Displacement Measurement Based On High-order Modes

Precision measurement technology including small transverse displacement measurement, which has been widely used in many areas such as optical imaging detection, inter-satellite position stabilization, and the motion tracking of biological particles, is one of the important applications of quantum optics. With the development of technology, measurement precision (sensitivity) is increasingly demanding, while the quantum noise gradually becomes a major factor limiting the sensitivity of the measurement. In recent years, spatial nonclassical multi-mode light has been used to reduce the quantum noise, surpassing the Standard Quantum Limit.Nonclassical light can be used to reduce the quantum noise to improve the signal to noise ratio, but it is complicated to realize and is very vulnerable to losses. Recently, Studies have shown that high-order modes with more complex transverse distribution contain more information so that they can be used in precision measurement. So high-order modes are used for small displacement measurement to enhance the measurement sensitivity.Our main works are around how to improve the sensitivity of displacement measurement. The key parts of this thesis are arranged as follow:(1)Optimizing displacement measurement using spatial squeezing light. In the experiment, using degenerate optical parametric amplifier, about 2.7 dB TEM10 mode vacuum squeezed light was produced. The output the DOPA are combined into a TEM00 mode coherent beam with a beam splitter (BS) which has a 98% reflectivity to generate the spatial squeezing light. The displacement modulated spatial squeezing light is then measured by the homodyne detection system, showing that the minimum detectable displacement is reduced from 1.17 A to 0.99 A(2)Optimizing displacement measurement using high-order modes light. The sensitivity limit (Cramer-Rao bound) for spatial small displacement detection based on high-order modes laser beam as investigated, showing that the sensitivity limit for high-order mode (TEMnO mode) is (1/2)(2n+1) times that of the fundamental mode. With balanced homodyne detection, we demonstrate experimentally the displacement measurement using the TEM00 and TEM10 modes as the signal modes, respectively. The results show, compared to the TEM00 mode, a factor of 1.41 improvement in measurement sensitivity using the TEM10 mode as the signal beam. We also provide a kind of array detection scheme based on high-order modes. With the practical parameters, numerical simulation of this detection scheme proves that our detection scheme is simple and effective for laser small displacement measurement.