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Data Center interconnection currently provides 100GB/S data rate via optical signals. As demand for higher-capacity data streams continues to grow, data center operators and service providers turn to 400 GB/s speed and finding ways to reduce the relative power consumption.

By using coherent optical technology, data center interconnection can speed up to 400G.   Internet traffic continues to grow exponentially, and communication networks must evolve to meet the need for big data and high speed.  Emerging technologies such as 5G, the Internet of things (IoT) , and virtual reality are placing unprecedented demands on data centers.   And  data centers need to manage larger volumes of traffic and achieve faster response speed.

Distributed data centers need to communicate with each other to share data, balance workloads, provide backups, and expand capacity when needed. In the campus or urban area, the distributed data center needs to increase the interconnection capacity by a large margin.


The 400ZR supports 400G DCI

Data Center interconnection currently provides 100 GB/s data speeds via optical signals . As demand for higher-capacity data streams continues to grow, data center operators and service providers turn to  400 GB/s data speed and finding ways to reduce the relative power consumption. The development of integrated photonics technology and new standards paves the way for a new class of economical DCI based on coherent optics technology.  


What is 400 ZR?

The OIF is currently developing the 400ZR network implementation protocol (IA) for Pluggable Digital Coherent Optical Communication . The 400ZR standard will use dense wavelength division multiplexing (DWDM) technology and higher modulation to transmit multiple 400(GE)  over DCI links up to 80 km distance. The goal is to ensure long-range implementation based on a single carrier 400G. The single-carrier 400G uses 16 QAM amplitude modulation at a rate of about 60G baud. Only through coherent detection and advanced digital signal processing (DSP) technology to achieve this goal. The 400ZR IA will reduce the cost and complexity of high-bandwidth data center interconnection and improve interoperability between optical modules from different manufacturers.

On the host side, the 400ZR uses the 400GAUI-8 interface. The complete data path from the interface to the coherent optical signal on the line side is described in detail in 400ZR IA. It also gives a complete definition of cascaded forward error correction (FEC) scheme, which consists of hard decision (HD) external FEC and soft decision (SD) internal FEC.

Data center operators are interested in using 400ZR coherent interfaces to connect to distributed data centers, which can reach up to 80 kilometers. Although IA is not for specific shapes, the specification was developed with the use of QSFP-DD, OSFP, or COBO modules. This allows a direct connection to the data center switch like a client-side optical module, eliminating the need for expensive and cumbersome transport networking equipment inside the data center. In addition, the Telecom industry wants to use 400ZR for 200gb/s of Home return traffic, which uses 64GB baud signaling and QPSK technology.


What are 400GBASE-ZR and 100GBASE-ZR?

The IEEE approved Project 802.3 CT in 2018. IEEE 802.3ct will make use of the 400ZR IA of OIF to establish 400GBASE-ZR standard, and realize the 400GB/s single-wavelength transmission of up to 80km in DWDM system. DWDM systems involve multiplexing data signals from different transceivers using a single optical fiber. For 100GBASE-ZR, the IEEE makes use of the work of the International Telecommunication Union (ITU) in developing 100GB/S transmission standards, the standard uses the DP-DQPSK modulation scheme and the CableLabs full-duplex coherent optical specification.

400ZR and its applications

 The advantages of 400ZR

Although 400ZR technology is still in its infancy, it will have a significant impact on a number of industries once it becomes widespread.

Large-scale Data Center/Cloud service provider

Much of the demand for high-speed data center networking comes from the Google, Amazon, Microsoft, Facebook Baidu, Tencent and Alibaba, which owned large-scale data centers.  These massive data centers need improve connection speed  to accommodate the exponential growth of cloud services, Internet of Things devices, streaming video and other applications. The development of DCI and networking technologies helps  cloud and large-scale data centers adapt to the growing demand for higher bandwidth in the network.   

Distributed campuses and urban areas

Many organizations  cannot build large-scale data centers especially like  distributed campuses and urban areas.  Thus managing multiple data centers in these areas are the new normal due to space constraints and disaster recovery requirements. Distributed data centers need to communicate with each other to share data, balance workloads, provide backups, and expand data center capacity as needed. The 400ZR technology will support the high bandwidth interconnections for distributed data centers connection.


Telecom providers

Like data centers, Telecom providers are struggling to meet the demand of the explosion of network traffic, both at home and at work.  Including the coming 5G mobile network, consumers need higher connection speeds. The 400ZR will provide 400GB/s speeds for applications such as video streaming, online video games, video conferencing, and online backup services.


The 400ZR standard allows telecommunications companies to send back residential traffic. When running at 200gb/s, the 400ZR can use 64GB baud signaling and QPSK modulation to increase the range of high-loss transmissions. For 5G networks, the 400ZR provides mobile back-haul by aggregating multiple 25gb/s data streams.


400ZR+ and 400ZR-

Except to the interoperable 400G mode, the 400ZR transceiver is expected to support other modes to increase the range of addressable applications. These models are called 400ZR+ and 400ZR-. + Indicates that the power consumption of the module exceeds the 15W required by IA (and some pluggable devices), enabling the module to transmit over distances of hundreds of kilometers using more powerful signal processing technology.

- Indicates that modules support low speed modes, such as 300GB, 200GB, and 100GB, which provide rare flexibility for network operators.


Test 400G coherent optical components and transceivers

Arbitrary waveform generator and optical modulation analyzer

In telecommunication and data communication, the optimization of coherent optical transmitter is an important requirement, which aims to expand the coverage, improve the spectral efficiency and reduce power consumption. In coherent optical signal analysis, even common measurements can be quite complex, such as measuring EVM (error vector amplitude) , IQ bias, IQ imbalance, orthogonal errors, and offsets. To fully test an optical transmitter, you must simulate it with complex waveforms using different modulation modes and from different data sources. It is also important to properly offset and pre-distort the input signal to help you compensate for the linear loss in the test device and thus measure the true performance of the optical transmitter. A flexible, extensible test solution ensures that you test your optical transceiver quickly and accurately.


Testing 400G coherent optical transceiver and its sub-components requires that the test equipment can generate and analyze pure signal with at least 40ghz measurement bandwidth. The test instrument needs to be flexible enough to handle various modulation schemes and pulse shapes on four synchronous channels in order to test dual-polarized in-phase and orthogonal (IQ) signals on the excitation and analysis side. Combined with DAC and Analog-to-digital converter (ADC) , and a full set of common algorithms and efficient interfaces  software tools,       these requirements can be met.


Coherent optical device testing

The Photoelectric components used in coherent optical transmission systems brings unique testing challenges. For example, to test dual-polarized IQ modulators and heterodyne coherent receivers, we need to measure electro-optic (E/O) and optic-electro (O/E) conversion efficiencies respectively. The measurements of bandwidth, gain, imbalance, group delay and incline can be used to characterize coherent optical devices. These measurements are very complex and time consuming. The selection of appropriate testing equipment can save valuable time and reduce the development and verification cost of coherent optical devices.


The future of data center interconnection

As network data traffic continues to grow year by year, 400G coherent optics technology promises to provide faster data flow between data centers. The 400G solution, supported by new standards such as 400ZR and 400 ZR+, can provide great advantages and flexibility to meet the growing data needs. These new standards significantly increase bandwidth capacity and reduce operating costs (fewer transceivers) and reduce the space and power consumption of devices. The 400ZR and 400GBASE-ZR+ will enable large-scale data centers, distributed data centers and metro networks to provide the 400G interconnection speeds required by emerging technologies.


Manufacturers of optical components and equipment face new testing challenges. The new test equipment can generate and analyze 16-QAM signals with transmission rates up to 60gbaud and optical demultiplexing, helping manufacturers test their components and devices in 400G applications on multi-terabyte/second DWDM networks. Accurate testing of new 400gb/s optical coherent components and transceivers is essential to optimize the design of the next generation of DCI.


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