光子晶體的能隙（band gap）會限制可在光子晶體中傳播的電磁波的頻率，這是光子晶體的一項重要性質。光子晶體中製造一些缺陷 (defects) ，例如移去一整排的柱子，會改變在光子晶體中的傳播模態，使得電磁波被侷限在被移去柱子的區域內，用光子晶體來構成波導（PCW）常用的方法。 改變（1）波導兩旁柱子的半徑（後面以 PCWA來表示）或（2）在缺陷中排列一整排半徑不同的柱子，擔任波導的柱子的半徑（後面以 PCWD來表示），都會使波導的 band structure 產生改變，只要選擇適當的頻率，我們可以應用這種性質將不同頻率的電磁波分開來，而達到分波的效果。 ;The bang gap, which light is forbidden to propagate with certain frequency, is the most important characteristic in photonic crystal. If we can find propagating mode frequency in PC band gap by making defects in PC, then we can guide light from one location to another. Making line defects by removing one row dielectric material is one of photonic crystal wave guide (PCW) method. The first change: the rods′ radius beside the wave guide (PCWA, represented); The second change: a row of different rods′ radius that form the wave guide (PCWD, represented) Both arrangements will cause the band structure of the wave guide change. We can distinguish the electromagnetic waves of different frequencies via the former character to achieve the effect of partial waves by selecting the proper frequency.
