156 research outputs found
The Fourier Modal Method simplified for crossed subwavelength gratings B. Guizal
No full textInternational audienceWe present a simplification of the Fourier Modal Method (FMM) for crossed gratings with subwavelength heights. We show that in this case it is possible to compute the scattering matrix of the structure without solving the eigenvalue problem which is the most expensive computational part of the FMM algorithm. This approach is very efficient and thus suitable for periodic metasurfaces
Casimir torque and force on gratings
No full textInternational audienceWe will discuss recent results: (i) on the theory of the Casimir torque between two gratingsrotated by an angle θ with respect to each other [1]; and (ii) on the theory and experimenton the Casimir force between interpenetrating gratings [2]. These findings pave the way tothe design of contactless quantum vacuum torsional spring and sensors with possiblerelevance to micro and nanomechanical devices.References[1] Mauro Antezza, H. B. Chan, Brahim Guizal, V.N. Marachevsky, Riccardo Messina,Mingkang Wang, Phys. Rev. Lett. 124, 013903 (2020)[2] Mingkang Wang, L. Tang, C.Y. Ng, Riccardo Messina, Brahim Guizal, J. A. Crosse,Mauro Antezza, C.T. Chan, H.B. Chan, Nature Communication 12, 600 (2021
The Fourier Modal Method with Adaptive Spatial Resolution under conical mounting
No full textInternational audienceThe Fourier Modal Method equipped with the concept of Adaptive Spatial Resolution (FMMASR) is derived and presented, in details, in the case of lamellar diffraction gratings under conical mounting. In the present work, we focus on efficiency and reduction of the numerical load
Homogenization of metallic metamaterials and electrostatic resonances
No full textInternational audienceIt has been noted that the usual approaches for homogenization (e.g. Bruggeman) could lead to singularities when considering composites comprising materials with positive and negative permittivities. This situation is specifically encountered in the field of metamaterials, in particular in the visible range. The question then arises to unerstand if these resonances are just artifacts or possess, on the contrary, a clear physical meaning. In this work, we study the homogeneous properties of a bidimensional structure that is made of a periodic set of metallic wires embedded in a dielectric host medium. The structure is considered in a region of wavelengths that are much larger than the period of the structure. The work comprises a theoretical part where we develop a two-scale approach to the homogenization of the structure. As it is the case for the common physical approach, it leads to an effective permittivity with strong (electrostatic) resonances as well. The theoretical results, and the presence of resonances, are confirmed by numerical computations based on a rigorous modal approach. In the numerical results we consider specifically the case of silver and gold nanowires, described by a dispersive negative permittivity. We show that the main parameters for the onset of resonances is the optical filling ratio of the structure. Keeping in mind the possibility of performing experiments, it is far easier to keep the geometrical filling ratio constant and to consider strongly dispersive materials in the range of wavelengths considered. Here, besides the crucial fact that they are widely used in nanotechnology, silver and gold nanowires comply with our needs in the visible region of the spectrum
A simplified version of the Fourier Modal Method for graphene gratings
No full textInternational audienceThe Fourier Modal Method [1] (FMM) is very popular and efficient approach for modelling diffraction from gratings. It can be applied to graphene gratings either by using the Zero Thickness Model (ZTM) i.e. using directly the optical conductivity of graphene in the boundary conditions, or by using the Finite Thickness Model (FTM) where graphene is seen as a slab of atomic thickness and a relative dielectric permittivity deduced from its optical conduc- tivity. For 1D gratings, the FMM based on the ZTM proves to be very efficient for the transverse electric polarization case (electric filed parallel to the direction of invariance of the strips) but suffers from low convergence in the transverse magnetic polarization case (magnetic filed parallel to the direction of invariance of the strips). This is due to a an inappropriate use of the Fourier factorization rules [1]. The FMM based on the FTM, on the other hand, doesn’t experience such a limitation but at the expense of solving an eigenvalue problem inside the grating which has been given a finite thickness. This is very demanding from the computational point of view because solving an eigenvalue problem has a cost scaling with the third power of the dimension of the matrices in play. This increases the computational cost of the approach especially for crossed gratings. Furthermore, a in a recent work [2], the authors have shown the it is possible to avoid solving this eigenvalue problem if the grating has a deep subwavelength thickness. This condition is exactly fulfilled by graphene under the FTM where it is assumed to have an atomic thickness. I will show that using such a simplification lowers the computational cost of the FMM-FTM while giving reliable and accurate results
The Fourier Modal Method as applied to diffraction gratings : a historical overview
No full textInternational audienceIn this talk, I will give a historical overview of one of the most efficient and versatile methods devised to model diffraction from optical gratings
Homogenization of metallic metamaterials and electrostatic resonances
No full textInternational audienceIt has been noted that the usual approaches for homogenization (e.g. Bruggeman) could lead to singularities when considering composites comprising materials with positive and negative permittivities. This situation is specifically encountered in the field of metamaterials, in particular in the visible range. The question then arises to unerstand if these resonances are just artifacts or possess, on the contrary, a clear physical meaning. In this work, we study the homogeneous properties of a bidimensional structure that is made of a periodic set of metallic wires embedded in a dielectric host medium. The structure is considered in a region of wavelengths that are much larger than the period of the structure. The work comprises a theoretical part where we develop a two-scale approach to the homogenization of the structure. As it is the case for the common physical approach, it leads to an effective permittivity with strong (electrostatic) resonances as well. The theoretical results, and the presence of resonances, are confirmed by numerical computations based on a rigorous modal approach. In the numerical results we consider specifically the case of silver and gold nanowires, described by a dispersive negative permittivity. We show that the main parameters for the onset of resonances is the optical filling ratio of the structure. Keeping in mind the possibility of performing experiments, it is far easier to keep the geometrical filling ratio constant and to consider strongly dispersive materials in the range of wavelengths considered. Here, besides the crucial fact that they are widely used in nanotechnology, silver and gold nanowires comply with our needs in the visible region of the spectrum
Surface Plasmons and some of their applications
No full textSurface Plasmons (SP) are electromagnetic modes that do exist at the interface between a dielectric and a metal. For metallic particles (spheres, ellipsoids...), such modes are termed localized surface plasmons (LSP). They are at origin of the red colour of Au colloidal solutions and that of the famous Lycurgus cup (Roman glass cup now in the British muséum : it appears red when enlightened from inside and green if fenlightened from outside). Their unique properties (high sensitivity to the environment, extreme confinement, enhanced field strength, fields squeezing...) make them suitable for many applications ranging from chemical and biological sensors to extremely miniaturized optical devices. Furthermore, they play an important role in some recently discovered physical phenomena like "hot spots" on rough surfaces or the extraordinary enhanced transmission through "subwavelength photon sieves". In this talk, I will make a review on SP and LSP with special focus on their applications and I will present our recent research on strong coupling between SPs and optical waveguides
Surface Plasmons and some of their applications
No full textSurface Plasmons (SP) are electromagnetic modes that do exist at the interface between a dielectric and a metal. For metallic particles (spheres, ellipsoids...), such modes are termed localized surface plasmons (LSP). They are at origin of the red colour of Au colloidal solutions and that of the famous Lycurgus cup (Roman glass cup now in the British muséum : it appears red when enlightened from inside and green if fenlightened from outside). Their unique properties (high sensitivity to the environment, extreme confinement, enhanced field strength, fields squeezing...) make them suitable for many applications ranging from chemical and biological sensors to extremely miniaturized optical devices. Furthermore, they play an important role in some recently discovered physical phenomena like "hot spots" on rough surfaces or the extraordinary enhanced transmission through "subwavelength photon sieves". In this talk, I will make a review on SP and LSP with special focus on their applications and I will present our recent research on strong coupling between SPs and optical waveguides
Surface Plasmons and some of their applications
No full textSurface Plasmons (SP) are electromagnetic modes that do exist at the interface between a dielectric and a metal. For metallic particles (spheres, ellipsoids...), such modes are termed localized surface plasmons (LSP). They are at origin of the red colour of Au colloidal solutions and that of the famous Lycurgus cup (Roman glass cup now in the British muséum : it appears red when enlightened from inside and green if fenlightened from outside). Their unique properties (high sensitivity to the environment, extreme confinement, enhanced field strength, fields squeezing...) make them suitable for many applications ranging from chemical and biological sensors to extremely miniaturized optical devices. Furthermore, they play an important role in some recently discovered physical phenomena like "hot spots" on rough surfaces or the extraordinary enhanced transmission through "subwavelength photon sieves". In this talk, I will make a review on SP and LSP with special focus on their applications and I will present our recent research on strong coupling between SPs and optical waveguides
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