Wavefront Sensing by a Common-Path Interferometer for Wavefront Correction in Phase and Amplitude by a Liquid Crystal Spatial Light Modulator Aiming the Exoplanet Direct Imaging

Author(s):

Yudaev, Andrey; Kiselev, Alexander; Shashkova, Inna; Tavrov, Alexander; Lipatov, Alexander & Korablev, Oleg

Abstract:

“We implemented the common-path achromatic interfero-coronagraph both for the wavefront sensing and the on-axis image component suppression, aiming for the stellar coronagraphy. A common-path achromatic interfero-coronagraph has its optical scheme based on a nulling rotational-shear interferometer. The angle of rotational shear can be chosen at a small angular extent of about 10 deg. Such a small angular shear maintains the coronagraphic contrast degradation known as the stellar leakage effect, caused by a finite stellar size. We study the phase and amplitude wavefront control by a liquid crystal spatial light modulator of reflection type which is used as the pixilated active adaptive optics unit. Therefore, adaptive optics perform a wavefront-correcting input toward a stellar interfero-coronagraph aiming at the direct exoplanet imaging. Presented here are both the numeric evaluations and the lab experiment stand to prove the declared functionality output.”

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Publication: Photonics
Issue/Year: Photonics, Volume 10; Number 3; Pages 320; 2023
DOI: 10.3390/photonics10030320

Computational holographic ghost diffraction

Author(s):

Ye, Zhiyuan; Hou, Wanting; Zhao, Jilun; Wang, Hai-Bo & Xiong, Jun

Abstract:

“Since the paradigm shift in 2009 from pseudo-thermal ghost imaging (GI) to computational GI using a spatial light modulator, computational GI has enabled image formation via a single-pixel detector and thus has a cost-effective advantage in some unconventional wave bands. In this Letter, we propose an analogical paradigm known as computational holographic ghost diffraction (CH-GD) to shift ghost diffraction (GD) from classical to computational by using self-interferometer-assisted measurement of field correlation functions rather than intensity correlation functions. More than simply “seeing” the diffraction pattern of an unknown complex volume object with single-point detectors, CH-GD can retrieve the diffracted light field’s complex amplitude and can thus digitally refocus to any depth in the optical link. Moreover, CH-GD has the potential to obtain the multimodal information including intensity, phase, depth, polarization, and/or color in a more compact and lensless manner.”

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Publication: Optics Letters
Issue/Year: Optics Letters, Volume 48; Number 7; Pages 1618; 2023
DOI: 10.1364/ol.484537

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.”

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

Pixel super-resolution quantitative phase imaging based on modulation diversity

Author(s):

Gao, Yunhui & Cao, Liangcai

Abstract:

“Quantitative phase imaging with high resolution remains a long-term pursuit of many biomedical applications. However, the performance of coherent imaging systems is challenged by the intensity-only measurement mechanism and the sampling limit of the pixels. In this work, we introduce an imaging system that achieves pixel super-resolution quantitative phase imaging based on modulation diversity. A programmable phase-only spatial light modulator is used to generate various phase modulation patterns to the wavefront, providing data diversity for phase recovery at subpixel resolution. The system requires no mechanical displacements, enabling high-speed image acquisition, providing a competitive approach to high-throughput quantitative phase imaging applications.”

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Publication: Proc. SPIE 12318
Issue/Year: Proc. SPIE 12318, Holography, Diffractive Optics, and Applications XII, 123180Q, 2022
DOI: 10.1117/12.2642054

Pixel Super-Resolution Phase Retrieval for Lensless On-Chip Microscopy via Accelerated Wirtinger Flow

Author(s):

Gao, Yunhui; Yang, Feng & Cao, Liangcai

Abstract:

“Empowered by pixel super-resolution (PSR) and phase retrieval techniques, lensless onchip microscopy opens up new possibilities for high-throughput biomedical imaging. However, the current PSR phase retrieval approaches are time consuming in terms of both the measurement and reconstruction procedures. In this work, we present a novel computational framework for PSR phase retrieval to address these concerns. Specifically, a sparsity-promoting regularizer is introduced to enhance the well posedness of the nonconvex problem under limited measurements, and Nesterov’s momentum is used to accelerate the iterations. The resulting algorithm, termed accelerated Wirtinger flow (AWF), achieves at least an order of magnitude faster rate of convergence and allows a twofold reduction in the measurement number while maintaining competitive reconstruction quality. Furthermore, we provide general guidance for step size selection based on theoretical analyses, facilitating simple implementation without the need for complicated parameter tuning. The proposed AWF algorithm is compatible with most of the existing lensless on-chip microscopes and could help achieve label-free rapid whole slide imaging of dynamic biological activities at subpixel resolution.”

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Publication: Cells
Issue/Year: Cells, Volume 11; Number 13; Pages 1999; 2022
DOI: 10.3390/cells11131999

Experimental estimation of the longitudinal component of a highly focused electromagnetic field

Author(s):

Maluenda, David; Aviñoá, Marcos; Ahmadi, Kavan; Martínez-Herrero, Rosario & Carnicer, Artur

Abstract:

“The detection of the longitudinal component of a highly focused electromagnetic beam is not a simple task. Although in recent years several methods have been reported in the literature, this measure is still not routinely performed. This paper describes a method that allows us to estimate and visualize the longitudinal component of the field in a relatively simple way. First, we measure the transverse components of the focused field in several planes normal to the optical axis. Then, we determine the complex amplitude of the two transverse field components: the phase is obtained using a phase recovery algorithm, while the phase difference between the two components is determined from the Stokes parameters. Finally, the longitudinal component is estimated using the Gauss’s theorem. Experimental results show an excellent agreement with theoretical predictions.”

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Publication: Scientific Reports
Issue/Year: Scientific Reports, Volume 11; Number 1; 2021
DOI: 10.1038/s41598-021-97164-z

Generalized optimization framework for pixel super-resolution imaging in digital holography

Author(s):

Gao, Yunhui & Cao, Liangcai

Abstract:

“The imaging quality of in-line digital holography is challenged by the twin-image and aliasing effects because sensors only respond to intensity and pixels are of finite size. As a result, phase retrieval and pixel super-resolution techniques serve as two essential ingredients for high-fidelity and high-resolution holographic imaging. In this work, we combine the two as a unified optimization problem and propose a generalized algorithmic framework for pixelsuper-resolved phase retrieval. In particular, we introduce the iterative projection algorithms and gradient descent algorithms for solving this problem. The basic building blocks, namely the projection operator and the Wirtinger gradient, are derived and analyzed. As an example, the Wirtinger gradient descent algorithm for pixel-super-resolved phase retrieval, termed as Wirtinger-PSR, is proposed and compared with the classical error-reduction algorithm. The Wirtinger-PSR algorithm is verified with both simulated and experimental data. The proposed framework generalizes well to various physical settings and helps bridging the gap between empirical studies and theoretical analyses.”

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Publication: Optics Express
Issue/Year: Optics Express, Volume 29; Number 18; Pages 28805; 2021
DOI: 10.1364/oe.434449

Toward simple, generalizable neural networks with universal training for low-SWaP hybrid vision

Author(s):

Muminov, Baurzhan; Perry, Altai; Hyder, Rakib; Asif, M. Salman & Vuong, Luat T.

Abstract:

“Speed, generalizability, and robustness are fundamental issues for building lightweight computational cameras. Here we demonstrate generalizable image reconstruction with the simplest of hybrid machine vision systems: linear optical preprocessors combined with no-hidden-layer, “small-brain” neural networks. Surprisingly, such simple neural networks are capable of learning the image reconstruction from a range of coded diffraction patterns using two masks. We investigate the possibility of generalized or “universal training” with these small brains. Neural networks trained with sinusoidal or random patterns uniformly distribute errors around a reconstructed image, whereas models trained with a combination of sharp and curved shapes (the phase pattern of optical vortices) reconstruct edges more boldly. We illustrate variable convergence of these simple neural networks and relate learnability of an image to its singular value decomposition entropy of the image. We also provide heuristic experimental results. With thresholding, we achieve robust reconstruction of various disjoint datasets. Our work is favorable for future real-time low size, weight, and power hybrid vision: we reconstruct images on a 15 W laptop CPU with 15,000 frames per second: faster by a factor of 3 than previously reported results and 3 orders of magnitude faster than convolutional neural networks.”

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Publication: Photonics Research
Issue/Year: Photonics Research, Volume 9; Number 7; Pages B253; 2021
DOI: 10.1364/prj.416614

Broadband chromatic dispersion measurements in higher-order modes selectively excited in optical fibers using a spatial light modulator

Author(s):

Zolnacz, Kinga; Szatkowski, Mateusz; Masajada, Jan & Urbanczyk, Waclaw

Abstract:

“We propose an improvement of the interferometric method used up to now to measure the chromatic dispersion in single mode optical fibers, which enables dispersion measurements in higher-order modes over a wide spectral range. To selectively excite a specific mode, a spatial light modulator was used in the reflective configuration to generate an appropriate phase distribution across an input supercontinuum beam. We demonstrate the feasibility of the proposed approach using chromatic dispersion measurements of the six lowest order spatial modes supported by an optical fiber in the spectral range from 450 to 1600 nm. Moreover, we present the results of numerical simulations that confirm sufficient selectivity of higher-order mode excitation.”

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Publication: Optics Express
Issue/Year: Optics Express, Volume 29; Number 9; Pages 13256; 2021
DOI: 10.1364/oe.422736

WISHED: Wavefront imaging sensor with high resolution and depth ranging

Author(s):

Yicheng Wu, Fengqiang Li, Florian Willomitzer, Ashok Veeraraghavan, Oliver Cossairt

Abstract:

“Phase-retrieval based wavefront sensors have been shown to reconstruct the complex field from an object with a high spatial resolution. Although the reconstructed complex field encodes the depth information of the object, it is impractical to be used as a depth sensor for macroscopic objects, since the unambiguous depth imaging range is limited by the optical wavelength. To improve the depth range of imaging and handle depth discontinuities, we propose a novel three-dimensional sensor by leveraging wavelength diversity and wavefront sensing. Complex fields at two optical wavelengths are recorded, and a synthetic wavelength can be generated by correlating those wavefronts. The proposed system achieves high lateral and depth resolutions. Our experimental prototype shows an unambiguous range of more than 1,000 x larger compared with the optical wavelengths, while the depth precision is up to 9µm for smooth objects and up to 69µm for rough objects. We experimentally demonstrate 3D reconstructions for transparent, translucent, and opaque objects with smooth and rough surfaces.”

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Publication: 2020 IEEE International Conference on Computational Photography (ICCP)
DOI: 10.1109/ICCP48838.2020.9105280
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