Temporally-topological defect modes in photonic time crystals.

In this paper, we investigate the properties of temporally-topological defect modes (TTDMs) (or temporally-topological interface states) in the topological photonic time crystal (PTC) systems. The PTC systems are constructed by the cascade of multiple sub-PTCs that possess temporal inversion symmetries and different topologies. The cases of two-, three-, and multiple-sub-PTC for the topological PTC system are studied. By transfer matrix method, we find that the TTDMs appear when the topological signs of the corresponding gaps in the sub-PTCs are different. The positions of TTDMs can be adjusted by changing the modulation strength of the refractive index, the time duration, and the period of the sub-PTCs. Moreover, the number of TTDMs is one less than the number of sub-PTCs. In addition, the robustness of the systems is also studied. We find that the topological PTC systems have good robustness, especially on the random configuration of the refractive index and time duration for the temporal slabs in the systems. Such research may provide a new degree of freedom for PTC applications, such as novel PTC lasers, tunable band-stop or band-suppression PTC filters, and many others, in the field of integrated photonic circuits for optical communications.

Compact ring resonators of silicon nanorods for strong optomechanical interaction.

Optomechanical interaction in microstructures plays a more and more important role in the fields of quantum technology, information processing, and sensing, among others. It is still a challenge to obtain a strong optomechanical interaction in a compact device. Here, we propose and demonstrate that compact ring resonators consisting of silicon nanorods can realize strong optomechanical interaction even surpassing that of most optical microcavities. The proposed ring resonators can well confine infrared optical waves by the quasi-bound states in the continuum. Meanwhile, each nanorod in the resonator acts as a mechanical resonator of GHz resonating frequency, thus realizing an optomechanical coupling rate of up to 1.8 MHz. We have found that the interaction area can be extended by increasing the number of nanorods while maintaining the optomechanical interaction strength. Finally, we have studied the influence of supporting structures for suspended nanorods on the optomechanical interaction properties. The proposed ring resonators of silicon nanorods offer a promising platform for the study of optomechanical interaction.

The Transmission Properties of One-Dimensional Photonic Crystals with Gradient Materials.

In this paper, we studied the transmission properties, including photonic band gap (PBG) and defect mode properties, of one-dimensional photonic crystals (1D PCs) consisting of gradient materials. When keeping the average refractive index of the gradient materials in the 1D gradient-material PCs (1D GPCs) the same as the index of the corresponding normal materials in the 1D normal-material PCs (1D NPCs), by transfer matrix method, we found that the complete 1D GPCs with high-index gradient materials benefit to achieve larger omni-PBG than that in 1D NPCs. In our high-index gradient material case, for TE(TM) wave, the optimal omni-PBGs in 1D GPCs with first- and second-order gradient materials are 38.6% (50.2%) and 15.9% (22.3%) larger than that in 1D NPCs; while for the optimal relative bandwidths of omni-PBG, the corresponding promotions are 41.1% (52.3%) and 16.1% (22.6%), respectively. In addition, when defective 1D GPCs have gradient-material defect, the position of defect modes can be adjusted by selecting proper parameters of the gradient materials. These types of research are useful for designing wide PBG devices and tunable narrow-band filters which have potential application in optical communication.

Chitin-rich heteroglycan from Sporothrix schenckii sensu stricto potentiates fungal clearance in a mouse model of sporotrichosis and promotes macrophages phagocytosis.

BACKGROUND: Fungal cell wall polysaccharides maintain the integrity of fungi and interact with host immune cells. The immunomodulation of fungal polysaccharides has been demonstrated in previous studies. However, the effect of chitin-rich heteroglycan extracted from Sporothrix schenckii sensu stricto on the immune response has not been investigated. RESULTS: In this study, chitin-rich heteroglycan was extracted from S. schenckii sensu stricto, and immunomodulation was investigated via histopathological analysis of skin lesions in a mouse model of sporotrichosis and evaluation of the phagocytic function and cytokine secretion of macrophages in vitro. The results showed that the skin lesions regressed and granulomatous inflammation was reduced in infected mice within 5 weeks. Moreover, heteroglycan promoted the fungal phagocytosis by macrophages and modulated the cytokine secretion. Heteroglycan upregulated TNF-α expression early at 24 h and IL-12 expression late at 72 h after incubation, which might result from moderate activation of macrophages and contribute to the subsequent adaptive immune response. CONCLUSIONS: Chitin-rich heteroglycan extracted from S. schenckii sensu stricto potentiated fungal clearance in a mouse model of sporotrichosis. Moreover, chitin-rich heteroglycan promoted fungus phagocytosis by macrophages and modulated cytokines secretion. These results might indicate that chitin-rich heteroglycan could be considered as an immunomodulator used in the treatment of sporotrichosis.

Elongated-Hexagonal Photonic Crystal for Buffering, Sensing, and Modulation.

A paradigm for high buffering performance with an essential fulfillment for sensing and modulation was set forth. Through substituting the fundamental two rows of air holes in an elongated hexagonal photonic crystal (E-PhC) by one row of the triangular gaps, the EPCW is molded to form an irregular waveguide. By properly adjusting the triangle dimension solitary, we fulfilled the lowest favorable value of the physical-size of each stored bit by about µ5.5510 µm. Besides, the EPCW is highly sensitive to refractive index (RI) perturbation attributed to the medium through infiltrating the triangular gaps inside the EPCW by microfluid with high RI sensitivity of about 379.87 nm/RIU. Furthermore, dynamic modulation can be achieved by applying external voltage and high electro-optical (EO) sensitivity is obtained of about 748.407 nm/RIU. The higher sensitivity is attributable to strong optical confinement in the waveguide region and enhanced light-matter interaction in the region of the microfluid triangular gaps inside the EPCW and conventional gaps (air holes). The EPCW structure enhances the interaction between the light and the sensing medium.

Polarization-Independent Circulator Based on Composite Rod of Ferrite and Plasma in Photonic Crystal Structure.

We propose a type of polarization-independent circulator based on a composite rod of ferrite and plasma materials in a two-dimensional photonic crystal (PhC) slab. Only one composite rod was set at the center of the structure to provide circulation for both TE- and TM-polarized waves. Additionally, to improve the performance of the circulator, three additional rods were inserted to improve the coupling condition between the center magneto-optical microcavity and the corresponding waveguides. Finite element method was used to calculate the characteristics of the structure and the Nelder-Mead optimization method was employed to obtain the optimum parameters. The results show that a low insertion loss (~0.22 dB) and high isolation (~14 dB) can be achieved in our structure for waves of both TE and TM polarizations. The idea presented here may be useful for designing compact polarization devices in large-scale integrated photonic circuits.

Elastic Waves in Curved Space: Mimicking a Wormhole.

Transformation optics (TO) can be used to investigate nontrivial spacetime structures with inhomogeneous materials. However, the extreme curvature and large refractive indices make the implementation of a wormhole challenging. By considering flexural waves on a curved plate with geometric curvature, the stringent material requirement can be relaxed, and we demonstrate a two-dimensional analog of a wormhole using homogeneous materials within a curved laboratory frame. TO is used to understand wave propagation in such a curved space. This curved elastic space approach allows us to investigate not only geodesics but also wave redirection, tunneling, and virtual caustics of the wormhole, and will be useful to develop curvature-driven wave front shaping in general.

Unidirectional emission in an all-dielectric nanoantenna.

All-dielectric nanoantennas are a promising alternative to plasmonic optical antennas for engineering light emission because of their low-loss nature in the optical spectrum. Nevertheless, it is still challenging to manipulate directional light emission with subwavelength all-dielectric nanoantennas. Here, we propose and numerically demonstrate that a hollow silicon nanodisk can serve as a versatile antenna for directing and enhancing the emission from either an electric or magnetic dipole emitter. When primarily coupled to both electric and magnetic dipole modes of a nanoantenna, broadband nearly-unidirectional emission can be realized by the interference of two modes, which can be spectrally tuned via the geometric parameters in an easy way. More importantly, the emission directions for the magnetic and electric dipole emitters are shown as opposite to each other through control of the phase difference between the induced magnetic and electric dipole modes of the antenna. Meanwhile, the Purcell factors can be enhanced by more than one order of magnitude and high quantum efficiencies can be maintained at the visible spectrum for both kinds of dipole emitters. We further show that these unidirectional emission phenomena can withstand small disorder effects of in-plane dipole orientation and location. Our study provides a simple yet versatile platform that can shape the emission of both magnetic and electric dipole emitters.

Source Illusion Devices for Flexural Lamb Waves Using Elastic Metasurfaces.

Inspired by recent demonstrations of metasurfaces in achieving reduced versions of electromagnetic cloaks, we propose and experimentally demonstrate source illusion devices to manipulate flexural waves using metasurfaces. The approach is particularly useful for elastic waves due to the lack of form invariance in usual transformation methods. We demonstrate compact and simple-to-implement metasurfaces for shifting, transforming, and splitting a point source. The effects are measured to be broadband and robust against a change of source positions, with agreement from numerical simulations and the Huygens-Fresnel theory. The proposed method is potentially useful for applications such as nondestructive testing, high-resolution ultrasonography, and advanced signal modulation.

All-dielectric hollow nanodisk for tailoring magnetic dipole emission.

We propose a silicon hollow nanodisk for enhancing magnetic dipole (MD) emission. The Purcell factor can be more than 300, which is one order of magnitude larger than the silicon nanosphere case. It is demonstrated that the silicon hollow nanodisk resembles the function of an azimuthally polarized beam for tailoring the magnetic and electric dipole (ED) emission. It is shown that MD emission can be significantly enhanced, while ED emission will be suppressed when emitters are located in the hollow of the nanodisk. The dependence of the Purcell factor on the geometry parameters is also studied. Our results might facilitate the on-chip engineering of magnetic light emission.

Constructing metamaterials from subwavelength pixels with constant indices product.

We investigate a two-dimensional metamaterial template constructed from different pixels through a conservation law of effective indices: If the product of refractive indices along the principal axes is invariant for different anisotropic materials in a two-dimensional space, the product of indices of the effective medium remains constant after mixing these materials. Such effective media of constant indices product can be implemented using metamaterial structures. The orientation of the metamaterial structure in a single pixel controls the direction of the principal axis of the effective medium. Different pixels are assembled into an array to obtain reconfigurable anisotropy of the effective medium. These considerations would be useful for constructing reconfigurable metamaterials and transformation media with area-preserving maps.

Manipulating polarization and impedance signature: a reciprocal field transformation approach.

We introduce a field transformation method for wave manipulation based on completely reciprocal and passive materials. While coordinate transformations in transformation optics (TO) change the size and shape of an object, field transformations give us direct control on the impedance and polarization signature of an object. Using our approach, a new type of perfect conductor can be realized to completely convert between transverse electric and transverse magnetic polarizations at any incidence angles and a perfect magnetic conductor of arbitrary shape can be mimicked by using anisotropic materials. The approach can be further combined with TO to enhance existing TO devices. For example, a dielectric cylinder can become completely transparent for both polarizations using bianisotropic materials.

Space-coiling metamaterials with double negativity and conical dispersion.

Metamaterials are effectively homogeneous materials that display extraordinary dispersion. Negative index metamaterials, zero index metamaterials and extremely anisotropic metamaterials are just a few examples. Instead of using locally resonating elements that may cause undesirable absorption, there are huge efforts to seek alternative routes to obtain these unusual properties. Here, we demonstrate an alternative approach for constructing metamaterials with extreme dispersion by simply coiling up space with curled channels. Such a geometric approach also has an advantage that the ratio between the wavelength and the lattice constant in achieving a negative or zero index can be changed in principle. It allows us to construct for the first time an acoustic metamaterial with conical dispersion, leading to a clear demonstration of negative refraction from an acoustic metamaterial with airborne sound. We also design and realize a double-negative metamaterial for microwaves under the same principle.

Extreme acoustic metamaterial by coiling up space.

We show that by coiling up space using curled perforations, a two-dimensional acoustic metamaterial can be constructed to give a frequency dispersive spectrum of extreme constitutive parameters, including double negativity, a density near zero, and a large refractive index. Such an approach has band foldings at the effective medium regime without using local resonating subwavelength structures, while the principle can be easily generalized to three dimensions. Negative refraction with a double negative prism and tunneling with a density-near-zero metamaterial are numerically demonstrated.

Artificial Kerr-type medium using metamaterials.

We investigated an artificial Kerr-medium realized by actuated THz metamaterials. Instead of directly applying E-field inside the medium, we use micromechanical systems actuated by voltage to tune the phase shift. We established that the combined system can have a relationship between the phase shift and the voltage similar to a Kerr cell. A metamaterial Kerr-cell is designed to modulate the transmission phase difference by 0.99°/V² which is much stronger than natural Kerr crystals. It is attributed to the mechanical tunability of metamaterials with high indices in two orthogonal directions. A Lorentzian model is used in explaining the artificial Kerr cell.

Scaling two-dimensional photonic crystals for transformation optics.

We propose a method to manipulate Bloch waves in curved photonic crystals for achieving transformation optical devices in two dimensions. Instead of starting from an effectively homogeneous medium, we transform a regular photonic crystal into a curved one in the physical space. A scaling law is established to construct the curved photonic crystal with similar unit cells and different scales, which is made of dielectrics only. A wave compressor and a bending waveguide are designed using dielectrics with indices only from 1 to 4. The approach will be useful in constructing low-loss transformation media requiring small indices, or large anisotropy which is particularly difficult for E-polarization using the conventional effective medium approach.

Remote control of light behavior by transformation optical devices.

Based on the transformation optics, a general method of light-behavior remote control is proposed. From this method, the important coefficients of a cavity, i.e. the quality factor Q and the resonant frequency ?0 could be tuned in a wide range by a transformation optical device in distance, so that the light behavior can be remotely controlled. To confirm this original idea, three schemes, such as, the remote modification of output energy current from an absorptive cavity, the remote control of lasing behaviors, and the remote tuning of the resonant frequency or photonic band-gap, are presented and confirmed by our numerical simulations based on finite-difference time-domain and finite-element methods. With some special advantages, e.g., without physical change or damage of original devices, large tuning range, and easily to hide the controller, this method could be widely used in optical/photonic or electromagnetic designs in the future.