Design, fabrication, and test of micro-optics for biomedical applications

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Point Diffraction Interferometry

The point diffraction interferometer (PDI) employs a point-diffraction spherical wavefront as ideal measurement reference, and it overcomes the accuracy limitation of reference optics in traditional interferometers. To overcome the limitation of measurement range either with pinhole (low light transmission) or with single-mode fiber (low NA), a single-mode fiber with narrowed exit aperture has been proposed to obtain the point-diffraction wavefront with both high NA and high power. It is a key issue to analyze the point-diffraction wavefront error in PDI, which determines the achievable accuracy of the system. The FDTD method based on the vector diffraction theory provides a powerful tool for the design and optimization of the PDI system. In addition, a high-precision method based on shearing interferometry can be applied to measure point-diffraction wavefront with high NA, in which a double-step calibration including three-dimensional coordinate reconstruction and symmetric lateral displacement compensation is used to calibrate the geometric aberration. The PDI is expected to be a powerful tool for high-precision optical testing. With the PDI method, a high accuracy with RMS value better than subnanometer can be obtained in the optical surface testing and submicron in the absolute three-dimensional coordinate measurement, demonstrating the feasibility and wide application foreground of PDI

Curl-free ray mapping in three dimensions for freeform illumination design

An illumination design method that incorporates the entire 3-D geometry between the optical surface and target plane into the ray mapping calculation has been developed. The resulting mapping relationship is integrable along the specific contours of the optical surface instead of a 2-D plane. The method is capable of creating extremely high performance, off-axis designs (97% uniformity at 54-deg off-axis), and since it explicitly accounts for system geometry, appears to be easily generalizable. (C) 2019 Society of Photo-Optical Instrumentation Engineers (SPIE)National Institute of Biomedical Imaging and Bioengineering of the National Institutes of Health [UH2EB022623]; National Science Foundation Graduate Research Fellowship [DGE-1746060]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Accurate and fast two-step phase shifting algorithm based on principle component analysis and Lissajous ellipse fitting with random phase shift and no pre-filtering

To achieve high measurement accuracy with less computational time-in-phase shifting interferometry, a random phase-shifting algorithm based on principal component analysis and Lissajous ellipse fitting (PCA& LEF) is proposed. It doesn't need pre-filtering and can obtain relatively accurate phase distribution with only two phase shifted interferograms and less computational time and is suitable for different background intensity, modulation amplitude distributions and noises. Moreover, it can obtain absolutely accurate result when the background intensity and modulation amplitude are perfect and can partly suppress the effect of imperfect background intensity and modulation amplitude. Last but not least, it removes the restriction that PCA needs more than three interferograms with welldistributed phase shifts to subtract relatively accurate mean. The simulations and experiments verify the correctness and feasibility of PCA& LEF. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing AgreementNational Natural Science Foundation of China (NSFC) [11304034]; Department of Science and Technology of Jilin Province [20190701018GH]; Education Department of Jilin Province [JJKH20190691KJ]; State Key Laboratory of Applied OpticsOpen access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Fiber bundle imaging resolution enhancement using deep learning

We propose a deep learning based method to estimate high-resolution images from multiple fiber bundle images. Our approach first aligns raw fiber bundle image sequences with a motion estimation neural network and then applies a 3D convolution neural network to learn a mapping from aligned fiber bundle image sequences to their ground truth images. Evaluations on lens tissue samples and a 1951 USAF resolution target suggest that our proposed method can significantly improve spatial resolution for fiber bundle imaging systems.National Institute of Biomedical Imaging and Bioengineering (NIBIB) [R21EB022378]Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Phase unwrapping in optical metrology via denoised and convolutional segmentation networks

The interferometry technique is corn commonly used to obtain the phase information of an object in optical metrology. The obtained wrapped phase is subject to a 27 pi ambiguity. To remove the ambiguity and obtain the correct phase, phase unwrapping is essential. Conventional phase unwrapping approaches are time-consuming and noise sensitive. To address those issues, we propose a new approach, where we transfer the task of phase unwrapping into a multi-class classification problem and introduce an efficient segmentation network to identify classes. Moreover, a noise-to-noise denoised network is integrated to preprocess noisy wrapped phase. We have demonstrated the proposed method with simulated data and in a real interferometric system.China Scholarship Council (CSC) [201704910730]; National Science Foundation (NSF) [1455630]Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Laser modulation simulation of micro-crack morphology evolution during chemical etching

Subsurface micro-cracks will be generated during the grinding and polishing processes of optical components. Micro-cracks have a modulation effect on the laser, thereby reducing the laser damage threshold. The FDTD method is used to simulate the light intensity distribution modulated by micro-crack. By comparing the simulation results of radial crack, parabolic crack and elliptic crack, the modulation mechanism of micro-crack is revealed. The results show that for the crack with the same width and depth, light intensity enhancement factor (LIEF) modulated by radial crack on the rear surface and parabolic crack on the front surface is the largest; LIEF modulated by elliptical crack on the rear surface and radial crack on the front surface is the smallest. In addition, when the crack width-depth ratio is the same, the larger the depth, the higher the LIEF. As the width-depth ratio increases, the LIEF value increases firstly, then decreases, and finally approaches a stable value.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]