Polaritonic Photonic Crystals Research Articles

Analysis of photonic bandgap structure for a polaritonic photonic crystal in negative-index region

A photonic bandgap (PBG) structure for a polaritonic photonic crystal (PPC) containing lithium tantalate (LiTaO3) in the negative refractive index (NRI) region has been theoretically investigated. This region consists of a narrow frequency range of anomalous dispersion and a wide range of normal dispersion. The result shows that such PPC has a multiple-PBG structure with one gap located in the anomalous dispersion region and others in the normal dispersion region. PBG in the anomalous region is invariant with filling factor and scaling. This gap is further proven to be independent of the angle of incidence for both TE and TM nodes, leading to the existence of an omnidirectional gap. BPGs within the normal dispersion region are, however, strongly affected by the above three factors, especially for gaps near the upper limit of the NRI region.

Bandgap generation and enhancement in polaritonic cylinder square-lattice photonic crystals

A theoretical study based on the finite-difference time-domain method is presented to investigate the maximum possible extent of the lowest complete structural bandgap in a two-dimensional polaritonic photonic crystal and the corresponding slab structure consisting of polaritonic cylinders placed on a square lattice in an air matrix. Three different polaritonic materials, which are classified according to their polaritonic strength and high-frequency dielectric constant, are chosen to calculate the corresponding photonic band structures. Our results reveal a considerable amount of complete structural bandgap generation and enhancement in terahertz parts of the spectrum by optimizing both the lattice constant and the filling fraction. Gap generation and enhancement occur over spectral regions which are completely below the polariton resonance of the materials for both polarizations. One noticeable result shows that in contrast to the corresponding structures made of non-dispersive dielectric cylinders, a large complete structural gap is generated in the polaritonic photonic crystal made of ionic cylinders having a small high-frequency dielectric constant but robust photon–phonon interaction through the proper choice of design parameters.

Switching in Polaritonic–Photonic Crystal Nanofibers Doped with Quantum Dots

We have studied the acousto-optic effect in polaritonic nanofibers made by embedding a cylindrical polaritonic nanowire within a photonic crystal. Here the nanowire consists of either a phonon-polaritonic or an exciton-polaritonic material. The nanowire is doped with ensemble of noninteracting quantum dots. Quantum dots interact with the nanofiber via the exciton-polariton interaction. It is found that for the certain acoustic strain intensity the nanofiber has a localized-to-delocalized polariton transition similar to the metal-to-insulator transitions in doped semiconductors. It is also found that nanofiber has a transparent state due to the exciton-bound polariton coupling. The transparent state can be switched ON or OFF by the external acoustic strain intensity. These are very useful discoveries that can be used to fabricate new types of polaritonic nanoswitches and nanosensors.

Two-dimensional polaritonic photonic crystals as terahertz uniaxial metamaterials

Emerging technologies such as quantum cascade lasers enabled the investigation of the most interesting, yet very little explored, THz part of the electromagnetic (EM) spectrum. These THz sources impose a dire need for novel materials suitable for optical components at such frequencies, as traditional visible optics is not appropriate for THz. Here, we explore two-dimensional (2D) photonic crystals (PCs) with either or both constituents made of polar materials, having a polariton gap within or close to the THz regime. Our objective is to create polaritonic composites that behave as extraordinary effective homogeneous uniaxial media, with flexibly engineered EM wave dispersion and high transmissivity in the THz frequency region. Accordingly, it is most important to be able to identify when 2D composites act as effective bulk uniaxial media. Clearly, deviation from standard effective medium predictions does not necessarily imply bulk effective medium picture breakdown. We developed a reliable criterion which provides a clear angular signature of effective medium behavior in 2D composites, even in the presence of high losses. Relying on this criterion, we characterized polar-dielectric and polar-polar PC composites acting as homogeneous uniaxial metamaterials for any arbitrary incident angle. We selected certain cases of effective metamaterial composites which demonstrate a polarization filter behavior. In particular, our resultssuggestthatanunpolarizedsourcewillleadtoeitheranS-oraP-polarizedwavejustbychangingtheangle of incidence of the impinging wave, irrespective of the thickness of the composite metamaterial. Furthermore, we show that transmission through a LiF/NaCl composite can be as high as 20%, even though transmission through an identical slab made from either of the two polar constituents would be next to zero. We analyze and discuss the physical origins underpinning such extraordinary angular transmission profile of these metamaterial composites. Our results suggest that appropriate mixing of polar materials with each other or with high-index dielectrics provides a route to making advanced photonic materials that are highly attractive for THz optical components.

Acousto-optics studied in polaritonic photonic crystals

We have studied the acousto-optic effect on the photon transmission and the spontaneous emission in polaritonic photonic crystal. We have considered that photonic crystals are fabricated from polaritonic materials such as GaP, MgO, ${\text{LiNbO}}_{3}$, and ${\text{LiTaO}}_{3}$. A two-level quantum dot is doped in a polaritonic crystal to study the decay rate of the spontaneous emission. The decay rate of quantum dots, band structure, and photon transmission coefficient have been calculated. It is found that band-gap width and the decay rate of quantum dots depends strongly on the high-frequency dielectric constant of the polaritonic crystals while the photonic band edges vary inversely by the ratio of longitudinal- to transverse-optical phonon energies. The spontaneous decay rate of the quantum dot can be controlled by the external strain field. This finding is significant because it is well known that the spontaneous emission is source of undesirable noise in different types of electronic and optical devices. Finally, we have also found the system can be switched from transmitting state to reflecting state by applying an external strain field. These are distinct and interesting results and can be used to fabricate new types of photonic couplers and fibers which in turn can be used to fabricate all photonic switches.

Chiral properties in a two-dimensional chiral polaritonic photonic crystal

We theoretically investigated a format of two-dimensional dielectric-chiral photonic crystal structure that is composed of a dispersive chiral medium embedded in a dielectric background. The photonic band structure shows distinctive dispersion relationship for circularly polarized electromagnetic waves, leading to a number of intriguing wave properties, namely chirality dependent “node switching,” polarization sensitive transmission and handedness dependent mode localization. All of these effects are attributed to the strong interaction between the local resonant modes around the dispersive chiral rods and the Bloch modes of the bulk waves. The chirality dependent properties can find tremendous applications in polarization based optoelectronics devices and rapid separation of chiral compounds in pharmaceutical industry.

Negative effective permeability in metal cluster photonic crystal

We report a new metamaterial design made of a periodic array of metal nanowire clusters. For transverse-electric polarization, the metal nanowire supports an electric-dipole-like Mie resonance. When the nanowires are arranged into a regular array with sufficiently small spacing, the array exhibits a resonant behavior in effective permittivity. Furthermore, when the nanowires are arranged into a finite size cluster, they can support a magnetic Mie resonance in which magnetic field is strongly localized inside the cluster. Array of such clusters with sufficiently small spacing can then exhibit a resonant behavior in effective permeability. When the magnetic resonance is strong enough, permeability can become negative. The mechanism of producing negative permeability is similar to the ferroelectric and polaritonic photonic crystals but the metal cluster photonic crystal can exhibit stronger magnetic activity at optical frequencies. The availability of extensive synthesis and fabrication techniques for metal nanostructures makes the metal cluster photonic crystal a promising metamaterial platform for optical frequency operation.

Band structure and coupled surface states in one-dimensional photonic crystals

We study a one-dimensional photonic crystal with a complex, frequency-dependent dielectric function. This frequency dependency is either given by the Drude or a Lorentzian dielectric function. In the metallic case an omni-directional metallic bandgap is observed whose size can be controlled by geometric parameters. For the polaritonic photonic crystal one obtains a complete bandgap around the transversal optical plasma frequency. In the last section parallel propagation in such systems is studied: in particular, the surface states in a polaritonic photonic crystal exhibit very interesting features such as negative group velocity.

Applications of the expanded basis method to study the behavior of light in polaritonic photonic crystal slab with losses

We apply the expanded basis method (EBM) to investigate the behavior of light in polaritonic photonic crystal (PC) slabs with losses. The influence of losses on transmissivity is studied. It is found that the transmissivity is significantly lowered with the increase of losses, in particular, it is abruptly decreased in the vicinity of transverse-optical-phonon frequency. The electromagnetic (EM) dissipation is mainly dominated by the imaginary part of dielectric constant of PC. The larger the imaginary part of the dielectric constant, the more the EM energy depletion is. The variation of EM dissipation with the number of period layers in the PC slab is approximately linear or oscillatory increase with the number of period layers.

Theoretical analysis of three-dimensional polaritonic photonic crystals

The optical properties of three-dimensional photonic crystals consisting of polaritonic spheres in a dielectric host medium are studied by means of accurate numerical calculations using the on-shell layer-multiple-scattering method. The transmission characteristics of finite slabs of these materials are related to the complex band structure of the corresponding infinite crystals and the effect of dissipative losses is examined.

Negative effective permeability in polaritonic photonic crystals

We find that a two-dimensional photonic crystal composed of polaritonic materials behaves as an effective medium with negative permeability in the micron wavelength range. The resonance in μeff is due to the large values of ε(ω) attained near the transverse phonon frequency ωT. The minimal wavelength for achieving an effective permeability less than −1 in a LiTaO3 crystal, obtained by optimizing the rod size and the lattice constant, is around 12μm, a range previously inaccessible using dielectric metamaterials. For certain dissipation levels, we find that other polaritonic media also exhibit a resonant effect with μeff<−1 for wavelengths ranging from 2 to ∼100μm.

Nature of lossy Bloch states in polaritonic photonic crystals

We examine the effects of absorption losses in photonic crystal structures composed of polar materials which exhibit transverse phonon-polariton excitations. In order to explore the Bloch states of such a system, we study the two subspaces of the complete set of complex (k ,v) states consisting of either real frequency, accessible through a frequency-domain method, or real-wave vector, which we determine using a frequency-dependent time-domain method. We describe analytically the conditions under which the imaginary frequency component of a real-wave-vector state is related to the imaginary-wave-vector component of a real-frequency state through a factor of the group velocity, and we present a one-dimensional lossy crystal as an example that satisfies these constraints. We also discover that the real-frequency states of a two-dimensional crystal bear little resemblance to the class of real-wave-vector states, due to interplay between the prohibitively large spatial decay of the states near the edge of the Brillouin zone and the existence of metalliclike states localized to the surrounding ambient dielectric region with much lower levels of loss. We then put these results in the context of possible experiments, including reflection of a plane-wave from a slab structure, and discuss the viability for observing the node switching and flux expulsion phenomena previously discovered in lossless crystals.

Erratum: Field Expulsion and Reconfiguration in Polaritonic Photonic Crystals [Phys. Rev. Lett.90, 196402 (2003)

Erratum: Field Expulsion and Reconfiguration in Polaritonic Photonic Crystals [Phys. Rev. Lett.<b>90</b>, 196402 (2003)

Field expulsion and reconfiguration in polaritonic photonic crystals.

We uncover a rich set of optical phenomena stemming from the incorporation of polar materials exhibiting transverse phonon polariton excitations into a photonic crystal structure. We identify in the frequency spectrum two regimes in which the dielectric response of the polaritonic medium can induce extreme localization of the electromagnetic energy. Our analysis of the effect of polarization and the interaction between the polariton and photonic band gaps on the Bloch states leads to a pair of mechanisms for sensitive frequency-controlled relocation and/or reconfiguration of the fields.