Helicoidal Bianisotropic Mediums Research Articles

Reflection of an obliquely incident plane wave by a half space filled by a helicoidal bianisotropic medium

The one-point boundary-value problem of reflection of an obliquely incident plane wave by a half space occupied by a linear helicoidal bianisotropic medium (HBM) was solved. The solution procedure relies on the HBM being at least slightly dissipative, and also yields a modal representation for the fields therein. The solution procedure should also apply for a half space containing any linear material that varies periodically in the normal direction.

Reflection, transmission and circular dichroism in axially excited slab of a copper thin film helicoidal bianisotropic medium

The reflectance, transmittance and circular dichrosim in a chiral sculptured copper thin film slab of 1000–1600nm thickness in near infra-red and visible regions based on the relative permittivity of copper in the bulk state and volumetric fraction of copper inclusion of 0.2 are obtained. At higher volumetric fraction of metallic inclusions the reflection (due to low circular Bragg phenomenon) and transmission coefficients (due to increased absorption) are too small, while for thicker slabs numerical instabilities (overflow/underflow) occur in the computation. Therefore it is recommended that the chiral sculptured thin film slab to be considered as a half space.

Comparison of two methods for oblique propagation in helicoidal bianisotropic mediums

Two methods for oblique propagation in two dielectric examples of helicoidal bianisotropic mediums – chiral sculptured thin films and chiral smectic liquid crystals – are compared: (i) the series solution method, and (ii) the piecewise homogeneity approximation method. Both have to be numerically implemented, although only the former relies on an exact analytic solution of the frequency-domain Maxwell postulates. Convergence in the series solution method is investigated via calculations for a variety of planewave-illumination parameters and constitutive properties. Likewise, the maximum slice thickness for convergent results from the piecewise homogeneity approximation method is also studied. The computational efficiencies of both methods are compared.

Nominal model for structure-property relations of chiral dielectric sculptured thin films

The Bruggeman formalism is implemented to estimate the permittivity dyadics of chiral dielectric sculptured thin films (STFs), called thin-film helicoidal bianisotropic mediums (TFHBMs), modelled as helicoidally arranged stacks of ellipsoidal inclusions in vacuum. Spectral maximums of several observable optical properties of axially excited TFHBM slabs are examined as functions of inclusion shape, volume fraction and orientation. Changes in the transverse aspect ratio of the ellipsoidal inclusions significantly affect the predicted optical properties of the TFHBM. A critical value for the transverse aspect ratio of the ellipsoids can be found such that optical activity disappears when all other parameters are fixed. The orientation of the inclusions significantly affects the value of optical property maximums, and can be made to suppress optical activity completely. A distribution of orientations decreases various measures of optical activity.

Axial electromagnetic wave propagation in inhomogeneous dielectrics

We review the mathematical description of axial propagation in inhomogeneous dielectrics, focusing on two canonical examples: scalar Bragg gratings and thin film helicoidal bianisotropic media (TFHBM). Coupled wave analysis is reviewed for the former, and exact methods based on rotational transforms are discussed for the latter. There are many similarities between the physical descriptions that are emphasised in reviewing the modelling techniques, although the transform which allows the TFHBM case to be solved exactly is shown to be inapplicable in the scalar case.

Optical interconnects realizable with thin–film helicoidal bianisotropic mediums

Parallel–plate waveguides consisting of a thin–film helicoidal bianisotropic medium (TFHBM) layer bounded by dielectric half–spaces are shown to support guided wave propagation with guide wavenumbers dependent on the direction of signal propagation. Thus, the TFHBM interconnect behaves as a space–guide . The modal fields and power transmission distributions, as determined by the time-averaged Poynting vector, are investigated and a scheme classifying each guided wave mode as either hybrid electric or hybrid magnetic is presented.

Development and assessment of coupled wave theory of axial propagation in thin-film helicoidal bi-anisotropic media. Part 2: Dichroisms, ellipticity transformation and optical rotation

Development and assessment of coupled wave theory of axial propagation in thin-film helicoidal bi-anisotropic media. Part 2: Dichroisms, ellipticity transformation and optical rotation

Development and assessment of coupled wave theory of axial propagation in thin-film helicoidal bi-anisotropic media. Part 2: Dichroisms, ellipticity transformation and optical rotation

The coupled wave theory (CWT) for axial propagation of light in dielectric thin-film helicoidal bi-anisotropic mediums is exploited to obtain simple expressions for true and apparent circular dichroisms, true and apparent linear dichroisms, transmission ellipticity, and optical rotation. The effect of weak isotropic absorption on the circular Bragg phenomenon is elucidated, in terms of simple expressions. Comparison is made with exact results obtained with the full electromagnetic analysis (FEMA), any differences between the CWT and the FEMA results being due to the neglect of cross-polarized scattering by the CWT.

On absorption by non-axially excited slabs of dielectric thin-film helicoidal bianisotropic mediums

The spectral signatures of non-axially excited, absorbing TFHBM slabs are determined, after using a single-resonance Lorentzian model to describe the dispersive properties of the medium. Optical phenomena such as the optical rotation, circular dichroism and ellipticity transformation by absorbing TFHBM slabs are described. The effect of absorption on the functionality of TFHBM-based devices, such as multi-notch filters and ultranarrow-bandpass filters, are noted and engineering guidelines on the fabrication of such devices are provided.

Development and assessment of coupled wave theory of axial propagation in thin-film helicoidal bianisotropic media. Part 1: Reflectances and transmittances

The coupled wave theory (CWT) for axial propagation of light in dielectric thin-film helicoidal bianisotropic media is presented and compared with the full electromagnetic analysis (FEMA). Two sets of formulas are developed for the location and bandwidth of the wavelength regime wherein the circular Bragg phenomenon is exhibited. Multi-layer structures are also analysed using the CWT, the location of the spectral hole in a class of threelayer structures being determined analytically. Absorption and dispersion effects are considered.

Spectral-hole filter fabricated using sculptured thin-film technology

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.

Polarization-dependent narrowband spectral filtering by chiral sculptured thin films

We analyse theoretically transmission through two layers of different thin-film helicoidal bianisotropic mediums (TFHBMs), wherein the pitch of each layer bears a precisely determined relation to the overall thickness of the bi-layer. A spectral hole emerges from the interaction of the circular Bragg regimes of both TFHBM layers. Our results generalize a recently discovered scheme for producing spectral holes in fibre-Bragg gratings, with which comparison is made. The proposed TFHBM bi-layers may be useful for the simultaneous production of oppositely polarized beams with narrow bandwidths and a specific amplitude splitting ratio.

A comparative study of planewave propagation in helicoidal bianisotropic mediums and isotropic chiral mediums

Helicoidal bianisotropic mediums (HBMs) are periodically nonhomogeneous and possess structural chirality. We establish a variety of conditions concerning the equivalence of planewave propagation along the spirality axis of HBMs to propagation in isotropic chiral mediums (ICMs). These conditions illuminate the analogous roles of molecular chirality in ICMs and structural chirality in HBMs. In particular, structural chirality of even the simplest (i.e. dielectric) HBMs can be tailored to enhance optical activity in comparison to that of ICMs.

Vacuum deposition of chiral sculptured thin films with high optical activity

We present the technique of bideposition to realize thin-film helicoidal bianisotropic mediums (TFHBM's) that exhibit high optical activity. We show, by experiment as well as by simulation, that the optical rotation produced by these chiral sculptured thin films is roughly proportional to the square of the local linear birefringence. Experimental measurements on bideposited TFHBM's of titanium oxide yield a typical value of 5 degrees /mum for the effective specific rotation in the short-wavelength regime; the corresponding value determined for the standard unideposited TFHBM's is 1 degrees /mum. Both types of TFHBM's are highly optically active in comparison with quartz, fluorite films, and cholesteric liquid crystals. Bideposited TFHBM's will lend themselves to many different types of optical devices.

On percolation and circular Bragg phenomenon in metallic, helicoidally periodic, sculptured thin films

The concept of local homogenization is invoked in the visible and the sub-visible frequency regimes to estimate the permittivity dyadics of a thin-film helicoidal bianisotropic mediums (TFHBMs)~---~a canonical class of sculptured thin films with helicoidally periodic microstructure~---~made of a metal. Examination of the components of the permittivity dyadics, as well as of the co- and the cross-polarized reflectances of axially excited, metallic TFHBM halfspaces, reveals that three different absorbing-dielectric-to-metal transitions will occur as the metallic volumetric fraction is increased, but only two will be optically sensed using normally incident plane waves. The first transition is show to virtually eliminate the circular Bragg phenomenon characteristically displayed by axially excited, dielectric TFHBMs.

Electromagnetic plane–wave response characteristics of non–axially excited slabs of dielectric thin–film helicoidal bianisotropic mediums

Thin–film helicoidal bianisotropic mediums (TFHBMs) are rotationally non–homogeneous mediums whose microstructure consists of parallel helical columns. We characterize here the plane–wave response of non–axially excited dielectric TFHBM slabs. The constitutive relations for the dielectric TFHBMs are substituted into the time–harmonic Maxwell curl equations, and a 4 × 4 matrix ordinary differential equation is obtained. The piecewise homogeneity approximation method is shown to be reasonably robust to solve the differential equation. Bragg reflection by non–axially excited dielectric TFHBM slabs is investigated, and transmission characteristics are examined. The effects of several key illumination and constitutive parameters on the response of non–axially excited dielectric TFHBM slabs are studied to elucidate trends in functional relationships. A TFHBM bilayer is presented as an example of a device based on non–axially excited dielectric TFHBMs.

Correction for Venugopal and Lakhtakia, Second harmonic emission from an axially excited slab of a dielectric thin-film helicoidal bianisotropic medium

You have accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Venugopal V. C. and Lakhtakia A. 1999Correction for Venugopal and Lakhtakia, Second harmonic emission from an axially excited slab of a dielectric thin-film helicoidal bianisotropic mediumProc. R. Soc. Lond. A.4554383http://doi.org/10.1098/rspa.1998.1000SectionYou have accessCorrection for Venugopal and Lakhtakia, Second harmonic emission from an axially excited slab of a dielectric thin-film helicoidal bianisotropic medium V. C. Venugopal V. C. Venugopal Google Scholar Find this author on PubMed Search for more papers by this author and A. Lakhtakia A. Lakhtakia Google Scholar Find this author on PubMed Search for more papers by this author V. C. Venugopal V. C. Venugopal Google Scholar Find this author on PubMed Search for more papers by this author and A. Lakhtakia A. Lakhtakia Google Scholar Find this author on PubMed Search for more papers by this author Published:08 December 1999https://doi.org/10.1098/rspa.1998.1000This article corrects the followingResearch ArticleSecond harmonic emission from an axially excited slab of a dielectric thin-film helicoidal bianisotropic mediumhttps://doi.org/10.1098/rspa.1998.0221 Vijayakumar C. Venugopal and Akhlesh Lakhtakia volume 454issue 1974Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences08 June 1998AbstractCorrection for ‘Second harmonic emission from an axially excited slab of a dielectric thin-film helicoidal bianisotropic medium’ by V. C. Venugopal and A. Lakhtakia (Proc. R. Soc. Lond. A 454, 1535–1571. (doi: 10.1098/rspa.1998.0221)).The correct form of equation (2.28d) is presented here. Previous ArticleNext Article VIEW FULL TEXT DOWNLOAD PDF FiguresRelatedReferencesDetailsCited by Faryad M and Lakhtakia A (2014) The circular Bragg phenomenon, Advances in Optics and Photonics, 10.1364/AOP.6.000225, 6:2, (225), Online publication date: 30-Jun-2014. Lakhtakia A (2002) Local inclination angle: a key structural factor in emission from chiral sculptured thin films, Optics Communications, 10.1016/S0030-4018(01)01696-0, 202:1-3, (103-111), Online publication date: 1-Feb-2002. Sherwin J and Lakhtakia A (2001) Nominal model for structure-property relations of chiral dielectric sculptured thin films, Mathematical and Computer Modelling, 10.1016/S0895-7177(01)00142-X, 34:12-13, (1499-1514), Online publication date: 1-Dec-2001. Related articlesSecond harmonic emission from an axially excited slab of a dielectric thin-film helicoidal bianisotropic medium08 June 1998Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences This Issue08 December 1999Volume 455Issue 1992 Article InformationDOI:https://doi.org/10.1098/rspa.1998.1000Published by:Royal SocietyPrint ISSN:1364-5021Online ISSN:1471-2946History: Published online08/12/1999Published in print08/12/1999 License: Citations and impact

On the Quasistatic Approximation for Helicoidal Bianisotropic Mediums

ABSTRACT The quasistatic approximation is implemented for general, linear, helicoidal bianisotropic mediums. A pair of coupled ordinary differential equations with periodic coefficients emerges for scalar electric and magnetic potentials. These equations reduce to coupled one-dimensional Laplace equations for axially varying potentials. A matrix polynomial expansion technique is devised for nonaxially varying potentials. The electric potential in a cholesteric liquid crystal is solved using a series solution technique.

Spectral signatures of axially excited slabs of dielectric thin-film helicoidal bianisotropic mediums

Dielectric thin-film helicoidal bianisotropic mediums (TFHBMs) are rotationally nonhomogeneous nano-engineered materials of recent vintage. Here, optical signatures of axially excited TFHBM slabs are calculated after solving a boundary value problem, after assuming the chosen materials to have single-resonance Lorentzian dielectric response properties. The spectrum of co- and cross-polarized reflectances and transmittances, true and apparent circular dichroisms, true and apparent linear dichroisms, ellipticity transformation, and optical rotation are presented. The role of the structural period in the spectral location of the circular Bragg phenomenon is delineated, and measures to deepen that phenomenon are discussed. The effects of structural handedness on the spectrum are also identified.

Bragg‐regime absorption in axially excited slabs of dielectric thin‐film helicoidal bianisotropic media

Bragg‐regime absorption in axially excited slabs of dielectric thin‐film helicoidal bianisotropic media