Loop distribution using coherent detection [fiber optic networks]

A novel architecture is described for point-to-multipoint distribution using coherent detection and a totally passive fiber bus. Coherent technology is used initially to provide transmission at rates of a few hundred Mb/s without the need for a local oscillator at each station. It is expected that this architecture can then be expanded via WDM (wavelength-division multiplexing) to transport multiple wavelengths as coherent technology matures. The performance of the proposed topology is analyzed and compared to that of previous bus structures using variable and fixed taps with direct-detection receivers. This performance analysis consists essentially of a loss budget calculation intended to determine the relative numbers of stations which each of the architectures could support. Because the rates and loop lengths are modest and the spectral width of the sources associated with coherent communication are very small, dispersion (or rise-time budgeting) is not expected to present any real limitation for the systems considered here. A performance analysis and comparison of three tree structures is presented. Engineering issues and open questions are discussed