In this paper, we review our recent works in on-chip multiplexing/demultiplexing silicon photonic devices and technologies. On-chip demultiplexing of polarization and wavelength multiplexed OFDM/OQAM 64/128-QAM signals using silicon 2D grating coupler and microring resonators and on-chip two/three mode (de)multiplexing of OFDM 64/128/256-QAM signals using tapered silicon asymmetrical directional couplers are demonstrated in the experiments.