A plug in communications module for achieving bi-directional communication along a single fiber-optic cable in a fiber-optic network. The plug in module is made such that it plugs directly into fiber-optic communication equipment of standard form factors. Bi-directional communication is achieved by using a low-cost circulator. The plug in module also has a receptacle that is used for attaching a patch cable between the fiber-optic network in the plug in module.