This section describes the application of optical modules in data centers


Published:

2020-05-07

In recent years, application markets such as big data, cloud computing, 5G, Internet of Things and artificial intelligence have developed rapidly. The coming driverless application market has brought explosive growth to data traffic, and data center interconnection has gradually developed into a research hotspot of optical communication.

This section describes the application of optical modules in data centers

In recent years, application markets such as big data, cloud computing, 5G, Internet of Things and artificial intelligence have developed rapidly. The coming driverless application market has brought explosive growth to data traffic, and data center interconnection has gradually developed into a research hotspot of optical communication.

The current data center is no longer just one or several machine rooms, but a group of data center clusters. In order to realize the normal operation of various Internet services and application markets, data centers are required to operate cooperatively. Massive real-time information interaction between data centers has produced the demand for data center interconnection network, and optical fiber communication has become a necessary means to realize interconnection.

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Different from traditional telecom access network transmission equipment, data center interconnection requires higher speed, lower power consumption, and miniaturization to achieve more information and more intensive transmission. A core factor that determines whether these properties can be achieved is the optical module. The information network mainly uses optical fiber as the transmission medium, but the calculation and analysis must be based on electric signal at present. Optical module is the core device to realize photoelectric conversion.

The core component of the optical module is composed of Transimitter(optical transmission sub-module)/Receiver(optical reception sub-module) or Transceiver(optical transceiver integrated module), electrical chip, in addition, including lens, splitter, beam synthesizer and other passive devices and peripheral circuits.

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Common optical module encapsulation modes include SFP, XFP, QSFP, and CFP.

· Small Form-factor Pluggable (SFP) is a compact, pluggable transceiver module standard for telecommunications and data communication applications that can support up to 10Gbps transmission rates.

· 10 Gigabit Small Form Factor Pluggable (XFP) is the 10 gigabit Small form Factor pluggable transceiver module standard that supports various communication protocols, such as 10 gigabit Ethernet, 10 Gigabit Fibre Channel, and SONETOC-192. XFP transceivers can be used in the data communications and telecommunications markets and provide better power consumption characteristics than other 10Gbps transceivers.

QSFP(Quad Small Form-factor Pluggable) is a compact, pluggable transceiver standard for high-speed data communication applications. According to the speed, QSFP can be divided into 4×10G QSFP+, 4×25G QSFP28, 8×25G QSfp28-DD optical modules. QSFP28 has been widely used in data centers around the world.

·CFP(Centum gigabits Form Pluggable) is a standardized intensive wavelength division optical communication module with transmission rates up to 100-400Gbps. The CFP module is larger than the SFP/XFP/QSFP and is generally used for long-distance transmission such as the metropolitan area network.

Data center communication optical modules can be divided into three types according to connection types:

(1) From the data center to the user, it is generated by end-user behaviors such as browsing web pages, sending and receiving emails and video streaming by accessing the cloud;

(2) Data center interconnection, mainly used for data replication, software and system upgrade;

(3) Inside the data center, mainly used for information storage, generation and mining. According to the prediction of Cisco, the internal communication of data center accounts for more than 70% of the communication of data center. The great development of data center construction also gives birth to the development of high-speed optical module.

The continuous growth of data traffic and the trend of large and flat data centers promote the development of optical modules in two aspects:

· Increased demand for transmission rate

· Increase in quantity demand

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The upsizing trend of data centers increases the demand for transmission distance. The transmission distance of multi-mode fibers is limited by the increase of signal rate, and it is expected that single-mode fibers will gradually replace the transmission distance of multi-mode fibers. The link cost of optical fiber is composed of optical module and optical fiber, and there are different application schemes for different distances. In terms of medium and long distance interconnections needed for data center communications, there are two revolutionary solutions born out of Msas:

· PSM4(Parallel Single Mode 4 lanes)

· CWDM4(Coarse Wavelength Division Multiplexer 4 lanes)

Among them, PSM4 fiber use is 4 times that of CWDM4, when the link distance is longer, CWDM4 solution cost is relatively low.

Nowadays, the realization technology of 400G optical module has become the focus of the industry. The 400G optical module improves the data throughput and maximizes the bandwidth and port density of the data center. Its future trend is to achieve wide gain, low noise, miniaturization and integration, to meet the application requirements of the communication between the next generation wireless network and the very large scale data center.

Currently, the 400G optical modules mainly use 8-channel 53G NRZ or 4-channel 106G PAM4(4 Pulse Amplitude Modulation) signal modulation to realize 400G signal transmission.

In terms of module encapsulation, OSFP or QSFP-DD are used, both of which can provide 8-channel electrical interfaces. The smaller package size of QSFP-DD makes it more suitable for data center applications. OSFP has a slightly larger package size and higher power consumption, making it more suitable for telecommunications applications.