Carrier-assisted differential detection

William Shieh,Honglin Ji,Chuanbowen Sun

doi:10.1038/s41377-020-0253-8

Abstract

To overcome power fading induced by chromatic dispersion in optical fiber communications, optical field recovery is a promising solution for direct detection short-reach applications, such as fast-evolving data center interconnects (DCIs). To date, various direct detection schemes capable of optical field recovery have been proposed, including Kramers−Kronig (KK) and signal−signal beat interference (SSBI) iterative cancellation (IC) receivers. However, they are all restricted to the single sideband (SSB) modulation format, thus conspicuously losing half of the electrical spectral efficiency (SE) compared with double sideband (DSB) modulation. Additionally, SSB suffers from the noise folding issue, requiring a precise optical filter that complicates the receiver design. As such, it is highly desirable to investigate the field recovery of DSB signals via direct detection. In this paper, for the first time, we propose a novel receiver scheme called carrier-assisted differential detection (CADD) to realize optical field recovery of complex-valued DSB signals via direct detection. First, CADD doubles the electrical SE compared with the KK and SSBI IC receivers by adopting DSB modulation without sacrificing receiver sensitivities. Furthermore, by using direct detection without needing a precise receiver optical filter, CADD can employ cost-effective uncooled lasers as opposed to expensive temperature-controlled lasers in coherent systems. Our proposed receiver architecture opens a new class of direct detection schemes that are suitable for photonic integration analogous to homodyne receivers in coherent detection.

Highlights

Coherent detection has profoundly impacted optical communications due to its superior capability of recovering both optical intensity and phase, namely, field recovery[1,2]
An optical coupler is utilized to split the input into two paths, with an optical delay of time τ on one path, corresponding to C + S(t − τ)
This is justified, as the optical delay τ is on the order of the baud period, and the carrier phase change would be insignificant with a delay of τ

Summary

Introduction

Coherent detection has profoundly impacted optical communications due to its superior capability of recovering both optical intensity and phase, namely, field recovery[1,2]. Distinct from conventional intensity modulation with direct detection, field recovery enables inphase/quadrature (IQ) modulation, increasing the transmission spectral efficiency (SE). Coherent detection remains a suitable solution for medium- to long-haul transport[8], Since direct detection generally provides only intensity information, until now, signals have been mainly restricted to the single sideband (SSB) modulation format in various proposed intensity-only detection schemes[14]. For such detection schemes, signal−signal beating interference (SSBI) is the dominant limitation.

Methods

Results

Conclusion