Undesired reflection caused by impedance
mismatch can lead to significant power loss and other
unwanted effects. In the terahertz regime, anti-reflection
method has evolved from simple quarter-wave anti-
reflection coating to sophisticated metamaterial device
and photonic structures. In this paper, we examined and
compared the theories and techniques of several anti-
reflection implementations for terahertz waves, with
emphasis on gradient index photonic structures. A
comprehensive study is presented on the design, fabrica-
tion and evaluation of this new approach.