Real time and adaptive Kalman filter for joint nanometric displacement estimation, parameters tracking and drift correction of EFFPI sensor systems

This paper deals with the optimization of an Extrinsic Fiber Fabry-Pérot Interferometer used for very long term (more than one year) and high precision displacement measurements by a real time and adaptive estimation procedure based on a Kalman filter. By performing a sinusoidal laser diode current modulation, a wavelength modulation is created. The Kalman filter takes into account not only the correction of the measurement drift caused by the resultant Optical Power Modulation, but also the correction of the measurement noise and temperature fluctuations. The tracking algorithm is presented, the complete system has been set up, the Kalman filter and the demodulation are programmed on an FPGA board. Experimental results give an estimation error of about 2nm for a 7000nm displacement.