Add-drop photonic crystals filters

The transmission spectra of photonic crystal add-drop filters created in the microwave region are measured. The photonic crystal is a two dimensional square lattice of dielectric rods. The add-drop filters consist of two waveguides formed by removing rods along a line and a cavity lying between the two waveguides. The cavity is formed by removing rods or by replacing them with smaller diameter rods. Depending on the cavity geometry, certain wavelengths can be dropped from one waveguide and added to the other waveguide via resonant coupling through the cavity. A systematic study of the add-drop characteristics is performed as the cavity region is modified. Theoretical results, obtained from finite difference time domain calculations, are in good agreement with measurements.