arXiv subjects

Jun Guan

Publications and source records attributed to Jun Guan.

8 recordsLinked to original sources

arXiv2026

Pre-training Enables Extraordinary All-optical Image Denoising

Optical neural networks are emerging as powerful machine learning and information processing tools because of their potential advantages in speed and energy efficiency. The training methods of these physical models, however, remain underexplored compared to their digital counterparts and are leading to suboptimal performance. This paper reports a pre-training-driven approach that leads to snapshot image denoising with substantially improved quality. We demonstrated effective free-space optical denoising by a diffractive network optimized by a two-step process including (1) pre-training using a massive dataset of 3.45 million diverse but simple images and (2) fine-tuning with the corresponding task-specific datasets. Compared to conventional Fourier-domain filtering and directly trained diffractive networks, such a transfer learning process exhibited prominent advantages for denoising images degraded by severe noise, peak signal-to-noise ratio (PSNR) below 8 dB, while preserving fine image features and improving the PSNR to above 18 dB. Importantly, the same pre-trained optical network could be consistently fine-tuned to process degraded images from highly diverse styles ranging from handwritten digits (MNIST) and chest X-rays (ChestMNIST) to CIFAR-10 images and human faces (CelebA). We further demonstrated the critical role of our optical denoisers in vision-based applications, including face detection, plate recognition, and localization of UAVs in noisy conditions.

physics.optics↗

arXiv2025

Tight-binding photonics

Photonics, dealing with the generation, manipulation, and detection of photons in various systems, lays the foundation of many advanced technologies. A key task of photonics is to know how photons propagate in complex media such as periodic and aperiodic photonic crystals. The conventional wisdom is to numerically solve the Maxwell equations either by dedicated numerical techniques or brute-force finite-element calculations. Recently, the strict analogy between photonic crystals and theoretical tight-binding models provides an unprecedentedly convenient wayof understanding the spectra and wavefunctions of photonic systems by mapping the complicated differential equationsinto matrixed Hamiltonians that can be easily solved through the band theory and exact diagonalization. in this paper, we present a timely review of tight-binding-like photonics in various platforms, covering fundamental theories, experimental realizations, unique physical efiects, and their potential applications. We also provide a brief outlook on the future trends of this active area. Our review offers an in-depth and comprehensive picture on this rapidly developing field and may shed light on the future design on advanced tight-binding-like photonic devices.

physics.optics↗

arXiv2024

Spectral-isolated photonic topological corner mode with a tunable mode area and stable frequency

Emergent collective modes in lattices give birth to many intriguing physical phenomena in condensed matter physics. Among these collective modes, large-area modes typically feature small-level spacings, while a mode with stable frequency tends to be spatially tightly confined. Here, we theoretically propose and experimentally demonstrate a spectral-isolated photonic topological corner mode with a tunable mode area and stable frequency in a two-dimensional photonic crystal. This mode emerges from hybridizing the large-area homogeneous mode and in-gap topological corner modes. Remarkably, this large-area homogeneous mode possesses unique chirality and has a tunable mode area under the change of the mass term of the inner topological non-trivial lattice. We experimentally observe such topological large-area corner modes(TLCM) in a 2D photonic system and demonstrate the robustness by introducing disorders in the structure. Our findings have propelled the forefront of higher-order topology research, transitioning it from single-lattice systems to multi-lattice systems. They may support promising potential applications, particularly in vertical-cavity surface-emitting lasers.

cond-mat.mes-hall↗

arXiv2020

Laser-written integrated photonics in glass-ceramics Zerodur

We demonstrated fabrication of waveguide and directional coupler in bulk glass-ceramics Zerodur, through femtosecond laser direct-writing. Waveguide propagation loss of no more than 1.5 dB/cm was achieved. We expect this will lead to the deployment of Zerodur integrated photonics in fields like space-borne astronomy, quantum technology and fundamental physics, for both economic and technical benefits.

physics.app-ph↗

arXiv2019

A Photonic Topological Mode Bound to a Vortex

Topological photonics sheds light on some of the surprising phenomena seen in condensed matter physics that arise with the appearance of topological invariants. Optical waveguides provide a well-controlled platform to investigate effects that relate to different topological phases of matter, providing insight into phenomena such as topological insulators and superconductors by direct simulation of the states that are protected by the topology of the system. Here, we observe a mode associated with a topological defect in the bulk of a 2D photonic material by introducing a vortex distortion to an hexagonal lattice and analogous to graphene. These observations are made possible by advances in our experimental methods. We were able to manufacture uniform large two-dimensional photonic crystal structures, containing thousands of identical waveguides arranged in two dimensions, and we developed a new method to excite multiples of these waveguides with a well-defined light field. This allows us to probe the detailed spatial features of topological defect modes for the first time. The observed modes lie mid-gap at zero energy and are closely related to Majorana bound states in superconducting vortices. This is the first experimental demonstration of a mode that is a solution to the Dirac equation in the presence of a vortex, as proposed by Jackiw and Rossi.

cond-mat.mes-hall↗

arXiv2018

Ultrafast laser writing quill effect in low loss waveguide fabrication regime

Quill effect, one of the intriguing phenomena in ultrafast laser writing, to our knowledge, has not been studied in low-loss-waveguide (LLW) writing regime yet, probably due to its invisibility under conventional white-light microscope in that regime. In this report, with help of adaptive third harmonic generation microscopy we reveal the quill effect in LLW writing regime and study its influences on the properties of written photonic integrated components in term of polarization-related properties in fused silica and beam-splitting ratio of three-waveguide-coupler in borosilicate glass.

physics.app-ph↗

arXiv2018

Microscopic characterisation of laser-written phenomena for component-wise testing of photonic integrated circuits

Photonic integrated circuits (PICs) directly written with a femtosecond laser have shown great potential in many areas such as quantum information processing (QIP). Many applications, like photon-based quantum computing, demand the up-scaling of PICs and ever-higher optical performance, such as controllable polarisation dependence and lower loss. In order to overcome current limitations in fabrication precision, repeatability and material uniformity, a solution for non-destructive testing of large-scale PICs in a component-wise manner is desired to meet those ever-stricter demands. Here we demonstrate a solution for non-destructive component-wise testing by predicting the performance of a PIC component based on imaging with an adaptive optical third-harmonic-generation (THG) three-dimensional (3D) microscope. The 3D THG imaging can be performed on any component or part of it inside multi-component PIC. Moreover, through discovering new phenomena we also demonstrated that 3D THG microscopy provides a new pathway towards studying the fundamentals of light-matter interaction in transparent materials.

physics.optics↗

arXiv2014

Selective molecular capture mechanism in carbon nanotube networks

Recent air pollution issues have raised significant attention to develop efficient air filters, and one of the most promising candidates is that enabled by nanofibers. We explore here selective molecular capture mechanism for volatile organic compounds in carbon nanotube networks by performing atomistic simulations. The results are discussed with respect to the two key parameters that define the performance of nanofiltration, i.e. the capture efficiency and flow resistance, which validate the advantage of carbon nanotube networks with high surface-to-volume ratio and atomistically smooth surfaces. We also reveal the important roles of interfacial adhesion and diffusion that govern selective gas transport through the network.

cond-mat.mes-hall↗