A Model of Photonic Band-Gap Structures to DWDM Filter Design

The fiber optic transmission systems require a bandwidth of about 25 THz in the networks of telecommunications, for which it is necessary to resort to Dense Wavelength Division Multiplexing (DWDM) systems. These systems need optical filters to broadcast selectively or not in a given wavelength band. A very promising technology for these applications is the Photonic Crystals with forbidden band-gap (Photonic Band-Gap, PBG). In this chapter a powerful and efficient model to characterize photonic band-gap structures incorporating multiple defects, having arbitrary shape and dimensions, is reviewed. The importance of the defect-mode characterization in photonic band-gap materials is due to the intensive use of defects for light localization to design very promising optical devices. The model, based on the Leaky Mode Propagation method (LMP), provides to model defects in wave-guiding, finite-size photonic band gap devices and analytical and closed-form expressions for the reflection and transmission coefficients and out-of-plane losses, very useful and easy to be implemented for any operating conditions. Moreover, the method, implemented in a very fast code in FORTRAN 77 language, running on a personal computer, has been applied to look into the capabilities of wave-guiding photonic band gap devices in DWDM filtering applications. In particular the design of some optical filters has been carried out and optimal design rules have been drawn using the reviewed model.