One-Dimensional High-Resolution Wavefront Sensor Enabled by Subwavelength Compound Gratings

Author(s):

Meng, Yunlong; Shen, Xinyu; Xie, Junyang; Peng, Yao; Shao, Xiaowen; Yan, Feng & Yang, Cheng

Abstract:

“Angle sensors are widely used for wavefront measurements, which is attributed to their
integration and robustness. Currently, commercial sensors are available with pixel sizes in the order
of wavelengths. However, the spatial resolution of angle sensors still lags far behind. Here, we report
a one-dimensional, high-resolution wavefront sensor. It was produced by introducing subwavelength
compound gratings above the pixels. The gratings involved could be replaced by the sensor’s intrinsic
readout circuitry without additional operation. The experimental results showed that it had a spatial
resolution of 1.4 μm, two orders of magnitude higher than that of the Shack–Hartmann wavefront
sensor. The significant increase in spatial resolution enables angle sensors to reconstruct complex
wavefronts accurately.”

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Publication: Photonics
Issue/Year: Photonics, Volume 10; Number 4; Pages 420; 2023
DOI: 10.3390/photonics10040420

A Low-Complexity Joint Compensation Scheme of Carrier Recovery for Coherent Free-Space Optical Communication

Author(s):

Tang, Xinyu; Wang, Liqian; Zhang, Wei; Cai, Shanyong; Li, Yuemei & Zhang, Zhiguo

Abstract:

“In this paper, a low-complexity joint compensation scheme of carrier recovery (JCSCR) for coherent free-space optical (CFSO) communication is proposed. We applied the carrier recovery joint compensation approach to a CFSO communication system in the quadrature phase shift keying (QPSK) modulation format. A signal-preprocessing stage, which effectively avoided the repetitive operations found in traditional carrier recovery schemes, was proposed. Unlike in existing carrier recovery algorithms, the modulated phase of the received signal could be accurately removed using only the sum and subtraction of real absolute values in the signal-preprocessing stage, greatly reducing the complexity of the operation. Since this algorithm avoids the traditional fourth operation, the system’s complexity is reduced while additional noise generated by fourth cross-terms would be prevented and system noise immunity would be greatly enhanced. In addition, this algorithm uses joint compensation of phase errors in the final compensation stage, further reducing the complexity of the computation of the whole algorithmic scheme. A 10 Gbps QPSK CFSO communication transmission experiment was conducted in an atmospheric turbulence channel to verify the proposed technique and improvement in receiver sensitivity.”

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Publication: Photonics
Issue/Year: Photonics, Volume 10; Number 4; Pages 389; 2023
DOI: 10.3390/photonics10040389

Curve-shaped ultrashort laser pulses with programmable spatiotemporal behavior

Author(s):

Enar Franco, Óscar Martínez-Matos, and José A. Rodrigo

Abstract:

“Structured ultrashort laser pulses with controlled spatiotemporal properties are emerging as a key tool for the study and application of light–matter interactions in different fields such as microscopy, time-resolved imaging, laser micromachining, particle acceleration, and attosecond science. In practice, a structured ultrashort pulse focused along a target trajectory with controlled pulse dynamics is required, e.g., to set the trajectory and velocity of the resulting intensity peak. Here, to address this challenging problem, we present a technique and experimental setup that allows straightforward engineering of structured ultrashort laser pulses with control of their spatiotemporal properties enabling tailored pulse propagation dynamics along the target trajectory. Our theoretical framework describes the design and control of this kind of curve-shaped laser pulse in terms of the curve geometry and phase prescribed along it. We have derived a closed-form expression that describes the interplay between the curve geometry and prescribed phase governing the pulse dynamics, including the temporal behavior of the pulse peak intensity while preserving the pulse duration. The theoretical results and the corresponding numerical simulations allow us to analyze the pulse dynamics on the example of femtosecond curve-shaped vortex pulses, including contour-shaped pulses created to follow the outline of objects at micrometer scale. The experimental results demonstrate the generation of these structured ultrashort pulses. These findings could pave the way for the next generation of ultrashort laser-based optical tools for the study and control of light–matter interactions.”

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Publication: Optica
Issue/Year: Optica, Volume 10; Number 3; Pages 379–392; 2023
DOI: 10.1364/OPTICA.478086

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

Objective method for visual performance prediction

Author(s):

Torres-Sepúlveda, Walter; lveda; Mira-Agudelo, Alejandro; Barrera-Ramirez, John Fredy & Kolodziejczyk, Andrzej

Abstract:

“We propose, implement, and validate a new objective method for predicting the trends of visual acuity through-focus curves provided by specific optical elements. The proposed method utilized imaging of sinusoidal gratings provided by the optical elements and the definition of acuity. A custom-made monocular visual simulator equipped with active optics was used to implement the objective method and to validate it via subjective measurements. Visual acuity measurements were obtained monocularly from a set of six subjects with paralyzed accommodation for a naked eye and then that eye compensated by four multifocal optical elements. The objective methodology successfully predicts the trends of the visual acuity through-focus curve for all considered cases. The Pearson correlation coefficient was 0.878 for all tested optical elements, which agrees with results obtained by similar works. The proposed method constitutes an easy and direct alternative technique for the objective testing of optical elements for ophthalmic and optometric applications, which can be implemented before invasive, demanding, or costly procedures on real subjects.”

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Publication: Journal of the Optical Society of America A
Issue/Year: Journal of the Optical Society of America A, Volume 40; Number 4; Pages C138; 2023
DOI: 10.1364/josaa.478022

Simulated LCSLM with Inducible Diffractive Theory to Display Super-Gaussian Arrays Applying the Transport-of-Intensity Equation

Author(s):

Arriaga-Hernandez, Jesus; Cuevas-Otahola, Bolivia; Oliveros-Oliveros, Jacobo; Morin-Castillo, Maria; Martinez-Laguna, Ygnacio & Cedillo-Ramirez, Lilia

Abstract:

“We simulate a liquid crystal spatial light modulator (LCSLM), previously validated by Fraunhofer diffraction to observe super-Gaussian periodic profiles and analyze the wavefront of optical surfaces applying the transport-of-intensity equation (TIE). The LCSLM represents an alternative to the Ronchi Rulings, allowing to avoid all the related issues regarding diffractive and refractive properties, and noise. To this aim, we developed and numerically simulated a LCSLM resembling a fractal from a generating base. Such a base is constituted by an active square (values equal to one) and surrounded by eight switched-off pixels (zero-valued). We replicate the base in order to form 1 ×N-pixels and the successive rows to build the 1024×1024 LCSLM of active pixels. We visually test the LCSLM with calibration images as a diffractive object that is mathematically inducible, using mathematical induction over the N×N-shape (1×1, 2×2, 3×3, …, n×n pixels for the generalization). Finally, we experimentally generate periodic super-Gaussian profiles to be visualized in the LCSLM (transmission SLM, 1024×768-pixels LC 2012 Translucent SLM), modifying the TIE as an optical test in order to analyze the optical elements by comparing the results with ZYGO/APEX.”

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Publication: Photonics
Issue/Year: Photonics, Volume 10; Number 1; Pages 39; 2022
DOI: 10.3390/photonics10010039

Adaptive optics visual simulators: a review of recent optical designs and applications [Invited]

Author(s):

Marcos, Susana; Artal, Pablo; Atchison, David A.; Hampson, Karen; Legras, Richard; Lundström, Linda & Yoon, Geunyoung

Abstract:

“In their pioneering work demonstrating measurement and full correction of the eye’s optical aberrations, Liang, Williams and Miller, [JOSA A 14, 2884 (1997) [CrossRef]] showed improvement in visual performance using adaptive optics (AO). Since then, AO visual simulators have been developed to explore the spatial limits to human vision and as platforms to test non-invasively optical corrections for presbyopia, myopia, or corneal irregularities. These applications have allowed new psychophysics bypassing the optics of the eye, ranging from studying the impact of the interactions of monochromatic and chromatic aberrations on vision to neural adaptation. Other applications address new paradigms of lens designs and corrections of ocular errors. The current paper describes a series of AO visual simulators developed in laboratories around the world, key applications, and current trends and challenges. As the field moves into its second quarter century, new available technologies and a solid reception by the clinical community promise a vigorous and expanding use of AO simulation in years to come.”

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Publication: Biomedical Optics Express
Issue/Year: Biomedical Optics Express, Volume 13; Number 12; Pages 6508; 2022
DOI: 10.1364/boe.473458

Accommodation through simulated multifocal optics

Author(s):

Vedhakrishnan, Shrilekha; de Castro, Alberto; Vinas, Maria; Aissati, Sara & Marcos, Susana

Abstract:

“We evaluated the interaction of multifocal patterns with eye’s accommodation. Seven patterns were mapped on the spatial light modulator and the deformable mirror of an adaptive optics visual simulator, and projected onto the subjects eyes, representing different contact lens designs: NoLens, Bifocal Center Distance (+2.50D), Bifocal Center Near (+2.50D) and Multifocal Center Near-MediumAdd (+1.75D) and Center Near HighAdd (+2.50D), positive and negative spherical aberration (±1µm). The change in spherical aberration and the accommodative response to accommodative demands were obtained from Hartmann-Shack measurements. Positive spherical aberration and Center Distance designs are consistent with a higher accommodative response (p=0.001 & p=0.003): steeper shift of SA towards negative values and lower accommodative lag.”

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Publication: Biomedical Optics Express
Issue/Year: Biomedical Optics Express, Volume 13; Number 12; Pages 6695; 2022
DOI: 10.1364/boe.473595

Adaptive Detection of Wave Aberrations Based on the Multichannel Filter

Author(s):

Khorin, Pavel A.; Porfirev, Alexey P. & Khonina, Svetlana N.

Abstract:

“An adaptive method for determining the type and magnitude of aberration in a wide range is proposed on the basis of an optical processing of the analyzed wavefront using a multichannel filter matched to the adjustable Zernike phase functions. The approach is based on an adaptive (or step-by-step) compensation of wavefront aberrations based on a dynamically tunable multichannel filter implemented on a spatial light modulator. For adaptive filter adjustment, a set of criteria is proposed that takes into account not only the magnitude of the correlation peak, but also the maximum intensity, compactness, and orientation of the distribution in each diffraction order. The experimental results have shown the efficiency of the proposed approach for detecting wavefront aberrations in a wide range (from 0.1 λ to λ).”

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Publication: Photonics
Issue/Year: Photonics, Volume 9; Number 3; Pages 204; 2022
DOI: 10.3390/photonics9030204

Parametric characterization of ground surfaces with laser speckles

Author(s):

León Schweickhardt, Andreas Tausendfreund, Dirk Stöbener, and Andreas Fischer

Abstract:

“With well-known speckle measurement techniques, the root mean square height as well as the autocorrelation length of isotropic surfaces can be determined quickly and over a large area of interest. Beyond that, the present article studies the speckle-based measurement of anisotropic surfaces. For this purpose, a measurement setup and evaluation algorithm are presented that enable the characterization of unidirectionally anisotropic surfaces machined by grinding. As a result, four measurands are obtained from one speckle image: the machining direction, the autocorrelation length perpendicular to the machining direction, as well as two root mean square roughness parameters parallel and perpendicular to the machining direction. The first two measurands are obtained from a two-dimensional fast Fourier transform of the diffraction pattern resulting from the unidirectional tool marks and the latter two by a bidirectional evaluation of the speckle contrast. In addition to measurements on physical reference samples, a spatial light modulator is used to create a large number of surface topographies with known model parameters in order to quantify the measurement uncertainty.”

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Publication: Optics Express
Issue/Year: Optics Express, Volume 30; Number 8; Pages 12615; 2022
DOI: 10.1364/oe.454741
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