Intra-datacenter Interconnects Research Articles

Comparison of null-subcarriers reservation and adaptive notch filter for narrowband interference cancellation in intra-data center interconnect with DMT signal transmission.

In this paper, we experimentally compare the performance of two different narrowband interference suppression schemes in 120 Gb/s intensity modulation and direct detection (IM/DD) system with discrete multi-tone (DMT) signal transmission for intra-data center interconnect (Intra-DCI). Digital pre-equalization and DFT-spread techniques are applied for system bandwidth limitation induced signal distortion compensation and signal peak to average power ratio (PAPR) reduction, respectively. Null-subcarriers reservation (NSR) and adaptive notch filter (ANF) techniques are compared during the suppression of digital-to-analog convertor (DAC) clock leakage induced narrowband interference. 1.2 dB and 1.8 dB DMT receiver sensitivity improvements can be achieved at a bit-error rate of 3.8 × 10-3 in optical back-to-back (OBTB) transmission when optimized NSR and ANF schemes are applied for narrowband interference cancellation, respectively. After 2-km single mode fiber (SMF) transmission, the required received optical power (ROP) of DMT signal with optimized NSR and ANF for narrowband interference cancellation at BER of 3.8 × 10-3 are -6.5 dBm and -7.1 dBm, respectively. Obviously, ANF outperforms NSR scheme in narrowband interference cancellation for DMT system.

Free Space Intra-Datacenter Interconnects Based on 2D Optical Beam Steering Enabled by Photonic Integrated Circuits

Data centers are continuously growing in scale and can contain more than one million servers spreading across thousands of racks; requiring a large-scale switching network to provide broadband and reconfigurable interconnections of low latency. Traditional data center network architectures, through the use of electrical packet switches in a multi-tier topology, has fundamental weaknesses such as oversubscription and cabling complexity. Wireless intra-data center interconnection solutions have been proposed to deal with the cabling problem and can simultaneously address the over-provisioning problem by offering efficient topology re-configurability. In this work we introduce a novel free space optical interconnect solution for intra-data center networks that utilizes 2D optical beam steering for the transmitter, and high bandwidth wide-area photodiode arrays for the receiver. This new breed of free space optical interconnects can be developed on a photonic integrated circuit; offering ns switching at sub-μW consumption. The proposed interconnects together with a networking architecture that is suitable for utilizing those devices could support next generation intra-data center networks, fulfilling the requirements of seamless operation, high connectivity, and agility in terms of the reconfiguration time.

Real-time 100 Gbps/λ/core NRZ and EDB IM/DD transmission over multicore fiber for intra-datacenter communication networks.

A BiCMOS chip-based real-time intensity modulation/direct detection spatial division multiplexing system is experimentally demonstrated for both optical interconnects. 100 Gbps/λ/core electrical duobinary (EDB) transmission over 1 km 7-core multicore fiber (MCF) is carried out, achieving KP4 forward error correction (FEC) limit (BER < 2E-4). Using optical dispersion compensation, 7 × 100 Gbps/λ/core transmission of both non-return-to-zero (NRZ) and EDB signals over 10 km MCF transmission is achieved with BER lower than 7% overhead hard-decision FEC limit (BER < 3.8E-3). The integrated low complexity transceiver IC and analog signal processing approach make such a system highly attractive for the high-speed intra-datacenter interconnects.

DSP-free 'coherent-lite' transceiver for next generation single wavelength optical intra-datacenter interconnects.

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 × 10-4. 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.

56 Gbps signal generation from one 10-G class laser diode for 400G intra-data center interconnection

Abstract We have demonstrated up to 56-Gb/s cost-efficient transmission for intra-data center interconnection over 10-km SMF-28 with negative power penalty. This 56-Gb/s transmitter comprises a low-cost 10-G-class directly-modulated distributed-feedback (DFB) laser without requiring expensive digital to analog converter (DAC), analog-to-digital converter (ADC) and power-consumptive digital signal processing (DSP).

200-Gb/s Baudrate-Pilot-Aided QPSK/Direct Detection With Single-Section Quantum-Well Mode-Locked Laser

We demonstrate transmission of a 200-Gb/s superchannel over 3-km single-mode optical fiber (SMF) targeting intra-data center interconnect applications using a novel single-section quantum-well passive-mode-locked laser that generates an optical frequency comb. The transmitted optical signal consists of 16 subcarriers filtered from the optical frequency comb of the laser and modulated with an advanced modulation format of Baudrate-pilot-aided quadrature phase-shift keying (QPSK) modulation that enables direct detection. Bit error rates below the forward error correction limit have been confirmed for all subcarriers, and the detailed noise characteristics of the passive-mode-locked laser have been investigated to support the understanding of the system performance.

Large-Scale and Simple-Configuration Optical Switch Enabled by Asymmetric-Port-Count Subswitches

We propose a novel optical switch architecture for intra-datacenter interconnection. The proposed switch consists of asymmetric-port-count delivery-and-coupling (DC) switches and wavelength-routing (WR) switches based on arrayed-waveguide gratings (AWGs). To compensate for the insertion loss of the DC switch part and to suppress the passband-frequency deviation inherent in multiple-input-port AWGs, we employ a combination of an aggregation coupler, an erbium-doped fiber amplifier, and a single-input-port AWG for the WR-switch part. Moreover, we can reduce complicated fiber connections between the DC switches and the WR switches by making their port counts asymmetric. To confirm feasibility of the proposed switch architecture, we fabricate a 24 $\times$ 4 DC switch and a 16 $\times$ 8 DC switch with planar-lightwave-circuit technologies and evaluate the overall switching system. We construct part of 768 $\times$ 768 optical switch and part of 1536 $\times$ 1536 optical switch with the fabricated DC switches. Their excellent transmission characteristics are experimentally confirmed.

SDN-Enabled OPS With QoS Guarantee for Reconfigurable Virtual Data Center Networks

Optical packet switching (OPS) can enhance the performance of data center networks (DCNs) by providing fast and large-capacity switching capability. Benefiting from the software-defined networking (SDN) control plane, which could update the look-up-table (LUT) of the OPS, virtual DCNs can be flexibly created and reconfigured. In this work, we have implemented and assessed an SDN-based control framework for an OPS node, where the OpenFlow protocol has been extended in support of the OPS switching paradigm. Application flows are switched by the OPS at submicrosecond hardware speed, decoupled from the slower (millisecond timescale) SDN control operation. By the DCN infrastructure provider, the virtual networks become directly programmable with the abstraction of the underlying OPS node. Experimental results validate the successful setup of virtual network slices for intra-data center interconnect and quality of service (QoS) guarantee for high-priority application flows. Data plane resources are efficiently shared by exploiting statistical multiplexing. In addition, the capability of exposing per-port OPS traffic statistics information to the SDN controller enables the implementation and experimental validation of load balancing algorithms to improve the QoS performance.