An optical data link using a single optical fiber for bi-directional optical communication. Bi-direction optical transceivers couple to the single optical fiber having two optical channels of communication. An optical subassembly in each optical transceiver to multiplex an optical transmit signal and demultiplex an optical receive signal within the bi-direction optical transceiver. The optical subassembly includes an optical block with an optical filter to reflect at least one wavelength of light and to allow passage of another wavelength of light. Embodiments of the optical block with the optical filter are described.