A (001) oriented three-dimensionally periodic photonic crystal, free of cracks, has been fabricated via a modified template-assisted colloidal self-assembly method with polystyrene spheres. Analysis of the opal-type crystals has revealed the structure to be noncubic. This is a face-centered tetragonal (fct), (001) oriented photonic crystal. The optical properties of the crystals have been characterized at near-normal incidence by reflectance spectroscopy. It is found that the photonic stop band shifts to shorter wavelengths compared with an identical cubic structure oriented along the (001) direction. We have also simulated the stop band behavior of such fct crystals and their inverse silicon analogs, revealing that the polymer opal could provide an inverse template for the formation of photonic crystals with a complete band gap.

A method for increasing the coupling efficiency between ridge optical waveguides and PhCCRWs is described. This increase is achieved via W1 channel waveguide sections, formed within a two-dimensional triangular lattice photonic crystal using mode-matching. The modematching is achieved by low quality-factor modified cavities added to both the input and output ports of the PhCCRW. A three dimensional finitedifference time-domain method has been used to simulate light propagation through the modified PhCCRW. We have fabricated PhCCRWs working at 1.5μm in silicon-on-insulator material. Measurements and simulations show that the overall transmission is improved by a factor of two.

A wave demultiplexer system with channels in a two-dimensional photonic crystal is proposed. The demultiplexer is realized by the coupling among an ultra-low-quality factor microcavity and resonators with high-quality factor. The coupling mode theory is employed to analyze the behavior of this system. The analytic results reveal that the reflection is fully absent at the peak frequencies for all channels. The simulations obtained by multiple-scattering method and experimental results in the microwave region show that the analysis is valid. This method might also be valuable for the design of other all-optical functional circuits.

We propose a frequency selective demultiplexer that is realized by the directly resonant tunneling between waveguides and point defects in a two-dimensional photonic crystal. The multiple scattering method is used to simulate the behavior of the demultiplexer. Results show that the demultiplexing efficiency is very high when the point defects are symmetrically arranged at both sides of the central line of the inlet waveguide. The selective frequency is only determined by the defect mode of the corresponding point defect in the photonic crystal and is not affected by the other point defects. A microwave experiment results agree well with the simulation. This structure may be valuable for the design of all-optical integrated circuits.

Two-dimensional amorphous photonic materials are created, which do not possess any long-range order but have only short-range order. Our calculation of the multiple-scattering method shows that, for S-polarized waves, these materials have photonic gap that is independent of incident directions. Even though the detailed structures of amorphous photonic materials are different with each other, they possess a common photonic gap, if only they have the same short-range order. Based on our studies it may be confirmed that, for S-polarized waves, the first band gap of photonic crystals comes mainly from the short-range order, while the higher-order band gaps are related to the long-range order. The measured transmission spectrum of an amorphous photonic material agrees perfectly with the calculation.

We experimentally and numerically demonstrate dodecagonal and decagonal quasiperiodic photonic crystals in the microwave region. The results show that only a small number of rows are needed to create a frequency gap in the transmission spectrum, and that the gap position is insensitive to the incident angle. In particular, there is no defect state at the first gap of a dodecagonal quasiperiodic photonic crystal when there is a cavity in the center region, even though the cavity volume is much larger than the square of the wavelength. The decagonal quasiperiodic crystal can offer great possibilities for creating defect states. These quasiperiodic photonic crystals may find some important applications in photoelectric devices.

A two-dimensional octagonal quasiperiodic photonic crystal composed of alumina cylinders is prepared. The transmission spectra of the quasicrystal are measured in the microwave region for the TM wave. We find that the position and width of the band gap do not depend on the incident direction, while the band structure can appear for quite a small piece of the quasicrystal. Two types of waveguide, a straight guide and a bending guide with two sharp 90° corners, are fabricated by removing three rows of cylinders. The measured transmittances show that the guiding efficiency for both waveguides is high.

Three kinds of square metallodielectric photonic crystals have been fabricated. In these crystals, a very small metal cylinder is inserted into the center of each unit cell, while the dielectric cylinders are located at the corners of each unit cell. The transmissions of these photonic crystals have been measured in the microwave region. Compared with dielectric photonic crystals, the first photonic band gap is enlarged by a factor of 2. The experimental results agree well with the simulation obtained by the multiscattering approach. This method may be valuable for the design of photonic crystals with a large band gap.