A side-edge mountable parallel optical communications module and an optical communications system that incorporates one or more of the modules are provided. In the optical communications system, one or more of the side-edge mountable parallel optical communications modules are side-edge mounted in respective edge card connectors, which, in turn, are mounted on a surface of a motherboard PCB. Because the modules are relatively thin and because the spacing, or pitch, between the modules can be kept very small, the system can have a very high mounting density, and consequently, a very high bandwidth.