利用传输矩阵方法，从理论上研究了三缺陷层一维光子晶体的光学性质．在缺陷层间距足够大以致于出现缺陷态简并的情况下，调节第一或第三个缺陷层的光学厚度，光子晶体缺陷态的透射率会发生最大程度的变化．这种结构可同时具有窄带滤波器和光开关的功能，据此提出了一种低阈值光开关的设计．把折射率可调的向列型液晶作为晶体的第三个缺陷层，并用4×4传输矩阵方法计算了其缺陷态透射率与电场电压的关系．

By propagation matrix method,the property of one-dimensional photonic crystals with 3 defects was analyzed. On condition that the distance between adjacent defects in the photonic crystals was long enough for a degenerate defect mode to be produced,transmittance of the degenerate defect mode can be tuned to the full extent by a change of the optical path of one of defect layers in the photonic crystal. Nematic liquid crystal was introduced as one of the defect layers. As a result,the transmittance of the degenerate defect mode in the structure can be tuned by a change of the refractive index of the liquid crystal upon the application of an electric field. For the system,the maximum of transmittance was 1 and the minimum approachd 0,which were calculated by 4 × 4 propagation matrix. Possible applications of this system were discussed,especially in the field of communication where a optic switch can be produced.