为了满足光纤射频链路和相位阵列天线应用要求，提出并实验验证了基于半导体光放大器(SOA)的全光微波滤波器，该结构利用SOA的放大自发辐射的交叉增益调制(XGM)原理，可以实现通带和阻带的相互切换。它是基于由SOA和可调谐窄带光学滤波器构成的光纤延时环，利用SOA的放大自发辐射谱的交叉增益调制产生负系数。当可调谐窄带光学滤波器的中心波长对准激光器的波长时，可获得一个高Q的带通滤波器频率响应；当可调谐窄带光学滤波器的中心波长偏离激光器波长一定量时，可获得陷波宽度较窄和通带相对较平的陷波滤波器频率响应。此结构通过调节可调谐窄带滤波器的中心波长可实现高Q与通带相对较平的陷波频率响应的切换。

In order to satisfy the applications requirement in fiber-radio links and phased array antennas,a novel microwave photonic filter with passband and stopband interchanged is proposed and demonstrated. The filter is based on a recirculating delay line loop with a semiconductor optical amplifier (SOA) followed by a tunable narrowband optical filter. The negative tap is generated by using the wavelength conversion employing the cross-gain modulation of the amplified spontaneous emission spectrum of the SOA. When the central wavelength of the optical filter is aligned with the laser wavelength, a microwave bandpass filter is obtained. On the other hand, when the optical filter detunes from the laser wavelength a little, a narrow notch filter with flat passband is realized. The structure can be operated as a high Q or notch filter with flat passband by tuning the central wavelength of the optical filter.