All digital sliding mode observer of a feedback-free interferometer for high dynamic range detection.

A passive interferometry phase detection method is presented, which emulates the closed-loop high gain approach technique. This method comprises an all-digital closed-loop observer based on the variable structure and sliding modes nonlinear control theory, able to demodulate the phase of an open-loop feedback-free interferometer hardware. A proof-of-concept experiment is conducted by measuring complex displacements (module and angle) generated by a piezoelectric actuator.

Characterization of a thin-film metal-coated fiber optical phase modulator based on thermal effect with a nonlinear control interferometer.

In this work, an optical fiber was coated by a thin-film metal layer to work as a fiber optical phase modulator based on thermal effect. This device was assembled in one of the arms of an all-fiber Michelson interferometer stabilized by a nonlinear control system based on variable structure and sliding modes. The frequency response reached 200 Hz, which can be considered high for a device based on the thermal effect.

Wide dynamic range quadrature interferometer with high-gain approach and sliding mode control.

The present work concerns with the modeling, development and application of a novel control strategy based on sliding mode control, for two beam quadrature interferometers, with the high-gain approach. In this case, by reading the control signal the demodulation process does not require phase unwrapping algorithms, i.e.