On-chip optical combiners with high coupling efficiency can be fully exploited in both multiple gas sensing devices and telecommunication applications. In this paper, we will review the enabling technologies and discuss the basic operating characteristics of broadband optical couplers. In particular, the design of optimized, broadband optical duplexers based on angled multimode interference (AMMI) and directional coupler (DC) configurations will be detailed. A rigorous comparison between both configurations will be reported. The preliminary fabrication results of the duplexer will be detailed and, finally, the recent advances in the development of design and optimisation of duplexer and triplexer couplers having higher optical coupling efficiency at broadband regime will be also presented.