Carrier-assisted differential detection

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.

A Review of Self-Coherent Optical Transceivers: Fundamental Issues, Recent Advances, and Research Directions

“…As a result, the CADD receiver architecture initiates a new category of direct-detection-based schemes that are appropriate for photonic integration. This is comparable to the homodyne receivers in the COH detection [163,164].…”

Asymmetric Self-Coherent Detection Based on Mach-Zehnder Interferometers

“…4 iterations of SSBI mitigation are implemented for these SC-DSB-DD schemes. Note that the SSBI estimates are obtained from the reconstructed signal field as detailed in section II, which is different from the approach adopted in [23] where the SSBI estimates are based on clean symbols determined after equalization at the expense of higher complexity. In addition, we include the OSNR sensitivity of the KK scheme in this figure . For a fair comparison, we transmit a 50 Gbaud singlesideband 16 QAM signal in the KK scheme and an aggregate 50 Gbaud dual-sideband 16 QAM signal in the ASCD schemes, and the CADD scheme.…”

“…These benefits of SC-DSB-DD schemes are attractive for short-reach optical modems targeting a compact form factor and facing a tight power constraint. As such, several papers on SC-DSB-DD schemes are motivated in recent years [22][23]. [22] interleaves the CW-tone and signal into staggered time slots at the transmitter and detects the signal by means of a coherent receiver that beats the signal with its delayed copy.…”

“…Despite the removal of the LO, this scheme does not improve the ESE compared to IMDD because half of the time slots are not carrying signals. In [23], the carrier-assisted differential detection (CADD) scheme is proposed to improve the ESE of [22] close to that of coherent detection using a more complex receiver front-end composed of 5 PDs and three analog-todigital converters (ADC).…”

Carrier-Assisted Phase Retrieval

“…The CCA-PR enables the flexibility between CSPR and ESE. Compared with CADD or ASCD, the CSPR of CCA-PR could be reduced significantly because the CADD and ASCD rely on SSBI construction and iterative cancellation algorithm [4][5]. These iterative reconstruction algorithms require a high CSPR in the first several iterations for convergence, while a low CSPR enables the CCA-PR to eliminate the phase ambiguity and realize field recovery.…”