Experimental Analysis of a Self-Coherent M-QAM Receiver by Means of Recurrent Optical Spectrum Slicing and Direct Detection

2025-03-12

AI Summary

To address the high spectral efficiency and low-power requirements of 1.6-Tb/s pluggable optical modules, this work proposes an M-QAM receiver architecture combining direct detection with self-coherent phase recovery. The method eliminates the need for a local oscillator while enabling spectrally efficient operation. Key contributions include: (1) the first demonstration of a photonic-accelerated cyclic optical spectrum slicing (ROSS) architecture, integrated on a programmable photonic chip; (2) support for ultra-low-voltage modulator driving (Vπ/3 or less); and (3) synergistic use of linear digital signal processing (DSP) equalization and geometric constellation shaping to drastically reduce DSP complexity. Experimental results show error-free transmission (BER < FEC threshold) for 32-GBaud QAM-4 and QAM-16 over 25–75 km in the C-band. The complete transceiver achieves >40% lower power consumption than the state-of-the-art lightweight coherent solution, offering a viable pathway toward next-generation high-density optical interconnects.

Technology Category

• Computer Vision: Multi-modal Vision
• Machine Learning: Hardware-aware ML
• Search and Optimization: Distributed Search

Application Category

• Search and Retrieval-Augmented AI: Retrieval-Augmented Generation (RAG) and multi-modal RAG
• Systems and Infrastructure for Web, Mobile and WoT: Data management and stream processing for Web, mobile and wireless applications
• Security and Privacy: Data transparency and provenance

Abstract

High order modulation formats constitute the most prominent way for increasing spectral efficiency in transmission systems. Coherent transceivers that support such higher order formats require heavy digital signal processing (DSP), which increases the power consumption of coherent pluggables, well above the intensity modulation and direct detection (IM/DD) counterparts. Self-coherent or phase retrieval methods have emerged as potential solutions, trying to combine the merits of coherent technology with the simplicity of direct detection. In this work, we experimentally demonstrate the reception of quadrature amplitude modulation (QAM) modulation formats based on direct detection aided by the recurrent optical spectrum slicing (ROSS) photonic accelerator, utilizing minimal DSP and low modulator driving voltages. We experimentally demonstrate 32 Gbaud QAM-4/16 for 25 km, 50 km and 75 km in the C-band aided by a linear digital equalization and the use of programmable photonics as recurrent optical spectrum slicers. We showcase successful detection with driving swings below V{pi}/3 in contrast to the full swing required by conventional coherent transceivers. We further improve the system performance utilizing geometric constellation shaping. Finally, we explore the potential power consumption improvement for the next-generation 1.6T pluggables, showcasing over 40% reduction with respect to the most lightweight state of the art coherent solutions reported in literature

Problem

• Reducing power consumption in high-order modulation systems.
• Combining coherent technology with direct detection simplicity.
• Enhancing spectral efficiency with minimal digital signal processing.

Innovation

• Recurrent optical spectrum slicing for direct detection
• Minimal DSP with low modulator driving voltages
• Geometric constellation shaping enhances system performance