Add-drop filters in three-dimensional layer-by-layer photonic crystals using waveguides and resonant cavities

A three-dimensional layer-by-layer photonic crystal with a complete photonic band gap is used to experimentally and theoretically demonstrate a sharp tunable bandpass filter. The structure consists of input and output waveguide sections coupled through a nearby cavity. The authors show experimentally and verify with finite difference time domain simulations that this configuration is a bandpass filter where a particular resonant frequency of the cavity is selected from the input guide and transmitted to the output guide leaving out other input frequencies. An excellent coupling efficiency near 100% between the waveguide and the cavity is found for the drop frequencies.