Improved linear crosstalk tolerance in an un-amplified ring PON

There is increased interest in ring-based passive optical network (PON) architectures due to their local area network (LAN) capability among end users and inherent protection and restoration schemes. The ring architecture includes optical filters and switches with non-ideal channel isolation, leading to the generation of linear crosstalk, which can significantly degrade the system performance if it is not sufficiently suppressed. We use simulation to analyze the effects of linear crosstalk in an un-amplified TDM optical ring and show how we can improve the tolerance of the crosstalk in our architecture that employs optimized tap split ratios as a means of increasing the number of ONUs served. Our approach is based on simulation of the entire network using a combination of wavelength-domain and time-domain techniques. Typically, PON networks use two or three wavelengths that are separated by more than 50 nm to maintain the cost of components low and as such, it is logical that any crosstalk will be negligible. However, the subpar performance of such components motivated our study into the impact of crosstalk. We show that the tap ratio optimization which increases the number ONUs that can be served in the ring can also exacerbate the effects of linear interchannel crosstalk at the ONU’s downstream signal receivers. We also show that surplus power at the last ONU can be utilized to counter this degraded crosstalk performance by careful tap ratio selection, thereby improving the overall tolerance to linear crosstalk in the system.