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Author

Li Lu

Bio: Li Lu is an academic researcher from Beijing Information Science & Technology University. The author has contributed to research in topics: Speckle pattern & Polarization (waves). The author has an hindex of 1, co-authored 3 publications receiving 3 citations.

Papers
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Patent
16 Nov 2018
TL;DR: In this paper, a polarization four-step phase shifting method for digital speckle interferometry was proposed, which replaces piezoelectric ceramics with two rotatable polarizers.
Abstract: The invention discloses a polarization four-step phase shifting method for digital speckle interferometry. According to the polarization four-step phase shifting method for digital speckle interferometry, polarization beam splitting prisms, a beam expander, quarter wave plates and polarizers are adopted to establish a polarization four-step phase shifting optical path; in a phase shifting process,two polarizers are rotated, so that 0-degree, 90-degree, 180-degree and 270-degree four-step phase shifting can be realized, and corresponding speckle images are acquired; and a random phase field atan initial moment is restored through a four-step phase shifting algorithm. Compared with a traditional time phase shifting method, the method replaces piezoelectric ceramics with two rotatable polarizers, and therefore, the hysteresis, nonlinearity and creep interference of the piezoelectric ceramics can be avoided, stable speckle images can be acquired, and accurate random phase extraction canbe realized.

2 citations

Journal ArticleDOI
TL;DR: In this paper, a temporal 4-step phase shift technique for digital speckle pattern interferometry (DSPI) with one fixed and two rotatable polarizers is proposed.
Abstract: A temporal 4-step polarization phase-shifting technique for digital speckle pattern interferometry (DSPI) with one fixed and two rotatable polarizers is proposed. The fixed polarizer is used to filter out the reflected object beam in one polarization direction, and the two rotatable polarizers are used to perform the 4 times phase shifts. The Jones derivation illustrates the object surface phase distribution can be derived from the 4 speckle pattern interferograms, which are bright, gloomy, bright, and gloomy successively. The experiment shows that the proposed temporal polarization phase-shifting technique is able to extract the phase change caused by a tiny out-of-plane displacement. Unlike the PZT-driven phase-shifting, the polarization phase-shifting in this method is stable and accurate in the long term.

2 citations

Patent
23 Nov 2018
TL;DR: In this article, a time phase shifter consisting of a drive module and at least three phase shift modules with different thicknesses is presented, where the drive module can change the positions of the atleast three modules so as to introduce different phase shift amounts at different moments.
Abstract: The application discloses a time phase shifter comprising a drive module and at least three phase shift modules; the medium refraction index of the at least three phase shift modules is n; the at least three phase shift modules are arranged in a mode in which the thickness of said three modules decreases; the thickness difference of two adjacent phase shift modules can be solved by a formula (seedescription), wherein [delta] [phi] refers to a phase shift step length of the time phase shifter, and [lambda] refers to a light source wavelength; the drive module can change the positions of the atleast three phase shift modules so as to introduce different phase shift amounts at different moments. The time phase shifter sets the at least three phase shift modules with different thicknesses soas to accurately introduce the phase shift amount in a time phase shift process, thus effectively avoiding phase shift amount errors caused by piezoelectric ceramic creep properties, hysteresis, andnon-linear characteristics.

Cited by
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Journal ArticleDOI
TL;DR: A panoramic dual-directional shearography system is proposed to simultaneously determine out-of-plane deformation derivatives in two directions and globally inspect the object to be tested and theoretical analysis and experimental results demonstrated the utility of the system.
Abstract: A panoramic dual-directional shearography system is proposed to simultaneously determine out-of-plane deformation derivatives in two directions and globally inspect the object to be tested. A dichroic filter (DF), a 3CCD camera, and dual-wavelength light are used in the proposed shearography configuration. The dual-wavelength light coupled with the corresponding imaging sensors of the 3CCD camera provides independent color signals and shearograms. Through adjustment of the tilted stereo-angle of the DF, which offers a second wavelength-dependent measurement, an additional independent image-shearing can be introduced into the setup. The auxiliary bi-mirror surrounding the object helps to fully illuminate the object surface and capture it in a single shot. Theoretical analysis and experimental results demonstrated the utility of the system.

8 citations

Patent
20 Aug 2019
TL;DR: In this article, a point diffraction interference device and method for object vibration measurement is described, which consists of a light source, a light path processing module and a measuring module.
Abstract: The invention discloses a point diffraction interference device and method for object vibration measurement. The device comprises a light source, a light path processing module and a measuring module,wherein the light source emits initial light to the light path processing module; the light path processing module converts the initial light into a plurality of beams of emergent light to be mergedinto the measuring module; and the measuring module is connected to a measured object for collecting and processing an interference pattern generated by the incident light. Laser emitted by a single-longitudinal-mode laser enters the measuring module through the light path processing module, and the incident light is interfered after the incident light passes through a polarizing film array arranged in front of a polar digital camera; a four-step phase-shifting interference pattern and an interference pattern of each transient position are recorded; and spatial three-dimensional coordinate values of different transient positions are analyzed according to the interference pattern, and an object vibration process is measured. According to the device and the method, the measured object and ameasuring probe are fixed, and the interference pattern of each transient position in the vibration process is collected by the polar digital camera, the spatial three-dimensional coordinates of eachtransient position are analyzed, the object vibration is measured, and the anti-interference capability of the device is improved.
Patent
23 Aug 2019
TL;DR: In this paper, an optical fiber point diffraction interference apparatus for transient three-coordinate measurement is presented, which consists of a light source, which is configured to provide initial incident light to an optical path adjustment module; the optical path adjusting module, which divides the incident light into a plurality of beams of polarized light; adigital polarized camera, which receives emitted light and acquire a desired interference image; and a computer, connected with the digital polarized camera and is configuredto process the image information.
Abstract: The present invention discloses an optical fiber point diffraction interference apparatus for transient three-coordinate measurement. The apparatus comprises: a light source, which is configured to provide initial incident light to an optical path adjustment module; the optical path adjustment module, which is configured to divide the incident light into a plurality of beams of polarized light; adigital polarized camera, which is configured to receive emitted light and acquire a desired interference image; and a computer, which is connected with the digital polarized camera and is configuredto process the image information. The substantial effects of the technical scheme of the present invention comprise that: a polarized digital camera is used to acquire circularly polarized light of p-polarized light and s-polarized light with opposite rotation directions obtained by a quarter-wave plate whose fast axis direction has an angle of 45 DEG with the X-axis, two beams of the polarized light with opposite rotation directions are interfered by the polarization plate array in the front of the polarized digital camera, and as the polarization plate rotates in the light transmission axisdirection, the phase of the interference fringe changes, so that the micro-displacement is realized without the requirement of the PZT, the complexity of detecting the system components is reduced, and the anti-interference ability of the point diffraction interference system is improved.