Shanghai Institute of Optics and Fine Mechanics

Multimode fibers (MMFs) play an increasing role in optical communication, ultra-thin fiber endoscopy systems, and fiber lasers. The characterization of light propagation properties through active and passive MMFs attracts high interest as many linear optical phenomena fundamentally depend on the interplay among multiple spatial modes. Access to the exact modal amplitudes and phase weights via mode decomposition (MD) provides a useful means of investigating the physical effects. It facilitates technological advances in telecommunications, endoscopy, sensors, and amplifiers that utilize MMFs. We present an untrained neural network assisted by a linear physical model of the multimode waveguide that carries out computational MD. For the first time, the reconstructed amplitude distribution achieves a high correlation coefficient, either for thousands of modes in a short MMF or for tens of modes in a 1-km-long MMF. We also investigate the limitations of MD based on single-shot intensity images by evaluating the relative modal errors and the effect of image resolution on the decomposition accuracy. We demonstrate our network framework and results on both passive and active multimode photonic systems. Our approach holds great promise for applications in fiber lasers, endoscopic computational imaging, and especially in fiber-based communication, where fiber crosstalk is heavy and reference-free calibration techniques are required.

In high-power laser systems, extrinsic impurities-particularly Ce introduced during conventional ring polishing-have been identified as critical contributors to the degradation of laser-induced damage resistance in fused silica optical components. This study systematically investigates the effects of cerium substitutional doping on the electronic structure and optical properties of fused silica, integrating first-principles density functional theory calculations with experimental characterizations. The results demonstrate that substitutional incorporation of cerium atoms into the fused silica framework introduces deep-level defect states within the band gap, resulting in band gap narrowing and absorption edge redshift of the material. The energy position of the defect states depends on the Ce doping configuration. Among them, the Ce-4f orbital constitutes the dominant component of the defect state's electronic structure, while the neighboring atomic orbitals such as O-2p and Si-3s/3p participate in bonding through hybridization, thereby determining the depth and distribution characteristics of the defect levels. The optical absorption edge of cerium-doped fused silica undergoes a significant redshift from the intrinsic value of 222 nm to 468 nm in the dual-Ce adjacent-site doping configuration, thereby endowing the material with substantial optical absorption capability at a wavelength of 355 nm. μ-UVPL spectroscopy combined with μ-XRD and other characterization analyses confirmed that the characteristic emission peak at 450 nm on the surface region of fused silica originated from Ce-related defect centers; this spectral feature was consistent with the defect state electronic structure predicted by the diatomic nearest-neighbor doping model. LIDT tests further indicated that the Ce-contaminated area significantly weakened the material's laser damage resistance under 355 nm laser irradiation. This study further explained the mechanism by which traditional polishing-induced Ce element doping causes the low laser damage threshold of fused silica optical components, providing a theoretical basis for improving their performance.

In this article, we demonstrate a silicon-based carrier-injection optical single-sideband (OSSB) modulator featuring a double-parallel Mach-Zehnder interferometer architecture. This design simultaneously achieves ultra-low driving voltage and high sideband suppression ratio (SSR). By optimizing the p- and n-doping profiles, the device achieves a V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</sub>·L of approximately 0.0375 V·cm. In OSSB operation, the unwanted sideband is suppressed by around 33 dB, highlighting the modulator’s exceptional sideband suppression. These characteristics—low driving voltage, low loss, and high suppression—make the device highly suitable for homodyne phase-locking, on-chip sensing, and other integrated photonic applications.

ABSTRACT Emerging as essential tools for interrogating ultrafast nonequilibrium processes in quantum materials, ultrashort long‐wavelength infrared (LWIR) pulses demand both high performance and fine characterization. In this letter, we present a high‐repetition‐rate (50 kHz) LWIR source with peak fields exceeding 14.8 MV cm −1 and spectral tunability (8–12.5 µm), generated via difference frequency generation scheme between a Yb:YAG pump laser and its parametrically amplified signal. Spatio‐temporal coupling pulse characterization is realized through nonlinear optical imaging of time‐resolved four‐wave mixing between LWIR and near‐infrared pulses in a 1‐µm‐thick silicon film. The multi‐dimensional pulse characterization confirms the excellent temporal characteristics and high beam quality of the generated LWIR characterization pulses, providing a reliable foundation for applications in nonlinear spectroscopy, high‐harmonic generation, and related fields.

To compare the efficacy and safety of 0.50% and 0.75% pilocarpine ophthalmic solutions for treating presbyopia. In this prospective study, 22 presbyopic subjects (44 eyes) were assigned to use 0.50% or 0.75% pilocarpine bilaterally, once daily for 2 weeks. Primary outcomes included distance-corrected intermediate visual acuity (DCIVA) at 66 cm and distance-corrected near visual acuity (DCNVA) at 40 cm under photopic and mesopic conditions, pupil size, refractive error, intraocular pressure (IOP) and patient-reported adverse events. Assessments were conducted at baseline, day 1 (after 1 and 6 h) and week 2 (after 1 h). No serious adverse events occurred. Neither formulation affected IOP or refractive error significantly. Pupil constriction was greater in the 0.75% group than the 0.50% group (2.8 ± 1.1 vs. 2.0 ± 0.8 mm, p = 0.02). After 2 weeks, the gain in photopic DCNVA was 0.18 logMAR for both concentrations (p = 0.70). The respective gain in visual acuity measures for the 0.75% and 0.50% groups was: mesopic DCNVA, 0.14 and 0.19 logMAR (p = 0.25); photopic DCIVA, 0.14 and 0.09 logMAR (p = 0.02); mesopic DCIVA, 0.12 and 0.10 logMAR (p = 0.18). Both 0.50% and 0.75% pilocarpine improved visual performance in presbyopia significantly, suggesting it is a promising treatment option. Chinese Clinical Trial Registry (ChiCTR), 2023/3/2, No.ChiCTR2300068971.

Vacuum manifests itself as a nonlinear polarization medium for photons in the presence of strong fields. This hallmark prediction of quantum electrodynamics remains experimentally elusive due to the weak amplitude of light-light interaction in vacuum and the difficulty of distinguishing signals from backgrounds. Here, we propose a scheme for detecting vacuum polarization effects by colliding an ultra-intense vortex laser with an X-ray free-electron laser. We uncover a super light-by-light scattering mechanism, wherein the localized azimuthal phase of the vortex laser imparts substantial tangential momentum to scattered photons. This phase-gradient-induced momentum transfer exceeds the transverse momentum of laser-photons, allowing signal photons to be kinematically deflected out of the X-ray cone. This mechanism simultaneously achieves a high signal size and a high signal-to-noise ratio without the need for X-ray polarization filtering, and paves the way for single-shot detection of nonlinear optical phenomena in quantum vacuum with current ultra-intense laser and X-ray technologies. Driven by strong fields, vacuum manifests itself as a nonlinear polarization medium, yet this hallmark prediction of quantum electrodynamics remains experimentally elusive for 90 years. Here, the authors uncover a super light-by-light scattering effect in vacuum, and propose an experimental scheme that holds promise for single-shot detection of this vacuum polarization effect with current technologies

What is believed to be a new method for generating high-resolution, high-flatness electro-optic frequency combs (EOFCs) based on multi-frequency small-signal modulation with a Single-driver Mach-Zehnder modulator (MZM) biased at its minimum-transmission point. This approach suppresses the optical carrier and even-order sidebands while minimizing the distortion from higher-order odd sidebands. Two EOFCs with repetition rates of 1 MHz and 1.000025 MHz were generated, each containing approximately 8000 comb lines with <1 dB local flatness (40 MHz optical spectral span). These combs were employed in a dual-comb spectroscopy system to measure the molecular absorption near P (10) rotational transition of the H13C14N. In addition, the proposed EOFC was applied to the measurement of stimulated Brillouin scattering (SBS) in a single-mode optical fiber, demonstrating its capability for high-resolution spectral characterization. The experimental results confirmed the effectiveness and versatility of the proposed EOFC scheme for precision spectroscopic applications.