Rahman Chowdhury Mahdy

Negative Refraction with Superior Transmission in Graphene-Hexagonal Boron Nitride (hBN) Multilayer Hyper Crystal

In this article, we have theoretically investigated the performance of graphene-hexagonal Boron Nitride (hBN) multilayer structure (hyper crystal) to demonstrate all angle negative refraction along with superior transmission. hBN, one of the latest natural hyperbolic materials, can be a very strong contender to form a hyper crystal with graphene due to its excellence as a graphene-compatible substrate. Although bare hBN can exhibit negative refraction, the transmission is generally low due to its high reflectivity. Whereas due to graphene’s 2D nature and metallic characteristics in the frequency range where hBN behaves as a type-I hyperbolic material, we have found graphene-hBN hyper-crystals to exhibit all angle negative refraction with superior transmission. Interestingly, superior transmission from the whole structure can be fully controlled by the tunability of graphene without hampering the negative refraction originated mainly from hBN. We have also presented an effective medium description of the hyper crystal in the low-k limit and validated the proposed theory analytically and with full wave simulations. Along with the current extensive research on hybridization of graphene plasmon polaritons with (hyperbolic) hBN phonon polaritons, this work might have some substantial impact on this field of research and can be very useful in applications such as hyper-lensing.

Robust Optical Fiber Using Single Negative Metamaterial Cladding

We introduce the idea of optical fibers made up of single negative metamaterial photonic crystal cladding with zero effective phase bandgap. Fiber characteristics are analyzed both at sub-wavelength and non sub-wavelength crystal dimension by varying cladding thickness and core radius. We find that in both cases they are robust with respect to incident angle, polarization of the light, crystal constant, and cladding irregularities. The fiber is found to behave like a step index fiber but the guided modes are leaky like Bragg fiber. It is shown that a fixed cladding thickness produces fixed loss around impedance matching frequency irrespective of crystal constant.

Broad angle negative refraction in lossless all dielectric or semiconductor based asymmetric anisotropic metamaterial

In this article, it has been theoretically shown that broad angle negative refraction is possible with asymmetric anisotropic metamaterials (AAMs) constructed by only dielectrics or lossless semiconductors at the telecommunication and relative wavelength range. Though natural uniaxial materials can exhibit negative refraction, the maximum angle of negative refraction and critical incident angle lie in a very narrow range. This problem can be overcome by our proposed structure. In our structures, negative refraction originates from the highly asymmetric elliptical iso-frequency. This is artificially created by the rotated multilayer sub-wavelength dielectric or semiconductor stack, which acts as an effective AAM. This negative refraction is achieved without using any negative permittivity materials such as metals. As we are using simple dielectrics, fabrication of such structures would be less complex than that of the metal based metamaterials. By considering the time harmonic field incidence, negative refraction has been demonstrated for two dimensional bi-dielectric structures for TM polarization with realistic parameters. Our proposed ideas have been validated by the full wave simulations considering both the effective medium approach and realistic structure model. This device might find some important applications in photonics and optoelectronics.

Single Negative Metamaterial-Based Hollow-Core Bandgap Fiber With Multilayer Cladding

We propose a single negative metamaterial (MTM)-based hollow-core fiber with multilayer cladding employing zero-effective-phase bandgap for optical confinement in this paper. The cladding is formed from a ternary 1-D photonic crystal (T-1DPC) unit cell, which is basically a Mu-negative material sandwiched by different Mu-negative and Epsilon-negative materials. We demonstrate its capability for broadband transmission by numerically simulating and analyzing the photonic bandgap (PBG) and the modal loss characteristics. The results show that the T-1DPC-based cladding can effectively broaden the PBG. Compared with that for the binary 1-D photonic crystal unit cell-based fiber, the radiation loss for the T-1DPC-based fiber can be reduced by three orders of magnitude over most of the PBG range for equal number of unit cells. This MTM fiber, depending on the operating wavelength, shows surface plasmon guidance or classical wave guidance or both simultaneously. We also investigate the effect of variations in the design parameters and material absorption on the wave guidance of this fiber.

Tunable slow light with graphene based hyperbolic metamaterial

Slow light has always been a topic of extreme interest for researchers and scientists in order to utilize the full potential of light in switching, memory devices and in quantum optics. However, slow light phenomena and its potential applications in switching and memory devices by tunable graphene based hyperbolic metamaterial have not still been introduced in literature. Here we theoretically propose and numerically analyze a graphene based tunable slow light device from the concept of controlling the group velocity of light in hyperbolic metamaterials. In THz range, graphene-dielectric stack can behave as hyperbolic metamaterials and hyperbolic metamaterials can demonstrate slow light phenomena while being cladded by air. By utilizing the tunability option of graphene, proposed devices can be made tunable, which is the most important criteria to manage the full advantage of slow light. It ultimately paves a fully new way to find novel applications in photonic switch, optical buffers and memory devices. Interestingly, in such graphene based devices, voltage will play a vital role to control the group velocity of light from slow to fast and the carriers are photons instead of electrons.

Control of reflection through epsilon near zero graphene based anisotropic metamaterial

In graphene dielectric multilayer structure, a very interesting phenomena such as epsilon near zero property rises naturally. However, this epsilon near zero property (along with the proper control of chemical potential and gate voltage) of graphene multi-layer stack has not been used so far to make novel photonic switches. In this article, we have shown theoretically that in graphene-dielectric stack, which acts as an anisotropic metamaterial, full control of reflection and so transmission of light at a specific wavelength or frequency can be controlled very simply by external gate voltage. This external voltage tunes the chemical potential and so the parallel permittivity of the anisotropic structure. Our theoretical prediction may pave the way to novel voltage control photonic logic switches, which may play as an intermediate solution before entering into all optical commercial switches (as current silicon and electron based CMOS technology is facing a dead end).

Conceptual and practical realization of reduced size multi-band circular microstrip patch antenna loaded with MNG metamaterial

In this paper, an MNG metamaterial loaded circular microstrip patch antenna has been reported. This antenna not only shows multi-band performance but also provides maximum possible size reduction (35%) with realizable gain performance. Achieving triple band performance was made possible by modifying TMδ10(0<;δ<;1) mode (using μ-negative metamaterial) along with TM210 mode modification with symmetrical slots. At first, simulation performance of this antenna on the basis of proper design algorithm [1] has been shown. Later, with appropriate choice of parameters, a practical modeling of MNG metamaterial using helices that can be used to fabricate this sort antenna, has been demonstrated for verification. In [2] three helices were used to fabricate MNG metamaterial, but here it is shown that one helix provides better directivity instead of three. This will certainly minimize fabrication complexity in MNG metamaterial.

A novel miniaturized triple-band antenna

In this work we have theoretically analysed a bi-layer waveguide placing a magnetic metamaterial on Double Positive (DPS) material and then implemented the waveguide as substrate for microstrip patch antenna and achieved 30% size reduction. This patch antenna operates at three different bands and the radiation gain at each band is quite high with a moderate bandwidth of each band. These bands have potential applications in WLAN and WiMAX devices. Flexibility for band tuning is possible in this antenna.

Highly Directive Epsilon Negative Metamaterial-Loaded Circular Patch Antenna for Triple-Band Performance

Based on the idea of additional modified mode(s) (Mahdy et al., IEEE Antennas Wirel Propag Lett 10:869–872, 2011), metamaterial-loaded triple-band rectangular patch antennas have been reported in (Mahdy et al., Prog Electromagn Res Lett 21:99–107, 2011). But the idea of additional modified mode(s) to achieve multiband performance in circular patch antenna has not been reported so far. Recently we have reported the idea of “additional modified mode(s)” in circular shaped patch antennas loaded with metamaterials to achieve multiband performance (Ferdous et al., IET Microw Antennas Propag J 7:768–776, 2013). On the basis of the design algorithm reported in (Ferdous et al., IET Microw Antennas Propag J 7:768–776, 2013), in this chapter, a triple-band circular patch antenna loaded with ENG metamaterial has been proposed. The proposed antenna not only provides good resonance, but also ensures satisfactory radiation performances (directivity, radiation efficiency, and gain) for all the three bands. Achieving a triple-band performance has been possible by modifying TM δ10(1 < δ < 2) mode (using e negative metamaterial) along with TM210 mode modification (due to symmetrical slotting). It is expected that this sort of antenna will be really effective in multiband highly directive applications, especially in satellite communication.

Achieving tetra band performance in simple dielectric and in metamaterial filled patch antennas

In this contribution, we have proposed a robust technique to achieve tetra-band performance in both conventional dielectric (elliptical shape) and also metamaterial loaded (rectangular shape) patch antennas. Incorporation of symmetric slots over the patch in both type of antennas have been shown here by using the concept of additional modified modes and perturbation approach. At first, we have shown that if and only if, elliptical shape patch antenna is properly optimized along with symmetrical slots over metallic patch, it is possible to achieve satisfactory four- band performance without the aid of any complex procedure currently present in literature. Later, we have reported a compact metamaterial loaded tetra band rectangular patch antenna to achieve extremely high gain and directivity performances for all the four bands, which may not be possible with conventional dielectric antennas.