Analysis of optical coupling between air-holes photonic crystal and tapered dielectric waveguides

Two types of structures for the optical coupling between photonic crystal waveguide (PCW) with triangular air-holes lattice and tapered dielectric waveguide (TDW) are investigated. The TDWs are coupled with PCW at the input and output connections of the PCW, which can constitute a unidirectional waveguide structure. The transmission efficiencies of the input and output coupling are analyzed theoretically for different coupling structures. It is found that the coupling efficiencies vary with the width and length of coupling region. When the light transmitted from TDW to PCW, the highest transmission efficiency is 92.6%, and it is 99.6% when the light transmitted from PCW to TDW. Then the total transmission efficiency of the entire waveguide is simulated and it can reach 92.3% for one type of structure and is a little lower for the other type of structure under the chosen optimal structure parameters. Considering the current processing accuracy, the structure mentioned above should be an effective coupling manner that can be easily realized.