An intra-board chip-to-chip optical communications system has a high bit rate and high data throughput based on the use of a silicon photonic interposer. The system includes a multi-substrate electro-optical structure for communications with CMOS and/or BiCMOS IC chips of a PCB. The structure includes a multi-chip module primary substrate mounted over the supporting PCB. The multi-chip module primary substrate implements high frequency electrical interconnections between transceiver circuit chips, mounted on the silicon photonic interposer, and the IC chips.