Abstract

Optical noise that limits the performance of lightwave communication systems is typically interference or ‘beat’ noise. Traditionally this is due to the signal beating with amplified spontaneous emission (ASE), an unavoidable by-product of optical amplification. But systems can also be limited by noise from inband crosstalk, in which signals beat with delayed replicas of themselves or with other signals they overlap spectrally. Such interference noise can result, for example, from crosstalk in photonic devices, ^1,2 multiple reflections along a transmission link³ or Rayleigh scattering within fiber amplifiers.^4–6 Interference between a signal and delayed replicas of itself (‘echoes’) is called multiple path interference (MPI). This refers to multiple paths taken by the signal light before interfering at a square-law receiver. The desire to increase optical functionality or optical reach in lightwave systems could lead to elevated levels of MPI at the receivers as signals pass through an increasing number of photonic devices in an all-optical network, or as distributed Raman amplification is deployed to increase system reach.

© 2002 Optical Society of America