Core concepts in singular optics, especially the polarization singularities, have rapidly penetrated the surging fields of topological and non-Hermitian photonics. For open photonic structures with ...non-Hermitian degeneracies in particular, polarization singularities would inevitably encounter another sweeping concept of Berry phase. Several investigations have discussed, in an inexplicit way, connections between both concepts, hinting at that nonzero topological charges for far-field polarizations on a loop are inextricably linked to its nontrivial Berry phase when degeneracies are enclosed. In this work, we reexamine the seminal photonic crystal slab that supports the fundamental two-level non-Hermitian degeneracies. Regardless of the invariance of nontrivial Berry phase (concerning near-field Bloch modes defined on the momentum torus) for different loops enclosing both degeneracies, we demonstrate that the associated far polarization fields (defined on the momentum sphere) exhibit topologically inequivalent patterns that are characterized by variant topological charges, including even the trivial scenario of zero charge. Moreover, the charge carried by the Fermi arc actually is not well defined, which could be different on opposite bands. It is further revealed that for both bands, the seemingly complex evolutions of polarizations are bounded by the global charge conservation, with extra points of circular polarizations playing indispensable roles. This indicates that although not directly associated with any local charges, the invariant Berry phase is directly linked to the globally conserved charge, physical principles underlying which have all been further clarified by a two-level Hamiltonian with an extra chirality term. Our work can potentially trigger extra explorations beyond photonics connecting Berry phase and singularities.
The elastic optical network (EON) adopting virtual network function (VNF) is a new type of network, in which the routing, spectrum, and data center allocation are key and challenging problems, and ...solving these three problems simultaneously can not only improve the network efficiency for network providers, but also let users obtain better service. However, few existing works handle these three problems simultaneously. To tackle the three problems simultaneously, given a set of network function chains (i.e., a set of tasks), we set up a new multi-objective optimization model in which the total length of paths for all tasks is minimized, the totally occupied spectrums are minimized, and the loads on all data centers are most balanced, simultaneously. To solve the model, we design two new evolutionary algorithms. The experiments are conducted on 16 cases of 4 widely used types of networks, and the results indicate that the proposed model and algorithms are effective.
We investigate how the optical gain or loss (characterized by isotropic complex refractive indexes) influence the ideal Kerker scattering of exactly zero backward scattering. It was previously shown ...that, for non-magnetic homogeneous spheres with incident plane waves, either gain or loss prohibit ideal Kerker scattering, provided that only electric and magnetic multipoles of a specific order are present and contributions from other multipoles can all be made precisely zero. Here we reveal that, when two multipoles of a fixed order are perfectly matched in terms of both phase and magnitude, multipoles of at least the next two orders cannot possibly be tuned to be all precisely zero or even perfectly matched, and consequently cannot directly produce ideal Kerker scattering. Moreover, we further demonstrate that, when multipoles of different orders are simultaneously taken into consideration, loss or gain can serve as helpful rather than harmful contributing factors, for the elimination of backward scattering.
In
various subdisciplines of optics and photonics, Mie theory has
been serving as a fundamental language and playing indispensable roles
widely. Conventional studies related to Mie scattering largely ...focus
on local properties such as differential cross sections and angular
polarization distributions. Though spatially integrated features of
total cross sections in terms of both scattering and absorption are
routine for investigations, they are intrinsically dependent on the
specific morphologies of both the scattering bodies and the incident
waves, consequently manifesting no sign of global invariance. Here,
we propose a global Mie scattering theory to explore topological invariants
for the characterization of scatterings by any obstacles of arbitrarily
structured or polarized coherent light. It is revealed that, independent
of distributions and interactions among the scattering bodies of arbitrary
geometric and optical parameters, in the far field, inevitably, there
are directions where the scatterings are either zero or circularly
polarized. Furthermore, for each such singular direction, we can assign
a half-integer index and the index sum of all those directions are
bounded to be a global topological invariant of 2. The global Mie
theory we propose, which is mathematically simple but conceptually
penetrating, can render new perspectives for light scattering and
topological photonics in both linear and nonlinear regimes and would
potentially shed new light on the scattering of acoustic and matter
waves of various forms.
Scattering activities are generally manifest through different optical responses of scattering bodies to circularly polarized light of opposite handedness. Similar to the ubiquitous roles played by ...scattering theory across different branches of photonics, scattering activities can serve as a fundamental concept to clarify underlying mechanisms of various chiroptical effects, both within and beyond scattering systems. In this work, we investigate scattering activities for reciprocal systems that exhibit various geometric symmetries but are intrinsically achiral. We reveal how scattering activities are generally bounded by reciprocity and parity conservation, demonstrating that though extinction activity is usually excluded by symmetry, scattering activities in forms of distinct absorptions, scatterings or angular scattering patterns can more widely emerge. Since our analyses are solely based on fundamental laws of reciprocity and parity conservation, regardless of geometric and optical parameters of the scattering systems, the principles revealed are generically applicable. The intuitive and pictorial framework we have established is beyond any specific coupling models, able to reveal hidden connections between seemingly unrelated chiral manifestations, and thus more accessible for a unified understanding of various chiroptical effects.
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Laser wireless power transmission (LWPT) has various applications for mobile devices and specific equipment under extreme conditions. The light spot received by laser photovoltaics is usually ...non-uniform, resulting in system efficiency reduction. The output characteristics of 1 × 1 cm2 GaAs laser photovoltaics were measured under various illuminated areas. The experimental results showed that the efficiency decreased from 40.8% at the full irradiated area to 26.7% at 1/10 irradiated area. Furthermore, the drop in short-circuit current was the main factor for decreasing the efficiency. A three-dimensional (3D) finite element model was used to investigate this factor. The simulation results indicated that non-uniform irradiation could increase the total non-radiative recombination rate. The recombination rate of the absorption region increased from 6.0 × 1020 cm−3/s to 2.5 × 1021 cm−3/s, reducing the short-circuit current.
Chiral optical effects are generally quantified along some specific incident directions of exciting waves (especially for extrinsic chiralities of achiral structures) or defined as ...direction-independent properties by averaging the responses among all structure orientations. Though of great significance for various applications, chirality extremization (maximized or minimized) with respect to incident directions or structure orientations has not been explored, especially in a systematic manner. In this study we examine the chiral responses of open photonic structures from perspectives of quasinormal modes and polarization singularities of their far-field radiations. The nontrivial topology of the momentum sphere secures the existence of generic singularity directions along which mode radiations are either circularly or linearly polarized. When plane waves are incident along those directions, the reciprocity ensures ideal maximization and minimization of optical chiralities, for corresponding mode radiations of circular and linear polarizations, respectively. For directions of general elliptical polarizations, we have unveiled the subtle equality of a Stokes parameter and the circular dichroism, showing that an intrinsically (geometrically) chiral structure can unexpectedly exhibit no optical chirality at all or even optical chiralities of opposite handedness for different incident directions. The framework we establish can be applied to not only finite scattering bodies but also infinite structures, encompassing both intrinsic and extrinsic optical chiralities. We have effectively merged two vibrant disciplines of chiral and singular optics, which can potentially trigger more optical chirality-singularity related interdisciplinary studies.
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To summarize the clinical experiences of microsurgical and endovascular treatments of complicated arteriovenous malformation (AVM) in the conditions of hybrid operating room.
The clinical data were ...collected and analyzed for 8 patients of complex AVM between June 2012 to June 2013. There were Spetzler grade III (n = 2) and grade IV (n = 6). And the lesions were complicated with intracranial aneurysms (n = 3) and located in motor area (n = 2) and basal ganglia (n = 2). Five cases of AVM with cerebral hemorrhage underwent emergency surgery, including digital subtraction angiography (DSA) plus intraoperative embolization plus surgical resection of AVM plus intraoperative DSA (iDSA). Two cases underwent embolization plus aneurysm surgery while another had AVM embolization plus AVM resection and γ knife treatment.
All surgical procedures, including iDSA, were completed in the same hybrid operating room. There was no change of surgical position or intraoperative mortality. Five patients of AVM hemorrhage undergoing
Efficient power distribution to multiple receivers with controlled amounts is critical for wireless communication and sensing systems. Previous efforts have attempted to improve power transfer ...efficiency through strong coupling and parity‐time (PT) symmetry, providing attractive opportunities for flexible energy flow control. In this study, a novel method for achieving arbitrary power distribution is proposed and numerically demonstrated by leveraging the unique properties inside an epsilon near‐zero (ENZ) environment. Specifically, it shows that the power from a single source can be transferred to multiple receivers inside an ENZ medium with negligible loss by modifying optical properties of receivers rather than introducing sophisticated active control modules. Importantly, full power transfer is independent of the size and shape of the ENZ medium, as well as the positions of the receivers and source. A realizable system is further designed with effective zero index at microwave frequencies to confirm the high efficiency of energy transfer. The innovative approach, employing photonic doping for advanced and efficient wireless power transfer, may shed light on the new generation of energy efficient communication/sensing systems with versatile control functionalities.
The distinctive characteristics of an Epsilon Near Zero (ENZ) environment enable the arbitrary distribution of energy among the source (S) and receivers (R) in wireless power transfer, eliminating the need for complex configurations and communications.
The scattering and resonant properties of optical scatterers/resonators are determined by the relative ratios among the associated multipole components, the calculation of which usually is ...analytically tedious and numerically complicated for complex structures. Here we identify the constraints as well as the relative relations among electromagnetic multipoles for the eigenmodes of symmetric scatterers/resonators. By reducing the symmetry properties of the vector spherical harmonic waves to those of the modified generating functions, we systematically study the required conditions for electromagnetic multipoles under several fundamental symmetry operations, i.e., 2D rotation and reflection operations and 3D proper and improper rotations. Taking a 2D scatterer with C
as an example, we show that each irreducible representation of C
can be assigned to corresponding electromagnetic multipoles, and consequently the constraints of the electromagnetic multipoles can be easily extracted. Such group approach can easily be extended to more complex 3D scatterers with higher symmetry group. Subsequently, we use the same procedure to map out the complete relation and constraint on the electromagnetic multipoles of a 3D scatterer imposed by D
symmetry. Our theoretical analyses are in perfect agreements with the fullwave finite element calculations of the eigenmodes of the symmetric scatters.
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