S-polarized Waves Research Articles

Tunable polarization-dependent defect modes and lateral shifts of one-dimensional photonic crystals containing Dirac semimetal-based hyperbolic metamaterials and chiral materials

The transmission and lateral shift properties of the one-dimensional photonic crystals containing Dirac semimetal-based hyperbolic metamaterials and chiral material defects are theoretically investigated by using the transfer matrix method in terahertz. It is found that the angle-independent omnidirectional photonic bandgaps (PBGs) for p-polarization can be realized in the photonic crystals made of dielectric and the Dirac semimetal-based hyperbolic metamaterials. However, the PBGs are blue-shifted with the incident angle for s-polarized wave. The omnidirectional PBGs can be tunable with the Fermi energy of the Dirac semimetal, the thickness ratio of the constitute layers and the structural parameters. When one or two isotropic chiral material layers are introduced in the photonic crystals, double or four polarization-dependent defect modes are found in the bandgap under oblique incidence due to the coupling and conversion between different polarized waves in the chiral defects. The frequency interval of the defect modes changes with the chirality parameter and the incident angle. It is also found that when a light is incident on the defective photonic crystals, the giant positive and negative Goos-Hänchen shifts of co-polarization reflected waves can be induced around the defect modes, which are sensitive to the polarization, the incident angle, the incident frequency and the chirality. The special optical properties of the proposed defective multiplayers provide possibilities for practical applications in designing polarization sensitive optical devices, such as filter and sensor.

Scaling behavior of the localization length for TE waves at critical incidence on short-range correlated stratified random media

We theoretically investigate the scaling behavior of the localization length for s-polarized electromagnetic waves incident at a critical angle on stratified random media with short-range correlated disorder. By employing the invariant embedding method, extended to waves in correlated random media, and utilizing the Shapiro–Loginov formula of differentiation, we accurately compute the localization length ξ of s waves incident obliquely on stratified random media that exhibit short-range correlated dichotomous randomness in the dielectric permittivity. The random component of the permittivity is characterized by the disorder strength parameter σ2 and the disorder correlation length lc. Away from the critical angle, ξ depends on these parameters independently. However, precisely at the critical angle, we discover that for waves with wavenumber k, kξ depends on the single parameter klcσ2, satisfying a universal equation kξ≈1.3717klcσ2−1/3 across the entire range of parameter values. Additionally, we find that ξ scales as λ4/3 for the entire range of the wavelength λ, regardless of the values of σ2 and lc. We demonstrate that under sufficiently strong disorder, the scaling behavior of the localization length for all other incident angles converges to that for the critical incidence.

High Transmission in layered composite with graphene and hyperbolic metamaterials

The transmission characteristics are presented for the sandwich composite structure containing hyperbolic metamaterials (HMMs) and graphene. The numerical results show that the high transmittance (larger than 0.9) within a ultra wide incident angle range (0 ∼ 68.1°, 0 ∼ 75.7°) can be obtained by optimizing the chemical potential (μc=0.5,0.6eV) for both s-polarized and p-polarized waves under the certain incident frequency (30THz). Meanwhile, to acquire the transmission enhancement in a wide incident angle range, the thickness of HMMs and the number of graphene layers should also be chosen appropriately. Additionally, the broadband and wide-angle of the transmission enhancement for s-polarized and p-polarized waves can be acquired by adjusting the incident angles and frequencies, which has the potential application for bandpass and high-pass filters.

Using Hocker and Burns numerical method to analyze the dispersion properties of a planar waveguide with an exponentially graded-index core layer for s-polarized light

Although not realistic, the theory of step-index waveguide has been discussed in most published works. Electric and magnetic fields can be written as well-known functions such as exponential, sine and cosine functions. However, the index distribution of the most practical waveguides is better described as graded. Despite certain similarities, step-index and graded-index waveguide structures also have considerable differences. The characteristic equation of s-polarized wave propagating in a planar waveguide with an exponentially graded-index thin core layer is examined in this work using the Hocker and Burns numerical approach. This method utilizes the effective index method of analyzing waveguides with 2D confinement. It was efficiently applied to problems of channel waveguides formed by diffusion. The technique depends on finding the phase shift of the curved optical path in the graded index zone as stacked infinite thin layers. Three factors contribute to the total transverse phase shift: (1) film-cladding interface phase delay, (2) film-substrate interface phase delay, and (3) phase delay caused by the zigzag optical path of the guiding film. The findings revealed the following intriguing observations. The dispersion curves of the graded-index waveguide structure are in the normal shape in which the generalized guide index (GeGI) increases with the rise of the normalized frequency. At high values of the normalized frequency, the GeGI displays less dependence on it. The dispersion curves show cut-off thicknesses which increase for higher asymmetry measure values. A comparison between graded-index and step-index waveguide structures is carried out.

Quasi phase matched second order reflection and transmission coefficients

We report the study of reflection and transmission coefficients, when a S-polarized electromagnetic wave is used to excite a linear dielectric NID–nonlinear dielectric NID planar interface. Nonlinear medium in our study is of second harmonic generation type hence we only studied the second order reflectivity and transmittance characteristics. Wave propagation in NID mediums are modeled by using method of separation of variables in NID space and the solution of the nonlinear wave equation is obtained by using the quasi phase matching approximation. As a special case of the original geometry we also studied the changes in the behavior of the coefficients when EN–NID and MN–NID mediums are taken as reflected mediums. In all these cases impact of the non-linearity and noninteger dimensions are noted separately. We also report the specific ranges of the permittivities and permeability in which maximum amplitude of the coefficients can be achieved.

Probing the response of metals to low-frequency s-polarized evanescent fields

An experimental test for the response function of metals to the low-frequency s-polarized evanescent waves is proposed by measuring the lateral component of the magnetic field of an oscillating magnetic dipole spaced above a thick metallic plate. This suggestion is motivated by the fact that the Lifshitz theory using the Drude response function is in contradiction with high-precision measurements of the Casimir force performed at separations exceeding 150 nm. Analytic expressions for the lateral components of the magnetic field, which are fully determined by the s-polarized evanescent waves, are reported in terms of the reflection coefficients of the plate metal. Numerical computations are performed for the reasonable values of the experimental parameters for different models of the dielectric response. The resulting fields differ by the orders of magnitude depending on whether the Drude or plasma response function is used in computations. Thus, the measurement of the magnetic field will allow to discriminate between these two options. Possible applications of the obtained results are discussed.

One-Dimensional Photonic Crystals with Different Termination Layer Thicknesses and Very Narrow Bloch Surface Wave and Guided Wave Based Resonances for Sensing Applications

We demonstrate an efficient sensing of both gaseous and aqueous analytes utilizing Bloch surface waves (BSWs) and guided waves (GWs) excited on a truncated one-dimensional photonic crystal (1DPhC) composed of six TiO2/SiO2 bilayers with a termination layer of TiO2. For the gaseous analytes, we show that 1DPhC can support the GW excited by an s-polarized wave and the theoretical shift of the resonance wavelength is linear for small changes in the analyte refractive index (RI), giving a constant RI sensitivity of 87 nm per RI unit (RIU). In addition, for the aqueous analytes, the GW excited by s-polarized and BSW by p-polarized waves can be resolved and exploited for sensing applications. We compare two designed and realized 1DPhCs with termination layer thicknesses of 60 nm and 50 nm, respectively, and show experimentally the differences in their very narrow reflectance and phase responses. An RI sensitivity and figure of merit as high as 544.3 nm/RIU and 303 RIU−1, respectively, are obtained for the smaller thickness when both s- and p-polarized BSWs are excited. This is the first demonstration of both very deep BSW-based resonances in two orthogonal polarizations and a very narrow resonance in one of them.

Optical theorem of an infinite circular cylinder in weakly absorbing media

The conventional optical theorem cannot consider losses of host media. As a fundamental problem of light scattering, the generalized optical theorem of an infinite cylinder embedded in a weakly absorbing host is studied in this paper. Using the analytical way, we derive the generalized far-field and distance-independent extinction efficiencies per unit length of the cylinder under normally incident p- and s-polarized waves, which reduce to the conventional formulas in the transparent host media. For large cylinders, the increasing absorption of the host medium leads to an increasing amplitude of interference oscillation and the emergence of negative extinction, which is similar to that for spheres. Furthermore, the absorption of the host medium is proved to destroy the morphology-dependent resonance structure in extinction and suppress the electric field resonance inside the cylinder. For small cylinders in a weakly absorbing host medium, we present the conditions for negative extinction and quantitatively analyze the differences in extinction between the absorbing host medium and the nonabsorbing counterpart. It is found that the ratio of the extinction from the generalized theory to conventional formulas depends only on the refraction indices of the cylinder and the host medium. The results for small cylinders are rather sensitive to the state of polarization of the light. By illustrating the significant differences between the generalized optical theorem and the conventional theory with a specific case of a Ge cylinder in polyethylene, we show the non-negligible impacts of the absorption of the host media on the optical extinction of the cylinder for the two polarizations.

CHANGES IN ELECTROMAGNETIC WAVE POLARIZATION RESULTING FROM ITS REFLECTION AT A UNIAXIAL PLASMONIC METASURFACE ON TOP OF A DIELECTRIC LAYER

Subject and Purpose. The analysis of the electromagnetic waves’ polarizational transformations that may accompany their reflection from a metasurface is of considerable scientific and practical interest from the point of possibilities for improving characteristics of nanoelectronic and optical devices, and creating novel types of these. This work has been aimed at finding the conditions for efficient conversion of a p-polarized electromagnetic wave incident upon a uniaxial plasmonic metasurface at the boundary of a dielectric layer, into a wave of s-polarization. Methods and Methodology. The effects of conversion of p-polarized electromagnetic waves incident upon a uniaxial plasmonic metasurface, into s-polarized waves were explored through numerical modeling. The approach has allowed determining the wave frequencies and thicknesses of the dielectric layer best suitable for ensuring full conversion. Results. The presence of a uniaxial plasmonic metasurface on top of a dielectric layer can provide for full conversion of an incident p-polarized electromagnetic wave into a wave of s-polarization. As has been established, the effect takes place if the plane of incidence of the p-polarized wave makes an acute angle with the principal axis of the plasmonic metasurface. Another finding is that the full conversion is possible for a variety of permittivity values of the dielectric layer. Conclusions. The uniaxial plasmonic metasurface placed on a dielectric layer is characterized by unique reflective properties. It can have a noticeable impact on polarization of the p-polarized wave’s incident upon the layer. Dielectric layers provided with uniaxial metasurfaces can be used for creating optical and nanoelectronic devices of new types.

Enhanced terahertz emission from mushroom-shaped InAs nanowire network induced by linear and nonlinear optical effects

The development of powerful terahertz (THz) emitters is the cornerstone for future THz applications, such as communication, medical biology, non-destructive inspection, and scientific research. Here, we report the THz emission properties and mechanisms of mushroom-shaped InAs nanowire (NW) network using linearly polarized laser excitation. By investigating the dependence of THz signal to the incidence pump light properties (e.g. incident angle, direction, fluence, and polarization angle), we conclude that the THz wave emission from the InAs NW network is induced by the combination of linear and nonlinear optical effects. The former is a transient photocurrent accelerated by the photo-Dember field, while the latter is related to the resonant optical rectification effect. Moreover, the p-polarized THz wave emission component is governed by the linear optical effect with a proportion of ∼85% and the nonlinear optical effect of ∼15%. In comparison, the s-polarized THz wave emission component is mainly decided by the nonlinear optical effect. The THz emission is speculated to be enhanced by the localized surface plasmon resonance absorption of the In droplets on top of the NWs. This work verifies the nonlinear optical mechanism in the THz generation of semiconductor NWs and provides an enlightening reference for the structural design of powerful and flexible THz surface and interface emitters in transmission geometry.

Efficient Optical Sensing Based on Phase Shift of Waves Supported by a One-Dimensional Photonic Crystal.

Interferometric methods of optical sensing based on the phase shift of the Bloch surface waves (BSWs) and guided waves (GWs) supported by a one-dimensional photonic crystal are presented. The photonic crystal, composed of six SiO2/TiO2 bilayers with a termination layer of TiO2, is employed in the Kretschmann configuration. Under resonance condition, an abrupt phase change is revealed, and the corresponding phase shift is measured by interferometric techniques applied in both the spectral and spatial domains. The spectral interferometric technique employing a birefringent quartz crystal is used to obtain interference of projections of p- and s-polarized light waves reflected from the photonic crystal. The phase shifts are retrieved by processing the spectral interferograms recorded for various values of relative humidity (RH) of air, giving the sensitivity to the RH as high as 0.029 rad/%RH and 0.012 rad/%RH for the BSW and GW, respectively. The spatial interferometric technique employs a Wollaston prism and an analyzer to generate an interference pattern, which is processed to retrieve the phase difference, and results are in good agreement with those obtained by sensing the phase shift in the spectral domain. In addition, from the derivative of the spectral phase shifts, the peak positions are obtained, and their changes with the RH give the sensitivities of 0.094 nm/%RH and 0.061 nm/%RH for the BSW and GW, respectively. These experimental results demonstrate an efficient optical sensing with a lot of applications in various research areas.

Enhanced photonic spin Hall effect via singularity induced by destructive interference.

In this work, we report a simple and effective method for enhancing the photonic spin Hall effect (SHE) via singularity induced by destructive interference in an ultrathin uniaxial slab. Deriving from anisotropy, the incident angles corresponding to destructive interference for p- and s-polarized waves will be deviated, leading to an enhancement peak in transverse spin shift. Interestingly, by adjusting the thickness of slab, the destructive interference and the Brewster effect can act together. At this point, the photonic SHE exhibits great singularity, and the maximum transverse spin shift can approach about three times more than that of the Brewster effect acting alone. This Letter reveals the influence of the interference effect on photonic SHE in layered media and provides a simple way to achieve enhanced photonic SHE.

Terahertz time-domain ellipsometry with high precision for the evaluation of GaN crystals with carrier densities up to 1020\xa0cm\u22123

Gallium nitride (GaN) is one of the most technologically important semiconductors and a fundamental component in many optoelectronic and power devices. Low-resistivity GaN wafers are in demand and actively being developed to improve the performance of vertical GaN power devices necessary for high-voltage and high-frequency applications. For the development of GaN devices, nondestructive characterization of electrical properties particularly for carrier densities in the order of 1019 cm−3 or higher is highly favorable. In this study, we investigated GaN single crystals with different carrier densities of up to 1020 cm−3 using THz time-domain ellipsometry in reflection configuration. The p- and s-polarized THz waves reflected off the GaN samples are measured and then corrected based on the analysis of multiple waveforms measured with a rotating analyzer. We show that performing such analysis leads to a ten times higher precision than by merely measuring the polarization components. As a result, the carrier density and mobility parameters can be unambiguously determined even at high conductivities.

High performance liquid analyte sensing based on Bloch surface wave resonances in the spectral domain

In this paper, we report a design of a truncated one-dimensional photonic crystal (1DPhC) comprising six bi-layers of TiO2/SiO2 with a termination layer of TiO2 to realize a highly sensitive liquid analyte sensor utilizing Bloch surface wave (BSW) resonances in the spectral domain. We demonstrate that the BSW excitation shows up as a dip for both p- and s-polarized waves. Reflectance response for a p-polarized BSW is due to the spectral interference with maximum depth, and resonance thus obtained is comparable in magnitude with surface plasmon resonance (SPR). In the theoretical analysis, the spectral reflectance, phase difference and its derivative are determined for aqueous solutions of NaCl when the refractive index (RI) is changed in a range of 1.3330–1.3482. We revealed that the BSW resonances for the p-polarized wave give a sensitivity of 1602 nm per RI unit (RIU) and figure of merit (FOM) of 106 RIU−1, respectively. For an s-polarized BSW, they are increased to 1933 nm/RIU and 434 RIU−1, respectively. Moreover, the theoretical results are experimentally verified, and very good agreement is confirmed. The spectral responses for aqueous solutions of NaCl with the RI up to 1.3547 give for the p-polarized BSW a sensitivity of 2022 nm/RIU and FOM of 109 RIU−1, respectively, and using the spectral derivative of the BSW phase difference, the FOM is increased to 301 RIU−1. BSW based sensors with responses in both polarizations thus represent an effective alternative to SPR sensors with advantages including a higher FOM and mechanical robustness.

Highly Sensitive Salinity and Temperature Sensor Using Tamm Resonance

In this paper, a Tamm plasmon resonance-based sensor is theoretically studied to calculate the salinity of seawater as well as a temperature sensor based on photonic crystals. The transfer matrix method (TMM) is used to systematically study and analyze the reflected s-polarized electromagnetic waves from the sensing structure. The proposed structure composes of prism/Au/water/\({(\mathrm{S}\mathrm{i}/{\mathrm{S}\mathrm{i}\mathrm{O}}_{2})}^{N}\)/Si. The sensitivity, figure-of-merit, quality factor, and detection limit of the sensors are improved by optimizing the thickness of the seawater layer, incident angle, salinity concentration, and temperature. The proposed salinity sensor records a very high sensitivity of 8.5 × \({10}^{4}\) nm/RIU and quality factor of \(3\times {10}^{3}\), and a very low detection limit of \({10}^{-7}\) nm. Besides, the suggested temperature sensor achieves high sensitivity (from 2.8 to 10.8 nm/°C), high-quality factor of \(3.5\times {10}^{3}\), and a very low detection limit of \({3\times 10}^{-7}\) nm. These results indicate that the proposed sensor is a strong candidate for salinity and temperature measurements.

Tunable broadband angular selectivity for s-polarized terahertz incidences

While achieving broadband angular selectivity for p-polarized wave has been well studied, it is still challenging for s-polarized wave. The reason is that at high frequencies such as terahertz spectrum, the permeability of materials has always approached unity. Here, we propose a solution to implement broadband angular selectivity for s-polarized incidences by combining an effective anisotropic diamagnetic medium and a staggered photonic structure. The diamagnetic medium is constructed with periodically arranged metallic rings, exhibiting negligible frequency dispersion in an ultra-wide terahertz band. By incorporating temperature-dependent dielectric into staggered structure, a thermally tunable broadband angular selectivity system is presented, with an adjustable selective angle ranging from 0° to 40°. Full-wave simulations verify the effectiveness of the proposed approach, breaking through the polarization limitation of the existing angular selectivity technology. The proposed approach is simple, robust, and scalable from microwave to terahertz frequencies.

Strong spin–orbit interaction of photonic skyrmions at the general optical interface

Abstract Photonic skyrmions have applications in many areas, including the vectorial and chiral optics, optical manipulation, deep-subwavelength imaging and nanometrology. Much effort has been focused on the experimental characterization of photonic skyrmions. Here, we give an insight into the spin and orbital features of photonic skyrmions constructed by the p-polarized and s-polarized surface waves at an interface with various electric and magnetic properties by analyzing the continuity of chirality, energy flow and momentum densities through the electric and magnetic interface. The continuity of chirality density indicates that the photonic skyrmion has a property of the optical transverse spin. Most importantly, the continuity of energy flow and momentum densities results in four spin–orbit interaction quantities, which indicate the gradient of electric polarizability or permeability governs the spin–orbit interaction of photonic skyrmions and leads to the discontinuity and even the reversal of spin orientation through the optical interface. Our investigations on the spin–orbit properties of photonic skyrmions, which can give rise to the spin-dependent force and topological unidirectional transportation, is thorough and can be extended to other classical wave, such as acoustic and fluid waves. The findings help in understanding the spin–orbit feature of photonic topological texture and in constructing further optical manipulation, sensing, quantum and topological techniques.

Terahertz Nonreciprocal Isolator Based on Magneto-Plasmon and Destructive Interference at Room Temperature

A terahertz isolator is demonstrated for the THz nonreciprocal reflections in the magneto-optical microstructure composed of InSb and metasurface with a dielectric interlayer. In the Voigt magnetic field configuration, the reflectance of the p-polarization waves obliquely impinging on the InSb wafer exhibits high nonreciprocity, while the reflectance of the s-polarized wave is reciprocal. Based on the unique magneto-plasmonic modes on the InSb surface, the nonreciprocal reflection in this device can be enhanced by using the destructive interference between the direct reflection and the multiple reflections in the resonance cavity between the InSb and metasurface. After the optimization, the isolation power of the device exceeds 55 dB with the insertion loss of only −3.92 dB under a very weak magnetic field of 0.2 T at room temperature. More importantly, the introduction of the metasurface can reduce the operating frequency of the isolator from 2.434 THz to 2.136 THz. This low-loss, weak magnetic field, room temperature operating, and high isolation THz isolator shows its broad potential in THz application systems.

Near-field radiative heat transfer between nanowire-based dual uniaxial magneto-dielectric metamaterials

Over past several years, much attention has been paid on near-field radiation with super-Planckian heat flux due to resonant coupling of surface polaritons and non-resonant hyperbolic modes but mainly with non-magnetic materials. With nanowire-based magneto-dielectric metamaterials, this work theoretically investigates the near-field radiative heat transfer associated with both uniaxial magnetic and electric responses. Maxwell–Garnett effective medium theory is used to obtain the dual uniaxial effective permeability and permittivity of the magneto-dielectric metamaterials. With the fluctuational electrodynamics, multiple resonant and non-resonant modes associated with both magnetic and electric responses that spectrally enhance the radiative heat transfer, such as magnetic and electric hyperbolic modes, magnetic and electric surface polaritons, mu- and epsilon-near-pole modes, are identified and elucidated at different wave polarizations. Effects of filling ratio, magnetic and electric scattering rates, and vacuum gap distance are also studied, and it is found that the spectral and total heat fluxes of s-polarized waves, which are usually neglected for non-magnetic materials, are much enhanced and comparable with that of p-polarized waves. The results here will deepen the fundamental understanding in magneto-dielectric metamaterials and facilitate their applications in the area of near-field thermal radiation.

Effect of orientation on excitation of surface-plasmon-polariton waves guided by a columnar thin film deposited on a metal grating

The excitation of surface-plasmon-polariton (SPP) waves guided by a columnar thin film (CTF) deposited on a one-dimensional metallic surface-relief grating was studied employing the rigorous coupled-wave approach, when the grating plane, the plane of incidence, and the morphologically significant plane of the CTF are all different. The incident plane wave in this grating-coupled configuration could be either p- or s-polarized. The absorptance was plotted against the polar angle of incidence at a fixed value of the free-space wavelength, and absorptance peaks were correlated with the solution of the dispersion equation of the underlying canonical boundary-value problem for SPP waves. Both p-polarized and s-polarized plane waves can excite SPP waves, provided that either the plane of incidence and/or the morphologically significant plane of the CTF do not coincide with the grating plane. None, one, or multiple SPP-wave excitations are possible, depending on the orientations of the grating plane and the morphologically significant plane with respect to the plane of incidence. The direction of propagation of an SPP wave thus excited may not wholly lie in the plane of incidence.