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.

Identification of fractional-order transfer functions using exponentially modulated signals with arbitrary excitation waveforms.

This paper proposes a new identification method based on an exponential modulation scheme for the determination of the coefficients and exponents of a fractional-order transfer function. The proposed approach has a broader scope of application compared to a previous method based on step response data, in that it allows for the use of arbitrary input signals. Moreover, it dispenses with the need for repeated simulations during the search for the best fractional exponents, which significantly reduces the computational workload involved in the identification process.

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.

Nonlinear control system for optical interferometry based on variable structure control and sliding modes.

This work presents a novel nonlinear control system designed for interferometry based on variable structure control and sliding modes. This approach can fully compensate the nonlinear behavior of the interferometer and lead to high accuracy control for large disturbances, featuring low cost, ease of implementation and high robustness, without a reset circuit (when compared with a linear control system). A deep stability analysis was accomplished and the global asymptotic stability of the system was proved.