We show the physical realization and experimental demonstration of an exceptional point of sixth-order degeneracy in a triple-ladder (or three-way) microwave waveguide realized using three coupled microstrips on a gro...
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We show the physical realization and experimental demonstration of an exceptional point of sixth-order degeneracy in a triple-ladder (or three-way) microwave waveguide realized using three coupled microstrips on a grounded dielectric substrate. This three-way waveguide supports six Bloch eigenmodes, and all coalesce into a degenerate single eigenmode at a given frequency. The three-way waveguide is gainless, and this exceptional point is associated with a vanishing-group velocity and its multiple derivatives. Indeed, the ω−k dispersion diagram that we call the sixth-order degenerate band edge (6DBE) has six coalescing branches. We provide experimental verification of a sixth-order exceptional point by evaluating the degenerate wave number–frequency-dispersion diagram from the measurement of scattering parameters of a six-port unit cell. We also show the resonant behavior of a cavity made of the three-way waveguide with finite length. The unique properties of 6DBE can be exploited to design innovative high-Q resonators, oscillators, filters, and pulse-shaping devices.
Coupling among closely packed waveguides is a common optical phenomenon, and plays an important role in optical routing and integration. Unfortunately, this coupling property is usually sensitive to the working wavele...
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Coupling among closely packed waveguides is a common optical phenomenon, and plays an important role in optical routing and integration. Unfortunately, this coupling property is usually sensitive to the working wavelength and structure features that hinder the broadband and robust functions. Here, we report a new strategy utilizing an artificial gauge field (AGF) to engineer the coupling dispersion and realize a dispersionless coupling among waveguides with periodically bending modulation. The AGF-induced dispersionless coupling is experimentally verified in a silicon waveguide platform, which already has well-established broadband and robust routing functions (directional coupling and splitting), suggesting potential applications in integrated photonics. As examples, we further demonstrate a three-level-cascaded AGF waveguide network to route broadband light to desired ports with an overwhelming advantage over the conventional ones in comparison. Our method provides a new route of coupling dispersion control by AGF and benefits applications that fundamentally rely on waveguide coupling.
Exceptional points (EPs) are the branch point singularities, where two coupled eigenvalues and the associated eigenvectors simultaneously coalesce. Lately, various open photonic systems hosting EPs have attracted atte...
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ISBN:
(纸本)9798350345995
Exceptional points (EPs) are the branch point singularities, where two coupled eigenvalues and the associated eigenvectors simultaneously coalesce. Lately, various open photonic systems hosting EPs have attracted attention to meet different applications in diverse photonic structures, where various vivid applications have been explored [1]–[3]. In this work, using the framework of a 1D photonic bandgap waveguide (WG), we implement two individual complementary active perturbations in terms of an unbalanced gain-loss profile in the designed waveguides to host a pair of conjugate EP2s $(EP2\ \&\ EP2^{\ast})$ between two coupled TE modes ( $TE_{0}$ and $TE_{1}$ ). The dynamical encirclements of the $EP2$ and $EP2^{\ast}$ with the length-dependent gain-loss distribution establish particularly opposite robust chiral output response (to differentiate, we can term as chiral and reverse chiral responses) of two complementary 1D photonic bandgap waveguide designs. We propose the design of a 1D
It is shown that in rotationally symmetric periodic waveguides with a reflection symmetry, bound states in the continuum with nonzero angular momentum are nonrobust, but they can be preserved by tuning one structural ...
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ISBN:
(纸本)9781957171258
It is shown that in rotationally symmetric periodic waveguides with a reflection symmetry, bound states in the continuum with nonzero angular momentum are nonrobust, but they can be preserved by tuning one structural parameter.
We use phase-resolved imaging to directly study the nonlinear modification of the wavelength of spin waves propagating in 100-nm-thick in-plane magnetized yttrium iron garnet waveguides. We show that, by using moderat...
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We use phase-resolved imaging to directly study the nonlinear modification of the wavelength of spin waves propagating in 100-nm-thick in-plane magnetized yttrium iron garnet waveguides. We show that, by using moderate microwave power, one can realize spin waves with large amplitudes corresponding to precession angles in excess of 10° and nonlinear wavelength variation of up to 18% in this system. We also find that, at large precession angles, the propagation of spin waves is strongly affected by the onset of nonlinear damping, which results in a strong spatial dependence of the wavelength. This effect leads to spatially dependent controllability of the wavelength by the microwave power. Furthermore, it leads to the saturation of nonlinear spectral shift effects several micrometers away from the excitation point. These findings are important for the development of nonlinear integrated spin-wave signal-processing devices and can be used to optimize their characteristics.
Photonic structures offer a flexible platform for studying and demonstrating parity-time (PT) symmetry phenomena. In these platforms, electric dipoles are often used as accurate models for electromagnetic sources, and...
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Photonic structures offer a flexible platform for studying and demonstrating parity-time (PT) symmetry phenomena. In these platforms, electric dipoles are often used as accurate models for electromagnetic sources, and elliptical dipoles were shown to provide for directional mode excitation. Here we introduce tailored dipole sources for directional excitation in a PT-symmetric structure made of two coupled waveguides. By eliminating one mode in the device, a qualitatively different wave propagation on the two sides of the dipole is achieved. Interestingly, before the exceptional point, a linear dipole suffices to have mode beatings on only one side. Furthermore, beyond the exceptional point, gain can be created on one side only. Finally, at the exceptional point, a near-complete directionality can be achieved due to the mode merging. We explain these effects via a detailed analysis of the modes, and the subsequent mode excitation of the dipole is analytically described. In the end, these various types of contrasting phenomena offer possibilities for integrated photonics applications, routing setups, and lasing behavior.
The generation of non-Abelian geometric phases from a system of evanescently coupled waveguides is considered within the framework of nonorthogonal coupled-mode theory. Here, we study an experimentally feasible tripod...
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The generation of non-Abelian geometric phases from a system of evanescently coupled waveguides is considered within the framework of nonorthogonal coupled-mode theory. Here, we study an experimentally feasible tripod arrangement of waveguides that contain dark states from which a nontrivial U(2) mixing can be obtained by means of an adiabatic parameter variation. We investigate the influence of higher-order contributions beyond nearest-neighbor coupling as well as self-coupling on the stability of a non-Abelian U(3) phase generated from an optical tetrapod setup. Our results indicate that, despite the mode nonorthogonality, the symmetry of dark states protects the geometric evolution of light from distortion.
We consider the magnonic properties of two dipolarly coupled magnetic stripes, both deposited on a normal conductive substrate with strong spin-orbit coupling. A charge current in the substrate acts on the adjacent ma...
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We consider the magnonic properties of two dipolarly coupled magnetic stripes, both deposited on a normal conductive substrate with strong spin-orbit coupling. A charge current in the substrate acts on the adjacent magnets with spin-orbit torques, which result in magnonic damping or antidamping of the spin waves, and hence a gain-loss coupling of the two magnetic stripes. The whole setup is demonstrated to exhibit features typical for parity-time- (PT) symmetric systems. Phenomena are demonstrated that can be functionalized in magnonic devices, including reconfigurable magnonic diodes and logic devices. Alternative stripe designs and PT-symmetric, periodic, coupled magnonic textures are studied. Analytical and full numerical analysis identify the conditions for the appearance of exceptional points (EPs), where magnonic gain and loss are balanced and evidence nonreciprocal magnon propagation and enhanced magnon excitation around EPs. Furthermore, the dipolar coupling is shown to bring in a wave-vector-dependent PT-symmetric behavior. Proposing and simulating a PT-symmetric magnonic crystal, we show how EPs and hence associated phenomena can be steered to a particular wave vector in a gaped spectrum via material design. The phenomena offer additional tools for magnonic based communication and computational devices.
We present the design of silicon optical add-drop filters made using sub-wavelength-grating-assisted, contra-directional couplers. We demonstrate that such devices can have broad bandwidths, up to 45 nm, while maintai...
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ISBN:
(纸本)9781957171258
We present the design of silicon optical add-drop filters made using sub-wavelength-grating-assisted, contra-directional couplers. We demonstrate that such devices can have broad bandwidths, up to 45 nm, while maintaining low losses and high out-of-band isolations.
Recent experiments demonstrate strongly directional coupling of light into waveguide modes. Here, the symmetry mechanisms behind this effect are studied, and it is shown that the analysis of the symmetries and symmetr...
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Recent experiments demonstrate strongly directional coupling of light into waveguide modes. Here, the symmetry mechanisms behind this effect are studied, and it is shown that the analysis of the symmetries and symmetry-breakings of the emitter-waveguide system allows to qualitatively understand directional coupling in several situations. The authors consider emitters either centered in a median plane of the waveguide, or displaced from it, and whose emissions have a well-defined angular momentum in either one of the two different axis typically chosen experimentally, which are called transverse and vertical. These insights are matched by simulations, and previous experimental measurements. It is shown that handedness plays a secondary role in directional coupling. The spin-momentum locking concept is generalized to an exponentially strong locking between the transverse angular momentum and the preferential coupling direction. A new selection rule is obtained that controls the coupling of electric(magnetic) multipolar emissions into waveguide modes. An experiment is proposed featuring a transverse magnetic bias that aggregates the directional emissions from many quantum dots on top of waveguides, in contrast to the typically used vertical bias, which effectively restricts experiments to using a single quantum dot. Finally, the Huygens' dipole is analyzed and the symmetries that enable its directional behavior revealed.
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