  Optical modulation plays arguably the utmost important role in microwave
photonic (MWP) systems. Precise synthesis of modulated optical spectra dictates
virtually all aspects of MWP system quality including loss, noise figure,
linearity, and the types of functionality that can be executed. But for such a
critical function, the versatility to generate and transform analog optical
modulation is severely lacking, blocking the pathways to truly unique MWP
functions including ultra-linear links and low-loss high rejection filters.
Here we demonstrate versatile RF photonic spectrum synthesis in an
all-integrated silicon photonic circuit, enabling electrically-tailorable
universal analog modulation transformation. We show a series of unprecedented
RF filtering experiments through monolithic integration of the
spectrum-synthesis circuit with a network of reconfigurable ring resonators.
