Martin W. McCall

The negative index of refraction demystified

We study electromagnetic wave propagation in media in which the effective relative permittivity and the effective relative permeability are allowed to take any value in the upper half of the complex plane. A general condition is derived for the phase velocity to be oppositely directed to the power flow. That extends the recently studied case of propagation in media for which the relative permittivity and relative permeability are both simultaneously negative, to include dissipation as well. An illustrative case study demonstrates that in general the spectrum divides into five distinct regions.

Spacerless circular-polarization spectral-hole filters using chiral sculptured thin films: theory and experiment

Abstract In the Bragg wavelength regime, a sculptured thin film with chiral micromorphology permits light of a particular circular polarization state to pass virtually unhindered, but light of the other polarization state is reflected almost completely. On cascading two such films, but with one film twisted with respect to the other by an angle of 90°, a hole appears in the reflection spectrum. This is proved theoretically as well as experimentally in this paper. Also, it is shown that the design wavelength of the filter can be tuned by a modest amount by tilting the filter with respect to the incident beam.

Sculptured-thin-film spectral holes for optical sensing of fluids

A novel class of fluid sensors is proposed based on monitoring the optical properties of multi-section chiral sculptured thin films (STFs) that function as spectral reflection holes. Using a nominal model that treats a chiral STF as a two-phase composite material with locally biaxial dielectric properties, we predict that the presence of a fluid in the porous film results in a red-shift of the spectral holes. Several device operation modes are proposed, and their relative merits are compared. Proof-of-concept experiments with both circularly polarized and unpolarized incident light confirm the red-shift of the spectral holes, and demonstrate operation in a practical situation.

On the application of coupled mode theory for modeling fiber Bragg gratings

We remove some ambiguities associated with the coupled mode description of light propagation in fiber Bragg gratings (FBCs). We show, in particular, that different methods employed in the literature lead to physically distinct results. The significant distinctions are discussed both for interferometric systems and intensity-only spectral measurements. Analysis of the reflection spectrum of a suitably designed double-grating structure is shown to result in a novel form of spectral hole, similar to the well-known effect derived from discontinuous phase gratings.

Chiral mirror and optical resonator designs for circularly polarized light: suppression of cross-polarized reflectances and transmittances

Abstract A left-handed chiral sculptured thin film (STF) that reflects strongly at the wavelength of the circular Bragg resonance tends to partially convert the handedness of incident LCP (left-circularly-polarized) light to RCP (right-circularly-polarized). We show that the cross-polarized component of the reflected RCP beam can be eliminated by interference with an additional RCP beam that is reflected at the interface of an isotropic cover and an AR (antireflecting) layer. For best results the refractive index and thickness of the AR layer need to accommodate a phase change on reflection that occurs at the chiral film. Effective suppression of the reflectances RRR, RRL, RLR and the transmittances TRL, TLR can be achieved by sandwiching the chiral reflector between such amplitude and phase-matched AR coatings. Co-polarized chiral reflectors of this type may form efficient handed optical resonators. For LCP light the optical properties of such a handed resonator are formally the same as the properties of the isotropic passive or active Fabry–Perot resonators, but the handed resonator is transparent to RCP light.

Sculptured thin films as ultranarrow-bandpass circular-polarization filters

In the Bragg wavelength-regime, a sculptured thin film with chiral micromorphology permits light of a particular circular polarization state to pass virtually unhindered, but light of the other polarization state is reflected almost completely. This circular Bragg phenomenon is shown here to admit narrow-band spectral reflection holes analogous to those well-studied as phase defects within grating structures. Application to the design of an ultranarrow-bandpass circular-polarization filter is considered, with the location, bandwidth and polarization selectivity quantified via a particular set of numerical examples.

Causality-Based Criteria for a Negative Refractive Index Must Be Used With Care

Using the principle of causality as expressed in the Kramers-Kronig relations, we derive a generalized criterion for a negative refractive index that admits imperfect transparency at an observation frequency omega. It also allows us to relate the global properties of the loss (i.e., its frequency response) to its local behavior at omega. However, causality-based criteria rely on the group velocity, not the Poynting vector. Since the two are not equivalent, we provide some simple examples to compare the two criteria.

Spectral-hole filter fabricated using sculptured thin-film technology

Abstract A Fabry–Perot description of the three-layer spectral-hole filter (SHF) fabricated using sculptured thin-film technology is presented. The identical outer layers are made of a thin-film helicoidal bianisotropic medium, and individually act as Bragg reflectors of one circular polarization. The middle layer, made of a homogeneous, isotropic, dielectric medium, functions as a quarter-wave spacer layer at the center-wavelength of the Bragg regime. The measured transmittance spectrums of the fabricated SHF are evaluated relative to exact theoretical results.

Spectral holes in Bragg reflection from chiral sculptured thin films: circular polarization filters

Abstract Chiral sculptured thin films (STFs) display the circular Bragg phenomenon, whereby their planewave transmittance spectrums exhibit narrow-bandstop characteristics in several wavelength regimes. The insertion of a homogeneous, anisotropic, thin layer between two layers of the same chiral STF is shown to result in the exhibition of ultranarrow-bandpass characteristics, which can be tuned by rotating the three-layer structure.

Tutorials in Complex Photonic Media

Foreword Introduction List of Contributors 1 Negative Refraction Martin W. McCall and Graeme Dewar 1.1 Introduction 1.2 Background 1.3 Beyond natural media: waves that run backwards 1.4 Wires and rings 1.5 Experimental confirmation 1.6 The perfect lens 1.7 The formal criterion for achieving negative phase velocity propagation 1.8 Fermats principle and negative space 1.9 Cloaking 1.10 Conclusions 1.11 Appendices Appendix I: The [epsilon]([omega]) of a square wire array Appendix II: Physics of the wire arrays plasma frequency and damping rate References 2 Optical Hyperspace: Negative Refractive Index and Subwavelength Imaging Leonid V. Alekseyev, Zubin Jacob, and Evgenii Narimanov.