Mr. Lei Liu Profile

Lei Liu

at Institute of Optics and Electronics CAS

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Publications (2)

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Proceedings Article | 24 November 2021 Paper

Application of structured illumination microscopy in fast and accurate measurement of complex-surface and steep-edge

Lei Liu, Tang Yan, Song Hu

Proceedings Volume 12066, 120660U (2021) https://doi.org/10.1117/12.2604945

KEYWORDS: Modulation, Fringe analysis, Microscopy, Fourier transforms, Phase shifts, Phase shift keying, Confocal microscopy, Charge-coupled devices, Mirrors, Digital micromirror devices

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With the wide application of micro-nano structures in various fields, micro-nano technology has been developed continuously. Among them, micro-nano surface morphology detection technology has become a research hotspot, because the surface geometry and morphology of micro-nano devices determine the functional level and service life of devices. With the increasing complexity of micro nano device surface morphology and the increasing sharp edges, the detection technologies are facing severe challenges. Among various detection methods, structured illumination microscopy (SIM) has attracted many research interests due to the characteristics of high accuracy, strong adaptability and high efficiency. The existing SIM are mainly based on phase-shift technique, Hilbert transform technique and global Fourier transform technique. However, for complex-surface and steep-edge measurements, it is difficult for traditional SIM to achieve both high accuracy and high efficiency. In this paper, a method based on SIM which combines vertical scan and phase-shift is proposed. In this proposed measurement system, vertical scanning of the object is synchronized with the switching of the phase-shifted fringe pattern and only one fringe pattern needs to be projected, which enables a point-to-point processing defined as local Fourier transform method in this paper to be utilized to extract the modulation information which will reserve high-frequency information of the image so it can be applied to both smooth and rough surfaces. Simulation and experiment are carried out to demonstrate that the proposed method can successfully realize fast and accurate detection of complex-surface and steep-edge.

SPIE Journal Paper | 15 October 2021 Open Access

Accurate and stable two-step LED position calibration method for Fourier ptychographic microscopy

Haojie Wei, Jing Du, Lei Liu, Yu He, Yong Yang, Song Hu, Yan Tang

JBO, Vol. 26, Issue 10, 106502, (October 2021) https://doi.org/10.1117/12.10.1117/1.JBO.26.10.106502

KEYWORDS: Light emitting diodes, Calibration, Reconstruction algorithms, Microscopy, Lawrencium, Image restoration, Image processing, Error analysis, Optical arrays, Imaging systems

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Significance: Fourier ptychography microscopy (FPM) is a computational optical imaging technology that employs angularly varying illuminations and a phase retrieval algorithm to achieve a wide field of view and high-resolution imaging simultaneously. In the FPM, LED position error will reduce the quality of the reconstructed high-resolution image. To correct the LED positions, current methods consider each of the LED positions as independent and use an optimization algorithm to get each of the positions. When the positional misalignment is large or the search position falls into a local optimal value, the current methods may lack stability and accuracy. Aim: We improve the model of the LED position and propose an accurate and stable two-step correction scheme (tcFPM) to calibrate the LED position error. Approach: The improved LED positions model combines the overall offset, which represents the relative deviation of the LED array and the optical axis, with the slight deviation of each LED’s independent position. In the tcFPM, the overall offset of the LED array is corrected at first, which obtains an approximate value of the overall offset of the LED array. Then the position of each LED is precisely adjusted, which obtains the slight offset of each LED. Results: This LED position error model is more in line with the actual situation. The simulation and experimental results show that the method has high accuracy in correcting the LED position. Furthermore, the reconstruction process of tcFPM is more stable and significantly improves the quality of the reconstruction results, which is compared with some LED position error correction methods. Conclusions: An LED position error correction technology is proposed, which has a stable iterative process and improves the reconstruction accuracy of complex amplitude.

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