Journal of Optics A: Pure and Applied Optics

For scalar light, the current is the familiar expectation value of the intensity-weighted momentum operator. Current is distinct from the local wavevector (not weighted) that could be observed by means of quantum weak measurement. For vector light, the current (Poynting vector) contains an additional term corresponding to the photon spin, recently identified for paraxial light by Bekshaev and Soskin but valid generally after a modification to restore 'electric–magnetic democracy'; this term has physical consequences. A number of examples demonstrate that there is usually no connection between optical vortices and angular momentum, and between C singularities and angular momentum. The optical wave current is distinct from the rays of geometrical optics in all nontrivial cases.

In this paper we explore the existence of surface electromagnetic modes in corrugated surfaces of perfect conductors. We analyse two cases: one-dimensional arrays of grooves and two-dimensional arrays of holes. In both cases we find that these structures support surface bound states and that the dispersions of these modes have strong similarities with the dispersion of the surface plasmon polariton bands of real metals. Importantly, the dispersion relation of these surface states is mainly dictated by the geometry of the grooves or holes and these results open the possibility of tailoring the properties of these modes by just tuning the geometrical parameters of the surface.

The evolution of a wave starting at z = 0 as exp(i αϕ) (), i.e. with unit amplitude and a phase step 2πα on the positive x axis, is studied exactly and paraxially. For integer steps (α = n), the singularity at the origin r = 0 becomes for z>0 a strength n optical vortex, whose neighbourhood is described in detail. Far from the axis, the wave is the sum of exp{i (αϕ+kz)} anda diffracted wave from r = 0. The paraxial wave and the wave far from the vortex are incorporated into a uniform approximation that describes the wave with high accuracy, even well into the evanescent zone. For fractional α, no fractional-strength vortices can propagate; instead, the interference between an additional diffracted wave, from the phase step discontinuity, with exp{i (αϕ+kz)} andthe wave scattered from r = 0, generates a pattern of strength-1 vortex lines, whose total (signed) strength S_α is the nearest integer to α. For small |α−n|, these lines are close to the z axis. As α passes n+1/2, S_α jumps by unity, so a vortex is born. The mechanism involves an infinite chain of alternating-strength vortices close to the positive x axis for α = n+1/2, which annihilate in pairs differently when α>n+1/2 and when α<n+1/2. There is a partial analogy between α and the quantum flux in the Aharonov–Bohm effect.

Electromagnetic metamaterials are composed of periodically arranged artificial structures. They show peculiar properties, such as negative refraction and super-lensing, which are not seen in natural materials. The conventional metamaterials require both negative and negative μ to achieve negative refraction. Chiral metamaterial is a new class of metamaterials offering a simpler route to negative refraction. In this paper, we briefly review the history of metamaterials and the developments on chiral metamaterials. We study the wave propagation properties in chiral metamaterials and show that negative refraction can be realized in chiral metamaterials with a strong chirality, with neither nor μ negative required. We have developed a retrieval procedure, adopting a uniaxial bi-isotropic model to calculate the effective parameters such as n _± , κ, and μ of the chiral metamaterials. Our work on the design, numerical calculations and experimental measurements of chiral metamaterials is introduced. Strong chiral behaviors such as optical activity and circular dichroism are observed and negative refraction is obtained for circularly polarized waves in these chiral metamaterials. We show that 3D isotropic chiral metamaterials can eventually be realized.

Structures that cause colour or provide antireflection have been found in both living and extinct animals in a diversity of forms, including mirror-reflective and diffractive devices. An overview of this diversity is presented here, and behavioural and evolutionary implications are introduced.

Surface plasmon polaritons and localized surface plasmons are discussed in the context of photonic applications. Near-field imaging of scattering, reflection, interference and localization of surface polaritons is reviewed, and approaches for the implementation of elements of surface polariton optics are presented. Surface plasmon polaritonic crystals and their role in the determination of optical properties of periodically nanostructured metal films are described. Non-linear effects related to surface polaritons and localized surface plasmons allowing control of optical properties of nanostructured metal films with light are discussed. Surface plasmon optics opens up numerous possibilities for application of these intrinsically two-dimensional excitations in passive and active devices of all-optical integrated circuits.

We look at four length scales associated with the surface plasmon–polariton (SPP) modes in the visible and near-infrared. We examine some of the consequences of these length scales for exploiting surface plasmon–polariton modes as a means to provide sub-wavelength optics. The four length scales discussed are the SPP wavelength, the SPP propagation distance, and the penetration depths of the field associated with the SPP into the dielectric and metal media that bound the interface that supports the SPP. Length scales spanning seven orders of magnitude, from nanometres to centimetres, are of relevance to SPPs. This paper concludes by identifying some of the challenges that lie ahead.

We review the geometrical-optics evolution of an electromagnetic wave propagating along a curved ray trajectory in a gradient-index dielectric medium. A Coriolis-type term appears in Maxwell equations under transition to the rotating coordinate system accompanying the ray. This term describes the spin–orbit coupling of light which consists of (i) the Berry phase responsible for trajectory-dependent polarization variations and (ii) the spin Hall effect representing polarization-dependent trajectory perturbations. These mutual phenomena are described within universal geometrical structures underlying the problem and are explained by the dynamics of the intrinsic angular momentum carried by the wave. Such close geometrodynamical interrelations illuminate a dual physical nature of the phenomena.

This special section on theoretical and computational nano-photonics features papers presented at the first International Workshop on Theoretical and Computational Nano-Photonics (TaCoNa-Photonics 2008) held in Bad Honnef, Germany, 3–5 December 2008. The workshop covered a broad range of topics related to current developments and achievements in this interdisciplinary area of research.

Since the late 1960s, the word `photonics' has been understood as the science of generating, controlling, and detecting light. Nowadays, a routine fabrication of complex structures with micro- and nano-scale dimensions opens up many new and exciting possibilities in photonics. The science of generating, routing and detecting light in micro- and nano-structured matter, `nano-photonics', is becoming more important both in research and technology and offers many promising applications.

The inherently sub-wavelength character of the structures that nano-photonics deals with challenges modern theoretical and computational physics and engineering with many nontrivial questions: Up to what length-scale can one use a macroscopic phenomenological description of matter? Where is the interface between the classical and quantum description of light in nano-scale structures? How can one combine different physical systems, different time- and length-scales in a single computational model? How can one engineer nano-structured materials in order to achieve the desired optical properties for particular applications? Any attempt at answering these kinds of questions is impossible without the joint efforts of physicists, engineers, applied mathematicians and programmers. This is the reason why the major goal of the TaCoNa-Photonics workshops is to provide a forum where theoreticians and specialists in numerical methods from all branches of physics, engineering sciences and mathematics can compare their results, report on novel results and breakthroughs, and discuss new challenges ahead. In order to intensify theoretical discussions and to put them on `solid' ground it was decided to invite world-leading experts in experimental photonics for plenary talks.

Over three days, the workshop has brought together more than 70 specialists in theoretical and computational nano-photonics. The workshop took place in the historical `Physikzentrum Bad Honnef', whose unique atmosphere supported a multitude of highly interesting debates and discussions that often lasted until midnight and beyond. Different theoretical and numerical aspects of light generation, control and detection in general inhomogeneous media, photonic crystals, plasmonic structures, metamaterials and integrated optical systems were covered in 15 invited talks and 52 contributed oral and posters presentations. The plenary talks were given by Professor M Wegener (metamaterials) and Professor W Barnes (plasmonics).

This special section is a cross-sectional selection of papers which were submitted by the authors of invited and contributed oral presentations. It also includes two papers of the winners of the Best Poster Awards. We hope that these papers will enhance the interest of the scientific community regarding nano-photonics in general and regarding the TaCoNa-Photonics workshop series in particular.

It is our distinct pleasure to acknowledge the generous financial support of our sponsors: Karlsruhe School of Optics & Photonics (KSOP) (Germany), U.S. Army International Technology Center-Atlantic, Research Division (USA), and the Office of Naval Research Global (USA). Without the organizational assistance from the International Department of the Universität Karlsruhe GmbH (Germany) this event would simply have been impossible.

We describe a toolbox, implemented in Matlab, for the computational modelling of optical tweezers. The toolbox is designed for the calculation of optical forces and torques, and can be used for both spherical and nonspherical particles, in both Gaussian and other beams. The toolbox might also be useful for light scattering using either Lorenz–Mie theory or the T-matrix method.

The PDF file provided contains web links to all articles in this volume.

This special section on theoretical and computational nano-photonics features papers presented at the first International Workshop on Theoretical and Computational Nano-Photonics (TaCoNa-Photonics 2008) held in Bad Honnef, Germany, 3–5 December 2008. The workshop covered a broad range of topics related to current developments and achievements in this interdisciplinary area of research.

Since the late 1960s, the word `photonics' has been understood as the science of generating, controlling, and detecting light. Nowadays, a routine fabrication of complex structures with micro- and nano-scale dimensions opens up many new and exciting possibilities in photonics. The science of generating, routing and detecting light in micro- and nano-structured matter, `nano-photonics', is becoming more important both in research and technology and offers many promising applications.

The inherently sub-wavelength character of the structures that nano-photonics deals with challenges modern theoretical and computational physics and engineering with many nontrivial questions: Up to what length-scale can one use a macroscopic phenomenological description of matter? Where is the interface between the classical and quantum description of light in nano-scale structures? How can one combine different physical systems, different time- and length-scales in a single computational model? How can one engineer nano-structured materials in order to achieve the desired optical properties for particular applications? Any attempt at answering these kinds of questions is impossible without the joint efforts of physicists, engineers, applied mathematicians and programmers. This is the reason why the major goal of the TaCoNa-Photonics workshops is to provide a forum where theoreticians and specialists in numerical methods from all branches of physics, engineering sciences and mathematics can compare their results, report on novel results and breakthroughs, and discuss new challenges ahead. In order to intensify theoretical discussions and to put them on `solid' ground it was decided to invite world-leading experts in experimental photonics for plenary talks.

Over three days, the workshop has brought together more than 70 specialists in theoretical and computational nano-photonics. The workshop took place in the historical `Physikzentrum Bad Honnef', whose unique atmosphere supported a multitude of highly interesting debates and discussions that often lasted until midnight and beyond. Different theoretical and numerical aspects of light generation, control and detection in general inhomogeneous media, photonic crystals, plasmonic structures, metamaterials and integrated optical systems were covered in 15 invited talks and 52 contributed oral and posters presentations. The plenary talks were given by Professor M Wegener (metamaterials) and Professor W Barnes (plasmonics).

This special section is a cross-sectional selection of papers which were submitted by the authors of invited and contributed oral presentations. It also includes two papers of the winners of the Best Poster Awards. We hope that these papers will enhance the interest of the scientific community regarding nano-photonics in general and regarding the TaCoNa-Photonics workshop series in particular.

It is our distinct pleasure to acknowledge the generous financial support of our sponsors: Karlsruhe School of Optics & Photonics (KSOP) (Germany), U.S. Army International Technology Center-Atlantic, Research Division (USA), and the Office of Naval Research Global (USA). Without the organizational assistance from the International Department of the Universität Karlsruhe GmbH (Germany) this event would simply have been impossible.

This special section on Nanophotonics and Metamaterials is a follow-up to the second European Topical Meeting of the NANOMETA series of meetings (see www.nanometa.org) which took place on 5–8 January 2009, in Seefeld, Austria.

The main idea of the first NANOMETA meeting held in 2007 was to bring together the mature community of microwave electrical engineers with the emerging community of photonics researchers interested in the physics of light coupled to nanostructures.

In recent years the research landscape has shifted dramatically. A wider proliferation of nanofabrication techniques such as electron beam lithography, nanoimprint and focused ion beam milling, diagnostics techniques such as near-field scanning imaging, cathodoluminescence with nanoscale resolution and micro-spectrometry, and the availability of affordable broadband and ultrafast optical sources, have moved the research focus of the NANOMETA community to the optical domain. Quite naturally the ideas of the nonlinearity of materials and the coherency of light in the nanoscale realm have been widely discussed. Driven by the dream of untapped device and material functionality, nonlinear and switchable nanophotonic devices and photonic metamaterials, along with the concept of tailoring the electromagnetic space with metamaterials, appear to be the main avenues along which the subject will develop in the coming years.

Indeed, in the last 20 years photonics has played a key role in creating the world as we know it, with enormous beneficial social impact worldwide. It is impossible to imagine modern society without the globe-spanning broadband internet and mobile telephony made possible by the implementation of optical fibre core networks, optical disc data storage (underpinned by the development of compact semiconductor lasers), modern image display technologies and laser-assisted manufacturing.

We now anticipate that the next photonic revolution will continue to grow, explosively fuelled by a new dependence upon active and switchable photonic metamaterials and nanophotonic devices. This revolution will lead to dramatic new science and applications on a global scale in all technologies using light, from data storage to optical processing of information, from sensing to light harvesting and energy conversion.

Five plenary talks at the conference outlined its topical boundaries. They were given by Sir Michael Berry, Bristol University, UK, who spoke on the new topic of optical super-oscillations; Harry A Atwater, California Institute of Technology, USA, who gave an overview of recent developments in plasmonics; Christian Colliex, Université Paris-Sud, France, who presented the concept of electron energy-loss spectroscopy for the study of localized plasmons; Xiang Zhang, University of California at Berkeley, USA, who talked about recent achievements in the optical super-lens, and Antoinette Taylor, National Laboratory, Los Alamos, USA, who discussed recent work on tunable terahertz metamaterials. In the specially assigned `breakthrough' talks Steven Anlage, University of Maryland, USA, introduced the emerging field of superconducting meta-materials, Tobias Kippenberg, Max-Planck-Institut, Garching, Germany, talked about cavity optomechanics on a chip, while Misha Lukin, Harvard University, USA, explored the field of quantum plasmonics and Victor Prinz, Russian Academy of Science, Russia, introduced a novel class of metamaterials based on three-dimensional semiconductor nanostructures.

The topical scope of this special section, to a great extent, echoes the paradigm shift in the NANOMETA community and includes papers on nanofabrication of plasmonic structure, transformation optics and invisibility, mapping of fields in nanostructures, nonlinear and magnetoplasmonic media, coherent effects in metamaterials, loss compensation in nanostructures, slow light and ultrafast switching of plasmon signals, and many other topics.

The Guest Editor of this special section and the co-chairs of NANOMETA-2009, on behalf of the conference organising committee and the European Physical Society, would like to thank the Nature Publishing Group for sponsoring the meeting and IOP Publishing for supporting and putting together this follow-up special section. We would like to take this opportunity to invite members of the nanophotonics and metamaterials communities to take part in the next NANOMETA conference to be held in Seefeld, Austria, 3–6 January 2011.

A fractal-like (Cantor-like) stratified structure of chiral and convenient isotropic layers is considered. Peculiarities of the wave localization, self-similarity, scalability and sequential splitting in the reflected field of both the co-polarized and cross-polarized components are studied. The appearance of additional peak multiplets in stopbands is revealed and a correlation of their properties with the chirality parameter is established.

Crystalline sapphire is proposed as a test mass material for advanced and cryogenic gravitational wave detectors. While having many advantageous properties, its optical properties are not well understood. Here we present observations of the angular dependence of the amplitude of optical scattering in single crystal sapphire samples. We show that the scattering is a strong function of the incident light polarization relative the to crystal axis. Although the data are suggestive of dipole radiation associated with the polarizability of scattering centres in anisotropic crystals, we found that the scattering matrix is neither diagonal nor symmetric. Results show that for test masses with the incident beam along the a-axis of the crystal it is advantageous to align the incident light polarization perpendicular to the crystal optical axis (the c-axis) to minimize the total scattering.

A review report on nanoimprinted plasmonic components is given. The fabrication of different metal–dielectric geometries and nanostructured surfaces that support either propagating or localized surface plasmon modes is discussed. The main characteristics and advantages of the nanoimprint technology for the fabrication of various plasmonic structures are outlined. The discussion of plasmonic waveguiding structures focuses on planar waveguides based on metal strips embedded into a dielectric and on profiled metal surfaces. Nanoimprint-based fabrication of two-dimensional nanostructured plasmonic surfaces for enhanced transmission studies and sensor applications is also discussed. Throughout the report, the main fabrication schemes are described, as well as the challenges facing future manufacturing of plasmonic components for device applications.

Progress in plasmonics has been greatly assisted by developments in experimental techniques and in numerical modelling. In this paper I look at some of the difficulties that emerge when comparisons are made between experiment and theory. Using four examples I illustrate what some of these difficulties are, from the perspective of both experiment and of modelling. Although there are many aspects to consider, two seem to be of particular concern at the time of writing; identifying the most appropriate relative permittivity (dielectric function) to describe the optical response of the metals used, and how best to make space discrete when using numerical models that rely on this approach.

Electromagnetic metamaterials are composed of periodically arranged artificial structures. They show peculiar properties, such as negative refraction and super-lensing, which are not seen in natural materials. The conventional metamaterials require both negative and negative μ to achieve negative refraction. Chiral metamaterial is a new class of metamaterials offering a simpler route to negative refraction. In this paper, we briefly review the history of metamaterials and the developments on chiral metamaterials. We study the wave propagation properties in chiral metamaterials and show that negative refraction can be realized in chiral metamaterials with a strong chirality, with neither nor μ negative required. We have developed a retrieval procedure, adopting a uniaxial bi-isotropic model to calculate the effective parameters such as n _± , κ, and μ of the chiral metamaterials. Our work on the design, numerical calculations and experimental measurements of chiral metamaterials is introduced. Strong chiral behaviors such as optical activity and circular dichroism are observed and negative refraction is obtained for circularly polarized waves in these chiral metamaterials. We show that 3D isotropic chiral metamaterials can eventually be realized.

Recent experimental work on semiconductor-based harmonically mode-locked lasers geared toward low noise applications is reviewed. Active, harmonic mode-locking of semiconductor-based lasers has proven to be an excellent way to generate 10 GHz repetition rate pulse trains with pulse-to-pulse timing jitter of only a few femtoseconds without requiring active feedback stabilization. This level of timing jitter is achieved in long fiberized ring cavities and relies upon such factors as low noise rf sources as mode-lockers, high optical power, intracavity dispersion management and intracavity phase modulation. When a high finesse etalon is placed within the optical cavity, semiconductor-based harmonically mode-locked lasers can be used as optical frequency comb sources with 10 GHz mode spacing. When active mode-locking is replaced with regenerative mode-locking, a completely self-contained comb source is created, referenced to the intracavity etalon.

The efficiency of gas-based nonlinear processes is often limited by the diffraction of the pump laser as it propagates through the nonlinear medium. As a consequence, phenomena with strong nonlinear response requirements, such as high harmonic generation or Raman sideband generation, lack the required laser–matter interaction to fulfil their potential. Indeed, the conversion efficiency of these techniques is usually low and the experimental set-up cumbersome. The advent of hollow core photonic crystal fibre technology drafts new territories for nonlinear optics, and in particular offers new alternatives for sub-femtosecond pulse generation. The air-guiding fibre combines unprecedented laser confinement over long interaction lengths and, when filled with an adequate nonlinear gas, offers improved conversion efficiency and up to a million-fold reduction of the pump power threshold. This paper presents a review of the types of hollow core PCF available for nonlinear applications and the results obtained for efficient Raman conversion in H₂-filled hollow core PCF that led to the observation of a multi-octave frequency comb spanning from ∼325 to ∼2300 nm using a single pump laser with relatively low power. The generated ultra-broad spectrum creates a simple route towards a compact source of attosecond pulses.