Achieving arbitrary passband profiles and high stopband attenuation in microwave photonic filters

Microwave photonic filters utilizing optical frequency combs have been shown to achieve narrow bandwidths, high stopband attenuation as well as easy tunability of center frequency and bandwidth. The ability to achieve smooth apodization of optical frequency comb spectrum to specific spectral profiles is important to obtain high stopband attenuations. Previously, by utilizing an optical pulse shaper to crease a Gaussian profile spectrum, filters with high stopband attenuation and Gaussian passbands were demonstrated. However this technique is flexible and can be used to easily program the filter passband profile. We demonstrate this by creating filters with a flat top passband. We also demonstrate that the stopband attenuation can be significantly enhanced by utilizing frequency combs which achieve the necessary spectral shapes directly from the source. By generating an optical comb with a smooth quasi-Gaussian profile, we demonstrate filters with a record >60dB stopband attenuation.