Fourier-inspired neural module for real-time and high-fidelity computer-generated holography

Author(s):

Dong, Zhenxing; Xu, Chao; Ling, Yuye; Li, Yan & Su, Yikai

Abstract:

“Learning-based computer-generated holography (CGH) algorithms appear as novel alternatives to generate phase-only holograms. However, most existing learning-based approaches underperform their iterative peers regarding display quality. Here, we recognize that current convolutional neural networks have difficulty learning cross-domain tasks due to the limited receptive field. In order to overcome this limitation, we propose a Fourier-inspired neural module, which can be easily integrated into various CGH frameworks and significantly enhance the quality of reconstructed images. By explicitly leveraging Fourier transforms within the neural network architecture, the mesoscopic information within the phase-only hologram can be more handily extracted. Both simulation and experiment were performed to showcase its capability. By incorporating it into U-Net and HoloNet, the peak signal-to-noise ratio of reconstructed images is measured at 29.16 dB and 33.50 dB during the simulation, which is 4.97 dB and 1.52 dB higher than those by the baseline U-Net and HoloNet, respectively. Similar trends are observed in the experimental results. We also experimentally demonstrated that U-Net and HoloNet with the proposed module can generate a monochromatic 1080p hologram in 0.015 s and 0.020 s, respectively.”

Link to Publications Page

Publication: Optics Letters
Issue/Year: Optics Letters, Volume 48; Number 3; Pages 759; 2023
DOI: 10.1364/ol.477630

Measurement of the fractional topological charge of an optical vortex beam through interference fringe dislocation

Author(s):

Shikder, Allarakha & Nishchal, Naveen K.

Abstract:

“An optical vortex beam carrying fractional topological charge (TC) has become an immerging field of interest due to its unique intensity distribution and fractional phase front in a transverse plane. Potential applications include micro-particle manipulation, optical communication, quantum information processing, optical encryption, and optical imaging. In these applications, it is necessary to know the correct information of the orbital angular momentum, which is related to the fractional TC of the beam. Therefore, the accurate measurement of fractional TC is an important issue. In this study, we demonstrate a simple technique to measure the fractional TC of an optical vortex with a resolution of 0.05 using a spiral interferometer and fork-shaped interference patterns. We further show that the proposed technique provides satisfactory results in cases of low to moderate atmospheric turbulences, which has relevance in free-space optical communications.”

Link to Publications Page

Publication: Applied Optics
Issue/Year: Applied Optics, Volume 62; Number 10; Pages D58; 2023
DOI: 10.1364/ao.476455

Multimode fiber-based greyscale image projector enabled by neural networks with high generalization ability

Author(s):

Wang, Jian; Zhong, Guangchao; Wu, Daixuan; Huang, Sitong; Luo, Zhi-Chao & Shen, Yuecheng

Abstract:

“Multimode fibers (MMFs) are emerging as promising transmission media for delivering images. However, strong mode coupling inherent in MMFs induces difficulties in directly projecting two-dimensional images through MMFs. By training two subnetworks named Actor-net and Model-net synergetically, [Nature Machine Intelligence 2, 403 (2020) [CrossRef] ] alleviated this issue and demonstrated projecting images through MMFs with high fidelity. In this work, we make a step further by improving the generalization ability to greyscale images. The modified projector network contains three subnetworks, namely forward-net, backward-net, and holography-net, accounting for forward propagation, backward propagation, and the phase-retrieval process. As a proof of concept, we experimentally trained the projector network using randomly generated phase maps and their corresponding resultant speckle images output from a 1-meter-long MMF. With the network being trained, we successfully demonstrated projecting binary images from MNIST and EMNIST and greyscale images from Fashion-MNIST, exhibiting averaged Pearson’s correlation coefficients of 0.91, 0.92, and 0.87, respectively. Since all these projected images have never been seen by the projector network before, a strong generalization ability in projecting greyscale images is confirmed.”

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Publication: Optics Express
Issue/Year: Optics Express, Volume 31; Number 3; Pages 4839; 2023
DOI: 10.1364/oe.482551

Resolution and uniformity improvement of parallel confocal microscopy based on microlens arrays and a spatial light modulator

Author(s):

Luo, Tianpeng; Yuan, Jing; Chang, Jin; Dai, Yanfeng; Gong, Hui; Luo, Qingming & Yang, Xiaoquan

Abstract:

“In traditional fluorescence microscopy, it is hard to achieve a large uniform imaging field with high resolution. In this manuscript, we developed a confocal fluorescence microscope combining the microlens array with spatial light modulator to address this issue. In our system, a multi-spot array generated by a spatial light modulator passes through the microlens array to form an optical probe array. Then multi-spot adaptive pixel-reassignment method for image scanning microscopy (MAPR-ISM) will be introduced in this parallelized imaging to improve spatial resolution. To generate a uniform image, we employ an optimized double weighted Gerchberg–Saxton algorithm (ODWGS) using signal feedback from the camera. We have built a prototype system with a FOV of 3.5 mm × 3.5 mm illuminated by 2500 confocal points. The system provides a lateral resolution of ∼0.82 µm with ∼1.6 times resolution enhancement after ISM processing. And the nonuniformity across the whole imaging field is 3%. Experimental results of fluorescent beads, mouse brain slices and melanoma slices are presented to validate the applicability and effectiveness of our system.”

Link to Publications Page

Publication: Optics Express
Issue/Year: Optics Express, Volume 31; Number 3; Pages 4537; 2023
DOI: 10.1364/oe.478820