By Grieg A. Olson and Barbara L. Birrell, 3M Company & Michael J. Labiche and Rezin Pidgeon, Scientific Atlanta
Reflections in fiber optic AM CATV transmission systems are an important source of noise. Mechanical splices always introduce some reflection, which is a function of temperature. For two splices, the degradation in Carrier to Noise Ratio (CNR) is related to the magnitude of the co-polarized reflections. For multiple splices, the CNR degradation is related to the sum of the reflection contributions from every combination of splice pairs in the system: as well as reflection from Rayleigh scattering. The reflection induced noise also depends on laser characteristics, such as chirp and modulation index. Measurements using two reflections show excellent agreement with theory. Measurements using eight FibrlokTM mechanical splices at temperatures ranging from -40 C to +80 C confirm the theory for the multi-splice case, with only minor decline in system CNR.