Abstract
Nanometric
displacement measurements by Extrinsic Fiber Fabry-Perot interferometers (EFPI)
is extremely susceptible to external environmental changes. Temperature, in
particular, has a remarkable influence on the optical power and wavelength
of the laser diode in use, in addition to the thermal expansion of the mechanical
structure. In this paper we propose an optimization of the EFPI sensor in
order to use it for very long-term (more than one year) and for high-precision
displacement measurements. For this purpose, a real time and adaptive estimation
procedure based on a homodyne technique and a Kalman filter is established.
During a sinusoidal laser diode current modulation, the Kalman filter provides
a correction of the amplitude drift caused by the resultant optical power
modulation and external perturbations. Besides, stationary temperature transfer
operators are estimated via experimental measurements to reduce the additive
thermal noise induced in the optical phase and mechanical components. The tracking algorithm is presented while the complete
sensor system integrating the novel Kalman filter and the demodulation scheme
have been programmed on an FPGA board for real time processing. Short time
experimental results demonstrate an estimation error of 2 nm over a 7000 nm
sinusoidal displacement while temperature correction of long-term records
reduces errors by considerable factors (above 10).
© 2012 IEEE
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