Information capacity of direct detection optical transmission systems

TL;DR

This paper compares the spectral efficiency of direct detection optical systems to coherent detection systems, showing that the efficiency loss is at most 1 bit/s/Hz, highlighting the near-optimal performance of direct detection.

Contribution

It quantifies the maximum spectral efficiency gap between direct detection and coherent detection systems with the same modulation format.

Findings

Spectral efficiency of direct detection is at most 1 bit/s/Hz less than coherent detection.

Capacity per complex degree of freedom in direct detection is at most 1 bit lower.

Provides theoretical bounds on the performance difference between detection methods.

Abstract

We show that the spectral efficiency of a direct detection transmission system is at most 1 bit/s/Hz less than the spectral efficiency of a system employing coherent detection with the same modulation format. Correspondingly, the capacity per complex degree of freedom in systems using direct detection is lower by at most 1 bit.