Four-quadrant Detector Research Articles

An optical voltage transducer based on radial polarization demodulation and four quadrant detection

This paper proposes an optical voltage transducer based on radial polarization demodulation and a four-quadrant detector (FQD). The voltage has been sensed linearly using an annular radial polarization grating to convert the electro-optical (EO) phase delay into the synchronous rotation of a spot. The FQD is employed to locate the spot to achieve voltage measurement. Compared with the charge coupled device camera employed before for the spot positioning, the measurement resolution is improved by nearly 100 times in the range of ±40°, the EO phase delay and the measurement accuracy is improved from class 0.5 to class 0.2, and the cost of the image unit is greatly reduced by 95%.

Design and Construction of Torque Magnetometer for Magnetic Properties Investigation

In this research, cantilever based torque magnetometer was designed and built for investigation of magnetic properties of materials. Torque exerted on magnetic moment of the sample was detected by the deflection and torsion of the cantilever. The laser beam deflected from the sample platform was detected by a four-quadrant photodiode detector. The system can be used to measure anisotropy axis of a permanent magnet. By using this technique, external field and magnetic dipole moment of the sample does not affect the measured anisotropy axis.

Extended the linear measurement range of four-quadrant detector by using modified polynomial fitting algorithm in micro-displacement measuring system

In this paper, we propose new method to improve the linear measurement range of four-quadrant detector (4QD) in micro-displacement measuring system. Based combines the central approximation method and polynomial fitting algorithm due to their opposite error characteristics of the spot position measurements, the voltage-displacement curves of four spot models, circular spot with flat energy distribution, circular spot with Gaussian energy, a novel method is designed to analyze the detecting the linear measurement range on a 4QD. The experimental results show that the proposed algorithm improves the detecting sensitivity and effective measure ranges of the 4QD, which the measuring range of 4QD is extend from 20 μm up to 60 μm, and the resolution is 20 nm. Finally, the proposed method was designed to ensure the most efficient use of the detecting sensitivity and effective measure ranges of the 4QD.

A Linear Optical Current Transducer Based on Newton’s Ring Sub-Wavelength Grating

This paper presents a novel optical current transducer based on Newton’s ring sub-wavelength grating. It converts the Faraday rotation angle into synchronized rotation of the spot image and locates the spot with a four-quadrant detector to achieve real-time linear measurement of the current. The Newton’s ring grating is used instead of a radial grating as a polarization detection device so the extinction ratio is distributed uniformly in the radial directions and the polarization characteristics have no change with the radial direction, thereby a higher measurement accuracy has been achieved. The angle measurement range can reach ±40 degrees which breaks through the limitations of the intensity demodulation mode. The performance of the transducer has been verified by experiments and a 0.2 S class accuracy achieved with a linear measurement, no interference of optical power fluctuation, and minimized the effect of birefringence.

Quadrant response model and error analysis of four-quadrant detectors related to the non-uniform spot and blind area.

In the system of tracking and detection based on the four-quadrant detector (4-QD), the energy distribution of the incident spot and the blind area of the photosensitive surface will affect the location accuracy. The current model of the spot is based on the ideal circular Gauss spot, which makes the error caused by the spot shape easily ignored. In this paper, the model of the spot energy distribution is improved, which can adapt to the elliptical Gauss distribution. The width of the blind area is also added to the response models of the detector so that the output of each quadrant and the error of the localization algorithm can be calculated more accurately. The simulation results show that the measurement accuracy of 4-QD decreases with the increase of the blind area, the shape, and the inclination of the light spot. In the experiment, we first verify the correctness and practicability of the improved model of the spot energy distribution, and then the improved model is proved to be able to make the response and error calculation more accurate.

基于四象限探测器的光纤焦比退化的测量方法

基于四象限探测器的光纤焦比退化的测量方法

Thin film absorption characterization by focus error thermal lensing.

A simple, highly sensitive technique for measuring absorbed power in thin film dielectrics based on thermal lensing is demonstrated. Absorption of an amplitude modulated or pulsed incident pump beam by a thin film acts as a heat source that induces thermal lensing in the substrate. A second continuous wave collimated probe beam defocuses after passing through the sample. Determination of absorption is achieved by quantifying the change of the probe beam profile at the focal plane using a four-quadrant detector and cylindrical lenses to generate a focus error signal. This signal is inherently insensitive to deflection, which removes noise contribution from point beam stability. A linear dependence of the focus error signal on the absorbed power is shown for a dynamic range of over 105. This technique was used to measure absorption loss in dielectric thin films deposited on fused silica substrates. In pulsed configuration, a single shot sensitivity of about 20 ppm is demonstrated, providing a unique technique for the characterization of moving targets as found in thin film growth instrumentation.

Three-degree-of-freedom common-path laser measurement system

Common optical path arrangement was adopted to design a three-degree-of-freedom laser measurement system for measuring 1D displacement and 2D angles of a moving stage simultaneously on the basis of the principles of Michelson interference and laser auto-collimation. In the displacement measurement, the fine resolution of displacement measurement was achieved by using optical path difference doubling technique. Combined with polarization interference technology and signal differential processing, high-quality displacement output signal was obtained. In the angle measurement, changes in yaw and pitch of a moving stage caused the position change of the mirror which was mounted on the stage. The incident beam was reflected by the mirror and detected by a four-quadrant detector. According to the position change of the spot, yaw and pitch angles were obtained. The stability, resolution tests and the comparison experiments with the British Renishaw XL-80 laser interferometer were done. Experimental results show that the system has the resolution of 0.8 nm for displacement measurement and 0.2″ for angle measurement. Compared with the results of Renishaw XL-80 laser interferometer, the maximum deviation of displacement is less than 100 nm within the measurement range of 50 mm. The maximum deviations of yaw and pitch are 0.5″ and 0.4″.

Optical fiber positioning based on four-quadrant detector with Gaussian fitting method

With the development of large-scale spectral surveys, fiber positioning technology has been developing rapidly. Because of the performance advantages of a four-quadrant (4Q) detector, a fiber positioning and real-time monitoring system based on the 4Q detector is proposed. The detection accuracy of this system is directly determined by the precision of the center of the spot. A Gaussian fitting algorithm based on the 4Q detector is studied and applied in the fiber positioning process to improve the calculated accuracy of the spot center. The relationship between the center position of the incident spot and the detector output signal is deduced. An experimental platform is built to complete the simulated experiment. Then we use the Gaussian fitting method to process experimental data, compare the fitting value with the theoretical one and calculate the corresponding error.

Design of linear dynamic range and high sensitivity matrix quadrant APDs ROIC for position sensitive detector application

This paper presents a readout integrated circuits (ROIC) design for matrix quadrant APDs in position sensitive detector application, which eliminates three of the most important limits of the classical four-quadrant detectors: measurement range, dynamic range and sensitivity. The programmable gain control technique and low noise design technique were applied to widen linear dynamic range and increase the sensitivity in the proposed ROIC, respectively. In addition, the proposed ROIC with 32×32 receiver channels can track and position the incident light spot electrically and automatically within the active area of the APDs, supply four channels analog voltage output in parallel and output corresponding light spot position code in serial. The circuit is designed in a 0.18µm CMOS process. The ROIC achieves a high gain of 106dBΩ, a wide linear output swing of about 1V, an input referred noise current of 1.95pA/Hz and a minimum detectable signal of 0.5μA at SNR=3.3, leading to a linear dynamic range of 1:10,000 with a 3.3V power supply. The area of the ROIC chip is equal to 13×13mm2.

Method to measure the position offset of multiple light spots in a distributed aperture laser angle measurement system.

In this paper, an accurate measurement method of multiple spots' position offsets on a four-quadrant detector is proposed for a distributed aperture laser angle measurement system (DALAMS). The theoretical model is put forward, as well as the corresponding calculation method. This method includes two steps. First, as the initial estimation, integral approximation is applied to fit the distributed spots' offset function; second, the Boltzmann function is employed to compensate for the estimation error to improve detection accuracy. The simulation results attest to the correctness and effectiveness of the proposed method, and tolerance synthesis analysis of DALAMS is conducted to determine the maximum uncertainties of manufacturing and installation. The maximum angle error is less than 0.08° in the prototype distributed measurement system, which shows the stability and robustness for prospective applications.

四象限探测器的跟踪与通信复合探测技术

四象限探测器的跟踪与通信复合探测技术

空间激光通信中四象限光电探测器环形光斑检测及误差补偿

空间激光通信中四象限光电探测器环形光斑检测及误差补偿

四象限探测器基于高斯分布的激光光斑中心定位算法

四象限探测器基于高斯分布的激光光斑中心定位算法

四象限探测器基于高斯分布的激光光斑中心定位算法

四象限探测器基于高斯分布的激光光斑中心定位算法

Analysis of the Effects of Thermal Environment on Optical Systems for Navigation Guidance and Control in Supersonic Aircraft Based on Empirical Equations.

The thermal environment is an important factor in the design of optical systems. This study investigated the thermal analysis technology of optical systems for navigation guidance and control in supersonic aircraft by developing empirical equations for the front temperature gradient and rear thermal diffusion distance, and for basic factors such as flying parameters and the structure of the optical system. Finite element analysis (FEA) was used to study the relationship between flying and front dome parameters and the system temperature field. Systematic deduction was then conducted based on the effects of the temperature field on the physical geometry and ray tracing performance of the front dome and rear optical lenses, by deriving the relational expressions between the system temperature field and the spot size and positioning precision of the rear optical lens. The optical systems used for navigation guidance and control in supersonic aircraft when the flight speed is in the range of 1–5 Ma were analysed using the derived equations. Using this new method it was possible to control the precision within 10% when considering the light spot received by the four-quadrant detector, and computation time was reduced compared with the traditional method of separately analysing the temperature field of the front dome and rear optical lens using FEA. Thus, the method can effectively increase the efficiency of parameter analysis and computation in an airborne optical system, facilitating the systematic, effective and integrated thermal analysis of airborne optical systems for navigation guidance and control.

Large field distributed aperture laser semiactive angle measurement system design with imaging fiber bundles.

A type of laser semiactive angle measurement system is designed for target detecting and tracking. Only one detector is used to detect target location from four distributed aperture optical systems through a 4×1 imaging fiber bundle. A telecentric optical system in image space is designed to increase the efficiency of imaging fiber bundles. According to the working principle of a four-quadrant (4Q) detector, fiber diamond alignment is adopted between an optical system and a 4Q detector. The structure of the laser semiactive angle measurement system is, we believe, novel. Tolerance analysis is carried out to determine tolerance limits of manufacture and installation errors of the optical system. The performance of the proposed method is identified by computer simulations and experiments. It is demonstrated that the linear region of the system is ±12°, with measurement error of better than 0.2°. In general, this new system can be used with large field of view and high accuracy, providing an efficient, stable, and fast method for angle measurement in practical situations.

A high-precision roll angle measurement method

A novel high-precision measurement method for measuring roll is presented. The pentagonal prism and corner-cube prism are used as splitting element and sensitive element, respectively. A pair of parallel collimated beams generated by a pair of splitting pentagonal prisms is incident upon the target moving along linear guide. Two beams returning from two corner-cube prisms on the target reach two four-quadrant photoelectric detectors (QD1 and QD2), respectively. So the roll can be measured by differential measurement based on QD1 and QD2. Further, the measurement resolution can be doubled and resistance to common mode interference can be enhanced, by adopting common-path structure based on the polarization splitting prisms. Feasibility of the method is verified by theoretical analysis and experiments. When the system parameters apply to the values supposed, for the roll, the angular resolution can reach to 0.1″, and measuring accuracy is about 1″.

Effect of Specimen Geometry on Quantitative EDS Analysis with Four-Quadrant Super-X Detectors

In recent years, X-ray signal collection efficiency in energy dispersive X-ray spectrometry (EDS) has been significantly improved by incorporating state-of-the-art four-quadrant Super-X detectors in aberration-corrected microscopes [1, 2] and has enabled routine atomic-resolution EDS elemental mapping, as shown in Figure 1a. The breakthrough in detector technology has sparked interest in quantifying the chemical information directly from atomically resolved EDS maps [3-5]. In order to obtain an atomic-resolution EDS map, the specimen however must be tilted to a low index zone axis, resulting in different orientation with respect to each detector. This will inevitably result in different Xray signals arriving at each detector due to their different absorption distances and effective take-off angles. Such a variation could largely affect the ability to accurately quantify the overall EDS spectrum from four Super-X detectors without precautions as evidenced in this work. Therefore, understanding the X-ray signal variation from each detector under tilted specimen condition becomes both experimentally and theoretically important as a starting point for atomic-resolution EDS quantification.

Linear polarization optimized Stokes polarimeter based on four-quadrant detector.

A four-quadrant detector (4QD) consists of four well-balanced detectors. We report on a Stokes polarimeter with optimal linear polarization measurements based on a 4QD. We turned the four intensity-detection channels into four polarization-analyzing channels by placing four polarizers and one quarter-wave plate in front of the individual detectors. An optimization method for the four polarization-analyzing channels is proposed to improve measurement accuracy. Considering applications in favor of linear polarization measurements instead of global optimization for all the possible states of polarization (SOP), we optimize the polarimeter first for the linear polarization components and then for the circular polarization component. The polarimeter is capable of simultaneous measurements of fast varying SOP with improved performance for the linear polarizations.