DSP-free ‘coherent-lite’ transceiver for next generation single wavelength optical intra-datacenter interconnects

Abstract

We propose a DSP-free coherent-lite system that requires neither high-speed DSP nor high-resolution signal converters for deployment inside datacenters over single mode fiber links with reaches of 10 km and less. The removal of converters and DSP, in which some subsystems are fundamental for successful coherent detection, is enabled by either replacing DSP subsystems with optics having equivalent functions or by re-engineering the system. We validate in a proof-of-concept experiment the proposed DSP-free system using 50 Gbaud DP-16QAM delivering 400 Gb/s over 10 km of single mode fiber (SMF) below the KP4 forward error correction (FEC) threshold of 2.2 × 10. In addition, we perform a detailed experimental parametric study of the coherent-lite system in which various system parameters are swept such as baud rate, reach, laser power and laser linewidth. Our results verify that the coherent-lite system can be realized using low-cost DFB lasers with linewidths of a few hundred kHz. Moreover, we compare the performance of the coherent-lite system with that of a conventional coherent transceiver leveraging the full DSP stack. Then, we evaluate the power consumption savings achieved by the coherent-lite scheme relative to a classic DSP-based coherent system. Assuming a CMOS node ranging from 28 to 7 nm for DSP implementation, our estimate shows that the coherent-lite scheme can save 95 to 78% of the power consumed by the following subsystems: analog-to-digital converters, chromatic dispersion compensation, 2 × 2 MIMO polarization demultiplexing and carrier recovery. Finally, we compare the power consumption of the coherent-lite scheme with more standard 400G IM-DD systems utilizing either eight or four parallel WDM lanes (8 × 50G and 4 × 100G). The coherent-lite system is found to have similar module power consumption requirements as a corresponding 4 × 100G IM-DD system while bringing the benefits of coherent detection including improved sensitivity and higher spectral efficiency leading to fewer light sources per transceiver module. To the best of our knowledge, this work represents the first experimental demonstration of a DSP-free coherent-lite system for single channel 400G datacenter 10 km interconnects, a potential attractive solution due to its scalability to future 800G and 1.6T intra-datacenter optical interconnects.

Time Domain Equalization and Digital Back-Propagation Method-Based Receiver for Fiber Optic Communication Systems

“…In [18], a frequency domain equalizer has been suggested for FOCS to minimize PMD losses. Some researchers [19] have shown an analysis of coupling behaviors for two linear polarized modes using DSP up to 10 km transmission range. A demonstration of higher order modulation format data transmission with Raman amplifiers is performed with DSP techniques in [20].…”

“…where ε out and ε in present output and input power values of optical fiber and l is the fiber length. Similarly, OFCD effect is mentioned in Equations (18) and (19) given as…”

High-Capacity Coherent DCIs Using Pol-Muxed Carrier and LO-Less Receiver

“…However, none of the above propositions assures reduction in the signal processing complexity for controlling the power requirements at data centers. For reducing the power consumption and cost, analog domain signal processing has been proposed for coherent receivers [11]- [13]. Presented Rashmi work investigates an SH scheme to replace the PAM4 links with the aim of further increasing capacity using analog signal processing based receivers.…”

All-Analog Adaptive Equalizer for Coherent Data Center Interconnects

“…To overcome this issue an analog domain processing based solution was proposed, for the first time, in our previous work [10]. Since then a few other solutions using the analog domain (or DSP-free) processing for coherent optical links have been reported [9,[11][12][13][14][15]. For instance, [11] discusses an analytical study on the feasibility of DSP-free homodyne dual-polarization quadrature phase-shift keying (DP-QPSK) receivers for DCIs.…”