用级联缓变结构实现光子晶体波导和传统波导的耦合

为了提高光子晶体波导与传统介质波导的耦合效率,设计了级联缓变结构.先将传统介质波导中的光耦合进尺寸相当的光子晶体W5波导中,然后W5波导中的光被耦合进尺寸较小些的W3波导中,最后光被耦合进尺寸最小的W1波导.各级波导之间由半径逐渐增大的空气孔连接,空气孔半径逐渐变化相当于波导有效折射率在变化,所以各级波导可以看作是被折射率缓变结构连接起来.由于折射率的缓变,使得光从前一级波导耦合进相邻的后一级波导时反射很小,从而能有效地提高耦合效率.数值计算表明,在光子晶体禁带范围内,除了波导有限长度和波导微小禁带造成的微小不通带外,耦合系数一般能达80%左右,最高可达到95%.

Cascaded Taper for Mode Coupling Between Photonic Crystal Waveguide and Classical Waveguide

A cascades photonic crystal taper integrated with a classical waveguide and a photonic crystal waveguide for high efficiency mode coupling is presented.The tapering section is formed by increasing radii of air holes step by step.Numerical results obtained by 2D finite-difference time-domain calculations demonstrate that the highest coupling efficiency is as much as 95% and general coupling efficiency is also greater than 80%.