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Register a new userTheory of Dyakonov-Tamm waves at the planar interface of a sculptured nematic thin film and an isotropic dielectric material
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In order to ascertain conditions for surface-wave propagation guided by the planar interface of an isotropic dielectric material and a sculptured nematic thin film (SNTF) with periodic nonhomogeneity, we formulated a boundary-value problem, obtained a dispersion equation therefrom, and numerically solved it. The surface waves obtained are Dyakonov-Tamm waves. The angular domain formed by the directions of propagation of the Dyakonov--Tamm waves can be very wide (even as wide as to allow propagation in every direction in the interface plane), because of the periodic nonhomogeneity of the SNTF. A search for Dyakonov-Tamm waves is, at the present time, the most promising route to take for experimental verification of surface-wave propagation guided by the interface of two dielectric materials, at least one of which is anisotropic. That would also assist in realizing the potential of such surface waves for optical sensing of various types of analytes infiltrating one or both of the two dielectric materials.
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Surface waves can propagate on the planar interface of a linear electro-optic (EO) material and an isotropic dielectric material, for restricted ranges of the orientation angles of the EO material and the refractive index of the isotropic material. These ranges can be controlled by the application of a dc electric field, and depend on both the magnitude and the direction of the dc field. Thus, surface-wave propagation can be electrically controlled by exploiting the Pockels effect.
The solution of a boundary--value problem formulated for the Kretschmann configuration shows that the phase speed of a surface--plasmon--polariton (SPP) wave guided by the planar interface of a sufficiently thin metal film and a sculptured thin film (STF) depends on the vapor incidence angle used while fabricating the STF by physical vapor deposition. Furthermore, it may be possible to engineer the phase speed by periodically varying the vapor incidence angle. The phase speed of the SPP wave can be set by selecting higher mean value and/or the modulation amplitude of the vapor incidence angle.
The propagation of electromagnetic surface waves guided by the planar interface of two isotropic chiral materials, namely materials $calA$ and $calB$, was investigated by numerically solving the associated canonical boundary-value problem. Isotropic chiral material $calB$ was modeled as a homogenized composite material, arising from the homogenization of an isotropic chiral component material and an isotropic achiral, nonmagnetic, component material characterized by the relative permittivity $eps_a^calB$. Changes in the nature of the surface waves were explored as the volume fraction $f_a^calB$ of the achiral component material varied. Surface waves are supported only for certain ranges of $f_a^calB$; within these ranges only one surface wave, characterized by its relative wavenumber $q$, is supported at each value of $f_a^calB$. For $mbox{Re} lec eps_a^calB ric > 0 $, as $left| mbox{Im} lec eps_a^calB ric right|$ increases surface waves are supported for larger ranges of $f_a^calB$ and $left| mbox{Im} lec q ric right|$ for these surface waves increases. For $mbox{Re} lec eps_a^calB ric < 0 $, as $ mbox{Im} lec eps_a^calB ric $ increases the ranges of $f_a^calB$ that support surface-wave propagation are almost unchanged but $ mbox{Im} lec q ric $ for these surface waves decreases. The surface waves supported when $mbox{Re} lec eps_a^calB ric < 0 $ may be regarded as akin to surface-plasmon-polariton waves, but those supported for when $mbox{Re} lec eps_a^calB ric > 0 $ may not.
Dyakonov surface wave existing at the interface with anisotropy offers a promising way of guiding light in two-dimension with almost no loss. However, predicted decades ago, the experimental demonstration of the Dyakonov surface wave seems always challenging for the weak anisotropic indices from the natural materials. Here we experimentally demonstrated a Dyakonov surface wave mode propagating in a hyperbolic metasurface at the visible frequency. Dyakonov surface waves at the two surfaces of the metasurface can be supported simultaneously by the hyperbolic anisotropy and form a Dyakonov typed mode with low loss and a large allowed angle band. A detailed theoretical analysis and numerical simulations prove that the electric field of such a surface wave mode shows transverse spin, whose direction is determined by the orientations of the hyperbolic anisotropy and surface normal, based on which we experimentally observed the photonic spin Hall effect of the surface wave mode in our metasurface.
Highly directional and lossless surface wave has significant potential applications in the two-dimensional photonic circuits and devices. Here we experimentally demonstrate a selective Dyakonov surface wave coupling at the interface between a transparent polycarbonate material and nematic liquid crystal 5CB. By controlling the anisotropy of the nematic liquid crystal with an applied magnetic field, a single ray at a certain incident angle from a diverged incident beam can be selectively coupled into surface wave. The implementation of this property may lead to a new generation of on-chip integrated optics and two-dimensional photonic devices.
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