Luc Thévenaz

Humidity-insensitive optical fibers for distributed sensing applications

Tiago Filipe Pimentel Das Neves, Luc Thévenaz

Humidity is a critical environmental factor in various applications, and its temperature dependence must be considered when developing thermo-hygrometer fiber sensors. The optical fibers that constitute the sensor must have a temperature reference, which should be resistant to humidity to avoid cross-sensitivities. This paper presents two innovative optical fibers insensitive to humidity over temperatures ranging from −20∘C to 55°C. To the best of our knowledge, the novel standard size optical fibers coated with acrylate and silicone are tested under controlled conditions using an optical time-domain reflectometer sensor based on Rayleigh scattering. The sensor achieves meter-range resolution over kilometers of length with a response time of few minutes.

2023

New Sensing Technologies for Monitoring Machinery, Structures, and Manufacturing Processes

Yi Huang, Luc Thévenaz

Sensing is the fundamental technique for sensor data acquisition in monitoring the operation condition of the machinery, structures and manufacturing processes. In this paper, we briefly discuss the general idea and advances of various new sensing technologies, including multi-physics sensing, smart materials and metamaterials sensing, microwave sensing, fibre optic sensors, and terahertz sensing, for measuring vibration, deformation, strain, acoustics, temperature, spectroscopic, etc. Based on the observations from the state of the art, we provide comprehensive discussions on the possible opportunities and challenges of these new sensing technologies so as to steer the future development.

2023

Spun fibres: a quasi circularly birefringent medium

Ana Gabriela Correa Mena, Luc Thévenaz

A simplified model describing the polarisation characteristics of spun fibres is proposed, aiming at determining how close to a circularly birefringent medium such a fibre is. This is of crucial importance regarding the interest of such a medium for magneto-optic sensing using optical fibres, mostly exploited in fibre optics current sensors (FOCS). The spun fibre is modelled as a stack of thin linearly birefringent plates, each experiencing a slight incremental rotation. The eigenvalues and eigenvectors of the full stack of plates are determined, enabling us to assess how far a given spun fibre is from an ideal circularly birefringent medium for any spinning rate and linear birefringence. Experimental validation is carried out to compare the model results with real fibres.

SPIE2023

Study on the possibility of Φ-OTDR sensing in hollow-core fibres

Malak Mohamed Hossameldeen Omar Mohamed Galal, Luc Thévenaz, Yuting Yang

The backscattering process in hollow core fibres shows a large similarity with Rayleigh scattering, offering the potential to be exploited for distributed sensing. A classical Φ-OTDR implementation is used to observe the backscattering signal from the surface roughness at the silica-air interface in hollow-core photonic bandgap fibres. In contrast with standard single mode silica-core fibres, the hollow core photonic bandgap fibre shows a chaotic response when the temperature is slightly changed, but stable results under strictly constant temperature conditions. Another temperature-dependent effect is highly perturbing the coherent scattering response, and it is believed that higher-order guided modes cause detrimental interferences totally jamming the response. By using single-mode hollow core fibres it should be in principle possible to obtain the relevant temperature measurement pattern, though as anticipated the extreme weakness of the signal certainly represents an insurmountable challenge.

SPIE2023

Closed-loop technique based on gain balancing for real-time Brillouin optical time-domain analysis

Ana Gabriela Correa Mena, Luc Thévenaz, Zhisheng Yang, Li Zhang

A closed-loop servo control based on balancing the gain of two probing frequencies is proposed for real-time Brillouin optical time-domain analysis (BOTDA) without post-processing. With the most basic BOTDA hardware setup, the system can perform measurement in 150 ms and track a sudden Brillouin frequency shift (BFS) change in excess of 300 MHz (corresponding to a temperature change of more than 250°C) over ∼5 km of fiber with a spatial resolution of 2 m. Moreover, the feedback loop is independent of the loss experienced by the probe and pump, with no requirement on the BFS uniformity along the fiber. All these advantages make the proposed system suitable for field applications in harsh environments.

2022

Distributed Fibre Optic Thermo-hygrometer for Monitoring the Concrete Curing

Kenny Hey Tow, Tiago Filipe Pimentel Das Neves, Luc Thévenaz

The moisture content in concrete is a critical parameter for most of the degradation processes such as shrinkage and cracking. In this paper, we present the first kilometre-range thermo-hygrometer for monitoring the concrete curing.

Optica Publishing Group2022

Distributed measurement of mode group effective refractive index difference in a few mode optical fibers

Alejandro Dominguez Lopez, Luc Thévenaz, Zhisheng Yang

The possibility to perform distributed measurements of the effective refractive index difference between distinct modes in few mode optical fibers is demonstrated using phase sensitive optical time domain reflectometry. Effective refractive index differences between LP02, LP21a and LP21b modes are measured with for a spatial resolution of 24m.

2022

Distributed Temperature Sensing Using Gas-filled Conjoined-tube Anti-resonant Fiber

Malak Mohamed Hossameldeen Omar Mohamed Galal, Luc Thévenaz, Li Zhang

Distributed temperature measurement is conducted for the first time in a gas-filled conjoined-tube hollow-core anti-resonant fiber (HC-CAF) at a pressure of 34.7 bar. A Brillouin gain of 0.08 m−1W−1 and a temperature sensitivity of 2 MHz/K are yielded.

Optica Publishing Group2022

Luc Thévenaz

Humidity-insensitive optical fibers for distributed sensing applications

New Sensing Technologies for Monitoring Machinery, Structures, and Manufacturing Processes

Spun fibres: a quasi circularly birefringent medium

Study on the possibility of Φ-OTDR sensing in hollow-core fibres

Analytical prediction of the final error due to noise in a ϕ-OTDR system

Closed-loop technique based on gain balancing for real-time Brillouin optical time-domain analysis

Distributed Fibre Optic Thermo-hygrometer for Monitoring the Concrete Curing

Distributed measurement of mode group effective refractive index difference in a few mode optical fibers

Distributed Temperature Sensing Using Gas-filled Conjoined-tube Anti-resonant Fiber

Closed-loop technique based on gain balancing for real-time Brillouin optical time-domain analysis

Study on the possibility of Φ-OTDR sensing in hollow-core fibres

Humidity-insensitive optical fibers for distributed sensing applications

Spun fibres: a quasi circularly birefringent medium

New Sensing Technologies for Monitoring Machinery, Structures, and Manufacturing Processes

Analytical prediction of the final error due to noise in a ϕ-OTDR system

Distributed Fibre Optic Thermo-hygrometer for Monitoring the Concrete Curing

Distributed measurement of mode group effective refractive index difference in a few mode optical fibers

Distributed Temperature Sensing Using Gas-filled Conjoined-tube Anti-resonant Fiber