There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

The so-called Klein paradox—unimpeded penetration of relativistic particles through high and wide potential barriers—is one of the most exotic and counterintuitive consequences of quantum electrodynamics. The phenomenon is discussed in many contexts in particle, nuclear and astro-physics but direct tests of the Klein paradox using elementary particles have so far proved impossible. Here we show that the effect can be tested in a conceptually simple condensed-matter experiment using electrostatic barriers in single- and bi-layer graphene. Owing to the chiral nature of their quasiparticles, quantum tunnelling in these materials becomes highly anisotropic, qualitatively different from the case of normal, non-relativistic electrons. Massless Dirac fermions in graphene allow a close realization of Klein’s gedanken experiment, whereas massive chiral fermions in bilayer graphene offer an interesting complementary system that elucidates the basic physics involved.

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Chiral tunnelling and the Klein paradox in graphene

Microcavity physics and design will be reviewed. Following an overview of applications in quantum optics, communications and biosensing, recent advances in ultra-high-Q research will be presented.

Optical microcavities

Photonic cavities that strongly confine light are finding applications in many areas of physics and engineering, including coherent electron-photon interactions, ultra-small filters, low-threshold lasers, photonic chips, nonlinear optics and quantum information processing. Critical for these applications is the realization of a cavity with both high quality factor, Q, and small modal volume, V. The ratio Q/V determines the strength of the various cavity interactions, and an ultra-small cavity enables large-scale integration and single-mode operation for a broad range of wavelengths. However, a high-Q cavity of optical wavelength size is difficult to fabricate, as radiation loss increases in inverse proportion to cavity size. With the exception of a few recent theoretical studies, definitive theories and experiments for creating high-Q nanocavities have not been extensively investigated. Here we use a silicon-based two-dimensional photonic-crystal slab to fabricate a nanocavity with Q = 45,000 and V = 7.0 x 10(-14) cm3; the value of Q/V is 10-100 times larger than in previous studies. Underlying this development is the realization that light should be confined gently in order to be confined strongly. Integration with other photonic elements is straightforward, and a large free spectral range of 100 nm has been demonstrated.

High- Q photonic nanocavity in a two-dimensional photonic crystal

A two-steps wet-etching fabrication process producing high-quality GaAs microdisks is presented. We report an optical characterization of these microdisks, using the photoluminescence of InAs quantum boxes as an internal light source. Thanks to an improved smoothness of the microdisk sidewall, cavity Q’s as high as 12 000 are observed, which opens very challenging novel application prospects for semiconductor microdisks.

High-Q wet-etched GaAs microdisks containing InAs quantum boxes

In this Letter, we demonstrate experimentally that a patchwork of four metal-insulator-metal patches leads to an unpolarized wideband omnidirectional infrared absorption. Our structure absorbs 70% of the incident light on a 2.5 μm bandwidth at 8.5 μm. It paves the way to the design of wideband efficient plasmonic absorbers in the infrared spectrum.

Wideband omnidirectional infrared absorber with a patchwork of plasmonic nanoantennas

Arrays of plasmonic nanocavities with very low volumes, down to λ3/1000, have been fabricated by soft UV nanoimprint lithography. Nearly perfect omnidirectional absorption (3–70°) is demonstrated for the fundamental mode of the cavity (λ ≃ 1.15 μm). The second-order mode exhibits a sharper resonance with strong angular dependence and total optical absorption when the critical coupling condition is fulfilled (45–50°, λ ≃ 750 nm). It leads to high refractive index sensitivity (405 nm/RIU) and figure of merit (∼21) and offers new perspectives for efficient biosensing experiments in ultralow volumes.

λ3/1000 Plasmonic Nanocavities for Biosensing Fabricated by Soft UV Nanoimprint Lithography

We study the optical properties of subwavelength metallic waveguides made of nanoscale apertures in a metal. We develop analytical expressions for the fundamental optical modes in apertures. The results are in excellent agreement with finite element calculations. This model provides a physical understanding of the role of non-perfect metallic walls, and of the shape and size of the apertures. They reveal the effect of the skin depth and of the surface plasmon polariton coupling on the waveguide modes. The nanoscopic origin of the increase of the cut-off wavelength due to the electromagnetic penetration depth in the metal is described. Simple expressions and universal curves for the effective index and the cut-off wavelength of the fundamental guided mode of any rectangular metallic waveguide are presented. The results provide an efficient tool for the design of nanoscale waveguides with real metal.

Waveguiding in nanoscale metallic apertures

The electromagnetic modes of a GaAs quantum well between two AlGaAs barriers are studied. At the longitudinal optical phonon frequency, the system supports a phonon polariton mode confined in the thickness of the quantum well that we call epsilon-near-zero mode. This epsilon-near-zero mode can be resonantly excited through a grating resulting in a very large absorption localized in the single quantum well. We show that the reflectivity can be modulated by applying a voltage. This paves the way to a new class of active optoelectronic devices working in the midinfrared and far infrared at ambient temperature.

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Jean-Luc Pelouard

Papers

High-Q wet-etched GaAs microdisks containing InAs quantum boxes

Wideband omnidirectional infrared absorber with a patchwork of plasmonic nanoantennas

λ3/1000 Plasmonic Nanocavities for Biosensing Fabricated by Soft UV Nanoimprint Lithography

Waveguiding in nanoscale metallic apertures

Epsilon-near-zero mode for active optoelectronic devices.