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Bump offsets have harmful effects on the quality of flex-on-glass (FOG) bonding in liquid crystal display (LCD) module industry. Here we report a novel automatic optical inspection (AOI) method to achieve fast inspecting FOG bonding bump offsets. Overcoming difficulties to image targets at different depths in light absorption medium when using ultra-short-exposure and high-speed imaging, the proposed method innovatively achieves inspecting FOG bonding bump offsets using differential interference contrast imaging based on spatial Poisson point process approximation. Theoretical analysis proves that the proposed method has high reliability in FOG bonding bump offset AOI inspection. Experimental results show missed detection rate of the inspection algorithm is 0.01%, and false rate is 0.1%, and verify the accuracy and validity of the proposed method, all of which are significant for guiding practice in LCD module industry.

Under natural conditions, injured cells can be repaired rapidly through inherent biological processes. However, in the case of diabetes, cardiovascular disease, muscular dystrophy, and other degenerative conditions, the natural repair process is impaired. Repair of injury to the cell membrane is an important aspect of physiology. Inadequate membrane repair function is implicated in the pathophysiology of many human disorders. Recent studies show that Mitsugumin 53 (MG53), a TRIM family protein, plays a key role in repairing cell membrane damage and facilitating tissue regeneration. Clarifying the role of MG53 and its molecular mechanism are important for the application of MG53 in regenerative medicine. In this review, we analyze current research dissecting MG53′s function in cell membrane repair and tissue regeneration, and highlight the development of recombinant human MG53 protein as a potential therapeutic agent to repair multiple-organ injuries.

With the rapid development of electronic industry, higher and higher requirements are placed on the surface quality of optical components in electronic devices. Structured-Light Modulation Analysis Technique (SMAT) was recently proposed to detect the contamination and defects on specular surfaces. In this paper, the proposed mechanisms and mathematical models of SMAT are analyzed and established based on the theory of photometry and the optical characteristics of contamination and defects for the first time. What's more, a novel transmission system adopting SMAT is especially designed for the defect detection of transparent objects. For both reflection and transmission system, simulations and experiments were conducted, and comparative studies with uniform planar illumination were also carried out. Simulations on the influence of incident light source region showed that SMAT can eliminate the interference of ambient light while uniform planar illumination technique cannot. Experiments on samples with specular surface and transparent material demonstrated that the modulation values at the contamination and defects are much less than that at clean and intact place, and defects and contaminations were clearly distinguished based on SMAT, while they were almost indiscernible with uniform planar illumination. Therefore, SMAT can be applied to the whole-field inspection of optical components in industrial environments.

The fringe reflection technique (FRT) has been one of the most popular methods to measure the shape of specular surface these years. The existing system calibration methods of FRT usually contain two parts, which are camera calibration and geometric calibration. In geometric calibration, the liquid crystal display (LCD) screen position calibration is one of the most difficult steps among all the calibration procedures, and its accuracy is affected by the factors such as the imaging aberration, the plane mirror flatness, and LCD screen pixel size accuracy. In this paper, based on the deduction of FRT analytical phase–slope description, we present a novel calibration method with no requirement to calibrate the position of LCD screen. On the other hand, the system can be arbitrarily arranged, and the imaging system can either be telecentric or non-telecentric. In our experiment of measuring the 5000mm radius sphere mirror, the proposed calibration method achieves 2.5 times smaller measurement error than the geometric calibration method. In the wafer surface measuring experiment, the measurement result with the proposed calibration method is closer to the interferometer result than the geometric calibration method.

In modern industrial manufacturing, the demand for the surface inspection of specular objects has become more and more urgent. In this paper, a novel defect detection method with eliminating dust is systematically proposed to inspect surface defects of specular objects. The proposed approach can be applied to the defect detection of silicon wafers, optical lens, cell phone cover glass, etc. Structured-Light Modulation Analysis Technique (SMAT) is adopted to detect defects and dust simultaneously. Meanwhile, according to the discrepancy of polarization states between dust and other places, polarized illumination and a linear polarizer are exploited to photograph dust image exclusively. The dust image is used to remove dust from the modulation image; thus, the purified defect distribution can be obtained. Relevant experiments are also performed to prove the effectiveness of this proposed approach.

Fringe projection three-dimensional (3D) measurement technique is an effective technique to measure 3D shape of objects, in which phase retrieval is an important procedure. To overcome the need of pre-filtering process in the existing single-frame methods, this paper proposes a novel method to extract phase distribution solely from one-frame fringe pattern without pre-filtering, which reduces its complexity and retains more phase details. The proposed method consists of two stages. Firstly, the Hilbert transform is applied to one-frame fringe pattern to generate another frame of fringe pattern. Secondly, the phase distribution is calculated based on Lissajous Ellipse Fitting (LEF) technique by using original fringe pattern and the Hilbert transformed fringe pattern. The results provides a practically efficient methodology for single frame phase reconstruction, which shows potential useful means for reconstructing object in rapid measurement.

The detection of defects is one of the most crucial aspects of the manufacturing industry. There are many methods in the aspects of defects detection on the specular surface. However, in some cases, the detection results may be disturbed by the dusts on the specular surface. In this paper, a method which is based on the polarized structured-light illumination is proposed to detect the defects of specular surface with eliminating dusts. A linear polarizer is added to the structuredlight illumination system, and by controlling the polarization direction of the polarizer the dusts can be detected separately and removed in the end. Experiment results proved the effectiveness of the proposed method.

In this paper, a new generating technique of sinusoidal fringes for 3D shape measurement is presented. Specifically, a sinusoidal fringe is generated by expanding the inverted image of a filled binary sinusoidal pattern in a specified direction, and further, the phase shift is realized by switching the backlight sources of a set of sinusoidal patterns. In theory, sinusoidal fringes can be formed whether the projection is focused or defocused. Moreover, the technique has the potential for high frame rates due to the way the phase shift is performed. In particular, since the high shape precision of the binary sinusoidal pattern and the high accuracy of the phase shift can be easily realized by the photolithography process, the technique is very easy to implement.

Phase Measuring Deflectometry (PMD) is an effective metrology technique for specular surfaces, but it is hard to achieve rapid measurement precisely with prevenient fringe analysis methods. Inspired by recent successes of deep learning techniques for fringe analysis, we demonstrate for the first time that deep learning can be used to achieve high-precision three-dimensional (3D) measurement of specular surfaces with a single frame. In this research, it is proposed to use depthwise separable convolution to optimize measured results. Experimental results proved that this proposed method has better performance than the existing fringe analysis method employing deep learning.

A fringe projection profilometry (FPP) using portable consumer devices is attractive because it can realize optical three dimensional (3D) measurement for ordinary consumers in their daily lives. We demonstrate a FPP using a camera in a smart mobile phone and a digital consumer mini projector. In our experiment of testing the smart phone (iphone7) camera performance, the rare-facing camera in the iphone7 causes the FPP to have a fringe contrast ratio of 0.546, nonlinear carrier phase aberration value of 0.6 rad, and nonlinear phase error of 0.08 rad and RMS random phase error of 0.033 rad. In contrast, the FPP using the industrial camera has a fringe contrast ratio of 0.715, nonlinear carrier phase aberration value of 0.5 rad, nonlinear phase error of 0.05 rad and RMS random phase error of 0.011 rad. Good performance is achieved by using the FPP composed of an iphone7 and a mini projector. 3D information of a facemask with a size for an adult is also measured by using the FPP that uses portable consumer devices. After the system calibration, the 3D absolute information of the facemask is obtained. The measured results are in good agreement with the ones that are carried out in a traditional way. Our results show that it is possible to use portable consumer devices to construct a good FPP, which is useful for ordinary people to get 3D information in their daily lives.

Based on the coupled mode equations and elastic optic effect theory, the relationship between polarization maintaining fiber (PMF) beat length and external pressure was analyzed. Moreover, the beat length variation with different external pressure values F as well as angles θ between the pressure direction and PMF's x -axis was calculated numerically. The results demonstrated that the beat length variation was determined both by F and θ simultaneously. When F was a constant, the beat length was changed periodically in π cycle sinusoidal form with θ variation. Then, the minimum and maximum values of beat length would be obtained when θ were even and odd multiples of π /2, respectively. Meanwhile, the beat length variation was linear with F as θ was fixed. In this situation and with F increasing, if θ ∈ ( kπ + π /4, kπ + 3 π /4) ( k ∈ Z ), the beat length would increase linearly; otherwise, the beat length variation would be in the opposite direction while θ ∈ ( kπ − π /4, kπ + π /4) ( k ∈ Z ); however, it remained almost unchanged in the case of θ = kπ ± π /4 ( k ∈ Z ). Finally, the beat length was measured with different pressure values F and angles θ based on a Sagnac interferometer system, and the results shown a great agreement with the theoretical analysis and simulation.

The ability to accurately estimate the location and geometry of holes is often required in the field of quality control and automated assembly. Projected fringe profilometry is a potentially attractive technique on account of being non-contacting, of lower cost, and orders of magnitude faster than the traditional coordinate measuring machine (CMM). However, we demonstrate in this paper that fringe projection is susceptible to significant (hundreds of µm) measurement artefacts in the neighbourhood of hole edges, which give rise to errors of a similar magnitude in the estimated hole geometry. A mechanism for the phenomenon is identified based on the finite size of the imaging system’s point spread function and the resulting bias produced near to sample discontinuities in geometry and reflectivity. A mathematical model is proposed, from which a post-processing compensation algorithm is developed to suppress such errors around the holes. The algorithm includes a robust and accurate sub-pixel edge detection method based on a Fourier descriptor of the hole contour. The proposed algorithm was found to reduce significantly the measurement artefacts near the hole edges. As a result, the errors in estimated hole radius were reduced by up to one order of magnitude, to a few tens of µm for hole radii in the range 2-15 mm, compared to those from the uncompensated measurements.

A high Er3+-doped narrow linewidth fiber laser based on fiber Bragg grating Fabry-Perot cavity was demonstrated. The spatial hole burning effect was restrained by a fiber Faraday rotator. Two short fiber Bragg grating Fabry-Perot cavities as narrow bandwidth filters discriminated and selected laser longitudinal modes efficiently. A stable single-frequency 1534.83 nm laser was acquired. Pumped by two 976 nm laser diodes and two-ended output, the fiber laser exhibited a 12 mW threshold. Total 39.5 mW output power and one end 22 mW output power were obtained at the maximum 145 mW pump power. Optical-optical efficiency was 27% and slope efficiency was 29.7%. The output power seemed to be saturated when pump power increased. The 3 dB linewidth of the laser was less than 7.5 kHz, measured by the delayed self-heterodyne method with 15 km monomode fiber. The high power narrow linewidth fiber laser can be used in high resolution fiber sensor systems.

A convenient method based on fringe reflection technique with a single color fringe pattern is presented in this paper for dynamic measurements. A color screen and a color CCD camera are required in the system. The orthogonal color fringe pattern, which is composed with a horizontal fringe pattern in the red channel and a vertical fringe pattern in the blue channel, is displayed by the screen. The CCD camera captures the distorted color fringe pattern via the tested specular surface. The horizontal and vertical fringe patterns will be distinguished directly once the composite color fringe pattern is read by the software like MATLAB. After we get the phase of the horizontal and vertical fringe patterns by Fourier transform profilometry, the two directions’ slope distributions of the tested specular surface can be acquired by the slope-phase relation of fringe reflection technique, and the shape can be reconstructed by intergral of the slope. The whole shape measurement can be completed by a single fringe pattern. The experiment of measuring a plane mirror shows the phase error of the presented method is several times smaller than the existing method, and a vibrating wafer measuring experiment proves the ability of the proposed method to reach dynamic measurement.

The demands of the less-defective and high-flatness wafers are urgent in many wafer based technologies ranging from micro-electronics to the current photovoltaic industry. As the wafer becomes thinner and larger to cope with the advances in those industries, there is an increasing possibility of the emerging of crack and warp on the wafer surface. High-accuracy inspection of defects and profile are thus necessary to ensure the reliability of device. Phase measuring deflectometry(PMD) is a fast, cost-effective and high accuracy measurement technology which has been developed in recent years. As a slope measurement technology, PMD possesses a high sensitivity. Very small slope variation will lead to a large variation of the phase. PMD is very possible to have a good performance in the wafer inspection. In this paper, the requirements of the wafer inspection in the industries are discussed, and compatibility of PMD and those requirements is analyzed. In the experimental work, PMD gets the slope information of the wafer surface directly. The curvature or height information can be acquired simply by the derivation or integral of the slope. PMD is proved to make a superior result in high-precision defect detecting and shape measurement of wafer by the analysis of experiment results.

Fringe projection profilometry (FPP) has been widely used for 3-D surface shape measurement with the features of high accuracy, non-contact and fast speed. In FPP, the phase distribution is extracted from the captured distorted fringe pattern, and the height information could subsequently be obtained by the phase-height relation. In actual measurement, the captured pattern usually contains noises, which will influence the precision of the reconstructed result. In order to increase the accuracy of measurement, noise reduction procedure to these fringe patterns is required. The existing noise reducing methods (such as Fourier transform, Wavelet transform) have certain effect. However, they will eliminate some high frequencies generated by a surface with sharp change and make the image blurring. In this paper, we use Curvelet transform to enhance the accuracy of measurement in FPP. The Curvelet transform has the ability of multiscale and multidirection analysis in image processing. It has better descriptions of edges and detailed information of images. Simulations and the experimental results show that the Curvelet transform has an excellent performance in image denoising and it has a wonderful effect on accuracy enhancement of complex surface shape measurement in FPP.

In phase measuring deflectometry (PMD), a camera observes a sinusoidal fringe pattern via the surface of a specular object under test. Any slope variations of the surface lead to distortions of the observed pattern. Without height-angle ambiguity, carrier removal process is adopted to evaluate the variation of surface slope from phase distribution when a quasi-plane is measured. However, in the usual measurement system, the carrier phase will be nonlinear due to the restrictions of system geometries. In this paper, based on the analytical carrier phase description in PMD, a carrier removal method is proposed to remove the nonlinear carrier phase. Both the theoretical analysis and the experiment results are presented. By comparison with reference-subtraction method and series-expansion method, this proposed method can achieve carrier removal process with only the measurement of one single object, as well as high accuracy and time-saving.

The polarization maintaining fiber has been playing an important role in the fields of optical fiber sensing, communication, and so on. The beat length is one of the main parameters of polarization maintaining fiber, and it usually represents its polarization maintaining performance. In this paper, the beat length variation of Panda fiber with external force is investigated. The simulation results indicate that the beat length variation was determined both by the external force value F and the angle θ between the external force direction and the slow axis of Panda fiber. When F is a constant, the beat length of polarization maintaining fiber is changed in sinusoidal form whose various cycle is π with the variation of θ. Meanwhile, the minimum and maximum values of beat length will be obtained when the angles are even multiple of π/2 or odd multiple of π/2, respectively. When θ is a constant, the beat length is changed in linear form with the increasing of external force value. Finally, the experimental system of beat length measurement based on Sagnac interferometer loop is illustrated, and the result shows an excellent agreement with the theoretical analysis.

In phase measuring deflectometry (PMD), the fringe pattern deformed according to slope deviation of a specular surface is digitized employing a phase-shift technique. Without height-angle ambiguity, carrier-removal process is adopted to evaluate the variation of surface slope from phase distribution when a quasi-plane is measured. This paper investigates nonlinear carrier components introduced by the generalized imaging process in PMD and the nonlinear carrier removal methods. To remove the nonlinear carrier components in PMD, the reference subtraction technique, series-expansion technique and Zernike polynomials which are normally used in fringe projection profilometry are analyzed on accuracy, processing time and experimental simplicity. What’s more, a new nonlinear carrier removal technique is proposed according to the analytical expression of carrier phase. The theoretical analysis and the experiment results show that the new technique is accurate, simple and time-saving.

In phase measuring deflectometry, the measurement accuracy is relatively low with low reflectivity surface. Based on temporal phase unwrapping, two main noises are reduced to improve accuracy by least-square method and 3-frame method.

Calibration is a crucial step in fringe projection profilometry, which establishes the relationship between unwrapped phase and (FPP) three-dimensional (3-D) shape data (X,Y,h). For an arbitrarily arranged FPP system, a simple geometrical model and mathematical descriptions of the relationships among phase, height distribution, and transverse coordinate are presented. Based on this, a flexible global calibration method is presented to reconstruct 3-D shape by just using a checkerboard with known separation and alternating white and blue. The calibration board is placed at several random positions to determine the relationship between phase and height, and the relationship between pixel position and X, Y coordinates. To get high accuracy, distortion for each pixel is considered. The validity, flexibility, and practicality of this system and calibration technique are verified by experiments.

A color-encoded fringe reflection technique is presented for dynamic specular surface measurement. Only one color-encoded fringe pattern is required in this method. In comparison with the reported dynamic specular surface measuring method (the composite fringe pattern method), the proposed color-encoded fringe technique has higher phase accuracy. The color intensity crosstalk problem between the three channels is discussed. As a result, this problem will seldom affect the phase accuracy of the proposed method. This turns out to be the main reason why the presented method can achieve a higher measuring accuracy than the existing dynamic measurement method. In addition, the proposed color-encoded fringe technique is proven to be more suitable than the existing method for the complex tested surface. The vibrating measuring experiment of a wafer proves the ability of the proposed method to achieve dynamic measurement.

In phase measuring deflectometry (PMD), the fringe pattern deformed according to slope deviation of a specular surface is digitized employing a phase-shift technique. Without height-angle ambiguity, carrier-removal process is adopted to evaluate the variation of surface slope from phase distribution when a quasi-plane is measured. However, the difficulty lies in the fact that the nonlinearity is generally contained in the carrier frequency due to the restrictions of system geometries. This paper investigates nonlinear carrier components introduced by the generalized imaging process in PMD. Furthermore, the analytical expression of carrier components in PMD is presented for the first time. The presented analytical form of carrier components can be extended to analyze and describe various effects of system parameters on carrier distortion. Assuming a pinhole perspective model, carrier phase distribution of arbitrary geometric arrangement is modeled as a function of spatial variables by exploring ray tracing method. As shown by simulation and experimental results, the carrier distortion is greatly affected by non-telecentric camera operation. Experimental results on the basis of reference subtraction technique further demonstrate that restrictions on reflection system geometry can be eliminated when the carrier phase is removed elaborately.

Characterization of a phase modulator or phase shifter has always been an integral part of phase-modulating or phase-adjusting applications. We propose a simplified approach to characterize a phase modulator by investigating the performance of phase shifts from grabbed interferograms using the phase extraction method. After reviewing some phase analysis techniques, the interframe intensity correlation (IIC) matrix method is introduced to the investigation. The proposed strategy is illustrated by the measurement of a free-space electro-optic modulator (EOM). Placing the modulator in one arm of a Michelson interferometer, the global phase shifts are estimated by the IIC method from the phase-stepped interferograms. Experimental results demonstrate the tested EOM has a phase modulation response of at least 2π rad with a π/20 rad modulation precision for λ=1064 nm. In addition, our method is applicable to various types of phase modulator or phase shifter calibration, e.g., electro-optic phase modulator, spatial light modulator, or piezoelectric transducer (PZT).

Flattened ASE fiber sources with C+L bandwidth(1520-1620nm) are attractive. Long period fiber gratings (LPFG) have the characteristics of band-stopped, which can be used to flatten the spectrum of amplified spontaneous emission (ASE) light source. In this paper, spectrum flattening of ASE light source covering C-band and L-band based on a long period fiber grating is studied. As a flattening filter, LPFG is often placed in the end of the output port. The results in this paper show that the placed position of LPFG has great influence on the spectrum flattening of ASE light source. Output spectrum measured of filtered ASE source with the LPFG at different position is given, and the detailed theoretical analysis to explain the experimental results is followed. In the dual-stage double-pass structure, based on a long period fiber grating and two 980 nm high power semiconductor lasers, high power and ultra bandwidth ASE fiber source has been gained. The source has a bandwidth of 77 nm (1525.5 ~1602.5 nm) with ±1.6 dB ripple and 42 mw of output power.

In phase measuring deflectometry (PMD), the inspection accuracy of the defects and height of the specular surface are related to the level of phase errors. The usage of numeric integration in reconstructing the shape and the defocusing capture of the fringe pattern, which will amplify the phase errors, make error discussion more significant in PMD than other shape measurement techniques. Phase error analysis and reduction in PMD are presented. The random noises, nonlinear response function, the nontelecentric imaging of the charge-coupled device camera, and the nonlinear response function of the liquid crystal display screen are the main phase error sources in PMD. The analytical relation between the random phase error and its influence factors in PMD is deduced. From the relation formulation, the influence factors of random phase error are analyzed, and the results are proven by the simulation and experiment. A possible phase error-reduction method, which integrates several methods for congeneric errors in fringe projection profilometry, is investigated to reduce phase errors in PMD. This composite method is proven to have a good performance by a plane mirror experiment.

A one-dimensional Fourier transform of a Rayleigh backscattering traces matrix along the traces direction method has been proposed to simultaneously extract location and frequency information of vibration in the distributed vibration sensing system based on phase-sensitive optical time domain reflectometry. Meanwhile, the signal-to-noise ratio (SNR) of the proposed method also can be improved as the signals are processed in the frequency domain since in the frequency domain, noise is “slow change” compared with the vibration. Then, experiments on two-point vibrations have been done. An SNR of 9.5 dB was achieved, and the spatial resolution is also improved to 3.7 m with a 50 ns pulse width and 2.7 km long fiber owing to the improved SNR.

Phase unwrapping, which usually involves complicated and time-consuming procedures, is crucial for phase-measuring profilometry. Unwrapping isolated phase regions with global phase discontinuity is challenging for traditional reliability ordering based phase unwrapping methods. This paper presents a novel method that combines the advantages of digital point array based active triangulation profilometry with a reliability of modulation ordering algorithm. Table entries that store spatial coordinates of sampling points are established, and the true phases measured by geometrical relationships are used to direct phase unwrapping. Different from the proposed 2D spatial unwrapping algorithms until now, the fringe order can be easily identified by referencing the patterns of multiple points. Additionally, unwrapping from the interior part of isolated regions following an optimized path is guaranteed. The prevention of penetration through invalid pixels into isolated regions ensures this new method will alleviate errors due to phase ambiguity. Simulation and experimental results demonstrate that the proposed technique can feasibly measure objects with a wide range of height variation.