Research

10 pages, 4410 KiB

Open AccessCommunication

Oblique-Incidence Interferometric Measurement of Optical Surface Based on a Liquid-Crystal-on-Silicon Spatial Light Modulator

by Zhen Zeng, Chengzhao Jiang, Yuxuan Jia, Zhongsheng Zhai and Xiaodong Zhang

Photonics 2024, 11(2), 132; https://doi.org/10.3390/photonics11020132 - 30 Jan 2024

Viewed by 698

Abstract

An oblique-incidence interferometric measurement method is proposed to measure and adjust optical surfaces with a liquid-crystal-on-silicon spatial light modulator (LCoS-SLM). The optical system only consists of an interferometer and an LCoS-SLM with precision mounts. It could reduce the measuring cost and time consumption [...] Read more.

An oblique-incidence interferometric measurement method is proposed to measure and adjust optical surfaces with a liquid-crystal-on-silicon spatial light modulator (LCoS-SLM). The optical system only consists of an interferometer and an LCoS-SLM with precision mounts. It could reduce the measuring cost and time consumption due to the programmable function of the LCoS-SLM and offer the ability to align the optical system. The oblique-incidence measurement theory and optical system adjustment method are established based on an off-axis paraboloid model. The ray-tracing program to calculate the compensation phase map in the measurement is proposed with math models. In the optical alignment step, the off-axis paraboloid model is used to apply the LCoS-SLM as a phase compensator to generate a focusing spot or light spot array to adjust the measured optical surface. And in the interferometric measurement step, the calculated compensation phase map from the ray-tracing calculation is loaded on the LCoS-SLM using the same optical setup as the optical alignment step without any mechanical adjustment. Two interference measurement experiments of typical optical surfaces were carried out to verify the accuracy of the measuring system. Full article

(This article belongs to the Special Issue Optical Measurement Systems)

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22 pages, 10939 KiB

Open AccessArticle

Optical Phased Array-Based Laser Beam Array Subdivide Pixel Method for Improving Three-Dimensional Imaging Resolution

by Shuai Wang, Gang Yuan, Kun-Peng Wang, Guang-De Sun, Lei Liu, Ling Li, Bing Zhang and Lin Quan

Photonics 2023, 10(12), 1360; https://doi.org/10.3390/photonics10121360 - 09 Dec 2023

Viewed by 780

Abstract

The small number of pixels in the current linear mode avalanche photodiode (LM-APD) array limits its three-dimensional (3D) imaging resolution. We use an optical phased array-based beam array subdivided pixel method to improve the 3D imaging resolution, using an optical phased array to [...] Read more.

The small number of pixels in the current linear mode avalanche photodiode (LM-APD) array limits its three-dimensional (3D) imaging resolution. We use an optical phased array-based beam array subdivided pixel method to improve the 3D imaging resolution, using an optical phased array to generate a beam array with the same number of pixels as the LM-APD array and matching positions and controlling each sub-beam in the beam array to scan in the field of view of the corresponding pixel. The sub-beam divergence angle in the beam array is smaller than the instantaneous field of view angle of a single pixel in the LM-APD array. The sub-beam scanning in a single pixel’s field of view realizes the multiple acquisition of the target 3D information by the LM-APD array, thus improving the resolution of the LM-APD array. The distribution of the beam array in the far field is simulated, and the main performance parameters of 3D imaging are analyzed. Finally, a liquid crystal phase modulator is used as an optical phased array device to conduct experiments on a target 20 m away, and the results prove that our method can improve the resolution from 4 × 4 to 8 × 8, which can be improved at least four times. Full article

(This article belongs to the Special Issue Optical Measurement Systems)

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17 pages, 7354 KiB

Open AccessArticle

An Angle Precision Evaluation Method of Rotary Laser Scanning Measurement Systems with a High-Precision Turntable

by Rao Zhang, Jiarui Lin, Shendong Shi, Kunpeng Shao and Jigui Zhu

Photonics 2023, 10(11), 1224; https://doi.org/10.3390/photonics10111224 - 01 Nov 2023

Viewed by 725

Abstract

Rotary laser scanning measurement systems, such as the workshop measurement positioning system (wMPS), play critical roles in manufacturing industries. The wMPS realizes coordinate measurement through the intersection of multiple rotating fanned lasers. The measurement model of multi-laser plane intersection poses challenges in terms [...] Read more.

Rotary laser scanning measurement systems, such as the workshop measurement positioning system (wMPS), play critical roles in manufacturing industries. The wMPS realizes coordinate measurement through the intersection of multiple rotating fanned lasers. The measurement model of multi-laser plane intersection poses challenges in terms of accurately evaluating the system, making it difficult to establish a standardized evaluation method. The traditional evaluation method is based on horizontal and vertical angles derived from scanning angles, which are the direct observation of wMPS. However, the horizontal- and vertical-angle-based methods ignore the assembly errors of fanned laser devices and mechanical shafts. These errors introduce calculation errors and affect the accuracy of angle measurement evaluation. This work proposes a performance evaluation method for the scanning angle independent of the assembly errors above. The transmitter of the wMPS is installed on a high-precision turntable that provides the angle reference. The coordinates of enhanced reference points (ERP) distributed in the calibration space are measured by the laser tracker multilateration method. Then, the spatial relationship between the transmitter and the turntable is reconstructed based on the high-precision turntable and the good rotational repeatability of the transmitter. The simulation was carried out to validate the proposed method. We also studied the effect of fanned laser devices and shaft assembly errors on horizontal and vertical angles. Subsequently, the calibration results were validated by comparing the residuals with those derived from the space-resection method. Furthermore, the method was also validated by comparing the reference and scanning angles. The results show that the maximum angle measurement error was approximately 2.79″, while the average angle measurement error was approximately 1.26″. The uncertainty (k = 1) of the scanning angle was approximately 1.7″. Finally, the coordinate measurement test was carried out to verify the proposed method by laser tracker. The results show that the average re-scanning error was 2.17″. Full article

(This article belongs to the Special Issue Optical Measurement Systems)

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15 pages, 5882 KiB

Open AccessArticle

Research on the Detection Method of Projection Stellar Target Simulator

by Jianan Kang, Ru Zheng, Lingyun Wang, Chengwei Pang and Guangxi Li

Photonics 2023, 10(10), 1101; https://doi.org/10.3390/photonics10101101 - 29 Sep 2023

Viewed by 635

Abstract

The projection stellar target simulator is a stellar target simulator in which star points are projected to be imaged on a fixed plane at a fixed distance. Compared with conventional stellar target simulators, the projection stellar target simulator makes star points visible and [...] Read more.

The projection stellar target simulator is a stellar target simulator in which star points are projected to be imaged on a fixed plane at a fixed distance. Compared with conventional stellar target simulators, the projection stellar target simulator makes star points visible and provides the necessary condition for a semi-physical simulation test of the star camera. In this paper, the projection stellar target simulator optical system with high-quality imaging is designed by combining the projection technology, which breaks the collimated imaging of the conventional stellar target simulator optical system, and offers a new thought to solve the problem of decreasing the calibration accuracy caused by the influence of the coaxiality and other factors in the stellar target simulator calibrating the star camera. Based on the imaging behavior of the star map, this paper proposes a method to realize the automatic detection of a projection stellar target simulator by using CCD and introduces the composition and working principle of the detection system in detail. According to the imaging characteristics of star points, denoising and threshold segmentation of the star map are carried out, and an improved centroid algorithm is proposed to achieve high-precision positioning of the centroid coordinates of the star points. The measurement model and measuring formulas for the angular distance between stars are established. The error sources of the detection system are analyzed and obtain the theoretical error of 9.22″ for this detection system. The result of an actual test experiment shows that the position error of single star is less than 11″, in line with the theoretical analysis of the error, indicating the detection system has high detection precision and meets the requirement for the detection accuracy of the projection stellar target simulator. Full article

(This article belongs to the Special Issue Optical Measurement Systems)

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24 pages, 10476 KiB

Open AccessArticle

Slightly Off-Axis Digital Holography Using a Transmission Grating and GPU-Accelerated Parallel Phase Reconstruction

by Hongyi Bai, Jia Chen, Laijun Sun, Liyang Li and Jian Zhang

Photonics 2023, 10(9), 982; https://doi.org/10.3390/photonics10090982 - 28 Aug 2023

Viewed by 808

Abstract

Slightly off-axis digital holography is proposed using transmission grating to obtain quantitative phase distribution. The experimental device is based on an improved 4f optical system in which a two-window input plane is used to form the object beam and reference beam. Then, the [...] Read more.

Slightly off-axis digital holography is proposed using transmission grating to obtain quantitative phase distribution. The experimental device is based on an improved 4f optical system in which a two-window input plane is used to form the object beam and reference beam. Then, the two beams are diffracted into multiple orders by the transmission grating placed at the Fourier plane. By applying a modified Michelson configuration, the interference patterns can be generated by the object and reference beams from different diffraction orders. After translating the grating, a random phase shift can be introduced to the hologram. To demonstrate the feasibility of our method, both thick and thin phase specimens are retrieved using two carrier phase-shifting holograms. Furthermore, we use the phase reconstruction algorithm based on the NVIDIA CUDA programming model to reduce the retrieval time. Meanwhile, we optimize the discrete cosine transform (DCT)-based least-squares unwrapping algorithm to unwrap the phase. By porting the entire phase reconstruction process to the graphics processing unit (GPU), the phase retrieval acceleration and execution efficiency significantly improve. To demonstrate the feasibility of our method, it is found that our method can measure the surface profiles of standard elements, such as a plano-convex cylinder lens and a microlens array, with a relative error of about 0.5%. For holograms with a different phase shift, the root-mean-square (RMS) value of the phase difference for the main imaging region is about 0.2 rad. By accelerating the phase reconstruction with GPU implementation, a speedup ratio of about 20× for the thick phase specimen and a speedup ratio of about 15× for the thin-phase specimen can be obtained for holograms with a pixel size of 1024 × 1024. Full article

(This article belongs to the Special Issue Optical Measurement Systems)

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12 pages, 4342 KiB

Open AccessCommunication

Self-Mixing Interferometry Cooperating with Frequency Division Multiplexing for Multiple-Dimensional Displacement Measurement

by Dongmei Guo, Zhanwu Xie, Qin Yang, Wei Xia, Yanguang Yu and Ming Wang

Photonics 2023, 10(7), 839; https://doi.org/10.3390/photonics10070839 - 20 Jul 2023

Cited by 1 | Viewed by 918

Abstract

In this study, a multiple-dimensional displacement measurement technology is demonstrated by using self-mixing interferometry (SMI) cooperating with a frequency division multiplexing (FDM) technique. The proposed SMI configuration with a single laser generates three modulated light beams with different carrier frequencies. Each beam is [...] Read more.

In this study, a multiple-dimensional displacement measurement technology is demonstrated by using self-mixing interferometry (SMI) cooperating with a frequency division multiplexing (FDM) technique. The proposed SMI configuration with a single laser generates three modulated light beams with different carrier frequencies. Each beam is incident on a planar grating with its own auto-collimation diffraction angle. The diffracted beams return to the laser cavity and then self-mixing interference occurs. An algorithm based on FDM is developed for multiple-dimensional displacement reconstruction from a single SMI signal. Experiments are conducted to verify the proposed approach. This paper shows an attractive sensing system for multiple-dimensional displacement featuring compact configuration, high resolution and better immunity to environmental disturbances. Full article

(This article belongs to the Special Issue Optical Measurement Systems)

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9 pages, 5254 KiB

Open AccessCommunication

Tilt Measurement at the Quantum Cramer–Rao Bound Using a Higher-Order Hermite–Gaussian Mode

by Zhi Li, Yijian Wang, Hengxin Sun, Kui Liu and Jiangrui Gao

Photonics 2023, 10(5), 584; https://doi.org/10.3390/photonics10050584 - 17 May 2023

Cited by 1 | Viewed by 905

Abstract

The quantum Cramer–Rao bound (QCRB) provides an ultimate precision limit in parameter estimation. The sensitivity of spatial measurements can be improved by using the higher-order Hermite–Gaussian mode. However, to date, the QCRB-saturating tilt measurement has not been realized. Here, we experimentally demonstrate tilt [...] Read more.

The quantum Cramer–Rao bound (QCRB) provides an ultimate precision limit in parameter estimation. The sensitivity of spatial measurements can be improved by using the higher-order Hermite–Gaussian mode. However, to date, the QCRB-saturating tilt measurement has not been realized. Here, we experimentally demonstrate tilt measurements using a higher-order

H G_{40}

mode as the probe beam. Using the balanced homodyne detection with an optimal local beam, which involves the superposition of high-order

H G_{30}

and

H G_{50}

modes, we demonstrate the precision of the tilt measurement approaching the QCRB. The signal-to-noise ratio of the tilt measurement is enhanced by 9.2 dB compared with the traditional method using

H G_{00}

as the probe beam. This scheme is more practical and robust to losses, which has potential applications in areas such as laser interferometer gravitational-wave observatories and high-sensitivity atomic force microscopes. Full article

(This article belongs to the Special Issue Optical Measurement Systems)

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10 pages, 4773 KiB

Open AccessCommunication

Aided Imaging Phase Measuring Deflectometry Based on Concave Focusing Mirror

by Ziyu Li, Nan Gao, Zhaozong Meng, Zonghua Zhang, Feng Gao and Xiangqian Jiang

Photonics 2023, 10(5), 519; https://doi.org/10.3390/photonics10050519 - 01 May 2023

Cited by 2 | Viewed by 1354

Abstract

With the rapid development of aerospace, high-speed train, and automotive industries, the demand for the measurement of high-precision specular components is increasing. The acquisition of high-precision three-dimensional (3D) data is conducive to improving the performance of and extending the service life of these [...] Read more.

With the rapid development of aerospace, high-speed train, and automotive industries, the demand for the measurement of high-precision specular components is increasing. The acquisition of high-precision three-dimensional (3D) data is conducive to improving the performance of and extending the service life of these components. However, the existing 3D measurement methods of specular surfaces are affected by the inherent limitation of the depth of field (DOF) of camera lenses. Based on the principle of paraxial reflection imaging of a concave mirror, this paper introduces a concave mirror into a phase measuring deflectometry (PMD) system and proposes an aided imaging PMD (AIPMD) based on a concave focusing mirror. The proposed system realizes the clear imaging of the encoded patterns and the surface under test in the DOF of the camera lens, simultaneously. Meanwhile, the iterative coefficient specular reconstruction algorithm is studied based on this system. The feasibility and accuracy of the proposed method are verified by simulations and experiments. Full article

(This article belongs to the Special Issue Optical Measurement Systems)

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13 pages, 3996 KiB

Open AccessArticle

An Autofocus Method Based on Improved Differential Confocal Microscopy in Two-Photon Lithography

by Zhenyu Yang, Minfei He, Guozun Zhou, Cuifang Kuang and Xu Liu

Photonics 2023, 10(3), 338; https://doi.org/10.3390/photonics10030338 - 21 Mar 2023

Cited by 1 | Viewed by 1685

Abstract

Two-photon lithography (TPL) plays a vital role in microstructure fabrication due to its high processing accuracy and maskless characteristics. To optimize the manufacturing quality deteriorated by the defocus of the substrate, an autofocus approach based on improved differential confocal microscopy (IDCM) is proposed [...] Read more.

Two-photon lithography (TPL) plays a vital role in microstructure fabrication due to its high processing accuracy and maskless characteristics. To optimize the manufacturing quality deteriorated by the defocus of the substrate, an autofocus approach based on improved differential confocal microscopy (IDCM) is proposed in this paper. Through analyzing the intensity response signals from two detectors with symmetrical axial offset, the defocus amount is measured and compensated for with high precision and noise immunity to stabilize the substrate. The verification experiments on the coverslip reported a detection sensitivity of 5 nm, a repetitive measurement accuracy of less than 15 nm, and a focusing accuracy reaching around 5 nm. The consistency between simulation and characterization demonstrated the effectiveness and superior performance of the autofocus system for the high production quality of the metalens array. The proposed autofocus method shows promise for further application to the fabrication of complex structures on various substrates. Full article

(This article belongs to the Special Issue Optical Measurement Systems)

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28 pages, 26799 KiB

Open AccessArticle

Thermal Deformation Measurement of Aerospace Honeycomb Panel Based on Fusion of 3D-Digital Image Correlation and Finite Element Method

by Linghui Yang, Zezhi Fan, Ke Wang, Hui Sun, Shuotao Hu and Jigui Zhu

Photonics 2023, 10(2), 217; https://doi.org/10.3390/photonics10020217 - 16 Feb 2023

Viewed by 1795

Abstract

Aiming to solve the problem of the high-precision deformation measurement of large-scale satellite structures in manufacturing and testing environments, this paper proposes a measurement method based on the idea of fusing actual measurements with finite element analysis. The digital image correlation (DIC) method [...] Read more.

Aiming to solve the problem of the high-precision deformation measurement of large-scale satellite structures in manufacturing and testing environments, this paper proposes a measurement method based on the idea of fusing actual measurements with finite element analysis. The digital image correlation (DIC) method is used to obtain the high-precision deformation of the honeycomb panel, and the finite element method (FEM) model is introduced to remove the limitations of existing pure measurement methods. Data fusion based on a machine learning neural network is proposed to fuse high-precision deformation and physical information such as temperature to conduct multi-level training on FEM parameters. Through an interpolation of the analysis and calculation results after training, not only can the accuracy of the finite element be improved, but difference and extrapolation of the digital image correlation measurement results can be performed. In the experiments, the satellite on-orbit temperature data are substituted into the modified finite element model. The testing results shows that the prediction accuracy of the model under different temperature loads can be controlled within 10 μm under an 840 mm × 640 mm scale. A high predictive accuracy can be achieved for the revised model for the complete deformation of large structural sections. Full article

(This article belongs to the Special Issue Optical Measurement Systems)

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14 pages, 6531 KiB

Open AccessEditor’s ChoiceArticle

Distortion Detection of Lithographic Projection Lenses Based on Wavefront Measurement

by Tian Li, Jian Wang, Shaolin Zhou, Haiyang Quan, Lei Chen, Junbo Liu, Jing Du, Xianchang Zhu and Song Hu

Photonics 2023, 10(2), 168; https://doi.org/10.3390/photonics10020168 - 04 Feb 2023

Viewed by 2502

Abstract

As with the decreasing feature size prompted by Moore’s law and the continuous technological advancements in the semiconductor industry, the distortion of the projection lens is an important factor that affects the overlay. In this paper, we propose a wavefront-measurement-based method to detect [...] Read more.

As with the decreasing feature size prompted by Moore’s law and the continuous technological advancements in the semiconductor industry, the distortion of the projection lens is an important factor that affects the overlay. In this paper, we propose a wavefront-measurement-based method to detect the projection lens distortion in the lithographic system. By normalizing the coordinates of the Shack–Hartmann system with the image displacements represented in the Z₂ and Z₃ terms of Zernike coefficients, the offsets between the actual image points and the ideal image points can be determined. By offset collection at an array of 7 × 7 field points to establish an overdetermined system of equations, the proposed method can simultaneously detect the distortions of translation, magnification, rotation, decentering distortion, thin prism distortion, and third-order radial distortion. This distortion measurement method is highly flexible for distortion measurement with portable and compactly integrated sensors, enabling the real-time and cost-efficient measurement of wave aberration and distortion. For proof-of-concept experiments, a projection lens with a numerical aperture (NA) of 0.58 for i-line (365 nm) is used for experimental testing. The results reveal that the repeatability accuracy of distortion detection is 51 nm and the 72 h long-term reproducibility is 143 nm. Full article

(This article belongs to the Special Issue Optical Measurement Systems)

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15 pages, 4133 KiB

Open AccessArticle

Simulated LCSLM with Inducible Diffractive Theory to Display Super-Gaussian Arrays Applying the Transport-of-Intensity Equation

by Jesus Arriaga-Hernandez, Bolivia Cuevas-Otahola, Jacobo Oliveros-Oliveros, María Morín-Castillo, Ygnacio Martínez-Laguna and Lilia Cedillo-Ramírez

Photonics 2023, 10(1), 39; https://doi.org/10.3390/photonics10010039 - 30 Dec 2022

Viewed by 1471

Abstract

We simulate a liquid crystal spatial light modulator (LCSLM), previously validated by Fraunhofer diffraction to observe super-Gaussian periodic profiles and analyze the wavefront of optical surfaces applying the transport-of-intensity equation (TIE). The LCSLM represents an alternative to the Ronchi Rulings, allowing to avoid [...] Read more.

We simulate a liquid crystal spatial light modulator (LCSLM), previously validated by Fraunhofer diffraction to observe super-Gaussian periodic profiles and analyze the wavefront of optical surfaces applying the transport-of-intensity equation (TIE). The LCSLM represents an alternative to the Ronchi Rulings, allowing to avoid all the related issues regarding diffractive and refractive properties, and noise. To this aim, we developed and numerically simulated a LCSLM resembling a fractal from a generating base. Such a base is constituted by an active square (values equal to one) and surrounded by eight switched-off pixels (zero-valued). We replicate the base in order to form 1

\times N

-pixels and the successive rows to build the

1024 \times 1024

LCSLM of active pixels. We visually test the LCSLM with calibration images as a diffractive object that is mathematically inducible, using mathematical induction over the

N \times N

-shape (

1 \times 1

,

2 \times 2

,

3 \times 3

, …,

n \times n

pixels for the generalization). Finally, we experimentally generate periodic super-Gaussian profiles to be visualized in the LCSLM (transmission SLM,

1024 \times 768

-pixels LC 2012 Translucent SLM), modifying the TIE as an optical test in order to analyze the optical elements by comparing the results with ZYGO/APEX. Full article

(This article belongs to the Special Issue Optical Measurement Systems)

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