Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Report on the investigation of low cost multiplexing configurations for the optical seismometers, for field deployment

Several possible multiplexing techniques that could be used for this project have been explored. Since the final versions of the sensors are based on interferometric transducers then either time division or spatial multiplexing can be used. Initially, we tested a basic multiplexing topology for interferometric sensors multiplexed in time. This scheme would have had the benefit of a single photodetector and demodulator. This would have required sequential reading and fast electronics and pulsed laser. Acquisition of a fast-pulsed laser and pulsed electronics could not be accommodated, therefore such a solution was abandoned.

We also evaluated a transduction mechanism based on FBG. Then spatial division is most effective as an expensive WDM is not required and all the FBGs can be at the same wavelength. We implemented this design in the sensor presented within the result "Prototype of an optical sensor for structural dynamic and also quasi-static behaviour of buildings, to be used inside (based on FBGs)". But for tri-axial seismic sensing, our system evolved towards using Michelson interferometers and not FBG. Because we do not have a large number of sensors, a different configuration was adopted with shared path for the phase modulation and individual reading of each sensor. The system can take advantage of the low cost optoelectronic components for telecommunication wavelengths, 1300-1500 nm, now commonly available. The configuration used is that presented within the result "Report on the most suitable configuration of the optical seismometers along with dedicated instrumentation and software". This has allowed us to complete a triaxial sensor.

Reported by

CT2 7NH Canterbury
United Kingdom
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