In this paper we report TE-mode phase modulation obtained by inducing a capacitive charge on graphene layers embedded in the core of a waveguide.There is a biasing regime in which graphene absorption is negligible but...In this paper we report TE-mode phase modulation obtained by inducing a capacitive charge on graphene layers embedded in the core of a waveguide.There is a biasing regime in which graphene absorption is negligible but large index variations can be achieved with a voltage–length product as small as V_(π)L_(π)≃0.07 V cm for straight waveguides and V_(π)L_(π)≃0.0024 V cm for 12μm radius microring resonators.This phase modulation device uniquely enables a small signal amplitude<1 V with a micrometer-sized footprint for compatibility with CMOS circuit integration.Examples of phase-induced changes are computed for straight waveguides and for microring resonators,showing the possibility of implementing several optoelectronic functionalities as modulators,tunable filters,and switches.展开更多
Electromagnetic modeling provides an interesting context to present a link between physical phenomena and homology and cohomology theories.Over the past twenty-five years,a considerable effort has been invested by the...Electromagnetic modeling provides an interesting context to present a link between physical phenomena and homology and cohomology theories.Over the past twenty-five years,a considerable effort has been invested by the computational electromagnetics community to develop fast and general techniques for defining potentials.When magneto-quasi-static discrete formulations based on magnetic scalar potential are employed in problems which involve conductive regions with holes,cuts are needed to make the boundary value problem well defined.While an intimate connection with homology theory has been quickly recognized,heuristic definitions of cuts are surprisingly still dominant in the literature.The aim of this paper is first to survey several definitions of cuts together with their shortcomings.Then,cuts are defined as generators of the first cohomology group over integers of a finite CW-complex.This provably general definition has also the virtue of providing an automatic,general and efficient algorithm for the computation of cuts.Some counter-examples show that heuristic definitions of cuts should be abandoned.The use of cohomology theory is not an option but the invaluable tool expressly needed to solve this problem.展开更多
Prom Maxwell's equations, we compute the speed and the direction of propagation of active power refracted from air into a negative index material. We prove, both analytically and numerically that the power may ref...Prom Maxwell's equations, we compute the speed and the direction of propagation of active power refracted from air into a negative index material. We prove, both analytically and numerically that the power may refract positively even if phase fronts refract negatively. Considerations on the usage of ray optics in problems involving negative index materials are drawn.展开更多
文摘In this paper we report TE-mode phase modulation obtained by inducing a capacitive charge on graphene layers embedded in the core of a waveguide.There is a biasing regime in which graphene absorption is negligible but large index variations can be achieved with a voltage–length product as small as V_(π)L_(π)≃0.07 V cm for straight waveguides and V_(π)L_(π)≃0.0024 V cm for 12μm radius microring resonators.This phase modulation device uniquely enables a small signal amplitude<1 V with a micrometer-sized footprint for compatibility with CMOS circuit integration.Examples of phase-induced changes are computed for straight waveguides and for microring resonators,showing the possibility of implementing several optoelectronic functionalities as modulators,tunable filters,and switches.
基金partially supported by MNiSW grant N N206625439.
文摘Electromagnetic modeling provides an interesting context to present a link between physical phenomena and homology and cohomology theories.Over the past twenty-five years,a considerable effort has been invested by the computational electromagnetics community to develop fast and general techniques for defining potentials.When magneto-quasi-static discrete formulations based on magnetic scalar potential are employed in problems which involve conductive regions with holes,cuts are needed to make the boundary value problem well defined.While an intimate connection with homology theory has been quickly recognized,heuristic definitions of cuts are surprisingly still dominant in the literature.The aim of this paper is first to survey several definitions of cuts together with their shortcomings.Then,cuts are defined as generators of the first cohomology group over integers of a finite CW-complex.This provably general definition has also the virtue of providing an automatic,general and efficient algorithm for the computation of cuts.Some counter-examples show that heuristic definitions of cuts should be abandoned.The use of cohomology theory is not an option but the invaluable tool expressly needed to solve this problem.
文摘Prom Maxwell's equations, we compute the speed and the direction of propagation of active power refracted from air into a negative index material. We prove, both analytically and numerically that the power may refract positively even if phase fronts refract negatively. Considerations on the usage of ray optics in problems involving negative index materials are drawn.
