An optical module that implements with a tri-plexer assembly is disclosed. The tri-plexer module comprises a bi-directional module for transmitting digital input and output signals and an analogue optical assembly for receiving analog optical signals. The bi-directional module installs both a light-emitting device and a light-receiving device in a signal package. The analogue optical assembly is assembled such that the optical axis thereof makes a substantially right angle with the optical axis of the bi-directional module. The signal ground of the module is common to the analogue module and to a section for receiving the digital data; while, the chassis ground or the frame ground in the module is isolated from the signal ground.