Multiplexing configurations for optical seismometers
A number of multiplexing techniques were investigated and a system developed using low-cost optoelectronic components. A sensor was created which uses the 1300-1500nm wavelengths. The sensors operate on three axes: north-south, east-west and up-down. They have improved resolution and dynamic range, providing researchers with more accurate measurements. The signal to noise ratio was also dramatically improved between the sensors and the data loggers. The project replaced the complex mechanism of classical sensors with sophisticated electronics. All prototypes were calibrated in dedicated laboratories and tested under field conditions for the measurement of seismic activity. In order to enable a wide dynamic range, two types of sensor were created - one optical accelerometer of low resolution and the other of high resolution. A polarisation diversity receiver (PDR) was used for each of the low and high resolution sensors. This dramatically reduced polarisation signal fading. The sensors' wide dynamic range was also allowed by multiplexing the light from their laser source.
