Ali Masoudi

A distributed optical fibre dynamic strain sensor based on phase-OTDR

A distributed optical fibre sensor is introduced which is capable of quantifying multiple dynamic strain perturbations along 1 km of a sensing fibre simultaneously using a standard telecommunication single-mode optical fibre. The technique is based on measuring the phase between the Rayleigh scattered light from two sections of the fibre which define the gauge length. The phase is spatially determined along the entire length of the fibre with a single pulse. This allows multiple moving strain perturbation to be tracked and quantified along the entire length of the fibre. The demonstrated setup has a spatial resolution of 2 m with a frequency range of 500-5000 Hz. The minimum detectable strain perturbation of the sensor was measured to be 80 ne.

Contributed Review: Distributed optical fibre dynamic strain sensing

Extensive research on Brillouin- and Raman-based distributed optical fibre sensors over the past two decades has resulted in the commercialization of distributed sensors capable of measuring static and quasi-static phenomena such as temperature and strain. Recently, the focus has been shifted towards developing distributed sensors for measurement of dynamic phenomena such as dynamic strain and sound waves. This article reviews the current state of the art distributed optical fibre sensors capable of quantifying dynamic vibrations. The most important aspect of Rayleigh and Brillouin scattering processes which have been used for distributed dynamic measurement are studied. The principle of the sensing techniques used to measure dynamic perturbations are analyzed followed by a case study of the most recent advances in this field. It is shown that the Rayleigh-based sensors have longer sensing range and higher frequency range, but their spatial resolution is limited to 1 m. On the other hand, the Brillouin-based sensors have shown a higher spatial resolution, but relatively lower frequency and sensing ranges.

Distributed dynamic large strain optical fiber sensor based on the detection of spontaneous Brillouin scattering

A Brillouin-based distributed optical fiber dynamic strain sensor is described which converts strain-induced Brillouin frequency shift into optical intensity variations by using an imbalanced Mach-Zhender interferometer. A 3×3 coupler is used at the output of this interferometer to permit differentiate and cross multiply demodulation. The demonstrated sensor is capable of probing dynamic strain disturbances over 2 km of sensing length every 0.5 s up to a strain of 10 mε with an accuracy of ±50 με and spatial resolution of 1.3 m.

Distributed optical fiber dynamic magnetic field sensor based on magnetostriction.

A distributed optical fiber sensor is introduced which is capable of quantifying multiple magnetic fields along a 1 km sensing fiber with a spatial resolution of 1 m. The operation of the proposed sensor is based on measuring the magnetorestrictive induced strain of a nickel wire attached to an optical fiber. The strain coupled to the optical fiber was detected by measuring the strain-induced phase variation between the backscattered Rayleigh light from two segments of the sensing fiber. A magnetic field intensity resolution of 0.3 G over a bandwidth of 50-5000 Hz was demonstrated.

High spatial resolution distributed optical fibre dynamic strain sensor with enhanced frequency and strain resolution

A distributed optical fiber dynamic strain sensor with high spatial and frequency resolution is demonstrated. The sensor, which uses the ϕ-OTDR interrogation technique, exhibited a higher sensitivity thanks to an improved optical arrangement and a new signal processing procedure. The proposed sensing system is capable of fully quantifying multiple dynamic perturbations along a 5 km long sensing fiber with a frequency and spatial resolution of 5 Hz and 50 cm, respectively. The strain resolution of the sensor was measured to be 40 nε.

Distributed optical fibre audible frequency sensor

A distributed optical fibre sensor is demonstrated which is capable of quantifying acoustic and dynamic strain disturbances along a 1km sensing fibre. A phase-OTDR technique is used to detect the dynamic perturbations using the phase-difference between the backscattered light from two separate sections of the sensing fibre. The demonstrated sensor detects multiple dynamic perturbations simultaneously within a frequency range of 200Hz to 5000Hz with a frequency resolution of 10Hz and a spatial resolution of 1m.

First Demonstration of a 2-

We report the first demonstration of an optical time domain reflectometer (OTDR) designed for the emerging wavelength band of 2 μm. A dynamic range of 30 dB with a spatial resolution of 5 m is achieved. The characterization of three different fibers using the 2-μm OTDR is described. Two solid core fibers (SMF with a cutoff at 1.7 μm and SMF 28e) have been probed to ascertain their transmission loss values, while measurements in a 19-cell hollow core photonic bandgap fiber show the presence of carbon dioxide gas in the fiber core and allow the contribution that it makes to the fiber loss to be quantified.

\mu{\rm m}

A multi-port microcoil resonator magnetic field sensor based on a microfiber coupler coil resonator (MMCR) is presented. The microfiber coupler coil is fabricated by coiling a four-port microfiber coupler with a uniform waist region around a low index support rod. The MMCR is embedded in a low refractive index polymer to increase the robustness and operation stability. The enhanced sensor response to the magnetic field is ascribed to the diverse MMCR response to the light polarization state. The MMCR magnetic field sensor is compact and low cost, and exhibits a magnetic field sensitivity of 37.09 dB/T with an estimated minimum detection limit (DL) of ∼ 27 μT.

OTDR and Its Use in Photonic Bandgap

A Distributed Vibration Sensor Based on Phase-Sensitive OTDR is numerically modeled. The advantage of modeling the building blocks of the sensor individually and combining the blocks to analyse the behavior of the sensing system is discussed. It is shown that the numerical model can accurately imitate the response of the experimental setup to dynamic perturbations a signal processing procedure similar to that used to extract the phase information from sensing setup.

{\rm CO}_{2}

Thanks to the continuous progress of Mid-Infrared (MIR) detectors, related electronics and lenses, thermal imaging has now become a standard inspection technique in numerous industrial sectors, as well as in biomedical science and defence. Fibre endoscopy is a well-developed technology and often a critical component for imaging inaccessible areas. So far, the development of a MIR version that can be applied to thermal rather than optical imaging has proved challenging. Despite its large potential scientific and industrial impact, no commercial product is yet available on the market. Several fabrication approaches have been proposed over the years, using a broad range of material combinations [1, 3]. However, the overall performance of these bundles has been so far limited in terms of either optical properties (loss, size, cross-talk, _), compactness or mechanical flexibility. Indeed, the challenge consists in combining adequate materials, adopting suitable optical design engineering and developing a manufacturing process.