Subjects: Optics >> Quantum optics submitted time 2023-02-19
Peiheng Zhou
Gui-Geng Liu
Zihao Wang
Yuan-Hang Hu
Shuwei Li
Qindong Xie
Yunpeng Zhang
Xiang Xi
Zhen Gao
Longjiang Deng
Baile Zhang
Abstract： The field of topological photonics was initiated with the realization of a Chern insulator phase in a gyromagnetic photonic crystal (PhC) with broken time-reversal symmetry (T), hosting chiral edge states that are topologically protected propagating modes. Recent advances in higher-order band topology have discovered another type of topological state, as manifested by those modes localized at the corners of a sample, which are known as corner states. Here we report the realization of a quadrupole higher-order topological insulator phase in a gyromagnetic PhC, induced by a topological phase transition from the previously demonstrated Chern insulator phase. The evolution of the boundary modes from propagating chiral edge states to localized corner states has been characterized by microwave measurements. We also demonstrate topological bound states in the continuum, when the gyromagnetic PhC is magnetically tuned. These results extend the quadrupole topological insulator phase into T-broken systems, and integrate topologically protected propagating and localized modes in the same platform.
Peer Review Status:
Awaiting Review
Subjects: Optics >> Quantum optics submitted time 2023-02-19
Abstract： Bound states in the continuum (BICs) have been extensively studied in various systems since its first proposal in quantum mechanics. Photonic BICs can enable optical mode confinement and provide field enhancement for nonlinear optics, but they have rarely been explored in nonlinear integrated photonic waveguides. Applying BICs in photonic integrated circuits enables low-loss light guidance and routing in low-refractive-index waveguides on high-refractive-index substrates, which is suitable for integrated photonics with nonlinear materials. Here, we report experimental demonstration of second-harmonic generation from telecom to near-visible wavelengths on an etchless lithium niobate platform by using a photonic BIC for the second-harmonic mode. The devices feature second-harmonic conversion efficiency of 0.175%W-1cm-2 and excellent thermal stability with a wavelength shift of only 1.7 nm from 25{\deg}C to 100{\deg}C. Our results represent a new paradigm of nonlinear integrated photonics on a cost-effective and convenient platform, which can enable a broad range of on-chip applications such as optical parametric generation, signal processing, and quantum photonics.
Peer Review Status:Awaiting Review
Subjects: Optics >> Quantum optics submitted time 2023-02-19
Abstract： The textbook-accepted formulation of electromagnetic force was proposed by Lorentz in the 19th century, but its validity has been challenged due to incompatibility with the special relativity and momentum conservation. The Einstein-Laub formulation, which can reconcile those conflicts, was suggested as an alternative to the Lorentz formulation. However, intense debates on the exact force are still going on due to lack of experimental evidence. Here, we report the first experimental investigation of angular symmetry of optical force inside a solid dielectric, aiming to distinguish the two formulations. The experiments surprisingly show that the optical force exerted by a Gaussian beam has components with the angular mode number of both 2 and 0, which cannot be explained solely by the Lorentz or the Einstein-Laub formulation. Instead, we found a modified Helmholtz theory by combining the Lorentz force with additional electrostrictive force could explain our experimental results. Our results represent a fundamental leap forward in determining the correct force formulation, and will update the working principles of many applications involving electromagnetic forces.
Peer Review Status:Awaiting Review
Subjects: Optics >> Quantum optics submitted time 2023-02-19
Abstract： Bound states in the continuum (BICs) refer to physical states that possess intrinsic zero dissipation loss even though they are located in the continuous energy spectrum. BICs have been widely explored in optical and acoustic structures, leading to applications in sensing and lasing. Realizing BICs in micromechanical structures is of significant importance for both fundamental research and engineering applications. Here, we fabricated, with CMOS-compatible processes on a silicon chip, a wheel-shaped micromechanical resonator, in which we experimentally observed the BIC in the micromechanical domain. Such BICs result from destructive interference between two dissipative modes of the mechanical structure under broken azimuthal symmetry. These BICs are found to be robust against size variations of the dissipation channels. The demonstrated mechanical BIC can be obtained with a large and robust supporting structure, which substantially reduces device fabrication difficulty and allows for its operation in versatile environments for broader application areas. Our results open a new way of phonon trapping in micromechanical structures with dissipation channels, and produce long phonon lifetimes that are desired in many mechanical applications such as mechanical oscillators, sensors, and quantum information processors.
Peer Review Status:Awaiting Review
Subjects: Optics >> Quantum optics submitted time 2023-02-19
Jingwen Ma
Taojie Zhou
Mingchu Tang
Haochuan Li
Zhan Zhang
Xiang Xi
Mickael Martin
Thierry Baron
Huiyun Liu
Zhaoyu Zhang
Siming Chen
Xiankai Sun
Abstract： Robust laser sources are a fundamental building block for contemporary information technologies. Originating from condensed-matter physics, the concept of topology has recently entered the realm of optics, offering fundamentally new design principles for lasers with enhanced robustness. In analogy to the well-known Majorana fermions in topological superconductors, Dirac-vortex states have recently been investigated in passive photonic systems and are now considered as a promising candidate for single-mode large-area lasers. Here, we experimentally realize the first Dirac-vortex topological lasers in InAs/InGaAs quantum-dot materials monolithically grown on a silicon substrate. We observe room-temperature continuous-wave single-mode linearly polarized vertical laser emission at a telecom wavelength. Most importantly, we confirm that the wavelength of the Dirac-vortex laser is topologically robust against variations in the cavity size, and its free spectral range defies the universal inverse scaling law with the cavity size. These lasers will play an important role in CMOS-compatible photonic and optoelectronic systems on a chip.
Peer Review Status:Awaiting Review
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