A digital seismic measuring chain is an electromechanical system able to record the lowest natural ground motions
observable on Earth but also to measure signals from largest earthquakes. Its cornerstones are an inertial seismometer
and a digitizer. As equipments available on the market don't answer to all seismological applications CEA/DAM/DIF
(Commissariat a l'Energie Atomique/Direction des Applications Militaires/ Ile De France) is interested in, it has
developed the adequate digital seismic measuring chains. Today, the technologies used have reached their maturity. New
sensing techniques need to be developed.
Optical sensors are now widely used in vibrometry and motion measurements. Such devices generally use interferometry
and frange interpolation to achieve high resolution with a large dynamic range. We have developed macroscopic
prototype digital motion transducer from a Michelson interferometer in order to evaluate the potential of this technology
for seismological applications.
First, tests were carried out to validate the operation of these transducers and to estimate their main characteristics for
seismological applications. We focused on transducer motion range, intrinsic noise and temperature sensitivity.
We have evaluated and compared performances of such interferometers in visible (632 nm) and in infrared (1550 nm)
range. Then, we have experimentally evaluated noise sources in displacement measurement. Last, we designed
Michelson interferometer with integrated optics component with a company which is specialized in integrated optics.
Expected results are presented in this document.