Anti-Reflection for Self-Collimated Beams Using Graded Index Coupler

We propose a method to improve the transmission efficiency and minimize the reflection of self-collimated beams. By introducing graded index coupler at the input and output interfaces between photonic crystal and air, the reflection is reduced significantly, meanwhile with the transmission enhanced dramatically. We investigate the performance of the design by the finite-difference time-domain method with and without the coupler. It is shown that a wideband transmission of the microwave can be significantly improved through the gradually changed index at the interfaces. The anti-reflection and high efficiency transmission design may find applications in integrated photonics circuits.