Contents I Intorduction
In recent years, sub-millimeter and terahertz technology has the potential to develop new capabilities for imaging, short-range communications, sensors, spectroscopy, and material analyses etc. Nonetheless, the THz band (1 mm-) is one of the last unexplored frontiers in the electromagnetic spectrum due to a lack of low-loss chip-to-chip interconnected transmissions, sources, detectors, amplifiers, etc. Recently, in [2]–[3], a parallel plate metal waveguides have demonstrated excellent performance for guiding THz pulses with little distortion on centimeter length scales. However, there are some drawbacks in this structure. For example the beam can only travel in one direction and it seems to be difficult to control the electromagnetic wave beam freely in this structure. On the other hand, an alternative to the conventional transmission lines is the Post-Wall Waveguide. The post-wall waveguide is a substrate-integrated waveguide (SIW): a waveguide transmission line that can be embedded in a PCB[4]. Rows of cylindrical posts constitute the side walls and together with the top and bottom parallel metal-plate they compose a rectangular cross section similar to the waveguide. The posts can be either metallic posts or dielectric posts with a permittivity different from the background medium. PWWGs for application at microwave frequencies first acquired a Japanese patent (JP6053711) by F. Shigeki in 1994 [1]. It is known from both the analysis and the experiment that the SIW [5] has essentially the same guided wave characteristics as the corresponding conventional rectangular waveguide and are studied mainly in the microwave and mm-wave range, but not so at sub-millimeter and terahertz band. In contrast, it has first been discovered by Johon, Yablonovitch in 1987 [6], [7] and John D. Joannopoulos in 1995 [21] that in a spatially periodic arrangement of dielectric material, for most , “ EM waves propagate through a photonic crystal without scattering, but for some , EM waves can not propagate. With the properties of this photonic band gap (PBG), photonic crystals have the ability to provide extra degree of freedom in manipulating the EM waves. Although they lack a band gap in the direction perpendicular to the lattice plane, 2D photonic crystals have substantial advantages in terms of compactness, stability and fabrication, which make them attractive for sub-mm wave and THz devices. A commonly used type of 2D photonic lattice is the square and triangular lattice, due to its almost Brillouin zone and corresponding large bandgaps. As a result of multiple interference of Bragg scattering, some frequencies are not allowed to propagate inside PhCs, giving rise to forbidden and allowed bands. Therefore, many researchers seek their new ways in the THz regime from photonic crystal technology [e.g. 22]. This paper extends these ideas and simulates some typical models practically, by integrating Sub-millimeter and THz waveguide elements with dielectric 2-D photonic crystal lattices (Silicon is transparent to waves below 10THz [8]). The numerical techniques for electromagnetic field computation in the PhC waveguide can be divided into two classes; they are rigorous numerical methods and simple approximation methods. As well known, rigorous numerical methods such as finite-difference time-domain method (small grid sizes, small step sizes and large computational domains) are accurate and fit for complex geometries. In this paper, simulation has been carried out using simplified TD-BPM [10], FD-TD[11], and a full vectorial Finite Integration method (CST microwave studio has a general versatility as commercial software) in order to simulate wave propagation properties of PhC waveguide in design. Fig.l Two dimensional photonic crystal. The PhC's are square or triangular lattice columns of air holes or dielectric pillars and is homogeneous in the z-axis and periodic along x-y axis.
