Jean-Claude Rodier

Theory of surface plasmon generation at nanoslit apertures

In this Letter, we study the scattering of light by a single subwavelength slit in a metal screen. In contrast with previous theoretical works, we provide a microscopic description of the scattering process by emphasizing the generation of surface plasmons at the slit apertures. The analysis is supported by a rigorous formalism based on a normal-mode-decomposition technique and by a semianalytical model that provides accurate formulas for the plasmonic generation strengths. The generation is shown to be fairly efficient for metals with a low conductivity, such as gold in the visible regime. Verification of the theory is also shown by comparison with recent experimental data [H. F. Schouten, Phys. Rev. Lett. 94, 053901 (2005)].

Compact antenna for efficient and unidirectional launching and decoupling of surface plasmons.

Controlling the launching efficiencies and the directionality of surface plasmon polaritons (SPPs) and their decoupling to freely propagating light is a major goal for the development of plasmonic devices and systems. Here, we report on the design and experimental observation of a highly efficient unidirectional surface plasmon launcher composed of eleven subwavelength grooves, each with a distinct depth and width. Our observations show that, under normal illumination by a focused Gaussian beam, unidirectional SPP launching with an efficiency of at least 52% is achieved experimentally with a compact device of total length smaller than 8 μm. Reciprocally, we report that the same device can efficiently convert SPPs into a highly directive light beam emanating perpendicularly to the sample.

Ultra-High Q/V Fabry-Perot microcavity on SOI substrate

We experimentally demonstrate an ultra high Q/V nanocavity on SOI substrate. The design is based on modal adaptation within the cavity and allows to measure a quality factor of 58.000 for a modal volume of 0.6(lambda/n)(3) . This record Q/V value of 10(5) achieved for a structure standing on a physical substrate, rather than on membrane, is in very good agreement with theoretical predictions also shown. Based on these experimental results, we show that further refinements of the cavity design could lead to Q/V ratios close to 10(6).

Approximate model for surface-plasmon generation at slit apertures

We present a semianalytical model that quantitatively predicts the scattering of light by a single subwavelength slit in a thick metal screen. In contrast to previous theoretical works related to the transmission properties of the slit, the analysis emphasizes the generation of surface plasmons at the slit apertures. The model relies on a two-stage scattering mechanism, a purely geometric diffraction problem in the immediate vicinity of the slit aperture followed by the launching of a bounded surface-plasmon wave on the flat interfaces surrounding the aperture. By comparison with a full electromagnetic treatment, the model is shown to provide accurate formulas for the plasmonic generation strength coefficients, even for metals with a low conductivity. Limitations are outlined for large slit widths (>lambda) or oblique incidence (>30 degrees ) when the slit is illuminated by a plane wave.

Surface plasmons of metallic surfaces perforated by nanohole arrays

Recent works have dealt with the optical transmission on arrays of subwavelength holes perforated in a thick metallic film. We have performed simulations which quantitatively agree with experimental results and which unambiguously provide evidence that the extraordinary transmission is due to the excitation of a surface-plasmon-polariton (SPP) mode on the metallic film interfaces. We identify this SPP mode and show that its near field possesses a hybrid character, gathering collective and localized effects which are both essential for the transmission.

Ultra-high-reflectivity photonic-bandgap mirrors in a ridge SOI waveguide

Microcavities consisting of two identical tapered mirrors etched into silicon-on-insulator ridge waveguides are investigated for operation at telecommunication wavelengths. They offer very small modal volumes of approximately 0.6 (λ/n)3 and calculated intrinsic Q factors of 400 000. We have measured a Q factor of 8900 for a loaded cavity, in agreement with the theoretical value. In contrast to recent works performed on suspended membranes, the buried SiO2 layer is not removed. The cavities possess strong mechanical robustness, thus making them attractive from the viewpoint of integration in large systems. The cavity Q factor is much larger than those previously obtained for similar geometries on a substrate.

Ultracompact silicon-on-insulator ridge-waveguide mirrors with high reflectance

Microcavities offering small modal volumes V_0.6 __/n_3 and consisting of two identical tapered Bragg mirrors etched into a monomode silicon-on-insulator ridge waveguide are studied for operation at telecommunications wavelengths. The authors have measured a Q factor of 8900, for a loaded cavity with a peak transmission at resonance in excess of 60%. The measured Q value quantitatively agrees with the calculation results and is 20 times larger than those previously reported for similar geometries without tapers.

Wide-field-angle behavior of blazed-binary gratings in the resonance domain.

Blazed-binary gratings for which a blazed effect with binary etches is achieved under normal incidence offer first-order diffraction efficiencies larger than those of blazed-échelette gratings in the resonance domain [Opt. Lett. 23 1081 (1998)]. We provide further insight into the behavior of blazed-binary gratings and show that they operate efficiently under symmetrical mounting and over a wide field-angle interval. These properties are illustrated with theoretical and experimental results obtained for an approximately 1000-line/mm grating at 633 nm.

Statistical fluctuations of transmission in slow light photonic-crystal waveguides

We report statistical fluctuations for the transmissions of a series of photonic-crystal waveguides (PhCWs) that are supposedly identical and that only differ because of statistical structural fabrication-induced imperfections. For practical PhCW lengths offering tolerable -3dB attenuation with moderate group indices (n(g) approximately 60), the transmission spectra contains very narrow peaks (Q approximately 20,000) that vary from one waveguide to another. The physical origin of the peaks is explained by calculating the actual electromagnetic-field pattern inside the waveguide. The peaks that are observed in an intermediate regime between the ballistic and localization transports are responsible for a smearing of the local density of states, for a rapid broadening of the probability density function of the transmission, and bring a severe constraint on the effective use of slow light for on-chip optical information processing. The experimental results are quantitatively supported by theoretical results obtained with a coupled-Bloch-mode approach that takes into account multiple scattering and localization effects.

Accurate modeling of line-defect photonic crystal waveguides

An accurate three-dimensional method to calculate the Bloch modes of photonic crystal (PhC) waveguides is proposed. Good agreement with available experimental and numerical data is obtained. The originality of the method lies in the fact that the Bloch modes are seen as the electromagnetic fields associated to the complex poles of an in-plane transversal scattering matrix. In comparison with previous approaches, the computational domain discretized is smaller and a higher accuracy for the losses of PhC waveguides is achieved.