Fiber Optic Sensing

Optical fibres are thin, glass cables that can be attached to or embedded in materials to measure a range of physical, mechanical and chemical changes. Our laboratory works with acoustic, deformation, and temperature measurements and monitoring using fibre optics for geo- and infrastructure applications at both field and laboratory scales. Examples of applications include active and passive seismics, ground deformation, infrastructure monitoring, and laboratory specimen strain mapping.

Field measurements

Our main expertise in field measurements includes:

• Active seismic surveys using borehole and surface fibres,

• Passive seismic monitoring in boreholes and on the surface,

• Environmental and infrastructure acoustic monitoring (structural health, intrusions, natural hazards, etc.),

• Ground deformation and temperature change monitoring

Laboratory measurements

At the laboratory scale, we are able to perform:

• Deformation measurements on small rock and synthetic material samples during mechanical and hydraulic tests,

• Fracture and failure detection and monitoring,

• Estimation of temperature gradients and changes over time.

Equipment

Our Distributed Acoustic Sensing (DAS) interrogator, ASN OptoDAS, allows interrogation of over 100 km of fibre. The minimum distance between measuring points is just above 1 m, with a gauge length (the length of fibre section used to collect data assigned to a given measuring point) of around 2 m. The maximum sampling frequency is 100 kHz. In addition to measuring active and passive seismic and acoustic signals, the DAS interrogator can also be used for deformation monitoring (“low-frequency DAS”).

Our Distributed Strain Sensing (DSS) and Distributed Temperature Sensing (DTS) interrogator, Luna ODiSI, allows interrogation of multiple fibres of up to 100 m length each simultaneously. The distance between measuring points is under 1 mm, as are the gauge lengths. The maximum sampling frequency is 250 Hz and the sensitivity of the system is at sub-micron level. In addition to deformation and temperature measurements, this interrogator can also be used for low-frequency vibration monitoring.

The combination of our interrogators, auxiliary equipment, and experience allows us to prepare and install fibres, perform measurements, and analyse the results independently.