Laser beam shaping based on amplitude-phase control of a fiber laser array

Author(s):

Adamov, E. V.; Aksenov, V. P.; Atuchin, V. V.; Dudorov, V. V.; Kolosov, V. V. & Levitsky, M. E.

Abstract:

“A new technique is suggested for the generation of laser beams with an intensity profile specified. The technique is based on the coherent combining of radiation of a fiber laser array with adaptive control of the power and phase of Gaussian subbeams with plane wavefronts. The power and phase of the subbeams are determined for each intensity profile specified in the far field based on the inverse problem solution, for example, by the Gershberg–Saxton method. To form a required phase profile, the stochastic parallel gradient descent (SPGD) method is used along with the inversion of a required phase distribution with a phase corrector. The main advantages of the technique are the adaptive control of the intensity profile and a possibility of generating high-power laser beams. The results of numerical and field experiments are described.”

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Publication: OSA Continuum
Issue/Year: OSA Continuum, Volume 4; Number 1; Pages 182; 2021
DOI: 10.1364/osac.413956

3D reconstruction of weakly scattering objects from 2D intensity-only measurements using the Wolf transform

Author(s):

Ayoub, Ahmed B.; Lim, Joowon; Antoine, Elizabeth E. & Psaltis, Demetri

Abstract:

“A new approach to optical diffraction tomography (ODT) based on intensity measurements is presented. By applying the Wolf transform directly to intensity measurements, we observed unexpected behavior in the 3D reconstruction of the sample. Such a reconstruction does not explicitly represent a quantitative measure of the refractive index of the sample; however, it contains interesting qualitative information. This 3D reconstruction exhibits edge enhancement and contrast enhancement for nanostructures compared with the conventional 3D refractive index reconstruction and thus could be used to localize nanoparticles such as lipids inside a biological sample.”

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Publication: Optics Express
Issue/Year: Optics Express, Volume 29; Number 3; Pages 3976; 2021
DOI: 10.1364/oe.414543

Optimizing image quality for holographic near-eye displays with Michelson Holography

Author(s):

Choi, Suyeon; Kim, Jonghyun; Peng, Yifan & Wetzstein, Gordon

Abstract:

“We introduce Michelson holography (MH), a holographic display technology that optimizes image quality for emerging holographic near-eye displays. Using two spatial light modulators (SLMs), MH is capable of leveraging destructive interference to optically cancel out undiffracted light corrupting the observed image. We calibrate this system using emerging camera-in-the-loop holography techniques and demonstrate state-of-the-art 2D and multi-plane holographic image quality.”

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Publication: Optica
Issue/Year: Optica, Volume 8; Number 2; Pages 143; 2021
DOI: 10.1364/optica.410622

High-dimensional orbital angular momentum multiplexing nonlinear holography

Author(s):

Fang, Xinyuan; Yang, Haocheng; Yao, Wenzhe; Wang, Tianxin; Zhang, Yong; Gu, Min & Xiao, Min

Abstract:

“Nonlinear holography has been identified as a vital platform for optical multiplexing holographybecause of the appearance of new optical frequencies. However, due to nonlinear wave coupling innonlinear optical processes, the nonlinear harmonic field is coupled with the input field, laying a fundamentalbarrier to independent control of the interacting fields for holography. We propose and experimentallydemonstrate high-dimensional orbital angular momentum (OAM) multiplexing nonlinear holography toovercome this problem. By dividing the wavefront of the fundamental wave into different orthogonal OAMchannels, multiple OAM and polarization-dependent holographic images in both the fundamental wave andsecond-harmonic wave have been reconstructed independently in the spatial frequency domain through atype-II second harmonic generation process. Moreover, this method can be easily extended to cascaded χ2 nonlinear optical processes for multiplexing in more wavelength channels, leading to potential applicationsin multicasting in optical communications, multiwavelength display, multidimensional optical storage, anti-counterfeiting, and optical encryption.”

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Publication: Advanced Photonics
Issue/Year: Advanced Photonics, Volume 3; Number 01; 2021
DOI: 10.1117/1.ap.3.1.015001

GAN-Holo: Generative Adversarial Networks-Based Generated Holography Using Deep Learning

Author(s):

Khan, Aamir; Zhijiang, Zhang; Yu, Yingjie; Khan, Muhammad Amir; Yan, Ketao & Aziz, Khizar

Abstract:

“Current development in a deep neural network (DNN) has given an opportunity to a novel framework for the reconstruction of a holographic image and a phase recovery method with real-time performance. There are many deep learning-based techniques that have been proposed for the holographic image reconstruction, but these deep learning-based methods can still lack in performance, time complexity, accuracy, and real-time performance. Due to iterative calculation, the generation of a CGH requires a long computation time. A novel deep generative adversarial network holography (GAN-Holo) framework is proposed for hologram reconstruction. This novel framework consists of two phases. In phase one, we used the Fresnel-based method to make the dataset. In the second phase, we trained the raw input image and holographic label image data from phase one acquired images. Our method has the capability of the noniterative process of computer-generated holograms (CGHs). The experimental results have demonstrated that the proposed method outperforms the existing methods.”

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Publication: Complexity
Issue/Year: Complexity, Volume 2021; Pages 1-7; 2021
DOI: 10.1155/2021/6662161

Polymer Optical Waveguide Sensor Based on Fe-Amino-Triazole Complex Molecular Switches

Author(s):

Khan, Muhammad Shaukat; Farooq, Hunain; Wittmund, Christopher; Klimke, Stephen; Lachmayer, Roland; Renz, Franz & Roth, Bernhard

Abstract:

“We report on a polymer-waveguide-based temperature sensing system relying on switchable molecular complexes. The polymer waveguide cladding is fabricated using a maskless lithographic optical system and replicated onto polymer material (i.e., PMMA) using a hot embossing device. An iron-amino-triazole molecular complex material (i.e., [Fe(Htrz)2.85(NH2-trz)0.15](ClO4)2) is used to sense changes in ambient temperature. For this purpose, the core of the waveguide is filled with a mixture of core material (NOA68), and the molecular complex using doctor blading and UV curing is applied for solidification. The absorption spectrum of the molecular complex in the UV/VIS light range features two prominent absorption bands in the low-spin state. As temperature approaches room temperature, a spin-crossover transition occurs, and the molecular complex changes its color (i.e. spectral properties) from violet-pink to white. The measurement of the optical power transmitted through the waveguide as a function of temperature exhibits a memory effect with a hysteresis width of approx. 12 °C and sensitivity of 0.08 mW/°C. This enables optical rather than electronic temperature detection in environments where electromagnetic interference might influence the measurements”

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Publication: Polymers
Issue/Year: Polymers, Volume 13; Number 2; Pages 195; 2021
DOI: 10.3390/polym13020195

Deep-learning-based high-resolution recognition of fractional-spatial-mode-encoded data for free-space optical communications

Author(s):

Na, Youngbin & Ko, Do-Kyeong

Abstract:

“Structured light with spatial degrees of freedom (DoF) is considered a potential solution to address the unprecedented demand for data traffic, but there is a limit to effectively improving the communication capacity by its integer quantization. We propose a data transmission system using fractional mode encoding and deep-learning decoding. Spatial modes of Bessel-Gaussian beams separated by fractional intervals are employed to represent 8-bit symbols. Data encoded by switching phase holograms is efficiently decoded by a deep-learning classifier that only requires the intensity profile of transmitted modes. Our results show that the trained model can simultaneously recognize two independent DoF without any mode sorter and precisely detect small differences between fractional modes. Moreover, the proposed scheme successfully achieves image transmission despite its densely packed mode space. This research will present a new approach to realizing higher data rates for advanced optical communication systems.”

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Publication: Scientific Reports
Issue/Year: Scientific Reports, Volume 11; Number 1; 2021
DOI: 10.1038/s41598-021-82239-8

Giant Helical Dichroism of Single Chiral Nanostructures with Photonic Orbital Angular Momentum

Author(s):

Ni, Jincheng; Liu, Shunli; Hu, Guangwei; Hu, Yanlei; Lao, Zhaoxin; Li, Jiawen; Zhang, Qing; Wu, Dong; Dong, Shaohua; Chu, Jiaru & Qiu, Cheng-Wei

Abstract:

“Optical activity, demonstrating the chiral light-matter interaction, has attracted tremendous attention in both fundamental theoretical research and advanced applications of high-efficiency enantioselective sensing and next-generation chiroptical spectroscopic techniques. However, conventional chiroptical responses are normally limited in large assemblies of chiral materials by circularly polarized light, exhibiting extremely weak chiroptical signals in a single chiral nanostructure. Here, we demonstrate that an alternative chiral freedom of light—orbital angular momentum—can be utilized for generating strong helical dichroism in single chiral nanostructures. The helical dichroism by monochromatic vortex beams can unambiguously distinguish the intrinsic chirality of nanostructures, in an excellent agreement with theoretical predictions. The single planar-chiral nanostructure can exhibit giant helical dichroism of ∼20% at the visible wavelength. The vortex-dependent helical dichroism, expanding to single nanostructures and two-dimensional space, has implications for high-efficiency chiroptical detection of planar-chiral nanostructures in chiral optics and nanophotonic systems.”

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Publication: ACS Nano
Issue/Year: ACS Nano, Volume 15; Number 2; Pages 2893-2900; 2021
DOI: 10.1021/acsnano.0c08941

An interactive holographic projection system that uses a hand-drawn interface with a consumer CPU

Author(s):

Nishitsuji, Takashi; Kakue, Takashi; Blinder, David; Shimobaba, Tomoyoshi & Ito, Tomoyoshi

Abstract:

“Holography is a promising technology for photo-realistic three-dimensional (3D) displays because of its ability to replay the light reflected from an object using a spatial light modulator (SLM). However, the enormous computational requirements for calculating computer-generated holograms (CGHs)—which are displayed on an SLM as a diffraction pattern—are a significant problem for practical uses (e.g., for interactive 3D displays for remote navigation systems). Here, we demonstrate an interactive 3D display system using electro-holography that can operate with a consumer’s CPU. The proposed system integrates an efficient and fast CGH computation algorithm for line-drawn 3D objects with inter-frame differencing, so that the trajectory of a line-drawn object that is handwritten on a drawing tablet can be played back interactively using only the CPU. In this system, we used an SLM with 1,920 × 1,080 pixels and a pixel pitch of 8 μm × 8 μm, a drawing tablet as an interface, and an Intel Core i9–9900K 3.60 GHz CPU. Numerical and optical experiments using a dataset of handwritten inputs show that the proposed system is capable of reproducing handwritten 3D images in real time with sufficient interactivity and image quality.”

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Publication: Scientific Reports
Issue/Year: Scientific Reports, Volume 11; Number 1; 2021
DOI: 10.1038/s41598-020-78902-1

Depth-of-field engineering in coded aperture imaging

Author(s):

Rai, Mani Ratnam & Rosen, Joseph

Abstract:

“Extending the depth-of-field (DOF) of an optical imaging system without effecting the other imaging properties has been an important topic of research for a long time. In this work, we propose a new general technique of engineering the DOF of an imaging system beyond just a simple extension of the DOF. Engineering the DOF means in this study that the inherent DOF can be extended to one, or to several, separated different intervals of DOF, with controlled start and end points. Practically, because of the DOF engineering, entire objects in certain separated different input subvolumes are imaged with the same sharpness as if these objects are all in focus. Furthermore, the images from different subvolumes can be laterally shifted, each subvolume in a different shift, relative to their positions in the object space. By doing so, mutual hiding of images can be avoided. The proposed technique is introduced into a system of coded aperture imaging. In other words, the light from the object space is modulated by a coded aperture and recorded into the computer in which the desired image is reconstructed from the recorded pattern. The DOF engineering is done by designing the coded aperture composed of three diffractive elements. One element is a quadratic phase function dictating the start point of the in-focus axial interval and the second element is a quartic phase function which dictates the end point of this interval. Quasi-random coded phase mask is the third element, which enables the digital reconstruction. Multiplexing several sets of diffractive elements, each with different set of phase coefficients, can yield various axial reconstruction curves. The entire diffractive elements are displayed on a spatial light modulator such that real-time DOF engineering is enabled according to the user needs in the course of the observation. Experimental verifications of the proposed system with several examples of DOF engineering are presented, where the entire imaging of the observed scene is done by single camera shot.”

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Publication: Optics Express
Issue/Year: Optics Express, Volume 29; Number 2; Pages 1634; 2021
DOI: 10.1364/oe.412744
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