Dyakonov Tamm Waves Research Articles

Effect of chemical potential on Dyakonov–Tamm waves guided by a graphene-coated structurally chiral medium

We numerically investigated the effect of chemical potential on Dyakonov–Tamm waves (DTWs) guided by a graphene-coated structurally chiral medium in the terahertz and the visible spectral regimes. Only one DTW can propagate in a specific direction in wide angular sectors, but multiple DTWs can propagate in a specific direction in narrow angular sectors, in both spectral regimes. Although the phase speed of a DTW depends weakly on the chemical potential in both spectral regimes, the propagation distance can be strongly dependent on the chemical potential in the terahertz regime but not in the visible regime. This difference can be attributed to the real part of the surface conductivity of graphene, which varies significantly with the chemical potential in the terahertz regime but not in the visible regime.

Dyakonov–Tamm waves guided by the planar surface of a chiral sculptured thin film: erratum

Dyakonov–Tamm waves guided by the planar surface of a chiral sculptured thin film: erratum

Left/right asymmetry in Dyakonov–Tamm-wave propagation guided by a topological insulator and a structurally chiral material

The propagation of Dyakonov–Tamm waves guided by the planar interface of an isotropic topological insulator and a structurally chiral material, both assumed to be nonmagnetic, was investigated by numerically solving the associated canonical boundary-value problem. The topologically insulating surface states of the topological insulator were quantitated via a surface admittance , which significantly affects the phase speeds and the spatial profiles of the Dyakonov–Tamm waves. Most significantly, it is possible that a Dyakonov–Tamm wave propagates co-parallel to a vector in the interface plane, but no Dyakonov–Tamm wave propagates anti-parallel to . The left/right asymmetry, which vanishes for , is highly attractive for one-way on-chip optical communication.

Compound guided waves that mix characteristics of surface-plasmon-polariton, Tamm, Dyakonov–Tamm, and Uller–Zenneck waves

Solutions of the boundary-value problem for electromagnetic waves guided by a layer of a homogeneous and isotropic (metal or dielectric) material sandwiched between a structurally chiral material (SCM) and a periodically multi-layered isotropic dielectric (PMLID) material were numerically obtained and analyzed. If the sandwiched layer is sufficiently thick, the two bimaterial interfaces decouple from each other, and each interface may guide one or more electromagnetic surface waves (ESWs) by itself. Depending on the constitution of the two materials that partner to form an interface, the ESWs can be classified as surface-plasmon-polarition (SPP) waves, Tamm waves, Dyakonov-Tamm waves, or Uller-Zenneck waves. When the sandwiched layer is sufficiently thin, the ESWs for single bimaterial interfaces coalesce to form compound guided waves (CGWs). The phase speeds, propagation distances, and spatial profiles of the electromagnetic fields of CGWs are different from those of the ESWs. The energy of a CGW is distributed in both the SCM and the PMLID material, if the sandwiched layer is sufficiently thin. Some CGWs require the sandwiched layer to have a minimum thickness. Indeed, the coupling between the two faces of the sandwiched layer is affected by the ratio of the thickness of the sandwiched layer to the skin depth in that material and the rates at which the fields of the ESWs guided individually by the two interfaces decay away from their respective guiding interfaces.

Dyakonov–Tamm waves guided by the planar interface of a rugate filter and a columnar thin film

Dyakonov–Tamm waves guided by a planar interface of an anisotropic, homogeneous dielectric material, and an isotropic, periodically nonhomogeneous dielectric material was investigated in a canonical boundary-value problem. The former material was taken to be a columnar thin film (CTF) and the latter was a rugate filter. Dyakonov–Tamm waves are surface electromagnetic waves that have negligible propagation losses. In the chosen setup, multiple Dyakonov–Tamm waves of different phase speeds, degrees of localization, and spatial field profiles, but of the same frequency were found to exist. The effect of direction of propagation with respect to the morphologically significant plane of the CTF, the phase and the amplitude of modulation of the rugate filter was investigated. The number of Dyakonov–Tamm waves depends on the direction of propagation with respect to the morphologically significant plane of the CTF. The relative wavenumber and the degree of localization of the Dyakonov–Tamm waves increase with an increase in the amplitude of modulation of the rugate filter.

Dyakonov–Tamm waves-based optical sensing using sculptured nematic thin film

Dyakonov–Tamm (DT) waves are highly sensitive to the constitutive properties of the partnering materials near the interface. DT waves are excited at the interface of two dielectric materials of which at least one is anisotropic and periodically nonhomogeneous normal to their interface. Sculptured nematic thin film (SNTF) is a good candidate for the periodically nonhomogeneous dielectric partner for optical sensing of a fluid due to its porosity. The nanoscale parameters of an uninfiltrated SNTF obtained from the inverse Bruggeman homogenization formalism were used in the forward Bruggeman homogenization formalism to determine the constitutive parameters for the infiltrated SNTF. The sensitivity of DT waves to the refractive index was analyzed for two possible sensing modalities and it was found that the sensitivity was comparable to that of the chiral sculptured thin films (STFs) made of the same material as of the SNTF. This implies that the sensing with DT waves is robust, is independent of the morphology of the partnering nonhomogeneous dielectric material and could make the sensing easier since SNTFs are easier to fabricate than the chiral STFs.

An optical-sensing modality that exploits Dyakonov–Tamm waves

Surface-wave-based optical sensing of an analyte in a fluid relies on the sensitivity of the surface wave to the electromagnetic properties of the analyte-containing fluid in the vicinity of the guiding interface. Surface-plasmon-polariton (SPP) waves are most commonly used for optical sensing because of the ease of the excitation of an SPP wave when the fluid is partnered with a metal. If the fluid is replaced by a porous, anisotropic, and periodically nonhomogeneous solid filled with the fluid, while the metal is replaced by an isotropic homogeneous dielectric material, the surface wave is called a Dyakonov–Tamm (DT) wave. We have theoretically determined that the incorporation of the DT-waveguiding interface in a prism-coupled configuration provides an alternative to the analogous SPP wave-based sensor, with comparable dynamic sensitivity.

Theory of optical sensing with Dyakonov–Tamm waves

An optical modality to sense a fluid by exploiting Dyakonov–Tamm (DT) waves was devised. In the modality, the fluid is present on both sides of the guiding interface. Theoretical analysis indicated that the angular location of the reflectance dip in a practically implementable configuration will shift if the refractive index of the fluid changes. Furthermore, the detection sensitivity will decrease as the refractive index of the fluid increases over a wide range, and should be comparable to that for sensing modalities that exploit surface-plasmon-polariton (SPP) waves. Higher sensitivities are available with DT waves than with SPP waves, and the DT-wave-based sensor should be simpler to fabricate than the SPP-wave-based sensor. Multiple DT waves are excitable at the same frequency, leading to multiple channels for more reliable sensing as well as for sensing multiple analytes simultaneously.

Evolution of surface-plasmon-polariton and Dyakonov–Tamm waves with the ambichirality of a partnering dielectric material

The planar interface of an isotropic homogeneous metal and an ambichiral dielectric material can guide surface-plasmon-polariton waves. The planar interface of an isotropic, homogeneous dielectric material and an ambichiral dielectric material can guide Dyakonov-Tamm waves. In either instance, we found that, as the ambichiral partnering material evolves into a finely chiral material, the solutions of the dispersion equation for surface-wave propagation evince convergence. The convergence is faster for the surface waves with larger phase speeds than for the surface waves with smaller phase speeds.

Observation of the Dyakonov-Tamm Wave

A surface electromagnetic wave called the Dyakonov-Tamm wave has been theoretically predicted to exist at the interface of two dielectric materials at least one of which is both anisotropic and periodically nonhomogeneous. For experimental confirmation, a prism-coupled configuration was used to excite Dyakonov-Tamm waves guided by the interface of a dense thin film of magnesium fluoride and a chiral sculptured thin film of zinc selenide. The excitation was indicated by a reflection dip (with respect to the angle of incidence in the prism-coupled configuration) that is independent of the polarization state of the incident light as well as the thicknesses of both partnering materials beyond some thresholds. Applications to optical sensing and long-range on-chip communication are expected.

Dyakonov–Tamm waves guided by the planar surface of a chiral sculptured thin film

Propagation of Dyakonov–Tamm waves guided by the interface of air and a chiral sculptured thin film (STF) was investigated theoretically. The solution of the dispersion equation showed that the direction of propagation is either unrestricted or almost unrestricted in the interface plane. For very limited ranges of the direction of propagation, multiple Dyakonov–Tamm waves may even exist. These surface waves were theoretically found to be excitable in the Otto prism-coupled configuration by an incident plane wave of either linear polarization state, thereby lending hope for an easy way to observe Dyakonov–Tamm waves experimentally.

Parametric investigation of prism-coupled excitation of Dyakonov–Tamm waves

In order to pave the way for the yet-to-be reported experimental observation of the Dyakonov–Tamm wave, the excitation of this surface wave in a prism-coupled configuration was theoretically investigated when one partnering dielectric material is isotropic and homogeneous while the other is a chiral sculptured thin film (CSTF). The excitation of a Dyakonov–Tamm wave in the prism-coupled configuration was identified by those peaks in the plots of the absorptance versus the angle of incidence that were independent of the thicknesses of both partnering materials (beyond some thresholds) and the polarization state of the incident plane wave. The results of the prism-coupled configuration were successfully correlated with the underlying canonical boundary-value problem. An increase in either the structural period or the average vapor flux angle of the CSTF results in a larger angle of incidence for experimental excitation, whereas an increase in an offset angle results in a decrease of that angle. An increase in the bulk refractive index of the material from which the CSTF is fabricated is likely to increase the angle of incidence for experimental observation. It is highly preferable for the CSTF to be an integral number of periods in thickness, and that number does not have to be large.

Prism-coupled excitation of Dyakonov–Tamm waves

The prism-coupled excitation of Dyakonov–Tamm waves guided by the planar interface of a homogeneous, isotropic dielectric material and a periodically nonhomogeneous sculptured nematic thin film (SNTF) was investigated. The excitation of Dyakonov–Tamm waves was identified by correlating a high-absorptance band in the plots of absorptance vs. the incidence angle and the direction of propagation in the interface plane with the solutions of the underlying canonical boundary–value problem. Dyakonov–Tamm waves were found to have a much wider angular existence domain than Dyakonov waves, and broader absorptance peaks than both the Dyakonov and Tamm waves in the plots of absorptance vs. the incidence angle.

Dyakonov–Tamm waves guided by the planar interface of an isotropic dielectric material and an electro-optic ambichiral Reusch pile

The existence of an electromagnetic surface wave—classified as a Dyakonov–Tamm wave—guided by the planar interface of an isotropic, homogenous, dielectric material and an electro-optic ambichiral Reusch pile was theoretically established for various values of a dc electric field applied normal to the interface. For low magnitudes of the dc electric field, the spread of values of the refractive index ns of the isotropic partnering material supporting the surface waves is exceedingly small. A sufficient increase in the magnitude of the dc electric field considerably widens that range. The allowed propagation directions, in all cases, constitute an angular sector of several tens of degrees in width.

Surface electromagnetic waves: A review

AbstractFrom the beginning of the 20th century, researchers have been interested in surface electromagnetic waves guided by planar interfaces of dissimilar mediums. Much initial research on surface‐plasmon waves and surface‐plasmon‐polariton waves stemmed from theoretical curiosity, but the development of new experimental techniques propelled commercial exploitation for optical sensors of chemical and biological species. Additional surface waves called Dyakonov waves, Tamm waves, and Dyakonov–Tamm waves have emerged during the last 25 years. Experimental observation of Dyakonov waves was reported only in 2009, but the rapid development of experimental apparatus during the 1990s suggests that theoretical predictions will soon be evaluated experimentally, leading to further development of optical detection systems and optical circuitry.

Synoptic view of Dyakonov–Tamm waves localized to the planar interface of two chiral sculptured thin films

The Dyakonov-Tamm wave combines the features of the Dyakonov wave and the Tamm electronic state. Dyakonov-Tamm waves guided by the planar interface of two dissimilar chiral sculptured thin films (STFs) were systematically examined. The interfaces result from the chiral STFs being dissimilar in (a) orientation about the helical axis, (b) structural handedness, (c) structural period, (d) vapor incidence angle, (e) material, or (f) various combinations thereof. A boundary-value problem for the propagation of Dyakonov-Tamm waves was formulated and numerically solved. Up to three physical solutions were obtained for any specific combination of constitutive properties of the two chiral STFs. Each solution indicates the existence of a Dyakonov-Tamm wave. If more than one solution exists, the corresponding Dyakonov-Tamm waves differ in phase speed and degree of localization to the interface. Fewer solutions were found when the two chiral STFs differ in many attributes.

Dyakonov–Tamm waves guided by a phase–twist combination defect in a sculptured nematic thin film

The propagation of Dyakonov–Tamm waves guided by a phase–twist combination defect in a sculptured nematic thin film (SNTF) was studied theoretically by numerical solution of a dispersion equation. The phase defect was fixed at 180 °, whereas the twist defect was kept variable as also the direction of propagation. Multiple Dyakonov–Tamm waves that differ in spatial profile, degree of localization, and phase speed were found to propagate guided by the combination defect, depending on the angle between the morphologically significant planes of the SNTF on either side of the defect as well as on the direction of propagation. The most strongly localized Dyakonov–Tamm waves turned out to be essentially confined within one structural period of the SNTF normal to the combination defect.

Simultaneous propagation of two Dyakonov–Tamm waves guided by the planar interface created in a chiral sculptured thin film by a sudden change of vapor flux direction

While growing a chiral sculptured thin film by physical vapor deposition, a sudden change in the direction of the vapor flux creates a plane of discontinuity. In effect, this is a planar interface between two different structurally chiral materials. Theoretical analysis shows that more than one Dyakonov–Tamm waves, with different phase speeds and degrees of localization to this interface, may propagate in different directions guided by the interface.

Dyakonov-Tamm waves guided by the interface between two structurally chiral materials that differ only in handedness

The boundary-value problem of the propagation of Dyakonov-Tamm waves guided by the planar interface between two structurally chiral materials that are identical except for structural handedness was formulated and numerically solved. Detailed analysis showed that either two or three different Dyakonov-Tamm waves can propagate. These waves have different phase speeds and degrees of localization to the interface with a sudden handedness change. The most localized Dyakonov-Tamm waves are essentially confined to within a small number of structural periods of the interface on either side.

On Dyakonov-Tamm waves localized to a central twist defect in a structurally chiral material

The boundary-value problem of the propagation of Dyakonov-Tamm waves localized to a central twist defect in a structurally chiral material was formulated and numerically solved. The angular magnitude of the twist defect and the orientation of the twist defect relative to the direction of propagation were varied. Detailed analysis showed that either two or three different Dyakonov-Tamm waves can propagate, depending on the angular magnitude and the orientation of the twist defect. These waves have different phase speeds and degrees of localization to the twist-defect interface. The most localized Dyakonov-Tamm waves are essentially confined to within two structural periods of the twist-defect interface on either side.