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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.

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.

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.

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.

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.