Jiangping Zhu

Accurate and fast 3D surface measurement with temporal-spatial binary encoding structured illumination

Balancing the accuracy and speed for 3D surface measurement of object is crucial in many important applications. Binary encoding pattern utilizing the high-speed image switching rate of digital mirror device (DMD)-based projector could be used as the candidate for fast even high-speed 3D measurement, but current most schemes only enable the measurement speed, which limit their application scopes. In this paper, we present a binary encoding method and develop an experimental system aiming to solve such a situation. Our approach encodes one computer-generated standard 8 bit sinusoidal fringe pattern into multiple binary patterns (sequence) with designed temporal-spatial binary encoding tactics. The binary pattern sequence is then high-speed and in-focus projected onto the surface of tested object, and then captured by means of temporal-integration imaging to form one sinusoidal fringe image. Further the combination of phase-shifting technique and temporal phase unwrapping algorithm leads to fast and accurate 3D measurement. The systematic accuracy better than 0.08mm is achievable. The measurement results with mask and palm are given to confirm the feasibility.

Temporal-spatial encoding binary fringes toward three-dimensional shape measurement without projector nonlinearity

Abstract. Projector nonlinearity is a common problem for digital structured light-based three-dimensional (3-D) shape measurement techniques. A temporal-spatial binary encoding method is presented for the purpose of eluding it. We build a 3-D shape measurement scheme by combining our proposed method with phase measurement profiling. A standard sinusoidal fringe pattern is divided into more than two binary fringe patterns using specially designed temporal and spatial binary encoding rule based on intensity hierarchic quantification, and then are in-focus projected onto the measured object at a time sequence to reconstruct a frame phase-shifting fringe image. On account of the projected binary fringe pattern strictly consisting of zeros and ones, the influence of the projector nonlinearity on the measurement result can be effectively ruled out and simultaneously enables high-quality sinusoidality. In-depth investigations by theoretical analysis and experiments are conducted to demonstrate the performance of this method.

Gap-optimized Moire phase imaging alignment for proximity lithography

Abstract. The proposed four-quadrant Moiré alignment scheme to detect the misalignment between mask and wafer for proximity lithography can achieve the alignment accuracy with nanometer level. When implementing the scheme, however, the distribution of Moiré fringes associated with the mask–wafer gap indeed goes against the alignment, making the gap optimization highly urgent. The optimization model is established, and numerical simulation as well as experimental verification is also provided. Furthermore, an alignment accuracy of ∼3  nm with the illumination wavelength of 632.8 nm is experimentally attained. Simultaneously, the design mechanism of alignment marks for improving the availability of the alignment scheme is discussed.

Focusing Properties of Single-Focus Photon Sieve

In this letter, we present a single-focus photon sieve (SFPS), which can produce single focus with suppressed sidelobes, featuring a higher signal-to-noise ratio and improved image contrast. This is achieved through combining single-focus zone plates (SZPs) and photon sieves (PSs). Simulations and experiments were conducted to verify the single focusing property of SFPSs. The results illustrated the advantages of SFPSs over conventional PSs, as well as improved resolution compared with SZPs in terms of the same specific minimum feature size. SFPSs are extremely promising to replace PSs and Fresnel zone plates in the fields such as X-ray focusing, imaging, and nanometer lithography.

Three-dimensional shape measurement using color random binary encoding pattern projection

Abstract. Acquiring the three-dimensional (3-D) surface geometry of objects with a full-frame resolution is of great concern in many applications. This paper reports a 3-D measurement scheme based on single-frame pattern projection in the combination of random binary encoding and color encoding. Three random binary encoding patterns generated by a computer embedded in three channels of a color pattern lead to a color binary encoding pattern. Two color cameras with a stereo-vision arrangement simultaneously capture the measured scene under the proposed encoding structured illumination. From captured images, three encoding images are extracted and analyzed using the extended spatial–temporal correlation algorithm for 3-D reconstruction. Theoretical explanation and analysis concerning the encoding principle and reconstruction algorithm, followed by experiments for reconstructing 3-D geometry of stationary and dynamic scenes show the feasibility and practicality of the proposed method.

Adjustment Strategy for Inclination Moiré Fringes in Lithography by Spatial Frequency Decomposition

The recently proposed four-quadrant grating Moiré fringe alignment scheme was demonstrated to have the potential of achieving nanometer alignment for proximity lithography. The mask-wafer misalignment was accurately detected by comparing the phase between two sets of Moiré fringes averaged along with the fringe direction, making the inclination adjustment of Moiré fringes highly imperative. The inclination closely related with the included angle between mask (alignment mark) and wafer (alignment mark) largely influences the alignment accuracy. To solve this issue, we present an adjustment strategy based on the spatial frequency decomposition of two sets of differential Moiré fringes, by which the included angle can be accurately adjusted with an accuracy of better than 10-5 rad. The subsequent discussion indicates that the position of imaging system can be responsible for the inclination but actually it would not affect the mask-wafer alignment, so that our proposed adjustment strategy can be operated simply and feasibly, which is validated by the theoretical analysis and experimental results.

Moiré-Based Interferometry for Magnification Calibration of Bitelecentric Lens System

The bitelecentric lens system is widely used in many domains, such as 3-D measurements and tube inspection. The magnification calibration for such a system is a crucial problem for its further application in achieving precise measurements. However, it is difficult to obtain an accurate result using a general magnification calibration method. In this paper, the Moiré-based interferometry is demonstrated to accurately calibrate the magnification of bitelecentric lens system that increases the speed and precision of the measurement. Two special grating marks containing upper and lower parts with slightly different periods are designed to generate Moiré fringes. By analyzing the finally obtained Moiré fringes, the magnification could be determined through Fourier-based phase analysis and a phase unwrapping algorithm, and the further the deviation is from the theoretical value, the more obvious the differences between upper and lower periods will be. Both simulations and experiments are conducted to verify the feasibility and effectiveness of the proposed approach. Results indicate that the magnification could be calibrated at the accuracy of 0.4% with extraordinary sensitivity.