This paper describes a new single-component optical geophone. The oscillator system in this geophone is based on the mass spring, and the readout system is based on the moiré technique.
A moiré pattern is formed due to superimposing of the two gratings structures. We used two similar overlaid grids at a small angle, one of them is fixed to the frame of the sensor, and the other one is attached to the suspended mass. Moiré pattern is illuminated with a laser diode. The laser beam passes through the moiré pattern and a narrow slit and hits on a light detector. Due to moving the oscillatory mass and the fringes movements, the light intensity on the detector varies and is recorded as voltage. The obtained data is digitized and recorded by using a 16-bit ADC converter. Comparisons with conventional geophone show that, in terms of both noise and signal fidelity, the optical approach is quite viable. Our geophone was found to be compatible with the reference geophone.