Publications by authors named "Xuanyi Yu"

Non-Hermitian systems have recently attracted significant attention in photonics due to the realization that the interplay between gain and loss can lead to entirely new and unexpected features. Here, we propose and demonstrate a non-Hermitian Faraday system capable of non-reciprocal omni-polarizer action at the exceptional point. Notably, both forward and backward propagating light with arbitrary polarization converge to the same polarization state.

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Resonator-enhanced electro-optical (EO) combs could generate a series of comb lines with high coherence and stability. Recently, EO comb based on thin-film lithium niobate (TFLN) has begun to show great potential thanks to the high second-order nonlinearity coefficient of lithium niobate crystal. Here we demonstrate that EO comb envelope engineering based on mode crossing induced a quality factor reduction in the TFLN racetrack microcavity both in the numerical simulation and experiment.

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Erbium-ion-doped lithium niobate (LN) microcavity lasers working in the communication band have attracted extensive attention recently. However, their conversion efficiencies and laser thresholds still have significant room to improve. Here, we prepared microdisk cavities based on erbium-ytterbium-co-doped LN thin film by using ultraviolet lithography, argon ion etching, and a chemical-mechanical polishing process.

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Microresonators coupled with integrated waveguides operate stably but usually lack tunability for an optimal coupling state. In this Letter, we demonstrate a racetrack resonator with an electrically modulated coupling on an X-cut lithium niobate (LN) platform by introducing a Mach-Zehnder interferometer (MZI) with two balanced directional couplers (DCs) to realize light exchange. This device provides a wide-range coupling regulation, from under-coupling and critical coupling to deep over-coupling.

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Article Synopsis
  • The study presents a new method for achieving significant asymmetric reflection of circularly polarized light using single-layer extrinsic chiral metasurfaces at angles of incidence.
  • This reflection is driven by extrinsic chirality, resulting in a measured asymmetric reflection of about 40% and notable differences in phase, affecting how light's polarization states convert.
  • The findings indicate a reflective polarization shift of approximately 14° from the expected symmetry, offering insights for developing advanced systems to control electromagnetic waves.
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Integrated and stable microlasers are indispensable building blocks of micro-photonics. Here, we report the realization of an ytterbium-doped lithium niobate microring laser operating in the 1060-nm band under the pump of a 980-nm-band laser. The monolithic laser has a low threshold of 59.

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Integrated optical systems based on lithium niobate on insulator (LNOI) have attracted the interest of researchers. Recently, erbium-doped LNOI lasers have been realized. However, the reported lasers have a relatively lower conversion efficiency and only operate in the 1550 nm band.

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We designed a simple on-chip integrated optical isolator made up of a metal-insulator-metal waveguide and a disc cavity filled with magneto-optical material to enhance the transverse magneto-optical effect through the coin paradox spin-orbit interaction (SOI). The simulation results of the non-reciprocal transmission properties of this optical structure show that a high-performance on-chip integrated optical isolator is obtained. The maximum isolation ratio is greater than 60 dB with a corresponding insertion loss of about 2 dB.

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A plasmonic near-infrared multiple-channel filter is numerically and experimentally investigated based on a gold periodic composite nanocavities metasurface. By the interference among different excited plasmonic modes on the metasurface, the multipeak extraordinary optical transmission (EOT) phenomenon is induced and utilized to realize multiple-channel filtering. Investigated from the simulated transmission spectrum of the metasurface, the positions and intensity of transmission peaks are tuned by the geometrical parameters of the metasurface and environmental refractive index.

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A bidirectional electromagnetically induced transparency (EIT) arising from coupling of magnetic dipole modes is demonstrated numerically and experimentally based on nanoscale a-Si cuboid-bar metasurface. Analyzed by the finite-difference time-domain (FDTD) Solutions, both the bright and dark magnetic dipole mode is excited in the cuboid, while only the dark magnetic dipole mode is excited in the bar. By breaking the symmetry of the cuboid-bar structure, the destructive interference between bright and dark magnetic dipole modes is induced, resulting in the bidirectional EIT phenomenon.

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Lithium niobate on insulator (LNOI), regarded as an important candidate platform for optical integration due to its excellent nonlinear, electro-optic, and other physical properties, has become a research hotspot. A light source, as an essential component for an integrated optical system, is urgently needed. In this Letter, we reported the realization of 1550 nm band on-chip LNOI microlasers based on erbium-doped LNOI ring cavities with loaded quality factors higher than 1 million at ∼970, which were fabricated by using electron beam lithography and inductively coupled plasma reactive ion etching processes.

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A broadband near-perfect absorber is analyzed by an amorphous silicon (a-Si) hook shaped nanostructure metasurface. The transmission and reflection coefficients of the metasurface are investigated in the point electric and magnetic dipole approximation. By combining square and semicircle nanostructures, the effective polarizabilities of the a-Si metasurface calculated based on discrete dipole approximation (DDA) exhibit broadened peaks of electric dipole (ED) and magnetic dipole (MD) Mie resonances.

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A dielectric broadened band near-perfect absorber based on an amorphous silicon(a-Si) T-shaped nanostructure metasurface is investigated numerically and experimentally. The simultaneous suppressed transmission and reflection of the a-Si nanostructure metasurface are achieved by investigating the interference of the periodically adjustable electric dipole(ED) and magnetic dipole(MD) Mie resonances. The absorption of the a-Si nanostructure metasurface approaches the maximum of 95% in simulation and 80% in experiment with a top-hat shape in the spectral range from 580 nm to 620 nm by employing the T-shaped nanostructure.

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A nanoscale plasmonic optical differentiator based on subwavelength gold gratings is investigated theoretically and experimentally without Fourier transform lenses and prisms. In the vicinity of surface plasmon resonance (SPR), the transfer function of subwavelength gold gratings is derived by optical scattering matrix theory. Simulated by the finite difference time domain (FDTD) method, the wavelengths of optical spatial differentiation performed by subwavelength gold gratings are tuned by the grating period and duty cycle, while the throughput of edge extraction is mainly adjusted by the grating thickness.

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An end-pumped actively $Q$Q-switched ${\rm Nd}\!:\!{{\rm YVO}_4}/{{\rm YVO}_4}$Nd:YVO/YVO Raman laser with a folded coupled cavity is demonstrated to study the evolution of Raman beam quality. The theoretical mechanism of the beam cleanup effect of stimulated Raman scattering is analyzed. The beam quality ($M^2$M) of the Raman beam and the fundamental beams before and after the Raman conversion are measured experimentally.

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Circular dichroism (CD) is an interesting phenomenon originating from the interaction of light with chiral molecules or other nanostructures lacking mirror symmetries in three-dimensional (3D) or two-dimensional (2D) space. While the observable effects of optical chirality are very weak in most of the natural materials, they can be designed and significantly enhanced in synthetic chiral structures, where the spatial symmetry of their component are broken on a nanoscale. Therefore, fabrication of composites capable of cheap, time-saving, and giant CD is desirable for the advanced optical technologies.

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A dual-band polarization-independent coherent perfect absorber(CPA) based on metal-graphene nanostructure is proposed, which is composed of golden nanorings with different sizes on graphene monolayer. Based on the finite-difference time-domain (FDTD) solutions, coherent perfect absorptions of the metal-graphene CPA are achieved at frequencies of 50.54 THz and 43.

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We report an actively Q-switched Nd:YVO/YVO intracavity Raman laser at second-Stokes wavelength of 1313.6 nm, which is capable of operating efficiently under pulse repetition frequency higher than 80 kHz. A folded coupled cavity is adopted to optimize the fundamental and the Stokes resonators individually and make full use of the high pump intensity on the Raman crystal.

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We report herein an efficient actively Q-switched Nd:YVO/YVO intracavity Raman laser operating at 1176 nm. Factors such as resonator geometry and pumping scheme are optimized to strengthen the power scalability and the conversion efficiency of the intracavity Raman laser. With a folded coupled cavity adopted to make full use of the high pump intensity on the Raman crystal, the first-order Stokes output of 10.

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In this work, we demonstrate the strong extrinsic chirality of the larger-area metal nanocrescents by experiments and simulations. Our results show that the metal nanocrescent exhibits giant and tunable circular dichroism (CD) effect, which is intensively dependent on the incident angle of light. We attribute the giant extrinsic chirality of the metal nanocrescent to the excitation efficiencies difference of localized surface plasmon resonance (LSPR) modes for two kinds of circularly polarized light at a non-zero incident angle.

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Beam splitters are essential components in various optical and photonic applications, for example, interferometers, multiplexers, and so on. Present beam splitters based on cubes or plates are normally bulky. Realizing beam splitters in nanoscales is useful to reduce the total size of photonic devices.

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We propose and numerically investigate a novel ultra-high quality (Q) factor metallic micro-cavity based on concentric double metal-insulator-metal (MIM) rings (CDMR). In this CDMR cavity, because of the angular momentum matching, the strong coupling occurs between the same order modes of the inner and outer rings with huge resonance frequency difference. Consequently, the energy distribution between in the inner and outer rings presents enormous difference.

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A fast tunable dual-wavelength laser based on in-fiber acousto-optic Mach-Zehnder interferometer (AO-MZI) with new fabrication process is proposed. Not only could the center wavelength of the output laser be optimized with enhanced tuning range about 30 nm by tuning the polarization and the driving frequency of the radio frequency (RF) signal accordingly, but also the spectral spacing between the two output wavelengths could be tuned from ~0 nm to 2.65 nm by controlling the power of the RF signal.

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Here we propose an efficient diode-end-pumped actively Q-switched 1176-nm Nd:YAG/Nd:YVO hybrid gain intracavity Raman laser. By virtue of the construction of a coaxial double crystal, the laser not only can operate efficiently at low pulse repetition frequencies (PRFs), thereby realizing relatively high-energy and high-peak-power pulsed output, but also is capable of generating a high average output power at high PRFs. A maximum pulse energy of 0.

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Based on the conversion between the fundamental mode (LP01) and the higher-order mode (LP11) in a tapered fiber via a whispering gallery mode resonator, an add/drop filter was proposed and demonstrated experimentally, in which the resonator only interacted with one tapered fiber, rather than two tapered fibers as in conventional configurations. The filter gains advantages of easy alignment and low scattering loss over the other filters based on tapered fiber and resonator, and will be useful in application.

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Synopsis of recent research by authors named "Xuanyi Yu"

  • - Xuanyi Yu's recent research encompasses advancements in photonic systems, particularly focusing on non-Hermitian systems and their application in optical isolators and resonators, showcasing novel omni-polarized Faraday isolators and electrically tuned coupling mechanisms for enhancing light exchange in integrated waveguides
  • - The studies also delve into the development of high-efficiency lasers, particularly with erbium and ytterbium-doped lithium niobate microdisk and microring lasers, demonstrating improved conversion efficiencies and low thresholds, while exploring the potential of thin-film lithium niobate in electro-optical comb generation
  • - Yu's work highlights innovative designs in metamaterials, including giant circular dichroism and tunable optical filters, which leverage asymmetrical coupling in chiral metasurfaces, thus paving the way for advanced optical devices with enhanced functionalities in integrated photonics

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