Application of optical module in data center


In recent years, the application markets of big data, cloud computing, 5G, Internet of Things, and artificial intelligence have developed rapidly. The upcoming driverless application market has brought explosive growth to data traffic. Data center interconnection has gradually developed into optical communication research. hot spot.

data center

The current data center is no longer just one or several computer rooms, but a group of data center clusters. In order to realize the normal work of various Internet services and application markets, the data centers are required to work together. The real-time mass exchange of information between data centers creates the demand for data center interconnection networks, and fiber optic communication has become a necessary means of interconnection.

Unlike traditional telecommunications access network transmission equipment, data center interconnection requires greater and denser information transmission, requiring higher speed, lower power consumption, and more miniaturization of switching equipment. A core factor that determines whether these performances can be achieved is the optical module.

Optical Transceiver

The information network mainly uses optical fiber as the transmission medium, but at present, calculation and analysis must also be based on electrical signals, and the optical module is the core device for photoelectric conversion.

The core components of the optical module consist of Transimitter (optical transmission sub-module) / Receiver (optical reception sub-module) or Transceiver (optical transceiver integrated module), electrical chip, and also include passive devices such as lenses, splitters, and beam combiners and Peripheral circuit composition.

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

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

· XFP (10 Gigabit Small Form Factor Pluggable) is a standard for small pluggable transceiver modules at 10G rate, supporting multiple communication protocols such as 10G Ethernet, 10G 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, mainly used 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, etc. QSFP28 has been widely used in global data centers.

· CFP (Centum gigabits Form Pluggable) is based on standardized dense-wavelength division optical communication module with transmission rate up to 100-400Gbps. The size of the CFP module is larger than SFP / XFP / QSFP, and is generally used for long-distance transmission such as metropolitan area networks.

The communication optical modules in the data center can be divided into three categories according to the connection type:

(1) From the data center to the user, it is generated by the end user's behavior such as browsing the web, sending and receiving emails, and video streaming;

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

(3) Inside the data center, it is mainly used for information storage, generation and mining. According to Cisco's prediction, the internal communication of the data center accounts for more than 70% of the data center communication, and the great development of the data center construction has also spawned the development of high-speed optical modules.

Data traffic continues to grow, and the trend toward larger and flatter data centers has driven the development of optical modules in two ways:

· Increased transmission rate requirements

· Volume demand growth

optical module

The trend of large-scale data centers has led to an increase in transmission distance requirements. The transmission distance of multimode fiber is limited by the increase in signal rate, and it is expected to be gradually replaced by single-mode fiber. The cost of the optical fiber link is composed of two parts: the optical module and the optical fiber, and there are different applicable solutions for different distances. In terms of the medium and long distance interconnection required for data center communication, there are two revolutionary solutions born from MSA:

· PSM4(Parallel Single Mode 4 lanes)

· CWDM4(Coarse Wavelength Division Multiplexer 4 lanes)

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

Today, the implementation technology of 400G optical modules has become the focus of industry attention. The main function of the 400G optical module is to increase the data throughput and maximize the bandwidth and port density of the data center. Its future trend is to achieve wide gain, low noise, miniaturization and integration, etc., to meet the application requirements of next-generation wireless networks and ultra-large-scale data center communications.

In the current 400G optical modules, 8-channel 53G NRZ or 4-channel 106G PAM4 (4 Pulse Amplitude Modulation, 4-level pulse amplitude modulation) signal modulation is mainly used to realize 400G signal transmission.

In terms of module packaging, OSFP or QSFP-DD is used, both of which can provide 8-way electrical signal interface.

In comparison, the QSFP-DD package is smaller in size and more suitable for data center applications; the OSFP package is slightly larger in size and consumes more power, which is more suitable for telecommunications applications.

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