Contents I. Introduction
Photonic CRYSTALs (PhCs) are engineered periodic microstructure with photonic band gaps. And with proper design, they can possess many unusual properties [1]–[3]. The main application of them is that PhCs can control electromagnetic wave in tiny vicinity [4], and then make the integration of electromagnetic circuits achievable. However, coupling external signals into such microdevices is always a challenging work, because each different active component in the circuit may have different group index . Then at the point where signals passing on from one component to following ones, the reflection will occur, and cause the decrease of the transmitted signal power. This decrease may accumulate while the signals pass through the circuit, and make the processing of signals impossible, unless we set an amplifier unit in the circuit. But integrating an integratable amplifier may cause additional difficulties. Until now, many works have been done to enhance the coupling efficiency between different parts of signal path [5]–[8]. But structural simplicity and high transmission are still unsolved problems.
