Andre Tardy

DISTRIBUTED TEMPERATURE SENSOR USING HOLMIUM-DOPED OPTICAL FIBER AND SPREAD-SPECTRUM TECHNIQUES

This paper describes the feasibility analysis of using Holmium‐doped single‐mode fiber and spread‐spectrum techniques to monitor a temperature distribution in the cryogenic range. An optimized holmium‐doped fiber was realized and thermally characterized. For probing the sensitive fiber we realized an optical time domain reflectometer using pseudorandom sequences to improve the dynamic range at the operating wavelength and to obtain both rapid response time and high spatial resolution. The system, tested over a fiber length of 240 m, provides temperature dependent fiber attenuation measurements in good agreement with the transmission results. With a 10 MHz pseudorandom binary sequence the system detects changes of 24 °C with a spatial resolution of 30 m.

Multipoint Fibre Optic Refractive Index Sensors

We propose a multisensor network where the refractive index modulators are distributed in cascade along the optical fibre. Reflections at fibre glass-monitoring medium interfaces provide a train of time multiplexed pulses. Backscattered radiation in the fibre serves as a reference channel for the individual sensors which can be designed for temperature, pressure, chemical composition measurements.

Réflectomètre à haute résolution

RésuméCet article présente les performances d’un appareil de mesure, par rétrodiffusion optique résolue dans le temps, de fibres unimodales à 1,3 μm et 1,55 μm. L’appareil, portable, permet de détecter avec une résolution voisine de 1 m, un défaut ou une cassure jusqu’à 1,5 km de fibre ; la distance minimale de discrimination entre deux défauts consécutifs (soudures, microcourbures) étant comprise entre 3 et 4 m.AbstractMeasurement capabilities of a single mode optical time domain reflectometer (Otdr) are given. Fault location accuracy is 1 m (when the group index of refraction is known) and spatial resolution is 3 m.