Plasmonic antiresonance through subwavelength hole arrays.

It has been shown both experimentally and numerically that the phenomenon of extraordinary transmission through subwavelength hole arrays is generally associated with a drop in transmission located very close to it. Paradoxically, this antiresonant drop occurs at the wavelength that, at first glance, should provoke a resonant excitation of a surface plasmon propagating along the metallic surface of the screen. The present paper gives a theoretical demonstration of this phenomenon, which dispels the paradox. Our theory is supported by numerical calculations.

Linearly damped modes at gap edges of photonic crystals.

It is shown that for one-dimensional dielectric photonic crystals, the Bloch modes, a vital tool in the analysis of these structures, cannot provide a complete representation of the electromagnetic field at the edges of bandgaps. On these points, the couple of Bloch modes representing the propagation on both sides of the crystal reduces to a single one, with a stationary field, and a complete representation of the field inside the crystal illuminated by a plane wave must include a linearly damped mode (LDM), the amplitude of which behaves linearly in space. The theory of transfer matrices and the use of basic properties of the field allow a precise description of the LDM from a few parameters. An extension to two-dimensional photonic crystals is proposed.

Total absorption of light by lamellar metallic gratings.

Lamellar gratings illuminated in conical (off-plane) mounting can achieve with suitable optogeometrical parameters (grating profile, angle of incidence and wavelength) a total absorption of light for any polarization provided there is only the zeroth propagating order. A detailed analysis shows that electromagnetic resonances are involved and their nature strongly depends on the polarization. When the incident electric field is parallel to the cross-section of the grating, the resonance is provoked by the excitation of surface plasmons. For the orthogonal polarization, total absorption occurs for deep gratings only, when the grooves behave like resonant optical cavities. It is possible to reduce the optimal grating height by filling the grooves with a high refractive index material.

Why a harmonic solution for lossless, perfectly homogeneous, left-handed material cannot exist.

In a preceding paper [J. Opt. Soc. Am. A21, 122 (2004)], we proposed proof of the nonexistence of harmonic solutions for a perfectly homogeneous left-handed material with both relative permittivity and relative permeability equal to -1 using the theorem of analytic continuation of an analytic function. The use of this theorem of analyticity has been questioned in a recent paper [Phys. Rev. E73, 046608 (2006)], arguing the possible inadequacy of the conditions of application of the theorem. We avoid the use of the analyticity theorem and propose a direct and simple proof of the nonexistence of such solutions. Furthermore, this proof is extended to any left-handed material with negative permeability and permittivity.

Enhanced SPR sensitivity using periodic metallic structures.

A sinusoidal silver grating is used to create a six-fold enhancement of the SPR response compared to a flat surface. The grating parameters are chosen to create a surface plasmon bandgap and it is shown that the enhancement of the sensitivity to bulk sample index occurs when operating near the bandgap. The Kretschmann configuration is considered and the Boundary Element Method is used to generate the dispersion curves.

Are optical forces derived from a scalar potential?

The expression of optical forces provoked by an incident light illuminating particles can be deduced from the Lorentz law. It is shown that these forces derive from a scalar potential in the 2D problem and s-polarization, with light propagating in the cross-section plane of the particles, a fact which shows that the separation between gradient and scattering forces could be questioned. This property does not extend to the p-polarization and 3D problem. In the general case, it is shown that one of the components of the optical force is intimately linked with the reactive energy inside the particle. A possible application is given.

Narrow-band filtering with whispering modes in gratings made of fibers.

We present a numerical study of whispering modes in gratings made of fibers. Due to the strong localization of the modes inside each fiber, it is possible to obtain narrow-band filters with very broad angular tolerance.

Perfect lenses made with left-handed materials: Alice's mirror?

In a recent paper, Pendry [Phys. Rev. Lett. 86, 3966 (2000)] mentioned the possibility of making perfect lenses by using a slab of left-handed material with relative permeability and permittivity equal to -1, a property first stated by Veselago [Sov. Phys. Usp. 10, 509 (1968)]. Pendry gave a demonstration of the vital effect of the evanescent waves in this process, arguing that these waves are amplified inside the slab. We present first a very simple theoretical demonstration that a homogeneous material with both relative permittivity and permeability equal to -1 cannot exist, even for a unique frequency. This demonstration shows that the perfect lens proposed by Pendry can be interpreted as a means to move in real space the virtual perfect image of a point source given by a plane mirror. We show that, owing to evanescent waves, the concept of effective medium for heterogeneous materials is questionable, even when the wavelength of the incident light is much larger than the size of the heterogeneities. The effect of heterogeneities is compared with that of absorption. We conclude that a material able to focus the light more efficiently than the current devices (but not perfectly) could exist.

Chromatic dispersion and losses of microstructured optical fibers.

Using a rigorous and vector multipole method, we compute both losses and dispersion properties of microstructured optical fibers with finite cross sections. We restrict our study to triangular lattices of air-hole inclusions in a silica matrix, taking into account material dispersion. The fiber core is modeled by a missing inclusion. The influence of pitch, hole diameter, and number of hole rings on chromatic dispersion is described, and physical insights are given to explain the behavior observed. It is shown that flattened dispersion curves obtained for certain microstructured fiber configurations are unsuitable for applications because of the fibers' high losses and that they cannot be improved by a simple increase of the number of air-hole rings.

Theoretical study of photonic band gaps in woodpile crystals.

We investigate numerically the existence of photonic band gaps in woodpile crystals. We present a numerical method specifically developed to solve Maxwell's equations in such photonic structures. It is based upon a rigorous mathematical formulation and leads to a considerable improvement of the convergence speed as compared to other existing numerical methods. We tested our method by comparing the calculated reflectivity with measurements on an actual sample, i.e., a silicon woodpile photonic crystal designed for 1.5 microm wavelength. Excellent agreement is obtained, provided the main structural imperfections of the sample are taken into account. We show that the existence of photonic band gaps in woodpile crystals requires an index contrast higher than 2.05 +/- 0.01. The effects of imperfections of such structures with an index contrast equal to 2.25 are also investigated. Thus, the relative band gap width falls from 3.5% to 2.2% with structurals imperfection similar to those of the sample.

Phenomenological theory of filtering by resonant dielectric gratings.

Using a phenomenological theory of diffraction gratings made by perturbing a planar waveguide allows us to deduce important properties of the sharp filtering phenomena generated by this kind of structure when the incident light excites a guided wave. It is shown that the resonance phenomenon occurring in these conditions acts on one of the two eigenvalues of the Hermitian reflection matrix only. As a consequence, we deduce a mathematical expression of the reflectivity and demonstrate that high-efficiency filtering of unpolarized light requires the simultaneous excitation of two uncoupled guided waves. Numerical examples are given.

Microstructured optical fibers: where's the edge?

We establish that Microstructured Optical Fibers (MOFs) have a fundamental mode cutoff, marking the transition between modal confinement and non-confinement, and give insight into the nature of this transition through two asymptotic models that provide a mapping to conventional fibers. A small parameter space region where neither of these asymptotic models holds exists for the fundamental mode but not for the second mode; we show that designs exploiting unique MOF characteristics tend to concentrate in this preferred region.