Frequency Modulation Continuous Wave Displacement Sensor Based on STM32H743
Han Yuan, Zheng Gang, Zhang Xiongxing, Sheng Qiming, and Bai Lang
Aiming at the problem of low signal sampling rate and signal processing speed of linear frequency modulation continuous wave displacement sensor, this paper designs a fiber optic displacement sensor with a Fabry?Perot interferometer structure based on STM32H743 chip. The optical fiber displacement sensor uses sawtooth wave to modulate the frequency of the laser, and selects STM32H743 as the core processor to improve the signal acquisition and processing speed. Its main frequency is 400 MHz, and the analog to digital converter maximum conversion rate is 4.5 MHz. Combined with frequency modulated continuous wave laser interferometry, the displacement of stainless steel pipe with fixed cavity length and moving target is measured. Experimental results show that in the 200?400 mm measurement experiment, the standard deviation of the measurement result of 1 mm/s is less than 3.3 nm, and the linear fitting coefficient in the range of 600 mm is above 0.99998, which has a good application prospect in the field of displacement measurement.
  • Jun. 09, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1112007 (2021)
  • DOI:10.3788/LOP202158.1112007
Placement Optimization of iGPS Transmitter Based on Immune Optimization Algorithm
Fan Jingtao, Huang Xiang, Zeng Qi, Zhao Ziyue, and Shi Zhufeng
To obtain a better transmitter layout and enable the system to achieve higher positioning accuracy, we propose an iGPS transmitter layout optimization method based on an immune optimization algorithm. According to the system's measurement principle, we obtain the measurement uncertainty model of the system. Besides, we establish the affinity function and utilize the immune optimization algorithm for optimizing the transmitter layout. Finally, we verify the results through the simulation. The simulation analysis shows that the proposed method can significantly optimize the transmitter layout and improve the system's measurement accuracy. Thus, the immune optimization algorithm has a better global optimization effect than the genetic algorithm and can obtain better placement of transmitters.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1112009 (2021)
  • DOI:10.3788/LOP202158.1112009
A Random Two-Step Phase Shift Algorithm Based on Polynomial Fitting Background Light
Li Jing, Tian Ailing, Wang Dasen, Liu Bingcai, Zhu Xueliang, and Wang Hongjun
The precision of phase extraction directly affects that of interferometry. The traditional fixed-step or equal-step length phase extraction algorithm must carry out phase calibration for the test system, but phase shift error is often introduced due to inaccurate phase calibration, which affects the precision of phase extraction. Therefore, this paper proposes a random two-step phase shift algorithm of K-order two-dimensional polynomial fitting background light (PFBL) to solve phase. This algorithm does not need to carry out phase calibration, and can solve the measured phase with only two frames of phase-shift interferogram when phase shift quantity, background light, modulation system and phase are unknown. When order number K value is greater than or equal to 2, it is determined by the simulation of K-order two-dimensional polynomial, the accuracy of the proposed algorithm for phase can be higher. At the same time, the algorithm robustness is analyzed by comparing the calculation accuracy of Gram-Schmidt orthogonalization (GS) two step phase-shift algorithm with the PFBL method. The results show that the PFBL method has good robustness in the interferogram phase shift, non-uniform illumination and noise, and the calculation accuracy of the PFBL method is obviously better than that of GS algorithm.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1112008 (2021)
  • DOI:10.3788/LOP202158.1112008
Traceable Accuracy Measurement of Underwater Sound Velocity Based on Femtosecond Laser
Liu Chao, Xue Bin, Xu Xinyang, Qian Zhiwen, and Wei Yaming
The traditional method for measuring sound velocity in seawater is developed on the basis of the piezoelectric effect. This traditional method is prone to errors because of its uncertain starting points when measuring the propagation time and distance. To address these problems, this study proposes an approach for measuring underwater sound velocity based on the acousto-optic effect between optical frequency comb and ultrasonic pulse. We introduce the acousto-optic effect with a clear interaction point between sound and laser. A dual Michelson interferometer system is built to measure the optical pulse markers generated when the ultrasonic pulse passes through two measuring arms. We measure the ultrasonic propagation time and distance using the cross-correlation technique. The traceability of the method is clear, however, the accuracy of the method has room for improvement. The experimental results show that the experimental system can achieve high precision measurement of underwater speed, and the measurement uncertainty is 0.023 m/s. It can be used as a new calibration device for measuring underwater sound velocity.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1112006 (2021)
  • DOI:10.3788/LOP202158.1112006
FSI Ranging Error Compensation Method Based on Laser Self-Mixing Vibration Measurement
Chai Xiaobo, Wu Tengfei, and Yin Pufu
In the process of laser frequency scanning interferometry ranging, the target vibration introduces Doppler shift in the ranging interference signals which results in the spectral broadening of the signal and the amplification effect of ranging errors. To reduce the effect of vibration on ranging results, we proposed a ranging error compensation method based on laser self-mixing vibration measurement. This method compensates the phase modulation of the target vibration on the ranging interference signal by synchronously measuring the phase change of the self-mixing interference signal, and meanwhile the frequency resampling method is used to correct the laser frequency modulation nonlinearity. Finally, the feasibility of the proposed method is verified by simulation and experiment. In the experiment, when the measured target amplitude was 7102.1 nm, the measured vibration standard deviation was 7.9 nm, the range measurement standard deviation before compensation was 3270.6 μm, and the range measurement standard deviation after compensation was reduced to 21.4 μm,which was close to the case of no vibration, indicating that the amplification problem of ranging errors caused by target vibration was effectively solved.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1112005 (2021)
  • DOI:10.3788/LOP202158.1112005
Rotor-Stator Axial Clearance Measurement Technique of Engine Based on Frequency-Swept Interferometry
Shao Bin, Zhang Wei, and Chen Weimin
Rotor-stator axial clearance measurement requires small-size sensing probe, large measurement range, and high measurement accuracy. However, existing measurement methods cannot meet these requirements. Considering the characteristics of rotor-stator axial clearance variation, we propose a measurement method based on frequency-swept interferometry and develop a corresponding high-speed real-time online measurement prototype. The prototype combined large-bandwidth high-speed frequency sweeping and periodical Doppler error smoothing to achieve a large measurement range and a high measurement accuracy and used a single-mode optical fiber to realize the small-size probe. To test the prototype performance, we built a simulation experiment platform for the proposed rotor-stator axial clearance measurement. Dynamic clearance experimental results showed that the measurement range of the prototype was 20 mm, and the measurement accuracy was 0.08% of the full range at 15000 r/min. The proposed prototype represents a new measurement technique for rotor-stator axial clearance measurement and provides an important reference for improving measurements.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1112004 (2021)
  • DOI:10.3788/LOP202158.1112004
Surface Defect Detection Based on Scattering Field Distribution Fitting Approximation
Wu Xiongxiao, Wang Hongjun, Wei Chen, Tian Ailing, Liu Bingcai, Zhu Xueliang, and Liu Weiguo
This study proposes a surface defect detection method based on the scattering field distribution fitting approximation to accurately detect different sizes of optical element surfaces, especially small-size defects, with typical optical element surface defects-pits and scratches-as the research target. Experimental results show that the method can rapidly and effectively detect small-size defects on optical element surfaces and the relative error between fitting calculation results and the original size of a sample is basically less than 5%, which verifies the effectiveness of the method. In addition, the method addresses the problems of low accuracy and complex structure of existing measurement methods and introduces a new idea for accurately detecting microsized defects on optical element surfaces.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1112003 (2021)
  • DOI:10.3788/LOP202158.1112003
Method for Calibrating Optical Axis Based on Characteristics of Optical Nodes
Gao Tianyuan, Zhang Han, Liu Zhiying, Jia Guiyuan, Han Xu, Wang Jiake, and Cheng Xiandong
The optical axis of a transmission optical system cannot be found directly. To solve this problem, an optical axis calibration method based on the characteristics of optical nodes is proposed. The method is used to investigate the characteristics of a node and an equivalent node, by observing the focal plane image point displacement change, the location of the node to calibrate the optical axis of the system is determined. Furthermore, based on this method, the bidirectional exchange standard double autocollimation optical axis calibration device of parallel light pipe is designed, including imaging thrusting at the receiving end type structure design, which can effectively avoid the influence of the wavefront error. Finally, the feasibility of the proposed method is verified. Experiment results show that the proposed method has high optical axis calibration accuracy and wide adaptability. The optical axis calibration accuracy of the lens optical system is 7.7", which provides an auxiliary means for testing and adjusting lens optical systems in space optics and national defense fields.
  • Jun. 07, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 11 1112002 (2021)
  • DOI:10.3788/LOP202158.1112002
Metal Surface Texture Reconstruction Based on Near-Field Photometric Stereo
Jian Zhenxiong, Wang Xi, Ren Jieji, and Ren Mingjun
The surface quality of precision metal parts will affect the performance and appearance of the product. For this reason, it is necessary to measure and evaluate the surface texture of the parts. Commonly used contact measurement methods have low measurement efficiency, and optical measurement methods are susceptible to the effects of surface highlight reflection. For this reason, a method based on near-field non-Lambertian photometric stereo vision for highlight metal surface texture reconstruction is proposed. In order to effectively describe the non-Lambertian reflection, this method uses an inverse reflectance model based on an inverse reflectance light source to decouple the surface normal vector and the nonlinear reflection model. This method uses neighborhood information to improve the robustness of the inverse model, and uses the maximum fusion strategy to overcome the influence of shadows and rendering generates targeted simulation datasets, thereby improving the adaptability to metal surface reflection. The results show that the proposed method can reconstruct the high-brightness metal surface texture with high precision, and the relative measurement error is less than 15%.
  • Jun. 07, 2021
  • Acta Optica Sinica
  • Vol.41 Issue, 11 1112002 (2021)
  • DOI:10.3788/AOS202141.1112002
Research on Key Technologies for Large-Scale Distributed Measurement Network Reconstruction
Ma Huiyu, Lin Jiarui, Zhang Rao, Cheng Dongyuan, and Zhu Jigui
The large-scale distributed measurement system is a measurement network based on multiple measurement fusion. The network structure is the key to improve the network performance, which has an important impact on the measurement accuracy, efficiency and even cost. To solve the network structure reconstruction caused by the changing of obstacles, measurement objects and requirements, based on the coverage performance of the network nodes, the method to determine the lost-of-light issue based on the fast collision detection algorithm is first investigated and the problem of blind spot judgement is solved. Then, the network reconstruction algorithm based on Next-Best-View (NBV) is studied. At the same time, in order to improve the networking efficiency, the improved grey wolf optimization algorithm is used as the best location search algorithm to rearrange the numbers and positions of nodes, and thus efficient networking is realized and the reconstruction accuracy is improved. Finally, with the workshop Measurement Positioning System (wMPS) as the verification platform and from three aspects of measurement coverage, accuracy and networking efficiency, the effectiveness of the proposed method is confirmed by changing measurement conditions and requirements.
  • Jun. 07, 2021
  • Acta Optica Sinica
  • Vol.41 Issue, 11 1112001 (2021)
  • DOI:10.3788/AOS202141.1112001