Optical Filters Design Using Dielectric Gratings Waveguides<br />DOI: 10.14209/jcis.1997.5

Abstract

The propagation characteristics of dielectric grating waveguides are analyzed here. It is shown that these structures behave as filters and may have total energy transfer between scattered, transmitted and reflected signals within a small range of variation of some given parameters. This type of anomaly, in the structures considered here, is associated with mode excitation that could be guided inside the periodic layer, and is known as the resonance anomaly. The structures considered here are planar, consisting of isotropic materials, with the periodic layer having a sinusoidally or step varying dielectric constant. A rigorous modal theory, applicable to fields with TE and TM polarization, is used. An analysis of the behavior of the excited modes inside the waveguides, which are responsible for the appearance of the resonance anomalies, is presented. For the case of small dielectric constant variations in the periodic layer it is noted that the design characteristics for the occurence of total reflection may be estimated from an analysis of the behavior of waveguides with homogeneous dielectric multilayers. It is shown how to design the waveguide presenting an arbitrary number of operating points as well as how to adjust the bandwidth around these points through the waveguide geometry and the physical characteristics of the dielectrics in the various layers. It is shown, in addition, how to obtain nearly ideal filters by means of a combination of the effects of resonance and antireflection dielectric gratings (AR).