrated hybrid sensor system with key
industrial applications. Distributed acoustic sensing and Raman temperature measurement are simultaneously performed
by exploiting cyclic Simplex pulse coding in a phase-sensitive OTDR and in Raman DTS using direct detection. Suitable
control and modulation of the DFB laser ensures inter-pulse incoherence and intra-pulse coherence, enabling accurate
long-distance measurement of vibrations and temperature with minimal post-processing.
We propose and experimentally demonstrate the feasibility of a highly efficient FBG-based quasi-distributed sensing system employing dual-wavelength cyclic pulse coding. Significant improvement in the measurement range, resolution and TDM multiplexing capabilities can be achieved, as well as crosstalk reduction with respect to a single wavelength TDM-based FBG interrogation scheme. The mechanism of noise reduction by quasi-periodic cyclic coding is experimentally demonstrated, pointing out significant improvement in accuracy with respect to dual-wavelength single pulse TDM-based FBG interrogation. The proposed technique can also enhance the sensing range of hybrid fiber optic sensor systems in which continuous monitoring of distributed and discrete points are simultaneously measured over the same sensing fiber.
In this paper we perform field validation of distributed Raman temperature sensing (RDTS) for oil leakage detection in soil. The capability of the distributed Raman sensor in detecting and locating, with high accuracy and spatial resolution, drop leakages in soil is demonstrated through a water leakage simulation in a field trial. The future trends and the high potential of the Raman DTS technology for oil and gas leakage detection in long pipelines is then outlined in this paper by reporting lab experiments demonstrating accurate meter scale temperature measurement over more than 50 km of standard single mode fiber. The proposed solution, based on distributed Simplex coding techniques, can be competitive in terms of cost and performance with respect to other distributed sensing technologies.
We propose and experimentally demonstrate a fully hybrid distributed sensing scheme that uses a single narrow-band laser to perform fast measurement of the BFS using BOTDA and simultaneous temperature measurement based on spontaneous Raman scattering over 10 km of single mode fiber. The use of cyclic pulse coding effectively reduces the pump peak power levels required for accurate Raman-based distributed temperature measurement, enhancing at the same time the speed of the BFS measurement in the BOTDA technique.
We propose and experimentally demonstrate a hybrid fiber optic sensing technique that effectively combines Brillouin
optical time-domain analysis and a time-domain multiplexing interrogation technique for Fiber Bragg Gratings (FBGs).
The highly-integrated proposed scheme employs broadband apodized low-reflectivity FBGs with a single optical source
and a shared receiver block, allowing for simultaneous measurements of distributed static and discrete dynamic
temperature and strain, over the same sensing fiber.
In this paper we demonstrate distributed Raman temperature sensing (RDTS) in a loop scheme employing anti-Stokes
light intensity only. Using a single-channel receiver and anti-Stokes traces measured in loop configuration, we
implement RDTS with inherent compensation of fiber wavelength-dependent losses, as well as local external
perturbations. Experimental results show a signal-to-noise ratio enhancement with respect to a standard RDTS in loop
configuration, providing a robust and reliable high-performance sensor for long sensing ranges.
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