Fiber optics sensors. J. Dubard. Laboratoire commun de métrologie LNE-CNAM

Transcription

1 Fiber optics sensors J. Dubard Laboratoire commun de métrologie LNE-CNAM

2 Outline Introduction Sensor metrology needs Biosensor Current sensor Temperature sensor Conclusion 2

3 Introduction Fiber optics sensors Many applications: building and structure monitoring, temperature control, leak or crack detection, biology, Based on optical fiber or fiber optics components characteristics Raman scattering (temp), Brillouin scattering (strain) Fiber Bragg grating based sensor Ring resonator 3

4 Metrology needs Traceability for accurate measurement of the measurand: Length: displacement, stress, Mass, force Temperature, Electricity: current, magnetic field Sensing based on optical characteristics of fiber or fiber components. Need for measurement techniques to: Evaluate the optical characteristics and their responsivity Define the proper measurement technique to discriminate multiple contributions 4

5 Biosensor Polymer based ring resonator Bus waveguide Horizontally or vertically coupled ring waveguide Microfluidic circuit for bio sensing Change of refractive index Needs high quality factor for high sensitivity 5

6 Biosensor Optical Low Coherence Interferometry Set-up developped for optical fiber and fiber optics componants characterisation in reflexion mode Two interferometers with common movable mirror: amplitude, phase, TE and TM polarization 6

7 Biosensor Fourier transform applied to the interferogram Amplitude (resonant wavelength) Phase (group delay) 7

8 Biosensor Measurement of NaCl concentration Sensitivity 15 ± 5 µg/ml (from group delay measurement) 8

9 Current sensor EMRP «Future Grids» project: development of a Fiber Optics Current Sensor FOCS Faraday effect: rotation of the polarization of a linearly polarized beam in a fiber under a colinear magnetic field V: Verdet constant V whenλ 9

10 Current sensor Analyser is rotated to reach minimum transmission without and with magnetic field 10

11 Current sensor LoBi single mode silica optical fiber with 7 mm spin pitch (University of Southampton) Working wavelength: 633 nm Magnetic field: 10 cm long homogenious field from 0 to 8 mt directed along the fiber Verdet constant: 3.97 rad/(t.m) 11

12 Distributed Temperature Sensing Raman Scattering 3 vibrationnal states of H 2 O : Inelastic collision (Excitating photon Vs. Crystal lattice) Energetic transition between two vibrationnal states of the lattice Emission of a Stokes radiation : most probable case (i.e Bose-Einstein distribution) Emission of an Anti-Stokes radiation : less probable, depending of the temperature Intensity The ratio of Stokes & Anti-Stokes intensities is dependant with the temperature Energy level Virtual energy levels Vibrationnal states 12 12

13 Distributed Temperature Sensing Application to the optical fibres Technologies based on the Optical Time Domain Reflectometry (OTDR) The optical fibre is the sensitive element Multimode optical fibres used as sensors (Telecom. standard) Fibres interrogated by nano-second pulsed laser (typically 1064 nm) Continuous measurement along the whole length of the optical fibre Absolute spatial resolution (sampling resolution) of 1 m Measurement range : 0 30 km Cladding (dia. 125 µm) Core (dia. 50 µm) Typical operating range : C (depending of the optical fibre intrinsic properties) Acrylate coating (dia. 250 µm) Interrogator Laser pulse (pump) Sensing optical fibre Pulsed laser source Detection Signal processing Backscattered light Display / Data file Sampling resolution Temperature Measured temperature profile Distance 13 13

14 Implementation of a Raman-DTS 6 km of wound MM. optical fibre Thermal enclosure (23 C) Temp. homogeneity within 0.05 C Temp. stability within 0.02 C over 5 h Temperature, C Distance over the optical fibre, m Trueness error observed (22 C Vs. 23 C) Signal-to-noise ratio breackdown Vs. Distance Due to the optical fibre attenuating factor Temperature resolution impacted Calibration procedure needed Linearity of detector Jitter characterization 14 14

15 Conclusion Many type of sensors for many applications Need Radiometry-Photometry metrology for measurement techniques Evaluate the optical characteristics and their responsivity Define the proper measurement technique to discriminate multiple contributions 15