Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Report on the most suitable configuration of the optical seismometers along with dedicated instrumentation and software

The problem to address was to devise sensors with a large dynamic range and according to principles of operation, which allow multiplexing.

To address the wide dynamic range required, two types of sensors have been devised, a low resolution one and another with high resolution (as already explained in the 3rd result summary -"Tri-axial versions of a low resolution and a high resolution optical accelerometer, based on Michelson interferometers").

Demultiplexing was implemented in Electronics, however a multiplexing optical configuration was employed to deliver the laser output.

For each high resolution sensor, a polarization diversity receiver is used, PDR (which drastically reduce the polarization-induced signal fading), which consists in 3 linear polarizers aligned at 120 degrees in respect with each-other, and 3 photodiodes PDs. The three signals are then amplified by a factor, which is the same for each PDR belonging to a given sensor, in a Gain Control block (part of the analog/digital interface). Then each output is processed in a demodulator block, of which there are 12 (also in the interface).

A single frequency pigtailed laser at a wavelength of 1.5 microns is used to drive all measuring system.

A Mach Zehnder in-fibre interferometer (MZI) is used as the generating interferometer, where each sensor will act as a receiving interferometer. Phase modulation in MZI will translate in intensity modulation of the signal received from the sensors. The phase variation of each sensor is composed from two parts, the sensing part due to the environmental factors and the phase carrier from the MZI.

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CT2 7NH Canterbury
United Kingdom
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