This paper proposes a new modulation scheme using high-order harmonic information to solve the so-called ambiguity problem of interferometry. To start with, we build a fiber Fabry-Perot interferometer to serve as a displacement sensor, which has two operation modes - coarse and fine modes. Integrating the afore-developed sensor, a piezoelectric actuator, and a scheduled proportional-integral/adaptive-sliding controller, we construct a dual-stage nanopositioning system. The experimental results show that the proposed system has the capability to extend the positioning range beyond the limit of the wavelength while keeping the naturally high resolution, ±5 nm, of interferometry.
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