Everything about QSFP28 optical transceiver

The continuous rapid development of the Internet and the demand for higher speed optical networks ceaselessly give impetus to the the entire optical communication industry, and the technology of optical communication devices has also been innovated and developed. The QSFP28 optical module is one of the representative, which has developed a mature series of products and industrial chain from 2013 to now. This paper will introduce QSFP28 optical transceiver in detail, including its types, application and market demand.

What are the main types of QSFP28 transceiver?

The QSFP28 has significant advantages over first-generation common form factor pluggable (CFP) and CFP4 modules. In terms of appearance, the CFP4 is 1/4 of the size of the first generation CFP, while the QSFP28 is even smaller than the CFP4 form-factor, making it suitable for higher density switches, thus achieving higher forwarding service capability for a single block switch and providing the possibility of building ultra-large scale data centers. In terms of intrinsic performance, the QSFP28 optical module is a 25Gb/s × 4-channel parallel transmission. Compared with the CFP module 10Gb/s × 10-channel transmission, it supports 100G Ethernet standard; compared with the QSFP+ optical module 10Gb/s × 4-channel transmission rate, it occupies the same number of channel resources, but can achieve 2.5 times the transmission performance, so it is the mainstream solution of 100G network, and is also the most demanded form factor in the market.

There are two key standard organizations for optical modules, IEEE and MSA (Multi Source Agreement), which complement and learn from each other. The standards beginning with 100G are proposed by IEEE802.3. For example, in the name of 100GBASE-LR4, “LR” means long rage, i.e. 10Km, and “4” means four channels, i.e. 4*25G, combined together as a 100G optical module that can transmit 10Km. Since the introduction of 100G networks, IEEE, the Multi-Source Agreement (MSA) industry consortium and other organizations have developed several standards for 100G optical modules. Taking 100G optical modules as an example, IEEE has defined standards such as 100GBASE-SR4, 100GBASE-LR4, 100GBASE-SR10, etc. Multi-Source Protocol (MSA) has 100G PSM4, 100G QSFP28 ER4, 100G CLR4, 100G SWDM4, etc. The QSFP28 optical transceiver is divided into four main types: SR4/LR4/CWDM4/PSM4.

QSFP28 transceiver

Comparison Table of Four Types QSFP28 Optical Modules

  1. 100G QSFP28 SR4 optical transceiver

The QSFP28 SR4 optical module is a parallel 100G optical module. QSFP28 SR4 100G full-duplex optical module provides 4 independent transmitting and receiving channels, each channel can operate at 25Gbps over OM4 MMF(Multi-mode Fiber). The overall data transmission rate is 100Gbps. When QSFP28 SR4 optical module transmits signals at the transmitting end, the electrical signals are converted into optical signals through 4 array lasers, and then transmitted in parallel on the banded multi-mode fiber. Then, when it reaches the receiving end, the 4-array photodiode converts the parallel optical signal into a parallel electrical signal. Compared to the other three types, it has the shortest transmission distance of 100m, so SR4 modules are usually used in data centers.

  1. 100G QSFP28 LR4 optical transceiver

The QSFP28 LR4 optical module generally adopts LC single-mode optical fiber for signal transmission, and the maximum transmission distance can reach 10km. The LR4 module converts four 25Gbps electrical signals into four LAN WDM optical signals, and then multiplexes them into a single channel by MUX or WDM to realize 100G optical signal transmission. At the receiving end, the LR4 module uses DEMUX to demultiplex 100G optical input into 4-channel LAN WDM optical signal, and then convert it into 4-channel electrical signal.

  1. 100G QSFP28 PSM4 optical transceiver

PSM means “Parallel Single-Mode Fiber”. The QSFP28 PSM4 optical transceiver is a high-speed and low-power-consumption product, which is specially used for optical interconnection in data communication applications. It conforms to PSM4 MSA optical interface specification, in hot-pluggable QSFP form factor and built-in digital diagnosis function. It has four independent full duplex channels, with a data rate of 25.78Gbps per channel and a wavelength of 1310nm. QSFP28 PSM4 transceiver is mainly used in 40G and 100G Ethernet. It’s a cost-saving solution for medium distance transmission.

  1. 100G QSFP28 CWDM4 optical transceiver

The transmission rate of the QSFP28 CWDM4 optical module is 103.1Gbp. It is mainly used in computing, high-frequency data transaction and other fields. Its cost is significantly higher than that of QSFP28 PSM4 optical module. Through coarse wavelength division multiplexing (CWDM) technology, the QSFP28 CWDM4 transceiver multiplexes four wavelengths – 1270nm, 1290nm, 1310nm and 1330nm – onto a single-mode fiber for signal transmission.

How to choose the QSFP28 transceiver according to transmission distance?

Transmission distance <100m

There are two options to achieve this kind of transmission. One is to use the length of 3m ~ 20m QSFP28 AOC for connection; another option is to use QSFP28 SR4 optical module with 12 core MTP OM3/OM4 fiber patch cable connection (can support 100m transmission distance.)

Transmission distance of 100m ~ 2km

For medium and long distance connection, the implementation process often needs to consider the cost, PSM4 QSFP28 optical module and CWDM4 QSFP28 optical module are suitable for operation in medium and long distance 100G network. QSFP28 100G CWDM4 optical module transmits a longer distance, with single-mode fiber, the transmission distance can reach 2km. PSM4 QSFP28 optical module used with 8 parallel single-mode fibers, the transmission distance is around 500 meters, which can also meet the requirements.

Transmission distance: ≤ 10km

For long-distance transmission, 100G QSFP28 LR4 optical module with LC interface is the best choice, which is usually used together with single-mode fiber. It is suitable for 100G network transmission in the same city or the same region. However, this model of optical module is now relatively high in cost and needs to be included in the selection considerations.

Transmission distance

What type of optical transceiver should we choose when the transmission distance is over 10km? In this case, the QSFP28 ER4 and the QSFP28 ZR4 are good options. The former can reach a maximum transmission distance of up to 40km while the later is the best choice for 100G long-distance DCI for that it can transmit data to 80km. In the actual application process, we will consider a series of factors such as cost, power consumption, transmission distance and fiber jumper type.

The market demand of QSFP28 transceiver

The main raw materials of optical modules include optical chips and components, integrated circuit chips and structural parts. Among them, optical chips and components are the core raw materials, accounting for more than 50% of the cost, and the higher the transmission rate of optical modules, the higher the cost of optical chips. At present, core components such as optical chips are monopolized by a few giant enterprises, and basic raw materials such as circuit boards are mainly from Chinese suppliers.

In recent years, the data center market has become the core driving force for the growth of the optical device market. On the one hand, this is due to the new demand brought by the new construction of the data center and the internal optical interconnection. On the other hand, most of the optical modules required by data centers are 100G QSFP28 and other more expensive high-speed optical modules. Currently, the demand structure of 100G optical module in the global data center market is changing significantly, with the demand for 100G QSFP28 CWDM4 increasing and the demand for 100G QSFP28 PSM4/LR4 decreasing.

The market demand of QSFP28 transceiver

Trend Analysis of QSFP28 Module in Data Center

The construction boom of super-scale data centers will promote the demand of high-speed optical modules, 100G optical module product technology lines are more mature, 400G modules of first-line manufacturers have started mass production, 100G high-speed optical module market share is expected to escalate steadily from 40% in 2017 to 45% in 2022, 400G high-speed optical module market share will grow rapidly from 1% in 2018 to 24% in 2022. The market share of 400G high-speed optical modules will grow rapidly from 1% in 2018 to 24% in 2022. Data center optical module market share will also grow from $5.6 billion in 2017 to $10 billion in 2022, with a compound growth rate of 12.3%.

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