General purpose signal processor on an optical chip

Integrated optical signal processors have many applications in photonic processing of microwave signals. They provides wideband and stable signal processing operations on miniaturized chips with ultimate control precision. Creating general-purpose processors by introducing programmability is a key to enable system function flexibility and therewith offer great potential for a wide range of applications. Here, we review the recent progress in this area with highlights of a number of key programmable chips and their promising applications.