Optical Interference Signal Processing in Precision Dimension Measurement

In this chapter, transient response of synchronous machines connected to stiff network is analyzed and discussed. Analysis of transients in electrical and mechanical subsystems of synchronous machines is relatively complex due to a relatively large number of state variables, such as the rotor position and speed, and the winding currents and flux linkages. Complexity of mathematical model does not help the process of understanding the nature of transients and hinders deriving corresponding conclusions. The analysis can be simplified by introducing the assumption that transients in electrical subsystem decay considerably faster than those of mechanical subsystem. In this way, analysis of transients in mechanical subsystem can be performed by using steady state model of electrical subsystem. In this way, results are made more legible and intuitive.

To simplify the model of DGIG and improve the robustness, the variable speed and constant frequency (VSCF) DFIG wind power generation systems from the perspective of energy and robustness were studied. It was based on passivity and sliding mode control (SMC) theory. Firstly, the model of DFIG based on Euler-Lagrange (EL) equations was established, so the original DFIG wind turbine system is divided into electrical and mechanical subsystems. For two subsystems, the electrical subsystem was designed. In contrast, the mechanical subsystem is an energy-consuming system and is stable through selecting suitable design parameters. Hence, the system control algorithm is simplified. A high-order terminal SMC was designed to get a faster speed and better robustness for the speed loop. Simulation results show that the proposed controller is simple and effective. It can guarantee the wind power system outputs constant frequency. The motor speed can also track the reference speed quickly, so the performance of the wind turbine system is improved.

A homodyne interferometer is described, using a He-Ne laser source and working in Twyman- Green configuration. By means of proper retardation plates and polarizing beam splitters, three signals at 90 degree(s) phase lag are made available. Such signals are digitized and fed into a desktop computer. Fitting procedures and computing algorithms are then implemented working out a phase angle; monitoring such a phase provides information on the optical path difference between the two arms of the interferometer. The general features of the approach are reviewed; examples of application are given, monitoring the fine displacement of mechanical parts and measuring the optical thickness variation of a soap film in air.

Polarizing beam splitters are key elements widely used in different optical instruments. This paper introduces the design and simulation of a novel thin-film multilayer polarizing micro beam splitter based on airgap layers (n = 1.002828 at 400 nm). The negligible absorption coefficient of the air over a wide spectral region (κ ≈ 0 from about 200 nm and higher) satisfies the conditions of a perfect low refractive index material (L). Moreover, using titanium dioxide (TiO2) as high refractive index material (H), a very high refractive index contrast is obtained. The micro beam splitter optical structure consists in a 7 optimized multilayer of TiO2 and air, providing a refractive contrast higher than 1.2. The polarizing beam splitter cube is projected in a borosilicate glass substrate (BK7) and the optical multilayer obtained, expressed in multiples of the quarter wavelength optical thickness – QWOT, is 1.6H L 1.1H 1.5L 1.1H L 1.6H. This optical structure ensures the transmission of p- polarization and the reflection of s- polarization, from visible to NIR spectral range, over a bandwidth higher than 170 nm. Additionally, the designed polarizing beam splitter can be fabricated using standard microtechnology fabrication processes.

The paper covers an issue of method and device for measurement of 2D retardance and principal plane azimuth distributions. The system based on the use of a laser return-path polarimeter which consists of a rotating polarizing beam splitter and a quarter wave plate. Two or four sets from four images are used for birefringence analysis. This allows to decrease the errors caused by imperfection of a polarizing beam splitter and a quarter wave plate. The basic expressions that describe the operation of the systems are presented. The main sources of error are discussed. The measured results of the 2D birefringence distribution of a plastic and standard phase plate of retardation are shown.

A polarization beam splitter (PBS) based on a giant-reflection to zero-order (GIRO) grating is presented. The GIRO grating is a simple binary diffraction grating with parameters chosen such that the excited optical modes in the grating interfere constructively and destructively at the respective interfaces. This interference results in high-zero-order reflection (>99%) with a high polarization-selective extinction ratio (+/-30 dB). The grating shows a low aspect ratio. The GIRO PBS is theoretically and experimentally shown to be an adequate PBS for use as an optical isolator in combination with a quarter-wave plate in a CO2-laser system.

The study is based on a premise that if the polarization information from the reflected radiation is extracted by an imaging polarimeter, it is possible to reveal details about the surface that are not obtainable by other imaging techniques. A polarimetric analysis system is expressed mathematically, and the resulting mathematical notation taking into account the effects caused by rotation of the various optical elements is derived. A basic system design consisting of an optical, sensor, polarimeter control, and image processing subsystems is presented. Computer analysis of the optical components is used for the optimization of the complete optical system. By including a filter, quarter-wave plate, and dichroic polarizer in the analysis, prediction of the focusing requirements of the system is made possible. Results of laboratory-based experiments are assessed.

This study employs the thin film design software TFCale to successfully design and realize a high-efficiency polarization beam splitter suitable for the visible light wavelength range of 400-700 nm, with incident angles between 40 and 50. The design objective was to achieve near 100% reflectance for S-polarized light and near 100% transmittance for P-polarized light. By optimizing the refractive index, thickness, and multilayer structure of the thin film materials, we achieved high-performance optical characteristics. During the design process, we conducted an in-depth investigation of the optical constants of various materials and combined the interference effects of multilayer films to ensure the desired polarization splitting effect within the specified range of incident angles. Simulation results indicate that the film exhibits high-efficiency polarization separation across the entire visible spectrum: the reflectance of S-polarized light remains above 80% within a certain angular range, and the transmittance of P-polarized light also remains above 80%. This high-efficiency polarization beam splitter has broad application prospects in optical instruments, laser systems, display technologies, and other fields requiring precise polarization control. Its superior performance not only enhances the efficiency and accuracy of optical systems but also provides valuable references for future optical thin film design. The study demonstrates that using TFCale for thin film design is an effective method to meet complex optical performance requirements and offers reliable solutions for practical applications

Tunable fiber comb filter based on simple waveplate combination and polarization-diversified loop

Rotating a half-wave plate by 45°: An ideal calibration method for the gain ratio in polarization lidars

In this work, the problem of parameter uncertainty of the Permanent Magnet Synchronous Motor (PMSM) model in the $dq$ reference frame is studied by implementing an adaptive control scheme. The starting point of this paper is to analyze the system structure and represent the system as an interconnection between the electric subsystem, which is a completely actuated system, and the mechanical subsystem which is not actuated. This decomposition allows the design of a current tracking control based on the Passivity Based Control (PBC) methodology for the electrical subsystem. The interconnection, which is power preserving, allows to consider the unactuated mechanical subsystem as a passive perturbation that is proven to be bounded. The numerical evaluation was done by a MATLAB Simulink simulation with a comparison that shows that the designed control is able to deal with the parameters uncertainties of the electrical subsystem.

The measurement speed and measurement accuracy of a displacement measuring interferometer are key parameters. To verify these parameters, a fast and high-accuracy motion is required. However, the displacement induced by a mechanical actuator generates disadvantageous features, such as slow motion, hysteresis, distortion, and vibration. This paper proposes a new method for a nonmechanical high-speed motion using an electro-optic modulator (EOM). The method is based on the principle that all displacement measuring interferometers measure the phase change to calculate the displacement. This means that the EOM can be used to accurately generate phase change rather than a mechanical actuator. The proposed method is then validated by placing the EOM into an arm of a frequency modulation interferometer. By using two lock-in amplifiers, the phase change in an EOM and, hence, the corresponding virtual displacement could be measured by the interferometer. The measurement showed that the system could achieve a displacement at 20 kHz, a speed of 6.08 mm/s, and a displacement noise level < 100 pm//√Hz above 2 kHz. The proposed virtual displacement can be applied to determine both the measurement speed and accuracy of displacement measuring interferometers, such as homodyne interferometers, heterodyne interferometers, and frequency modulated interferometers.

The <i>Infrared Multi-Object Spectrometer (IRMOS)</i> is a principle investigator-class instrument for the Kitt Peak National Observatory 2.1 m and Mayall 3.8 m telescopes. <i>IRMOS</i> is a near-IR (0.8-2.5 micron) spectrometer with low- to mid-resolving power (R = &#955;/&#916;&#955; = 300-3000). On the 3.8 m telescope, <i>IRMOS</i> produces simultaneous spectra of ~100 objects in its 2.8 x 2.0 arcmin field of view using a commercial micro electro-mechanical systems (MEMS) digital micro-mirror device (DMD) from Texas Instruments. The multi-mirror array DMD operates as a real-time programmable slit mask. The all-reflective optical design consists of two imaging subsystems. The focal reducer images the focal plane of the telescope onto the DMD field stop, and the spectrograph images the DMD onto a large-format detector. The instrument operates at ~90 K, cooled by a single electro-mechanical cryocooler. The bench and all components are made from aluminum 6061. There are three cryogenic mechanisms. We describe laboratory integration and test of <i>IRMOS</i> before shipment to Kitt Peak National Observatory. We give an overview of the optical alignment technique and integration of optical, mechanical, electrical and cryogenic subsystems. We compare optical test results to model predictions of point spread function size. We discuss some lessons learned and conclude with a prediction for performance on the telescope.

We present a faithful qubit transmission scheme with linear optics against collective noise, not resorting to ancillary qubits. Its setup is composed of three unbalanced polarization interferometers, based on a polarizing beam splitter, a beam splitter, and a half wave plate, which makes this scheme more feasible than others with present technology. The fidelity of successful transmission is 1, independent of the parameters of the collective noise, and the success probability for obtaining an uncorrupted state can be improved to 100% with some time delayers. Moreover, this scheme has some good applications in one-way quantum communication for rejecting the errors caused by the collective noise in quantum channel.

A brief description of the Water vapor, Cloud and Aerosol Lidar (WACAL) system is provided. To calibrate the volume linear depolarization ratio, the concept of “ Δ 90 ° -calibration” is applied in this study. This effective and accurate calibration method is adjusted according to the design of WACAL. Error calculations and analysis of the gain ratio, calibrated volume linear depolarization ratio and particle linear depolarization ratio are provided as well. In this method, the influences of the gain ratio, the rotation angle of the plane of polarization and the polarizing beam splitter are discussed in depth. Two groups of measurements with half wave plate (HWP) at angles of (0 ° , 45 ° ) and (22.5 ° , −22.5 ° ) are operated to calibrate the volume linear depolarization ratio. Then, the particle linear depolarization ratios measured by WACAL and CALIOP (the Cloud-Aerosol Lidar with Orthogonal Polarization) during the simultaneous observations were compared. Good agreements are found. The calibration method was applied in the third Tibetan Plateau Experiment of Atmospheric Sciences (TIPEX III) in 2013 and 2014 in China. Vertical profiles of the particle depolarization ratio of clouds and aerosol in the Tibetan Plateau were measured with WACAL in Litang (30.03° N, 100.28° E, 3949 m above sea level (a.s.l.)) in 2013 and Naqu (31.48° N, 92.06° E, 4508 m a.s.l.) in 2014. Then an analysis on the polarizing properties of the aerosol, clouds and cirrus over the Tibetan Plateau is provided. The particle depolarization ratio of cirrus clouds varies from 0.36 to 0.52, with a mean value of 0.44 ± 0.04. Cirrus clouds occurred between 5.2 and 12 km above ground level (a.g.l.). The cloud thickness ranges from 0.12 to 2.55 km with a mean thickness of 1.22 ± 0.70 km. It is found that the particle depolarization ratio of cirrus clouds become larger as the height increases. However, the increase rate of the particle depolarization ratio becomes smaller as the height increases.