We design and implement a system demonstrator based on vertical-cavity surface-emitting lasers, polymeric hologram grating couplers, and metal-semiconductor-metal photodetectors. As a preliminary experiment, we show the feasibility of board-to-board level substrate-guided wave optoelectronic interconnections in the real electrical system. First, we introduce a new architecture - centralized optical backplane - for board-to-board level interconnections. Second, the optoelectronic data channel is constructed compatible with standard PECL and capable of operating at 1.25 Gbps. Finally, it is employed to replace the conventional electrical data channel in a microprocessor system. We describe the performance of the entire system and discuss the future application of our centralized optical backplane in other electrical systems.