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Due to the non-overlapping Reststrahlen bands, both type I and type II hyperbolic responses are available in hexagonal boron nitride (hBN), which can be used as the guiding medium or the cladding medium in the slab waveguide. The characteristics of guided waves in the slab waveguide with hBN are theoretically investigated, and the existence conditions of the guided and surface modes of waveguides in the two types of hyperbolic responses are analyzed by using the graphic method. It is shown that, in the type-I hyperbolicity of the hBN waveguide, both TE and TM guided modes are existent. In the type-II hyperbolicity, both the guided and surface modes are existent for TM guided waves; however, the guided and surface modes of TE polarization are absent. In addition, the propagation constant and the normalized power versus the thickness of waveguide are showed and the cutoff thickness and the power localization are discussed. [ABSTRACT FROM AUTHOR]

We consider the transverse electric (TE) surface plasmon polaritons (SPPs) supported by a graphene parallel plate waveguide bounded by Kerr-type nonlinear media in the mid-infrared and terahertz frequencies. Through theoretical analysis of the exact dispersion relations, we reveal the existence conditions of the even mode and odd mode of nonlinear TE SPPs in this system. To be specific, if the linear permittivity of the nonlinear cladding is larger than the permittivity of the core, it only supports the even mode and two branches of the dispersion curve exist. However, when the linear permittivity of the nonlinear cladding is smaller than the permittivity of the core, both even and odd modes can be supported. Moreover, it is found that the propagation constant of even and odd modes decreases with the increasing Fermi energy of graphene. [ABSTRACT FROM AUTHOR]

An ultra-high sensitivity graphene optical sensor based on the surface plasmon resonance (SPR) is proposed using the graphene-aluminum (Al)-graphene sandwich-like structure. Here, the graphene sheets are introduced for enhancing the SPR and preventing the oxidation. It is found that our proposed graphene optical sensor is 3.4 times more sensitive than the Al-based sensor without the graphene layers. We demonstrate that a higher sensitivity can be obtained at the short wavelength due to the increases of the sensitivity with the decreases of wavelength. Especially, the sensitivity can be enhanced marked by increasing the number of graphene layers, which is totally different from the previous graphenebased optical sensor where the sensitivity is often decreased with the increases of the number of graphene layers. [ABSTRACT FROM AUTHOR]

We theoretically demonstrate the perfect absorption phenomena in the hexagonal boron nitride (hBN) crystals in the mid-infrared wavelength ranges by means of critical coupling with a onedimensional photonic crystal spaced by the air. Different from the polymer absorbing layer composed by a metal-dielectric composite film, the hyperbolic dispersion characteristics of hBN can meet the condition of critical coupling and achieve the total absorption in the mid-infrared wavelength ranges. However, the critical coupling phenomenon can only appear in the hBN crystals with the type II dispersion. Moreover, we discuss the influence of the thickness of hBN, the incident angle, and the thickness and permittivity of the space dielectric on the total absorption. Ultimately, the conditions for absorption enhancement and the optimization methods of perfect absorption are proposed, and the design rules for a totally absorbing system under the different conditions are achieved. [ABSTRACT FROM AUTHOR]

Thermally tunable and omnidirectional terahertz (THz) photonic bandgaps in the one-dimensional photonic crystals composed of alternating layers of semiconductor material InSb and dielectric material SiO2 are studied theoretically. This photonic bandgap is strongly dependent on the lattice constants and the thickness ratio of the constituent InSb and SiO2 layers. It is found that the lower-order gap is invariant on the lattice constants, but the higher-order gaps are all sensitive to the lattice constants. Moreover, the band-edges of the higher-order gaps shift to lower frequency as the increasing thickness ratio. Additionally, the Gap II is also angle-independent, and the omnidirectional bandgap can occur in the terahertz range. Omnidirectional bandwidth for both polarizations is about 1.5 THz at 220 K. Most important of all, the omnidirectional bandgap can be tuned by controlling the external temperature, which results from the dependence of the semiconductor plasma frequency on the temperature. As the temperature increases, the upper and lower frequency limits of the Gap II shift to higher frequency and the bandwidth becomes narrow. [ABSTRACT FROM AUTHOR]

The band edge formalism of zero-average-index photonic band gap for the one-dimensional photonic crystals containing dispersion negative-index metamaterial is obtained. By adopting the band edge formalism, the upper and lower frequencies limits of the zero-average-index band gap are analyzed, and the results are in complete agreement with the results got by the projected band structure method. It is shown that the width and the band edge of the zero-average-index photonic band gap are significantly affected by the each constitutive parameter of the component materials of the one-dimensional photonic crystals. Based on the band edge formalism, new method of extending the zero-average-index photonic band gap has been presented by tuning the constitutive parameter of the component materials. Moreover, the conditions for zero width zero-average-index band gap are obtained. The realizability of tuning the constitutive parameter of the Drude dispersion metamaterial constructed by the nonresonant composite right/left-handed transmission structures is also discussed. [ABSTRACT FROM AUTHOR]

We propose a graphene/planar waveguide hybrid structure, and demonstrate total absorption in the visible wavelength range by means of attenuated total reflectance. The excitation of planar waveguide mode, which has strong near field enhancement and increased light interaction length with graphene, plays a vital role in total absorption. We analyze the origin and physical insight of total absorption theoretically by using an approximated reflectance, and show how to design such hybrid structure numerically. Utilizing the tunability of doped graphene, we discuss the possible application in optical modulators. We also achieve broadband absorption enhancement in near-IR range by cascading multiple graphene-waveguide hybrid structures. We believe our results will be useful not only for potential applications in optical devices, but also for studying other two-dimension materials. [ABSTRACT FROM AUTHOR]

We investigate theoretically the optical bistability of reflection at the interface between graphene and Kerr-type nonlinear substrates. We derive a simple procedure to calculate the nonlinear reflectivity with graphene, and discuss the influence of the graphene sheets on the hysteretic response of the TM-polarization reflected light. It is found that the bistable behavior of the reflected light can be electrically controlled via suitably varying the applied voltage on the graphene. In THz, the bistable thresholds can be lowered markedly by increasing the Fermi energy. However, in near-infrared frequency, it requires multiple graphene layers to exhibit significant influence on the bistable thresholds. [ABSTRACT FROM AUTHOR]