On the Theoretical Performance Limits of Long Repeated/Regenerated Optical IMDD Links

Abstract

The introduction of optical amplifiers has drastically increased the capacity and the reach of optical transmission links. However, they add Amplified Spontaneous Emission (ASE) noise, which progressively degrades the Signal to Noise Ratio (SNR) when cascaded and ultimately limits the transmission reach and performance. This is conventionally offset using regenerators, typically Optical-Electrical-Optical (OEO) conversion devices, that recreate the signal restoring its source SNR, albeit with bit errors due to the hitherto accumulated noise. These OEO regenerators tend to be expensive and add to the link latency, which sets the scene for widespread commercial implementation of all-optical regenerators in the near future. Our work aims to analyze the ideal, best-case theoretical gains achievable using an all-regenerator optical link as compared to an all-repeater link. So, this analytical study serves as a benchmark against which future link performance gains can be compared. We also translate this bound on BER advantage to extra reach or lower transmission power. We compare and contrast the evolution of noise power and BER down the link using the derived analytical expressions. The theoretical comparative study is then evaluated by incorporating the physical parameters of the devices. Both results agree and prove the dramatic increase in link reach achievable using all-regenerator links with minor input power penalties. Further, certain approximations to reduce the computational overhead for the described methods are proposed, which should find applications in dynamic reconfigurable optical networks.