To find more simple and universal method to realize the topological photonic crystals (PCs), we use the fold effect of bands of PCs and the Su–Schrieffer–Heeger model. Through the change of structure parameters, a lattice can undergo the transformation from topologically trivial to nontrivial states. The fold effect of bands leads to the multiple topological edge bands, which increase the band width of topological states. Furthermore, the topological corner states can be formed in the designed structure.
To achieve a flexible and reconfigurable topological edge state waveguide, we construct a valley photonic crystal (VPC) with liquid crystal filled rods. The permittivity of the two inequivalent rods in a unit is determined through the external voltage, which leads to a VPC with different valley topological phases. The external voltage is controlled by the codes of “0” and “1” on a control panel. Through programming the codes, arbitrary paths of topological edge states are achieved. The results were demonstrated by field propagation simulations.
We propose a compound structure constructed by two magnetic cavities with parity-time (PT) symmetric configuration. Through the calculations based on transfer matrix, we find that the structure system has some unique properties that the usual PT symmetric structures do not have. The four incident conditions of the structure produce two sets of transmittance spectra and four different reflectance spectra in which the unusual amplification and absorption are shown. The huge amplification and absorption can be precisely tuned through the magnetic field. Furthermore, the amplification and absorption around the pole can be reversed through the change of incidence directions. Although the analysis of the scattering matrix shows that the transmission and reflection are not nonreciprocal, the diverse modulation ways (magnetic field and incidence directions) will make the structure more useful in the design of photonic switching and optical modulator.
In order to obtain reconfigurable topological photonic waveguides, we design a two-dimensional photonic crystal with compound triangular lattice. Through rotating the dielectric rods, we change the topological phase of the lattice and achieve the topological edge states. Through the rotation of rods, we divide the two-dimensional structure space into “0” and “1” blocks made of the topologically trivial and nontrivial lattices, respectively. Through programming the codes of “0” and “1,” we can realize diverse transport pathways of light flow. The controllable light pathways will play important role in the optical circuit. The programmable design results have been demonstrated through the simulations of electromagnetic wave transport.
The gas concentration can be detected through a parity-time (PT) -symmetry structure. The structure is constructed by placing a resonance cavity between two PT-symmetry Bragg reflectors. The cavity and some specific layers in the structure are filled with the air doped with another gas. The transmittance spectra of the structure are calculated by the transfer matrix method. The peak value of the defect mode is dependent on the concentration of the gas. The sensor detects the gas concentration by the transmittance of the defect mode, instead of the peak wavelength of the defect mode. The defect mode has a large peak value and high Q value because of the amplification effect of the PT-symmetry structure, which apparently enhances the sensor sensitivity.
In order to achieve tunable parity-time (PT) symmetry system, we design a PT-symmetry structure including magneto-optical material. We use the transfer matrix method to study the optical properties of the designed structure under the modulation of magnetic field. The structure system takes on twofold unidirectional properties, i.e., the reflectance and the transmittance are dependent on both the incidence direction and the incidence angle. The unique band-edge modes with the system have both enhanced reflectance and transmittance in one incidence direction or angle but lead to an absorption effect in the opposite incidence direction or angle. The reversal of magnetic field direction will all lead to the exchanging of the left band-edge modes and the right band-edge modes.
In order to obtain the waveguide of multiple functionalities, we design a coupled system of two unidirectional air waveguides and find it is a system of multiple modes through band calculations. Through numerical simulations, we also find that the mode excitation is dependent on the position of the source. With the same frequency the line source can excite either the even mode or the odd modes in one single waveguide or two waveguide just by changing the positions of the source. Such a system provides us the way to control the excitation of mode and obtain the waveguide modes with special applications.
Negative refractive-photonic crystal (NR-PC) lenses that can exceed the diffraction limit of focus resolution for imaging and target detection in the near field have gotten more and more special attention in recent years. Three flat lens groups with Ag defects based on NR-PC are designed, and the focusing imaging in the NR-PC three flat lens groups is concluded with the extension of Snell’s law, and the influence on the resolution for a target detection dynamic scanning scheme is simulated by using the finite difference time domain method. An optimal-doped structure with Ag defects is achieved by different simulation combinations. The refocusing resolution 0.18834λ is achieved in the optimal structure and there is approximately a 0.06806λ improvement in the refocusing resolution compared to those undoped with Ag (0.2564λ); it also possesses distinct smaller side-lobes than a single flat lens doped with Ag. This means the optimal detecting ability for the three NR-PC flat lens groups with Ag defects is more improved than that for a single undoped and doped with Ag. This is significant for the perfect imaging being achieved for a particle structure.
Nonreciprocal transmission is achieved through an optical prism coupling system composed of magneto-optical (MO) media. The transmission properties of the system are studied through the developed transfer matrix method for magnetic materials. The unusual result is that a tunable nonreciprocal resonance tunneling occurs if two MO cavities have reversal magnetization. The results are verified through an electromagnetic field simulation based on the finite element solver.
The characteristics of localized fields of doped photonic crystal fibers (PCFs) are studied by numerical simulation method in the paper. An interesting phenomenon is produced with the enhancement of stimulated radiation, which is the transmittivity being greater than one. And the numerical results show clearly the relation between the characteristics of localized fields, the abnormal group velocity in photonic band gaps and the negative imaginary component of the complex effective index of refraction of doped medium. Based on the relations the amplification of stimulated emission can be realized by introducing active impurities into the defect media of PCFs. Furthermore, the narrow transmission bands can be obtained by introducing line defects into the doped PCFs, which are used as channels in wavelength-division multiplexed (WDM) communication systems. And the doped PCFs can also be used to make optical amplifiers employed in dense WDM communication systems.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.