arXiv subjects

KyeoReh Lee

Publications and source records attributed to KyeoReh Lee.

At least 19 recordsLinked to original sources

arXiv2026

Tailoring complex coupling for efficient synchronization of semiconductor lasers

A grand challenge for laser synchronization is the intrinsic frequency disorder. We build an experimental platform for programming the complex coupling coefficients of semiconductor lasers to promote frequency and phase locking. The coupling amplitude between every pair of lasers in an array is tuned to scale with their frequency difference. Coupling phases are scanned to meet the phase matching conditions for constructive interference of coupled fields. The minimum coupling budget for global synchronization is significantly reduced, as shown experimentally for three vertical-cavity surface-emitting lasers with intrinsic frequency detuning. The customized coupling offers an efficient approach to stable synchronization of semiconductor laser arrays for coherent beam combining.

physics.optics↗

arXiv2026

Reconfigurable generation of high-power structured light via nonlinear beam shaping

High-power structured light has a wide range of applications, from material processing and high-capacity optical communications to programmable electron beams, plasmas, and nuclear states. On-demand generation of structured light and adaptive control of beam profiles are essential for many practical applications, but are difficult to achieve at high power. Here, we demonstrate reconfigurable generation of structured light from a high-power multimode-fiber laser amplifier through full-field control of a low-power seed. An efficient nonlinear beam shaping scheme based on a local linear approximation of the complex nonlinear input--output relation is developed and realized in situ. Diverse structured beams such as Gaussian, Bessel, vector and orbital angular momentum beams are directly generated from the fiber amplifier at powers exceeding 500 W. Our scheme enables real-time programmability of structured light and is readily scalable to even higher power levels. This work provides a general framework for controlling high-dimensional nonlinear systems without accurate knowledge or tractable model.

physics.optics↗

arXiv2026

Tailored Speckle Illumination Microscopy with Enhanced Sectioning and Image Quality

Optical speckle patterns have been widely used for illumination in computational imaging, optical sectioning microscopy, and super-resolution imaging. However, commonly used speckles satisfy Rayleigh statistics, which are not ideal for diverse imaging applications. Here we tailor three-dimensional speckle intensity statistics for dynamic speckle illumination microscopy based on linear fluorescence. Optical sectioning is enhanced by axially varying speckle contrast, and image reconstruction noise is minimized with in-focus speckles of binary intensities. The customized speckle statistics are shown to tolerate sample-induced aberration and scattering. We apply tailored speckle illumination to mouse brain vascular imaging and demonstrate much improved image quality than optical-sectioning structured illumination. These results establish customization of speckle intensity statistics as a promising strategy for robust, high-throughput fluorescence imaging in thick, scattering biological specimens.

physics.optics↗

arXiv2026

Video-rate holographic telepresence via single-shot, reference-free wavefront measurement

We present a reference-free holographic telepresence system that directly captures and replays complex optical wavefronts from a single intensity speckle measurement. Using a pre-characterized geometric phase diffuser, the incident field self-interferes to form a speckle pattern, from which the wavefront is recovered via a speckle-correlation scattering-matrix approach and refined using smoothed amplitude flow with Nesterov acceleration. The reconstructed phase is directly projected onto a spatial light modulator for holographic replay. We demonstrate volumetric refocusing, dynamic three-dimensional reconstruction, and sustained video-rate operation at approximately 28 frames per second with modest communication bandwidth. The results highlight measurement-driven wavefront acquisition as a practical pathway toward compact and physically faithful holographic telepresence.

physics.optics↗

arXiv2025

Speckle-based X-ray microtomography via preconditioned Wirtinger flow

Quantitative phase imaging has been extensively studied in X-ray microtomography to improve the sensitivity and specificity of measurements, especially for low atomic number materials. However, obtaining quantitative phase images typically requires additional measurements or assumptions, which significantly limits the practical applicability. Here, we present preconditioned Wirtinger flow (PWF): an assumption-free, single-shot quantitative X-ray phase imaging method. Accurate phase retrieval is demonstrated using a specialized gradient-based algorithm with an accurate physical model. Partial coherence of the source is taken into account, extending the potential applications to bench-top sources. Improved accuracy and spatial resolution over conventional speckle tracking methods are experimentally demonstrated. The various samples are explored to demonstrate the robustness and versatility of PWF.

physics.optics↗

arXiv2025

Quantitative X-ray Schlieren Nanotomography for Hyperspectral Phase and Absorption Imaging

Hyperspectral X-rays imaging holds promise for three-dimensional (3D) chemical analysis but remains limited in simultaneously capturing phase and absorption information due to complex setups and data burdens. We introduce quantitative X-ray schlieren nanotomography (XSN), a simple, fast, and high-resolution X-ray phase imaging technique that overcomes these limitations. XSN employs a partially coherent illumination and a pupil-plane cutoff filter to encode directional phase contrast, enabling single-shot acquisition. A quasi-Newton iterative algorithm reconstructs quantitative phase and absorption images from intensity data, even under strong scattering conditions. Scanning across X-ray energies further allows four-dimensional imaging (3D spatial & spectral). We validate the method's accuracy and resolution on reference samples and apply it to lithium battery cathodes, visualizing nanoscale microcracks and mapping chemical compositions. XSN provides a robust framework for hyperspectral phase nanotomography with broad applicability across materials science, biology, and energy research.

physics.optics↗

arXiv2025

Wavefront shaping enables high-power multimode fiber amplifier with output control

Over the past two decades there have been tremendous advances in high-power fiber lasers, which have provided a powerful tool for science, engineering and defense. A major roadblock for further power scaling of single-frequency fiber laser amplifiers is stimulated Brillouin scattering. Intense efforts were devoted to mitigate this nonlinear process, but mostly limited to single-mode or few-mode fiber amplifiers which have good beam quality. Here we explore a highly multimode fiber amplifier, where stimulated Brillouin scattering is greatly suppressed due to reduction of light intensity in a large fiber core and broadening of Brillouin scattering spectrum by multimode excitation. To control the output beam profile, we apply spatial wavefront shaping technique to the input light of a nonlinear amplifier to focus the output beam to a diffraction-limited spot outside the fiber facet. Our multimode fiber amplifier can operate at high power with high efficiency and narrow linewidth which ensures high coherence. Optical wavefront shaping enables coherent control of multimode laser amplification, with potential applications in coherent beam combining, large-scale interferometry and directed energy delivery.

physics.optics↗

arXiv2022

Non-resonant lasing in a deep-hole scattering cavity

Random lasers are promising in the spectral regime, wherein conventional lasers are unavailable, with advantages of low fabrication costs and applicability of diverse gain materials. However, their practical application is hindered by high threshold powers, low power efficiency, and difficulties in light collection. Here, we demonstrate a power-efficient easy-to-fabricate non-resonant laser using a deep hole on a porous gain material. The laser action in this counterintuitive cavity was enabled by nonresonant feedback from strong diffuse reflections on the inner surface. Additionally, significant enhancements in slope efficiency, threshold power, and directionality were obtained from cavities fabricated on a porous Nd:YAG ceramic.

physics.optics↗

arXiv2021

Enhancing sensitivity in absorption spectroscopy using a scattering cavity

Absorption spectroscopy is widely used to detect samples with spectral specificity. Here, we propose and demonstrate a method for enhancing the sensitivity of absorption spectroscopy. Exploiting multiple light scattering generated by a boron nitride (h-BN) scattering cavity, the optical path lengths of light inside a diffusive reflective cavity are significantly increased, resulting in more than ten times enhancement of sensitivity in absorption spectroscopy. We demonstrate highly sensitive spectral measurements of low concentrations of malachite green and crystal violet aqueous solutions. Because this method only requires the addition of a scattering cavity to existing absorption spectroscopy, it is expected to enable immediate and widespread applications in various fields, from analytical chemistry to environmental sciences.

physics.optics↗

arXiv2019

Reference-Free Single-Point Holographic Imaging and Realization of an Optical Bidirectional Transducer

One of the fundamental limitations in photonics is the lack of a bidirectional transducer that can convert optical information into electronic signals or vice versa. In acoustics or at microwave frequencies, wave signals can be simultaneously measured and modulated by a single transducer. In optics, however, optical fields are generally measured via reference-based interferometry or holography using silicone-based image sensors, whereas they are modulated using spatial light modulators. Here, we propose a scheme for an optical bidirectional transducer using a spatial light modulator. By exploiting the principle of time-reversal symmetry of light scattering, two-dimensional reference-free measurement and modulation of optical fields are realized. We experimentally demonstrate the optical bidirectional transducer for optical information consisting of 128 x 128 spatial modes at visible and short-wave infrared wavelengths.

physics.optics↗

arXiv2019

Intensity speckle presents the density matrix of light

We show that an intensity speckle can be directly interpreted as the properties of incident light - amplitude, phase, polarization, and coherency over spatial positions. Revisiting the speckle-correlation scattering matrix (SSM) method [Lee and Park, Nat. Comm. 7, 13359 (2016)], we successfully extract the intact information of incident light from an intensity speckle snapshot as the form of coherency matrix. The idea is verified experimentally by introducing the peculiar states of light that exhibit uneven amplitude, phase, polarization, and coherency features. We also find substantial practical advantage of the proposed method compared to the conventional coherency matrix measuring techniques such as Stokes polarimetry. We believe this physical interpretation of an intensity speckle could open a new avenue to study and to utilize the speckle phenomenon in vast subfields of wave physics.

physics.optics↗

arXiv2018

Low-coherent optical diffraction tomography by angle-scanning illumination

We propose and experimentally demonstrate temporally low-coherent optical diffraction tomography (ODT) based on angle-scanning Mach-Zehnder interferometry. Using a digital micromirror device based on diffractive tilting, we successfully maintain full-field interference of incoherent light during every scan sequence. The ODT reconstruction principles for temporally incoherent illuminations are thoroughly reviewed and developed. Several limitations of incoherent illumination are also discussed, such as the nondispersive assumption, optical sectioning capacity, and illumination angle limitation. Using the proposed setup and reconstruction algorithms, we successfully demonstrate low-coherent ODT imaging of microspheres, human red blood cells, and eukaryotic cells.

physics.optics↗

arXiv2018

High-resolution long-working-distance reference-free holographic microscopy exploiting speckle-correlation scattering matrix

Using conventional refraction-based optical lens, it is challenging to achieve both high-resolution imaging and long-working-distance condition. To increase the numerical aperture of a lens, the working distance should be compensated, and vice versa. Here we propose and demonstrate a new concept in optical microscopy that can achieve both high-resolution imaging and long-working-distance conditions by utilising a scattering layer instead of refractive optics. When light passes through a scattering layer, it creates a unique interference pattern. To retrieve the complex amplitude image from the interference pattern without introducing a reference beam, we utilised a speckle-correlation scattering matrix method. This property enables holographic microscopy without any lens or external reference beam. Importantly, the proposed method allows high-resolution imaging with a long working distance beyond what a conventional objective lens can achieve. As an experimental verification, we imaged various microscopic samples and compared their performance with off-axis digital holographic microscopy.

physics.optics↗

arXiv2017

Ultrahigh enhancement of light focusing through disordered media controlled by Megapixel modes

We propose and demonstrate a system for wavefront shaping which generates optical foci through complex disordered media and achieves an enhancement factor of greater than 100,000. To exploit the 1 Megapixel capacity of a digital micro-mirror device and its fast frame rate, we developed a fast and efficient method to handle the heavy matrix algebra computation involved in optimizing the focus. We achieved an average enhancement factor of 101,391 within an optimization time of 73 minutes. This unprecedented enhancement factor may open new possibilities for realistic image projection and the efficient delivery of energy through scattering media.

physics.optics↗

arXiv2016

The effects of spatiotemporal coherence on interferometric imaging

Illumination coherence plays a major role in various imaging systems, from microscopy, metrology, digital holography, optical coherence tomography, to ultrasound imaging. Here, we present a systematic study on the effects of degrees of spatiotemporal coherence of an illumination (DSTCI) on imaging quality. An optical field with arbitrary DSTCI was decomposed into wavelets with constituent spatiotemporal frequencies, and the effects on image quality were quantitatively investigated. The results show the synergistic effects on reduction of speckle noise when DSTCI is decreased. This study presents a method to systematically control DSTCI, and the result provides an essential reference on the effects of DSTCI on imaging quality. We believe that the presented methods and results can be implemented in various imaging systems for characterising and improving imaging quality.

physics.optics↗

arXiv2016

Universal sensitivity of speckle intensity correlations to wavefront change in light diffusers

Here, we present a concept based on the realization that a complex medium can be used as a simple interferometer. Changes in the wavefront of an incident coherent beam can be retrieved by analyzing changes in speckle patterns when the beam passes through a light diffuser. We demonstrate that the spatial intensity correlations of the speckle patterns are independent of the light diffusers, and are solely determined by the phase changes of an incident beam. With numerical simulations using the random matrix theory, and an experimental pressure-driven wavefront-deforming setup using a microfluidic channel, we theoretically and experimentally confirm the universal sensitivity of speckle intensity correlations, which is attributed to the conservation of optical field correlation despite multiple light scattering. This work demonstrates that a complex media is a simple interferometer, and presents opportunities to replace complicated reference-beam-assisted interferometers with a simple and compact scattering layer in various applications in metrology, analytical chemistry, and biomedicine.

physics.optics↗

arXiv2016

Collaborative effects of wavefront shaping and optical clearing agent in optical coherence tomography

We demonstrate that simultaneous application of optical clearing agents (OCAs) and complex wavefront shaping in optical coherence tomography (OCT) can provide significant enhancement of the penetration depth and imaging quality. OCA reduces optical inhomogeneity of a highly scattering sample, and the wavefront shaping of illumination light controls multiple scattering, resulting in an enhancement of the penetration depth and signal-to-noise ratio. A tissue phantom study shows that concurrent applications of OCA and wavefront shaping successfully operate in OCT imaging. The penetration depth enhancement is further demonstrated for ex vivo mouse ears, revealing hidden structures inaccessible with conventional OCT imaging.

physics.optics↗

arXiv2016

Time-reversing a monochromatic subwavelength optical focus by optical phase conjugation of multiply-scattered light

Due to its time-reversal nature, optical phase conjugation generates a monochromatic light wave which retraces its propagation paths. Here, we demonstrate the regeneration of a subwavelength optical focus by phase conjugation. Monochromatic light from a subwavelength source is scattered by random nanoparticles, and the scattered light is phase conjugated at the far-field region by coupling its wavefront into a single-mode optical reflector using a spatial light modulator. Then the conjugated beam retraces its propagation paths and forms a refocus on the source at the subwavelength scale. This is the first direct experimental realization of subwavelength focusing beyond the diffraction limit with far-field time reversal in the optical domain.

physics.optics↗