Application limits of single-wavelength communications by orthogonal modulation formats

The use of orthogonal modulation formats for the transmission of separate data streams over the same wavelength allows an efficient use of fiber infrastructure in any optical network. Particularly, Frequency-Shift Keying (FSK) and Intensity Modulation (IM) can be accomplished very simply by simultaneous direct and external modulation of an optical source giving rise to great cost reduction. However, non-perfect orthogonality between modulation formats leads to interference upon data reception, which has been analyzed. For this purpose, system parameters affecting mutual interference between data streams are identified and its effect quantified in terms of loss of Signal-to-Noise Ratio. Finally, the application of the analyzed scheme to some interesting scenarios is discussed. These scenarios include unidirectional and bidirectional examples, such as labelling in Optical Packet Switched Networks, multiple data-stream transmission in short-range applications such as automotive networks and remote-seeding in Passive Optical Networks. Analytical results presented in this paper are in good agreement with reported experimental results.