Retrieving the optical transmission matrix of a multimode fiber using the extended Kalman filter

Author(s):

Guoqiang Huang and Daixuan Wu and Jiawei Luo and Yin Huang and Yuecheng Shen

Abstract:

” Characterizing the transmission matrix (TM) of a multimode fiber (MMF) benefits many fiber-based applications and allows in-depth studies on the physical properties. For example, by modulating the incident field, the knowledge of the TM allows one to synthesize
any optical field at the distill end of the MMF. However, the extraction of optical fields usually requires holographic measurements with interferometry, which complicates the system design and introduces additional noise. In this work, we developed an efficient method to retrieve the TM of the MMF in a referenceless optical system. With pure intensity measurements, this method uses the extended Kalman filter (EKF) to recursively search for the optimum solution. To facilitate the computational process, a modified speckle-correlation scatter matrix (MSSM) is constructed as a low-fidelity initial estimation. This method, termed EKF-MSSM, only requires 4N intensity measurements to precisely solve for N unknown complex variables in the TM. Experimentally, we successfully retrieved the TM of the MMF with high precision, which allows optical focusing with the enhancement (>70%) close to the theoretical value. We anticipate that this method will serve as a useful tool for studying physical properties of the MMFs and potentially open new possibilities in a variety of applications in fiber optics.”

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Publication: Optics Express
Issue/Year/DOI: Vol. 28, Issue 7, pp. 9487-9500
DOI: 10.1364/OE.389133

Three-dimensional tomography of red blood cells using deep learning

Author(s):

Joowon Lim and Ahmed B. Ayoub and Demetri Psaltis

Abstract:

“We accurately reconstruct three-dimensional (3-D) refractive index (RI) distributions from highly
ill-posed two-dimensional (2-D) measurements using a deep neural network (DNN). Strong distortions are
introduced on reconstructions obtained by the Wolf transform inversion method due to the ill-posed
measurements acquired from the limited numerical apertures (NAs) of the optical system. Despite the
recent success of DNNs in solving ill-posed inverse problems, the application to 3-D optical imaging is
particularly challenging due to the lack of the ground truth. We overcome this limitation by generating
digital phantoms that serve as samples for the discrete dipole approximation (DDA) to generate multiple
2-D projection maps for a limited range of illumination angles. The presented samples are red blood cells
(RBCs), which are highly affected by the ill-posed problems due to their morphology. The trained network
using synthetic measurements from the digital phantoms successfully eliminates the introduced distortions.
Most importantly, we obtain high fidelity reconstructions from experimentally recorded projections of real RBC
sample using the network that was trained on digitally generated RBC phantoms. Finally, we confirm the
reconstruction accuracy using the DDA to calculate the 2-D projections of the 3-D reconstructions and
compare them to the experimentally recorded projections.”

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Publication: Advanced Photonics
Issue/Year/DOI: Vol. 2, Issues 2
DOI: 10.1117/1.AP.2.2.026001

Imaging of polarimetric-phase object through scattering medium by phase shifting

Author(s):

Li Chen and Ziyang Chen and Rakesh Kumar Singh and Jixiong Pu

Abstract:

“Light propagating through a scattering medium generates a random field, which is also known as a speckle. The scattering process hinders the direct retrieval of the information encoded in the light based on the randomly fluctuating field. In this study, we propose and experimentally demonstrate a method for the imaging of polarimetric-phase objects hidden behind a scattering medium based on two-point intensity correlation and phase-shifting techniques. One advantage of proposed method is that it does not require mechanical rotation of polarization elements. The method exploits the relationship between the two-point intensity correlation of the spatially fluctuating random field in the observation plane and the structure of the polarized source in the scattering plane. The polarimetric phase of the source structure is determined by replacing the interference intensity in traditional phase shift formula with the Fourier transform of the cross-covariance of the intensity. The imaging of the polarimetric-phase object is demonstrated by comparing three different phase-shifting techniques. We also evaluated the performance of the proposed technique on an unstable platform as well as using dynamic diffusers, which is implemented by replacing the diffuser with a new one during each phase-shifting step. The results were compared with that obtained with a fixed diffuser on a vibration-isolation platform during the phase-shifting process. A good match is found among the three cases, thus confirming that the proposed intensity-correlation-based technique is a useful one and should be applicable with dynamic diffusers as well as in unstable environments. ”

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Publication: Optics Express

Issue/Year/DOI: Vol. 28, Issue 6, pp. 8145-8155
DOI: 10.1364/OE.382551

Velocity measurements with structured light transmitted through a multimode optical fiber using digital optical phase conjugation

Author(s):

Lars Büttner and Martin Thümmler and Jürgen Czarske

Abstract:

“Lensless fiber microendoscopes enable optical diagnostics and therapy with minimal
invasiveness. Because of their small diameters, multimode fibers are ideal candidates, but mode
scrambling hinders the transmission of structured light fields. We present the generation of a
localized fringe system at variable distances from the distal fiber end by exploiting digital optical
phase conjugation. The replayed fringe system was used for quantitative metrology. Velocity
measurements of a microchannel flow in the immediate proximity of the fiber end without the
use of any imaging lenses are shown. Lensless multimode fiber systems are of interest especially
for biomedical imaging and stimulation as well as technical inspection and flow measurements. ”

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Publication: Optics Express

Issue/Year/DOI: Vol. 28, Issue 6, pp. 8064-8075
DOI: 10.1364/OE.386047

Compact lensless full-color holographic projection system with digital phase

Author(s):

Zhaoyu Gong and Xing Chen and Zhongyuan Guo and Feihong Yu

Abstract:

” A lensless full-color holographic projection system is proposed, satisfying the
requirement of compactness and flexibility. The system enables projection by illuminating a
single-chip spatial light modulator (SLM) simultaneously with red (R), green (G), and blue
(B) lasers, in which the SLM loads a color-multiplexed phase-only hologram. To strengthen
compactness, filtering and achromatic systems are achieved by digital phase, where the digital
lens phase focuses the light field onto the filter plane, and the digital blazed gratings shift the RGB
images to achieve a fine alignment. Besides, the flexibility of diffraction calculation is enhanced
by the cascaded D-FFT and S-FFT algorithm (CDS algorithm, where D-FFT is acronym of
double fast fourier transform and S-FFT is acronym of single fast fourier transform). Both
simulation and optical experiments are carried out. We conducted 2D image and animation
projection and multi-image-plane projection. The results confirm the feasibility of our method.”

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Publication: OSA Continuum
Issue/Year/DOI: Vol. 3, Issue 3, pp. 676-687
DOI: 10.1364/OSAC.380132

VioBio lab adaptive optics: technology and applications by women vision scientists

Author(s):

Susana Marcos, Clara Benedí‐García, Sara Aissati, Ana M Gonzalez‐Ramos, Carmen M Lago, Aiswaryah Radhkrishnan, Mercedes Romero, Shrilekha Vedhakrishnan, Lucie Sawides and Maria Vinas

Abstract:

“Purpose
Adaptive Optics allows measurement and manipulation of the optical aberrations of the eye. We review two Adaptive Optics set‐ups implemented at the Visual Optics and Biophotonics Laboratory, and present examples of their use in better understanding of the role of optical aberrations on visual perception, in normal and treated eyes.

Recent findings
Two systems (AOI and AOII) are described that measure ocular aberrations with a Hartmann‐Shack wavefront sensor, which operates in closed‐loop with an electromagnetic deformable mirror, and visual stimuli are projected in a visual display for psychophysical measurements. AOI operates in infrared radiation (IR) light. AOII is provided with a supercontiniuum laser source (IR and visible wavelengths), additional elements for simulation (spatial light modulator, temporal multiplexing with optotunable lenses, phase plates, cuvette for intraocular lenses‐IOLs), and a double‐pass retinal camera. We review several studies undertaken with these AO systems, including the evaluation of the visual benefits of AO correction, vision with simulated multifocal IOLs (MIOLs), optical aberrations in pseudophakic eyes, chromatic aberrations and their visual impact, and neural adaptation to ocular aberrations.

Summary
Monochromatic and chromatic aberrations have been measured in normal and treated eyes. AO systems have allowed understanding the visual benefit of correcting aberrations in normal eyes and the adaptation of the visual system to the eye’s native aberrations. Ocular corrections such as intraocular and contact lenses modify the wave aberrations. AO systems allow simulating vision with these corrections before they are implanted/fitted in the eye, or even before they are manufactured, revealing great potential for industry and the clinical practice. This review paper is part of a special issue of Ophthalmic & Physiological Optics on women in visual optics, and is co‐authored by all women scientists of the research team.”

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Publication: Ophthalmic and Physiological Optics
DOI: 10.1111/opo.12677

Super-resolved angular displacement estimation based upon a Sagnac interferometer and parity measurement

Author(s):

Jian-Dong Zhang, Zi-Jing Zhang, Long-Zhu Cen, Jun-Yan Hu and Yuan Zhao

Abstract:

“Super-resolved angular displacement estimation is of crucial significance to the field
of quantum information processing. Here we report an estimation protocol based on a Sagnac
interferometer fed by a coherent state carrying orbital angular momentum. In a lossless scenario,
through the use of parity measurement, our protocol can achieve a 4`-fold super-resolved output
with quantum number `; meanwhile, a shot-noise-limited sensitivity saturating the quantum
Cramér-Rao bound is reachable. We also consider the effects of several realistic factors, including
nonideal state preparation, photon loss, and inefficient measurement. Finally, with mean photon
number ¯N = 2.297 and ` = 1 taken, we experimentally demonstrate a super-resolved effect of
angular displacement with a factor of 7.88.”

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Publication: Optics Express

Issue/Year/DOI: Vol. 28, Issue 3, pp. 4320-4332
DOI: 10.1364/OE.384082

Three-Dimensional Holographic Reconstruction of Brain Tissue Based on Convolution Propagation

Author(s):

Rania M. Abdelazeem and Doaa Youssef and Jala El-Azab and Salah Hassab-Elnaby and Mostafa Agour

Abstract:

” In this study, a dynamic holographic projection system for brain tissue and its anatomical structures extracted from Magnetic Resonance (MR) plane slice is reported. Computer holograms are calculated using a modied Gerchberg-Saxton (GS) iterative algorithm where the projection is based on the plane wave decomposition. First, brain anatomy includes white matter (WM), grey matter (GM) and brain tissue are extracted. Then, phase holograms using the proposed method are generated. Finally, single phase hologram for the whole brain anatomy is generated and is optically reconstructed by a phase-only spatial light modulator (SLM) at dierent depths. The obtained results revealed that the three-dimensional holographic projection of MR brain tissue can aid to provide better interpretation of brain anatomical
structure to achieve better diagnostic results.”

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Publication: Journal of Physics: Conference Series
Issue/Year/DOI: Vol. 1472
DOI: 10.1088/1742-6596/1472/1/012008

Propagation properties of the circular Airy beam with a Gaussian envelope in Fourier space

Author(s):

Tao Geng and Xiuxiang Zhang

Abstract:

“We theoretically and experimentally study the propagation properties of the circular
Airy beam (CAB) with a Gaussian envelope in Fourier space. The two parameters of the Gaussian
function can be used to control the distribution of the spatial frequency, and thus to tune the
propagation properties of this modified CAB. When the two parameters are chosen appropriately,
the size of focal spot will be reduced, the maximum focal intensity and especially the abruptly
autofocusing property will be greatly enhanced. Meanwhile, the focal position can remain almost
the same with the common CAB. The experimental results show that the proposed beam can
be generated conveniently by using the same Fourier transform method as used to generate the
common CAB.”

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Publication: Optics Express

Issue/Year/DOI: Vol. 28, Issue 2, pp. 2447-2455
DOI: 10.1364/OE.384143

Wavefront-shaping-based correction of optically simulated cataracts

Author(s):

Augusto Arias and Pablo Artal

Abstract:

“Cataracts is a common ocular pathology where the crystalline lens tends to become opaque, degrading the quality of the retinal images because of the increase of both aberrations and scattering. In this work, we simultaneously generated and optically corrected the effects of cataracts in an optical bench by using a liquid crystal device spatial light modulator. The correction was carried out by implementing a feedback-based wavefront shaping technique with different spatial resolutions of the corrector phase maps. Its benefits were evaluated through objective and subjective descriptors of the quality of vision. The analysis of the experimental results, in addition to numerical calculations of the uncorrected and corrected ocular point spread functions, allowed us to understand the limitations of the technique and to present a strategy to overcome it for future in vivo applications.”

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Publication: Optica

Issue/Year/DOI: Vol. 7, Issue 1, pp. 22-27
DOI: 10.1364/OPTICA.7.000022