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The light localization characteristics of the near-infrared triangular-lattice photonic crystal annular microcavity are studied theoretically in this paper. The photonic crystal has a lattice constant of a=540 and it is composed of silicon rods each with a radius of r=135 immersed in air background. The two kinds of annular microcavities are obtained by removing 12 silicon rods which are located respectively at a distance of 2a and at a distance of √3a to the central rod. Five resonant wavelengths and the corresponding eigen mode profiles of the microcavity are studied. A coupled resonant optical waveguide is formed by integrating the microcavities with a periodic length of 7a in space. The group velocity of light beam propagation within multiple guiding bands are analyzed by the tight-binding approximation method. The maximum and minimum velocity of 0.0028c and 0.00082c are obtained, where c is the light velocity in vacuum. The light transmittance values and spatial steady distributions of the electric field's amplitude through the structure at several wavelengths within the guiding bands are studied by the finite-difference time-domain method. The results are consistent with that calculated by the plane wave expand method. Interleaving circular microcavities perpendicular to the direction of optical transmission at a lateral distance of 2√3a, the coupling region between the adjacent microcavities is changed, the difference in group velocity between guiding bands apparently decreases and the transmittance values of two frequency bands are enhanced.Keeping the size of silicon rods unchanged, two kinds of microcavities are constructed by removing the six rods with the distances of 2a and √3a from the center of the central silicon rod, respectively. The resonant wavelengths supported by the above two microcavities are studied. Two coupled-resonant optical waveguides with a periodic length of 7a are proposed. Connecting these two coupled cavity optical waveguides with the W1-typed input/output waveguides, the selecting and sharing function of guiding band are finally achieved for wavelengths within different frequency bands. Keeping the group velocity slowing down, a maximum value of one guiding band reaches 0.00047c.

We report the imaging properties of a two-dimensional rectangular-lattice photonic crystal (PC) slab consisting of rectangular metallic rods immersed in a dielectric background. By simulating the electromagnetic wave propagation through such a PC slab with the finite-difference time-domain method, we find that a point source placed in the vicinity of the PC slab can form a good-quality image through the slab. The frequency region where a good-quality image is formed can be controlled by choosing the direction along which the PC slab surface normal is placed.

We have investigated the analytical forms of the photonic density of states (DOS) in a photonic crystal in the interested frequency regime according to the rule of state conservation in a photonic crystal with pseudogaps, which states that, if a valley of the DOS appears in some range of frequencies, it must be compensated for by increasing over some other ranges. By using a model DOS with a state-conservative photonic pseudogap, we have also investigated the enhancement and suppression of spontaneous emission of two-level atoms with different frequency positions and widths of emission spectra in a state-conservative electromagnetic reservoir; and the DOS-induced suppression, enhancement, narrowing and redshifting or blueshifting of spontaneous emission spectra are naturally obtained.

Negative refraction and imaging properties of the electromagnetic wave through a two-dimensional photonic crystal (PC) slab, which consists of a square lattice of elliptical dielectric rods immersed in the air background, is studied by the plane-wave expansion method and the finite-difference time-domain method. A point source placed in the vicinity of the PC slab can form a good-quality image spot through the PC slab for the incident frequencies within the second photonic band. The calculated result also shows that negative refraction occurs in this kind of PC slab.

We propose a ring photonic crystal working in the near infrared region, where the air holes in the background material GaAs are arranged to form a series of rings. We find that the band gaps do not depend on the incident direction and only a small number of rows are needed to create a frequency gap in the transmission spectrum. The transmission spectra of both P and S polarizations show that there is a complete bandgap in the hexagonal ring photonic crystals and the ratio of gap width to mid-gap frequency is as high as 11%.

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.

thinner cylindrical inclusions in the centre of basic hexagonal units of the amorphous structure along a given path. This waveguide in amorphous structure is similar to the coupled resonator optical waveguides in periodic photonic crystals. The transmission of this waveguide for S-polarized waves is investigated by a multiple-scattering method. Compared with the conventional waveguide by removing a line of cells from amorphous photonic materials, the guiding properties of this waveguide, including the transmissivity and bandwidth, are improved significantly. Then we study the effect of various types of positional disorder on the functionality of this device. Our results show that the waveguide performance is quite sensitive to the disorder located on the boundary layer of the waveguide, but robust against the disorder in the other area in amorphous structure except the waveguide border. This disorder effect in amorphous photonic materials is similar to the case in periodic photonic crystals.

In this letter the propagation of electromagnetic wave in a round cavity of photonic crystals is analysed both theoretically and experimentally. Frequency sele cted propagation has been realized by changing the parameters of the photonic cr ystal. We have computed theoretically the transmission spectrum. In the experiment, we have also measured the transmission spectrum.

It is shown that there exist a conservation rule of the number of states in a photonic crystal with pseudogaps in the whole frequency regime, and a local conservation rule of the number of states in a photonic crystal with completely photonic band gaps in every band regime. These conservation rules state that, relative to the photonic density of states (DOS) in the effective medium of a photonic crystal, if a valley of the DOS in the photonic crystal appears in some range of frequencies, it must be compensated for by the increases over some other ranges. In this paper, using a model DOS with a state-conservative photonic pseudogap, we obtain naturally the enhancement and suppression of spontaneous emission of a two-level atom in a photonic crystal, and a DOS-induced suppression, enhancement, narrowing and redshift or blueshift of spontaneous emission spectra. Our theory will be especially appropriate in the problem of the spontaneous emission of a collection of dependently emitting atoms or molecules with essentially random dipole orientations in a photonic crystal with a photonic pseudogap.

The dynamical characteristics of the spontaneous decay of a single excited atom or molecule depend strongly on its position within a photonic crystal (PC) and the relative orientation of its dipole and the electric field there. Measuring its dynamical characteristics of the spontaneous decay in a PC can only obtain the local density of states (DOS) in the PC, but cannot reflect the total DOS in the PC. It is found, theoretically, that using different number density distributions of luminescent molecules within the PC, one can probe the partial information or even all of the total DOS in the PC. In this paper, we separate, for the first time to our knowledge, the total DOS into two parts, DOS in the scatterer and DOS in the matrix of the Wigner-Seitz unit cell, according to their origin, and demonstrate that a special number density distribution of fluorescent molecules can reflect the total scatterers DOS or total matrix DOS or even both of them, i.e. the total DOS in the PC. This is meaningful in explaining and designing the experiments of prohibiting and enhancing the spontaneous emission of excited molecules.

In this letter energy transfer between continuous channels is analysed both theoretically and experimentally. Energy transference has been realized by changing the parameters of combined wave-guides. In the experiment, we have also measured the transmission spectrum.