为了克服正抽头系数低通滤波的限制, 满足光载无线通信(ROF)、无线通信等系统对带通滤波器的需要, 提出了一种新的负系数带通微波光子滤波器结构。系统采用了一种偏振敏感的电吸收调制器, 其横向电场(TE)和横向磁场(TM)方向上具有不同的调制系数, 在小信号调制下仍为线性调制。通过旋转偏振控制单元的波片, 改变其快轴与TE方向的夹角, 可以得到任意偏振态的转换。当偏振控制单元由两个旋光方向相反的法拉第旋光片和一个1/2波片组合时实现了负系数滤波, 和一个1/4波片组合时得到了正系数滤波。

In order to overcome the restrictions of low-pass filters applied in radio-over-fiber(ROF) link, wireless communication system, etc, a new all-optical microwave photonic filter structure that can realize negative coefficients is presented and investigated. The system adopts a polarization sensitive electrical absorption modulator, of which the modulation factors for the transverse-magnetic(TM) polarized and the transverse-electric (TE) polarized lights are different. Its considered as linear modulation under small signal. The intersection angle between the fast axis and TE direction changes by rotating the plate of the polarization control unit (PCU), then the transformation of arbitrate polarization can be obtained. When the PCU is consisted of two reverse direction Faraday rotation tablets and a 1/2 plate, a negative coefficient filter is obtained, while combined with a 1/4 plate, a positive coefficient filter is obtained.