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: 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.”

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

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

Laguerre-Gaussian mode sorter

Author(s):

Fontaine, Nicolas K.; Ryf, Roland; Chen, Haoshuo; Neilson, David T.; Kim, Kwangwoong & Carpenter, Joel

Abstract:

“Exploiting a particular wave property for a particular application necessitates components capable of discriminating in the basis of that property. While spectral or polarisation decomposition can be straightforward, spatial decomposition is inherently more difficult and few options exist regardless of wave type. Fourier decomposition by a lens is a rare simple example of a spatial decomposition of great practical importance and practical simplicity; a two-dimensional decomposition of a beam into its linear momentum components. Yet this is often not the most appropriate spatial basis. Previously, no device existed capable of a two-dimensional decomposition into orbital angular momentum components, or indeed any discrete basis, despite it being a fundamental property in many wave phenomena. We demonstrate an optical device capable of decomposing a beam into a Cartesian grid of identical Gaussian spots each containing a single Laguerre-Gaussian component, using just a spatial light modulator and mirror.”

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Publication: Nature Communications
Issue/Year: Nature Communications, Volume 10; Number 1; 2019
DOI: 10.1038/s41467-019-09840-4

Raman imaging through multimode sapphire fiber

Author(s):

Sunan Deng, Damien Loterie, Georgia Konstantinou, Demetri Psaltis, and Christophe Moser
Abstract:

“We report on a sapphire fiber Raman imaging probe’s use for challenging applications where access is severely restricted. Small-dimension Raman probes have been developed previously for various clinical applications because they show great capability for diagnosing disease states in bodily fluids, cells, and tissues. However, applications of these sub-millimeter diameter Raman probes were constrained by two factors: first, it is difficult to incorporate filters and focusing optics at such small scale; second, the weak Raman signal is often obscured by strong background noise from the fiber probe material, especially the most commonly used silica, which has a strong broad background noise in low wavenumbers (<500-1700 cm−1). Here, we demonstrate the thinnest-known imaging Raman probe with a 60 μm diameter Sapphire multimode fiber in which both excitation and signal collection pass through. This probe takes advantage of the low fluorescence and narrow Raman peaks of Sapphire, its inherent high temperature and corrosion resistance, and large numerical aperture (NA). Raman images of Polystyrene beads, carbon nanotubes, and CaSO4 agglomerations are obtained with a spatial resolution of 1 μm and a field of view of 30 μm. Our imaging results show that single polystyrene bead (~15 µm diameter) can be differentiated from a mixture with CaSO4 agglomerations, which has a close Raman shift.”

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Publication: Optics Express
Issue/Year: Vol. 27, Issue 2, pp. 1090-1098 (2019)
DOI: 10.1364/OE.27.001090

Adaptive wavefront interferometry for unknown free-form surfaces

Author(s):

Shuai Xue, Shanyong Chen, Zhanbin Fan and Dede Zhai

Abstract:

“The primary problem of conventional wavefront interferometers is limited dynamic range. Unknown free-form surface figure error with large amplitude or slope is not measurable for too dense or invisible fringes. To troubleshoot this problem, we propose adaptive wavefront interferometry (AWI). AWI utilizes a wavefront sensor-less adaptive optics (AO) subsystem to intelligently speculate and compensate the unknown free-form surface figure error. In this subsystem, adaptive null optics is utilized to iteratively generate adaptive wavefronts to compensate the unknown severe surface figure error. The adaptive null optics is close-loop controlled (i.e., wavefront sensor-less optimization algorithms are utilized to control it by real time monitoring the compensation effects to guarantee convergence of the iteration). Ultimately, invisible fringes turn into resolvable ones, and null test is further realized. To demonstrate the feasibility of AWI, we designed one spatial light modulator (SLM) based AWI modality as an example. The system is based on a commercial interferometer and is easy to establish. No other elements are required besides the SLM. Principle, simulation, and experiments for the SLM based AWI are demonstrated. ”

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Publication: Optics Express
Issue/Year: Vol. 26, Issue 17, pp. 21910-21928 (2018)
DOI: 10.1364/OE.26.021910

Multiple-plane image formation by Walsh zone plates

Author(s):

Federico Machado, Vicente Ferrando, Fernando Giménez, Walter D. Furlan, and Juan A. Monsoriu

Abstract:

“A radial Walsh filter is a phase binary diffractive optical element characterized by a set of concentric rings that take the phase values 0 or π, corresponding to the values + 1 or −1 of a given radial Walsh function. Therefore, a Walsh filter can be re-interpreted as an aperiodic multifocal zone plate, capable to produce images of multiple planes simultaneously in a single output plane of an image forming system. In this paper, we experimentally demonstrate for the first time the focusing capabilities of these structures. Additionally, we report the first achievement of images of multiple-plane objects in a single image plane with these aperiodic diffractive lenses.”

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Publication: Optics Express
Issue/Year: Optics Express Volume 26, Issue 16
DOI: 10.1364/OE.26.021210

Wide-field in situ multiplexed Raman imaging with superresolution

Author(s):

Houkai Chen and Xiaojing Wu and Yuquan Zhang and Yong Yang and Changjun Min and Siwei Zhu and Xiaocong Yuan and Qiaoliang Bao and Jing Bu

Abstract:

“Because of the fingerprint-like specificity of its characteristic spectrogram, Raman spectral imaging has been applied widely in various research areas. Using a combination of structured illumination with the surfaceenhanced Raman scattering (SERS) technique, wide-field Raman imaging is developed with a significant improvement in spatial resolution. As a result of the relatively narrow Raman characteristic peaks, optically encoded SERS nanoparticles can be used to perform multiplexed imaging. The results show excellent superresolution wide-field multiplexed imaging performance. The developed technique has extraordinary potential for applications in biological imaging and other related fields.”

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Publication: Photonics Research
Issue/Year: Photonics Research Volume 6, Issue 6 pp. 530-534
DOI: 10.1364/PRJ.6.000530

Experimental demonstration of tunable refractometer based on orbital angular momentum of longitudinally structured light

Author(s):

Dorrah, Ahmed H and Zamboni-Rached, Michel and Mojahedi, Mo

Abstract:

“The index of refraction plays a decisive role in the design and classification of optical materials and devices; therefore, its proper and accurate determination is essential. In most refractive index (RI) sensing schemes, however, there is a trade-off between providing high-resolution measurements and covering a wide range of RIs. We propose and experimentally demonstrate a novel mechanism for sensing the index of refraction of a medium by utilizing the orbital angular momentum (OAM) of structured light. Using a superposition of co-propagating monochromatic higher order Bessel beams with equally spaced longitudinal wavenumbers, in a comb-like setting, we generate nondiffracting rotating light structures in which the orientation of the beam’s intensity profile is sensitive to the RI of the medium (here, a fluid). In principle, the sensitivity of this scheme can exceed ∼ 2700°/RIU with a resolution of ∼ 10-5 RI unit (RIU). Furthermore, we show how the unbounded degrees of freedom associated with OAM can be deployed to offer a wide dynamic range by generating structured light that evolves into different patterns based on the change in RI. The rotating light structures are generated by a programmable spatial light modulator (SLM). This provides dynamic control over the sensitivity, which can be tuned to perform coarse or fine measurements of the RI in real time. This, in turn, allows high sensitivity and resolution to be achieved simultaneously over a very wide dynamic range, which is a typical trade-off in all RI sensing schemes. We thus envision that this method will open new directions in refractometry and remote sensing.”

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Publication: Light: Science \& Applications
Issue/Year: Light: Science & Applications accepted article preview 18 May 2018
DOI: 10.1038/s41377-018-0034-9

Single camera shot interferenceless coded aperture correlation holography

Author(s):

Mani Ratnam Rai and A. Vijayakumar and Joseph Rosen

Abstract:

“We propose a new scheme for recording an incoherent digital hologram by a single camera shot. The method is based on a motionless, interferenceless, coded aperture correlation holography for 3D imaging. Two random-like coded phase masks (CPMs) are synthesized using the Gerchberg–Saxton algorithm with two different initial random phase profiles. The two CPMs are displayed side by side and used as the system aperture. Light from a pinhole is introduced into the system, and two impulse responses are recorded corresponding to the two CPMs. The two impulse responses are subtracted, and the resulting intensity profile is used as a reconstructing hologram. A library of reconstructing holograms is created corresponding to all possible axial locations. Following the above training stage, an object is placed within the axial limits of the library, and the intensity patterns of a single shot, corresponding to the same two CPMs, are recorded under identical conditions to generate the object hologram. The image of the object at any plane is reconstructed by a cross-correlation between the object hologram and the corresponding reconstructing hologram from the library.”

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Publication: Optics Letters
Issue/Year: Optics Letters Vol. 42, Issue 19, pp. 3992-3995 (2017)
DOI: 10.1364/OL.42.003992
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