A system including a transmitter mounted inside a pressure bulkhead of a drill tool transmitting a light at a first wavelength is provided. The system includes a receiver mounted inside the pressure bulkhead to detect a second light at a second wavelength. The system also includes a wavelength multiplex unit positioned within the first pressure bulkhead for coupling the light at the first wavelength and the light at the second wavelength with an optical coupler. The optical coupler provides the light at the first wavelength to an external medium via a pressure resistant window and receives the light at the second wavelength from the external medium via the pressure resistant window. A method of using the above system to transmit and receive messages in a downhole optical link is also provided.