arXiv subjects

Ming Yan

Publications and source records attributed to Ming Yan.

At least 37 records · Page 2Linked to original sources

arXiv2026

Unified Ergodic Primal-Dual Gap Rates with Unhalved Primal Stepsizes

We study ergodic primal-dual gap rates for first-order primal-dual methods applied to \[ \min_x f(x)+g(x)+h(Ax), \] where $f$ is smooth and convex, $g$ and $h$ are proper, closed, convex functions, and $A$ is linear. Standard gap-rate proofs often impose the halved smooth-stepsize condition $τ\le 1/L$, even though the corresponding convergence theory allows the larger range $τ<2/L$. We introduce a residual-to-gap transfer principle: positive residual terms in the one-step gap inequality are controlled by the decrease of a Lyapunov function. This yields $O(1/K)$ ergodic primal-dual gap bounds with the unhalved primal stepsize $τ<2/L$ for Condat--Vũ, PD3O, AFBA/PDDY, and PAPC/PDFP$^2$O, under their algorithm-dependent product conditions. We also give a two-dimensional counterexample showing that the fully separated rectangle $τ<2/L$, $τη\|A\|^2<4/3$ cannot hold in the general three-function setting.

math.OC↗

arXiv2026

Passive all-optical synchronization for polarization-maintaining ultrafast fiber lasers

We have proposed and implemented for the first time to our best knowledge a passive and all-optical pulse synchronization for polarization-maintaining ultrafast fiber lasers. Specifically, the synchronization system was comprised of two independent Yb-doped and Er-doped mode-locked fiber lasers in a master-slave configuration. Master pulses were injected into the slave laser cavity consisting of a nonlinear amplifying loop mirror, which provided an effective fast intensity modulator due to the periodic introduction of nonreciprocal phase difference. As a result, robust and tight timing synchronization was achieved with a cavity mismatch tolerance of 800 $μ$m and a relative timing jitter of 26 fs within 1-MHz bandwidth. In combination with all-polarization-maintaining structure of fiber lasers, long-term stable operation was demonstrated over 12 hours without the need of temperature stabilization and vibration isolation. The implemented synchronous laser system could find immediate applications such as pump-probe microscopy, two-color spectroscopy and nonlinear frequency mixing.

physics.optics↗

arXiv2026

Observation of spectral mode splitting in a pump-enhanced ring cavity for mid-infrared generation

We report on experimental and theoretical investigation of mode-splitting dynamics in a ring cavity under the perturbation of fractional Bragg reflection from a periodically-poled nonlinear crystal. Counterintuitively, pronounced mode splitting in the spectral domain could been observed even with a tiny intensity reflection of 0.0003. The breaking of running-wave operation in the ring-cavity configuration resulted in comparable circulating fields in forward- and counter-propagation directions, which thus dramatically reduced the enhancing factor for the resonating field. In contrast, a linear cavity with intrinsically bidirectional operation was immune to the small intra-cavity reflection. Therefore, the linear-cavity layout could provide an expedient solution for a given internal reflection to obtain more stable and higher enhancement, which was confirmed by comparative studies of mid-infrared generation based on pump-enhanced difference frequency conversion. The underlying mechanism was further modeled by numerical simulations, which agreed well with experimental results. These findings could not only shed light on the understanding of the exotic feature of concatenated optical cavities, but also provide a useful guide to practical design of enhancement cavities for cavity-based frequency conversion with periodically-poled nonlinear crystals.

physics.optics↗

arXiv2026

Passively synchronized dual-color mode-locked fiber lasers based on nonlinear amplifying loop mirrors

We have proposed and implemented a novel scheme for passive all-optical synchronization between erbium and ytterbium mode-locked fiber lasers. The passive locking of repetition rates for the dual-color pulses was realized by cross-phase modulation within phase-biased nonlinear amplifying loop mirrors. In contrast to previous demonstrations, the synchronization system was configured in an all-polarization-maintaining structure, thus gaining substantially improved stability and robustness. Consequently, the maximum tolerance of cavity-length mismatch of 16.2 mm was achieved unprecedentedly, which was at least one order of magnitude longer than previously reported results for comparable temporal durations of involved pulses. The corresponding relative timing jitter was measured to be 31 fs within 1-MHz bandwidth. Such tight and robust synchronization fiber laser system offers a great potential for various applications, such as pump-probe microscopy, Raman scattering spectroscopy and nonlinear frequency generation.

physics.optics↗

arXiv2026

SoLoPO: Unlocking Long-Context Capabilities in LLMs via Short-to-Long Preference Optimization

Despite advances in pretraining with extended context sizes, large language models (LLMs) still face challenges in effectively utilizing real-world long-context information, primarily due to insufficient long-context alignment caused by data quality issues, training inefficiencies, and the lack of well-designed optimization objectives. To address these limitations, we propose a framework named \textbf{S}h\textbf{o}rt-to-\textbf{Lo}ng \textbf{P}reference \textbf{O}ptimization (\textbf{SoLoPO}), decoupling long-context preference optimization (PO) into two components: short-context PO and short-to-long reward alignment (SoLo-RA), supported by both theoretical and empirical evidence. Specifically, short-context PO leverages preference pairs sampled from short contexts to enhance the model's contextual knowledge utilization ability. Meanwhile, SoLo-RA explicitly encourages reward score consistency for the responses when conditioned on both short and long contexts that contain identical task-relevant information. This facilitates transferring the model's ability to handle short contexts into long-context scenarios. SoLoPO is compatible with mainstream preference optimization algorithms, while substantially improving the efficiency of data construction and training processes. Experimental results show that SoLoPO enhances all these algorithms with respect to stronger length and domain generalization abilities across various long-context benchmarks, while achieving notable improvements in both computational and memory efficiency.

cs.CL↗

arXiv2026

Highly efficient difference-frequency generation for mid-infrared pulses by passively synchronous seeding

We have proposed and experimentally demonstrated a novel scheme for efficient mid-infrared difference-frequency generation based on passively synchronized fiber lasers. The adoption of coincident seeding pulses in the nonlinear conversion process could substantially lower the pumping threshold for mid-infrared parametric emission. Consequently, a picosecond mid-infrared source at 3.1 $μ$m was prepared with watt-level average power, and a maximum power conversion efficiency of 77\% was realized from pump to down-converted light. Additionally, the long-term stability of generated power was manifested with a relative fluctuation as low as 0.17\% over one hour. Thanks to the all-optical passive synchronization and all-polarization-maintaining fiber architecture, the implemented laser system was also featured with simplicity, compactness and robustness, which would favor subsequent applications beyond laboratory operation.

physics.optics↗

arXiv2026

Coincidence-pumping upconversion detector based on passively synchronized fiber laser system

We experimentally demonstrated a high-performance frequency upconversion detector for telecom-band photons based on a passively synchronized fiber laser system. The involved coincidence pumping technique enabled to spectrally convert the pulsed infrared photons into the visible regime with a conversion efficiency of 72\%. The overall detection efficiency of the upconversion detector reached to 30\% with a low noise equivalent power of $3\times10^{-17}\ \text{W/Hz}^{1/2}$. In contrast to previous demonstrations, the whole upconversion detection system was constructed in an all-polarization-maintaining fiber structure, thus favoring substantial improvement of compactness and robustness. Moreover, the long-term stability was manifested by at least ten-hour operation with a relative fluctuation of count rates as small as 0.26\%. The achieved features here would be desirable in many practical applications requiring efficient and robust coherent manipulation of pulsed optical fields by nonlinear frequency conversion.

physics.optics↗

arXiv2026

Wide-field mid-infrared single-photon upconversion imaging

Frequency upconversion technique, where the infrared signal is nonlinearly translated into the visible band to leverage the silicon sensors, offers a promising alternation for the mid-infrared (MIR) imaging. However, the intrinsic field of view (FOV) is typically limited by the phase-matching condition, thus imposing a remaining challenge to promote subsequent applications. Here, we demonstrate a wide-field upconversion imaging based on the aperiodic quasi-phase-matching configuration. The acceptance angle is significantly expanded to about 30$^\circ$, over tenfold larger than that with the periodical poling crystal. The extended FOV is realized in one shot without the need of parameter scanning or post-processing. Consequently, a fast snapshot allows to facilitate high-speed imaging at a frame rate up to 216 kHz. Alternatively, single-photon imaging at room temperature is permitted due to the substantially suppressed background noise by the spectro-temporal filtering. Furthermore, we have implemented high-resolution time-of-flight 3D imaging based on the picosecond optical gating. These presented MIR imaging features with wide field, fast speed, and high sensitivity might stimulate immediate applications, such as non-destructive defect inspection, in-vivo biomedical examination, and high-speed volumetric tomography.

physics.optics↗

arXiv2026

Highly sensitive detection for infrared photons by non-degenerate two-photon absorption under mid-infrared pumping

We have demonstrated highly-sensitive photon counting in the infrared based on the two-photon absorption (2PA) in a silicon avalanche photodiode, where the required photon energy for inducing effective conductivity was provided by an intense mid-infrared (MIR) field at 3 $μ$m. The used MIR pumping scheme could not only benefit from the enhanced 2PA coefficient in the non-degenerate regime, but also eliminate the detrimental background noises due to the pump harmonic excitation of the pump. Consequently, the enhancement factor for the signal counting rate unprecedented reached to about $10^{5}$ with input infrared pulses at the femtojoule level. Additionally, the noise equivalent power was substantially improved by two orders of magnitude comparing to conventional schemes with near-infrared pumping. Therefore, the presented configuration might provide an alternative to realize sensitive infrared detection and imaging with desirable features of room-temperature operation, no phase-matching requirement, and broadband responding window, which would find a variety of applications including remote ranging, sensitive sensing, biochemical imaging, and trace spectroscopy.

physics.optics↗

arXiv2026

Passive repetition-rate stabilization for a mode-locked fiber laser by electro-optic modulation

We report a passive stabilization of the repetition rate for a mode-locked fiber laser by using an electro-optic modulator in a phase-biased nonlinear amplifying loop mirror. The underlying mechanism, in contrast to active feedback operations, lies in the cross-phase modulation between electrical and optical pulses within an electro-optic crystal. The resulting spectral shift can automatically compensate the cavity-length drift via the group velocity dispersion. Consequently, the artificial actuator enables to obtain a capture range up to 2.3 mm, much longer than that achieved by index changes of the modulator. A robust and tight locking for the repetition rate is then realized with a standard deviation as low as 9 $μ$Hz with a 1-s sample time over 11 hours, corresponding to a fractional instability of 4.3$\times$10$^{-13}$. Furthermore, a dynamic optical sampling by repetition-rate tuning has been manifested with a fast refresh rate at 100 kHz and a broad scanning range over 305 ps. The demonstrated passive servo action may provide a simple yet effective way to stabilize the repetition rate with high precision, large bandwidth and wide tunability.

physics.optics↗

arXiv2026

Beyond Trajectory-Level Attribution: Graph-Based Credit Assignment for Agentic Reinforcement Learning

Group-based reinforcement learning (RL) methods have achieved remarkable success in improving the performance of large language models (LLMs) and have been rapidly extended to agentic tasks. However, their credit assignment relies heavily on coarse-grained trajectory-level attribution according to final outcomes, making it difficult to capture the contribution of individual steps, such as valuable steps obscured within failed trajectories. To uncover latent information and enable more faithful step-level credit assignment, we propose Graph-based Group Policy Optimization (GraphGPO), which first aggregates all rollout trajectories into a unified state-transition graph and then estimates the distance from each state to the task goal using the global information encoded in the graph. Finally, GraphGPO assigns credit to each edge by estimating a graph-based advantage, based on how much the transition reduces the distance to the task goal. In this way, GraphGPO significantly improves training efficiency and achieves state-of-the-art performance across a range of challenging benchmarks.

cs.LG↗

arXiv2026

Mid-Infrared Single-Photon Edge Enhanced Imaging based on Nonlinear Vortex Filtering

Edge enhanced imaging via the spiral phase contrast enables to reveal the phase or amplitude gradients of a target, which has been proved useful in feature recognition, machine vision, and object identification. A long quest is to extend the operation wavelength into the mid-infrared (MIR) region, as highly demanded in various fields including infrared sensing, astronomic observation, and biomedical diagnosis. Here, we demonstrated ultra-sensitive MIR imaging at the single-photon level based on nonlinear frequency upconversion, where the spectrally converted replica of the MIR object image at 3070 nm was captured by a silicon electron multiplying charged coupled device. The imaging sensitivity was significantly improved by the coincidence pulsed pumping with a spectro-temporal optimization. Furthermore, the edge enhancement has been realized by imprinting the spiral phase pattern of the pump onto the upconverted field at the Fourier plane within the nonlinear crystal. Such a nonlinear spatial filter not only provided an effective way to implement the required high-fidelity vortex screening in the edge enhanced detection, but also rendered the MIR illumination into a visible image in an efficient and low-noise fashion. The presented system for MIR edge enhanced imaging might facilitate immediate applications in label-free histopathological diagnosis and non-destructive defect inspection.

physics.optics↗

arXiv2026

Single-Photon Infrared Imaging with a Silicon Camera Based on Long-Wavelength-Pumping Two-Photon Absorption

We experimentally demonstrated an ultra-sensitive imaging system for telecom photons based on the non-degenerate two-photon absorption in a silicon-based electron multiplying charge-coupled device (EMCCD). The proposed long-wavelength-pumping scheme with mid-infrared pulsed excitation could not only effectively increase the two-photon absorption coefficient, but also significantly suppress the background noise caused by the harmonic absorption of the strong pumping field. In comparison to the photoelectric response via the degenerate two-photon absorption, the implemented configuration could offer over 30-folded enhancement of the photon-counting rate in the infrared imaging. The resulting detection sensitivity up to 1 photon/pixel/pulse was unprecedentedly approached, thus facilitating the single-photon operation. The elimination of the stringent phase matching as typically required in the optical parametric conversion has led to a high spatial resolution of 13 $μ$m. Moreover, the on-chip nonlinearity of the optical imager would enable a broadband spectral window and an enlarged field of view. In combination with the 5-ps temporal resolution due to the coincident optical gating, the presented imaging system would find various promising applications, such as low-light fluorescence lifetime microscopy and photon counting time-of-flight 3D imaging.

physics.optics↗

arXiv2026

High-precision passive stabilization of repetition rate for a mode-locked fiber laser based on optical pulse injection

We have proposed and implemented a novel scheme to obtain high-precision repetition rate stabilization for a polarization-maintaining mode-locked fiber laser. The essential technique lies in the periodic injection of electronically modulated optical pulses into a nonlinear amplifying loop mirror within the laser resonator. Thanks to the nonlinear cross-phase modulation effect, the injected pulses referenced to an external clock serves as a stable and precise timing trigger for an effective intensity modulator. Consequently, synchronous mode-locking can be initiated to output ultrafast pulses with a passively stabilized repetition rate. The capture range of the locking system reaches to a record of 1 mm, which enables a long-term stable operation over 15 hours without the need of temperature stabilization and vibration isolation. Meanwhile, the achieved standard deviation is as low as 100 $μ$Hz with a 1-s sample time, corresponding to a fluctuation instability of 5.0$\times10^{-12}$. Additionally, the repetition rate stabilization performance based on the passive synchronization has been systematically investigated by varying the average power, central wavelength and pulse duration of the optical injection.

physics.optics↗

arXiv2026

High-speed mid-infrared single-photon upconversion spectrometer

Sensitive and fast mid-infrared (MIR) spectroscopy is highly attractive in a variety of applications including astronomical observation, pharmaceutical synthesis, and environmental monitoring. However, the performance of conventional MIR spectrometers has long been hindered by the limited sensitivity of narrow-bandgap detectors and/or the deficient brightness of broadband light sources. Here, we devise and implement an ultra-sensitive and broadband MIR upconversion spectrometer, which integrates a supercontinuum source covering 1.5-4.2 $μ$m based on a silicon nitride nanophotonic waveguide. High-efficiency and low-noise nonlinear frequency upconversion is realized based on coincidence pulsed pumping with spectro-temporal optimization, which enables to leverage silicon detectors for facilitating MIR single-photon spectroscopy at 0.2 photons/nm/pulse. Furthermore, the upconversion-based array spectrometer is manifested with high-speed spectral acquisition rates beyond 200 kHz, which is about ten-fold faster than the state-of-the-art scan rates for FTIR-based spectrometers at a comparable spectral resolution. The achieved features of broadband spectral coverage, single-photon sensitivity, and sub-MHz refreshing rate might open up new possibilities in infrared transient spectral measurements in combustion analysis, high-throughput sorting and reaction tracking, among others.

physics.optics↗

arXiv2026

Mid-infrared single-photon 3D imaging

Active mid-infrared (MIR) imagers capable of retrieving three-dimensional (3D) structure and reflectivity information are highly attractive in a wide range of biomedical and industrial applications. However, the infrared 3D imaging at low-light levels is still challenging due to the deficiency of sensitive and fast MIR sensors. Here we propose and implement a MIR time-of-flight imaging system that operates at single-photon sensitivity and femtosecond timing resolution. Specifically, back-scattered infrared photons from a scene are optically gated by delay-controlled ultrashort pump pulses through nonlinear frequency upconversion. The upconverted images with time stamps are then recorded by a silicon camera to facilitate the 3D reconstruction with high lateral and depth resolutions. Moreover, an effective numerical denoiser based on spatiotemporal correlation allows us to reveal the object profile and reflectivity under photon-starving conditions with a detected flux below 0.05 photons/pixel/second. The presented MIR 3D imager features with high detection sensitivity, precise timing resolution, and wide-field operation, which may open new possibilities in life and material sciences.

physics.optics↗

arXiv2026

Mid-infrared single-pixel imaging at the single-photon level

Single-pixel cameras have recently emerged as promising alternatives to multi-pixel sensors due to reduced costs and superior durability, which are particularly attractive for mid-infrared (MIR) imaging pertinent to applications including industry inspection and biomedical diagnosis. To date, MIR single-pixel photon-sparse imaging has yet been realized, which urgently calls for high-sensitivity optical detectors and high-fidelity spatial modulators. Here, we demonstrate a MIR single-photon computational imaging with a single-element silicon detector. The underlying methodology relies on nonlinear structured detection, where the encoded time-varying pump patterns are optically imprinted onto the MIR object image through sum-frequency generation. Simultaneously, the MIR radiation is spectrally translated into the visible region, thus permitting infrared single-photon upconversion detection. Then, the use of advanced algorithms of compress sensing and deep learning allows us to reconstruct MIR images under sub-Nyquist sampling and photon-starving illumination. The presented paradigm of single-pixel upconversion imaging is featured with single-pixel simplicity, single-photon sensitivity, and room-temperature operation, which would establish a new path for sensitive imaging at longer infrared wavelengths or terahertz frequencies, where high-sensitivity photon counters and high-fidelity spatial modulators are typically hard to access.

physics.optics↗

arXiv2026

MPDocBench-Parse: Benchmarking Practical Multi-page Document Parsing

Document parsing converts visually rich documents into machine-readable structured representations, forming a crucial foundation for information systems. Although many benchmarks have been proposed for document parsing, they remain inadequate for realistic scenarios. Existing benchmarks either focus on specific tasks or assess only single-page, text-centric settings, making them insufficient for practical multi-page parsing. Moreover, they lack fine-grained evaluation of semantic continuity, hierarchical structure recovery, and visual content preservation. To address these gaps, we propose MPDocBench-Parse, a benchmark for multi-page document parsing in real-world applications. It contains 433 manually annotated documents with 3,246 pages, covering 15 document types in English and Chinese, with diverse layout styles, and supports document-level end-to-end evaluation. We further design a comprehensive protocol for content fidelity and logical structure, covering text, table, and formula recognition, truncated text and table merging, figure extraction, reading order, and heading hierarchy recovery. Experiments show that, while existing models perform well on basic text extraction, they still suffer clear limitations in semantic continuity integration, visual content parsing, and hierarchical structure recovery. MPDocBench-Parse provides a unified foundation for advancing document parsing toward more realistic scenarios.

cs.AI↗