Three-dimensional laser damage positioning by a deep-learning method

Author(s):

Zhan Li and Lu Han and Xiaoping Ouyang and Pan Zhang and Yajing Guo and Dean Liu and Jianqiang Zhu

Abstract:

“A holographic and deep learning-based method is presented for three-dimensional
laser damage location. The axial damage position is obtained by numerically focusing the
diffraction ring into the conjugate position. A neural network Diffraction-Net is proposed to
distinguish the diffraction ring from different surfaces and positions and obtain the lateral position.
Diffraction-Net, which is completely trained by simulative data, can distinguish the diffraction
rings with an overlap rate greater than 61% which is the best of results reported. In experiments,
the proposed method first achieves the damage pointing on each surface of cascade slabs using
diffraction rings, and the smallest inspect damage size is 8μm. A high precision result with the
lateral positioning error less than 38.5μm and axial positioning error less than 2.85mm illustrates
the practicability for locating the damage sites at online damage inspection.”

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Publication: Optics Express
Issue/Year/DOI: Vol. 28, Issue 7, pp. 10165-10178
DOI: 10.1364/OE.387987

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.”

Link to Publications Page

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. ”

Link to Publications Page

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. ”

Link to Publications Page

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.”

Link to Publications Page

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