Precise design of two-dimensional diffractive optical elements for beam shaping

Qu, Wei; Gu, Huarong; Tan, Qiaofeng; Jin, Guofan

doi:10.1364/ao.54.006521

Cited by 42 publications

(14 citation statements)

References 16 publications

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“…2(b), the experimental result was not as good as the designed result. The fabrication error is one reason, but the major reason may be that the sampling interval on the output plane is not small enough, only the intensity distribution of the selected sampling points was controlled by the optimization algorithm [19]. The intensity distribution of other points on the output plane is far away from the ideal distribution.…”

Section: Resultsmentioning

confidence: 99%

Beam Shaping and Speckle Reduction in Laser Projection Display Systems Using a Vibrating Diffractive Optical Element

Liang

Zhang

et al. 2017

Current Optics and Photonics

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The laser has been regarded as the potential illumination source for the next generation of projectors. However, currently the major issues in applying the laser as an illumination source for projectors are beam shaping and laser speckle. We present a compact solution for both issues by using a vibrating diffractive optical element (DOE). The DOE is designed and fabricated, and it successfully transforms the circular Gaussian laser beam to a low speckle contrast uniform rectangular pattern. Under a vibration frequency of 150 Hz and amplitude of 200 µm, the speckle contrast value is reduced from 67.67% to 13.78%, and the ANSI uniformity is improved from 24.36% to 85.54%. The experimental results demonstrate the feasibility and potential of the proposed scheme, and the proposed method is a feasible approach to the miniaturization of laser projection display illumination systems.

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Section: Resultsmentioning

confidence: 99%

Beam Shaping and Speckle Reduction in Laser Projection Display Systems Using a Vibrating Diffractive Optical Element

Liang

Zhang

et al. 2017

Current Optics and Photonics

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“…Some algorithms are proposed to alleviate the zero-amplitude limit, such as the gradual zero-padding method. 33 However, the optimization result becomes unsatisfactory again when the number of padding points increases. Because the zero-padding operation only pads virtual points around the DOE and does not actually increase the size of the DOE.…”

Section: Zero Padding Methodsmentioning

confidence: 99%

“…Kong et al 32 proposed a gradual zero-padding algorithm based on the GS algorithm, which alleviates the zero-amplitude limit at the zero-padded point in the iteration to control more sampling points effectively. 33 Qu et al 34 proposed a modified zeropadding algorithm by improving the limit of iterative amplitude to reduce the sampling interval on the output plane. However, the speckle cannot be reduced completely since the above methods only reduce the sampling interval on the output plane by half.…”

Section: Introductionmentioning

confidence: 99%

Speckle-reduced diffractive optical elements beam shaping with regional padding algorithm

Guo

Cai

et al. 2022

Opt. Eng.

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Diffractive optical elements (DOEs) have been widely used to realize beam shaping.However, the speckle noise always appears in the reshaped beam, which induces beam quality degradation. We proposed a regional padding algorithm based on the Gerchberg-Saxton algorithm to implement speckle-reduced beam shaping. A variable region is set in the DOE to iterate and optimize the phase of each part DOE. Zero padding is used around the DOE to decrease the sampling interval on the output plane. When the region expands and padded value reduction is controlled slowly, more sampling points on the output plane can be optimized effectively and suppress speckle noise. Numerical simulations and optical experiments have been performed to verify the feasibility of the proposed method.

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“…Diffractive optical elements (DOEs) can be designed to manipulate an incident terahertz wave by locally controlling its transmitted phase so as to generate a desired output intensity distribution. [11] Diffractive optics can be applied in multiple optical applications including neural networks, [12,13] beam shaping, [14,15] optical tweezers, [16,17] holograms, [18][19][20] quantum information, [21,22] novel microscopy, [23] and so on. The wavelength of terahertz radiation, ≈hundreds of micrometers, enables the fabrication of terahertz DOEs [24] through additive manufacturing techniques [25] with commercially available 3D printers, which is a cost-efficient rapid fabrication process.…”

Section: Introductionmentioning

confidence: 99%

Machine Learning Enables Multi‐Degree‐of‐Freedom Reconfigurable Terahertz Holograms with Cascaded Diffractive Optical Elements

Jia

Lin

Sensale‐Rodriguez

2023

Advanced Optical Materials

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In this context, terahertz holograms enabled by single-layer diffractive optical elements have been widely explored. [11,18,19,26] However, the reconfigurability of single-layer passive diffractive optical elements is very limited. Cascaded DOE structures have the advantage of enabling more functionality and information capacity compared to single-layer DOEs, as discussed in ref. [27]. Liao et al. [28] studied terahertz reconfigurable holographic imaging by mechanical translation of an absorber relative to two fixed discrete dielectric DOEs. Cascaded computer-generated phase-only diffractive optical elements for multiplane image formation were simulated by Alkan et al. [29] A lens was utilized in such a cascaded configuration for Fourier transform to project patterns on two imaging planes. In the visible range, Wang et al. [30] demonstrated azimuthal multiplexing with a stratified DOE layout optimized by iterative optimization algorithms. The optical information was encoded azimuthally in the DOEs and retrieved by rotating the DOEs relative to each other. It is to highlight that reconfigurable materials such as phase change materials, semiconductor layers, and MEMS structures integrated with metasurface structures [31][32][33][34][35][36] are also good candidates to realize reconfigurable terahertz devices and holograms.Diffractive optical neural networks (DONN) [12] have been successfully applied for the classification of handwritten digit images, [12,37] the design of spatially controlled wavelength demultiplexing systems, [38] and terahertz pulse shaping. [39] Such a machine learning method is an efficient and powerful tool for designing diffractive optics inverse problems in cascaded configurations. The pixel phase (height distributions) in the diffractive layers can be trained by stochastic gradient descent and error-backpropagation to achieve the desired diffraction pattern as the incident beam passes through the diffractive layers.The purpose of this work is to show that through such a DONN machine learning method, it is possible to realize holograms with a tailored reconfigurable operation when altering multiple degrees of freedom, i.e., either the number, spacing, rotational alignment, and/or order of the cascaded diffractive layers. The height distributions of the diffractive layers are trained by the network on the basis of an initial incident terahertz field distribution and predefined (target) diffraction patterns.For our proof-of-concept demonstration, five scenarios are demonstrated, each corresponding to the variation of an individual degree of freedom in the cascaded configuration. A Machine learning can empower the design of cascaded diffractive optical elements (DOEs) at terahertz frequencies enabling the realization of holograms with a tailored multi-degree-of-freedom reconfigurable operation when altering either the number, spacing, rotational alignment, and/or order of the elements. This unprecedented control over the spatial terahertz light distribution can profoundly impact multiple terahe...

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Precise design of two-dimensional diffractive optical elements for beam shaping

Cited by 42 publications

References 16 publications

Beam Shaping and Speckle Reduction in Laser Projection Display Systems Using a Vibrating Diffractive Optical Element

Beam Shaping and Speckle Reduction in Laser Projection Display Systems Using a Vibrating Diffractive Optical Element

Speckle-reduced diffractive optical elements beam shaping with regional padding algorithm

Machine Learning Enables Multi‐Degree‐of‐Freedom Reconfigurable Terahertz Holograms with Cascaded Diffractive Optical Elements

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