The light propagation characteristics through the annular coupled-resonator cavity waveguides are systematically analyzed by the finite-difference time-domain (FDTD) method. It is found that this kind of waveguide has more minbands owing to the increasing of the cavity’s size, compared with the traditional line-typed coupled-resonator waveguide. The group velocity of light propagation can be reduced for a further degree when the adjacent annular cavities are interlaced in the perpendicular direction, and a group velocity about 0.00067c (c is the light speed in vacuum) can be obtained.
We have designed and fabricated two types of two-port resonant tunneling filters with a triangular air-hole lattice in two-dimensional photonic crystal slabs.In order to improve the filtering efficiency,a feedback method is introduced by closing the waveguide.It is found that the relative position between the closed waveguide boundary and the resonator has an important impact on the dropping efficiency.Based on our analyses,two different types of filters are designed.The transmission spectra and scattering-light far-field patterns are measured,which agree well with theoretical prediction.In addition,the resonant filters are highly sensitive to the size of the resonant cavities,which are useful for practical applications.
Self-collimation characteristics of the two-dimensional square-lattice photonic crystal(PC) consisting of metal rods immersed in silicon are studied by the finite-difference time-domain method.The Drude dispersion model is adopted to describe the metal rod,and the self-collimation behaviours of the near-infrared light through the PC are studied.The frequency region and the tolerance of incident angle for the self-collimation behaviour can be controlled by changing the shape of the metal rods.
We present a novel and simple design of an air-slot mode-gap photonic crystal(PC) nanocavity by introducing a linear air slot to the center of a line-defect waveguide in a two dimensional triangular-lattice silicon PC slab.A high quality factor(Q factor) of 8.42*105 and an ultrasmall mode volume of 0.998 cubic wavelength are achieved in an optimized air-slot nanocavity which is a suitable choice for the strong matter-field interaction in free space.The high Q cavities with ultrasmall mode volume are important for applications such as quantum computation and nonlinear optics.
This paper studies the propagating characteristics of the electromagnetic waves through the coupled-resonator optical waveguides based on the two-dimensional square-lattice photonic crystals by the finite-difference time-domain method.When the traditional circular rods adjacent to the centre of the cavities are replaced by the oval rods,the simulated results show that the waveguide mode region can be adjusted only by the alteration of the oval rods' obliquity.When the obliquity of the oval rods around one cavity is different from the obliquity of that around the adjacent cavities,the group velocities of the waveguide modes can be greatly reduced and the information of different frequencies can be shared and chosen at the same time by the waveguide branches with different structures.If the obliquities of the oval rods around two adjacent cavities are equal and they alternate between two values,the group velocities can be further reduced and a maximum value of 0.0008c(c is the light velocity in vacuum) can be acquired.
Light propagation through a channel filter based on two-dimensional photonic crystals with elliptical-rod defects is studied by the finite-difference time-domain method. Shape alteration of the defects from the usual circle to an ellipse offers a powerful approach to engineer the resonant frequency of channel filters. It is found that the resonant frequency can be flexibly adjusted by just changing the orientation angle of the elliptical defects. The sensitivity of the resonant wavelength to the alteration of the oval rods' shape is also studied. This kind of multi-channel filter is very suitable for systems requiring a large number of output channel filters.
The light transmission properties through two-dimensional photonic crystal waveguides based on coupling of square cavities are studied by the finite-difference time-domain technique.Through interlacing the adjacent cavities along the direction vertical to the waveguide,the coupling distance between the adjacent cavities is extended,and the group velocity of the guiding modes can be slowed by five-fold compared with that in vacuum.Because of the different spatial field distributions of various resonant modes,the corresponding group velocities are also different for the same CROW structure.
Optoelectronic characteristics of p-type CuO nanorods, synthesized by a simple hydrothermal method, were investigated at different atmospheres and oxygen pressures. The CuO nanorods have lower resistance in air than in a vacuum, unlike the n-type semiconductors. This is explained in terms of the surface accumulation conduction. Measurements at different oxygen pressures indicate that oxygen has an important effect on the optoelectronic properties of p-type nanomaterials.
