Scaling Laws for Unamplified Coherent Transmission in Next-generation Short-Reach and Access Networks

TL;DR

This paper investigates the physical limitations and scaling laws of unamplified coherent optical transmission for short-reach networks, combining analytical modeling with experimental validation to support future technology shifts.

Contribution

It provides a detailed analytical and experimental study of unamplified coherent transmission limits, focusing on bit rate and power budget for short-reach optical links.

Findings

Analytical models accurately predict performance limits.

Experimental validation on a 37-km dark fiber demonstrates practical feasibility.

Scaling laws inform future design of coherent short-reach optical systems.

Abstract

International standardization bodies (IEEE and ITU-T) working on the evolution of transmission technologies are still considering traditional direct detection solutions for the most relevant short reach optical link applications, that are Passive Optical Networks (PON) and intra-data center interconnects. Anyway, future jumps towards even higher bit rates per wavelength will require a complete paradigm shift, moving towards coherent technologies. In this paper, we thus study both analytically and experimentally the scaling laws of unamplified coherent transmission in the short-reach communications ecosystems. We believe that, given the extremely tight techno-economic constraints, such a revolutionary transition towards coherent in short-reach first requires a very detailed study of its intrinsic capabilities in largely extending the limitation currently imposed by direct detection systems. To this end, this paper focuses on the ultimate physical layer limitations of unamplified coherent systems in terms of bit rate and power budget. The main parameters of our performance estimation model are extracted through fitting with a set of experimental characterizations and later used as the starting point of a scaling laws study regarding local oscillator power, modulator-induced attenuation, bit rate, and maximum achievable power budget. The analytically predicted performance is then verified through transmission experiments, including a demonstration on a 37-km installed metropolitan dark fiber in the city of Turin.