The function of the optical module is photoelectric conversion. Among them, the 400G rate optical module is a high-speed optical module suitable for high-performance computing applications. It has the characteristics of high-speed transmission and low latency. It is suitable for the currently booming intelligent computing centers and super-computing centers, and solves the bottleneck problem of data communication bandwidth. 400G optical modules use PAM4 optical port modulation, with a single-channel rate of up to 100G, achieving higher-speed transmission and lower power consumption at the same size. This article mainly discusses the relevant knowledge of 400G optical modules, including what is a 400G optical module, 400G optical module solutions, 400G optical module models, and answers to common questions about 400G optical modules such as 400G optical module compatibility, 400G optical module heat dissipation, and 400G optical module transmission distance. At the end of the article, the price of 400G optical modules is also discussed.
The 400G optical module is an optoelectronic conversion module with a transmission rate of micro-400G. It uses advanced PAM4 optical port modulation technology to achieve high-speed and low-latency data transmission. At present, this product is widely used in super-computing centers and intelligent computing centers.
The working principle of the 400G optical module is to convert electrical signals into optical signals and transmit them through the connected optical fiber. At the receiving end, the optical signal is converted into an electrical signal that can be recognized by the device. There are many types of 400G optical modules. There are four types on the market: CFP8, QSFP-DD, OSFP, and QSFP112. Each package type has different characteristics to meet the needs of various scenarios.
In optical module products, we often hear professionals discuss professional terms such as NRZ and PAM4. These words refer to whether the signal emitted by the chip is an NRZ signal or a PAM4 signal.
NRZ is non-return-to-zero modulation, which is a traditional modulation method. In NRZ signal encoding, a bit signal is converted into an electrical signal pulse, and the level of each pulse has two states: high level and low level (0, 1). The advantage of the NRZ solution is that the technology is mature and stable, but because the 400G optical module has a high transmission rate requirement, the NRZ solution with low spectrum efficiency is difficult to meet the 400G optical module. Secondly, NRZ encoding is sensitive to channel noise and is prone to introducing bit errors, especially in high-speed transmission conditions, which will lead to higher bit error rates. At present, this scheme has been gradually eliminated in 400G and 800G and higher-speed optical module schemes.
The PAM4 (Pulse Amplitude Modulation 4-level) scheme uses 4 different levels to represent one bit of information. Since PAM4 uses four different levels instead of two, more information bits can be carried in the same frequency bandwidth, thereby improving spectrum utilization. This reduces the bandwidth occupied by the signal while increasing the transmission rate, which is conducive to the effective use of existing network infrastructure. The spectrum efficiency of the PAM4 scheme is twice that of the NRZ scheme, so it can achieve a higher data transmission rate under the same bandwidth. PAM4 has significant advantages in spectrum efficiency, anti-noise performance, etc., and the PAM4 scheme has become the mainstream modulation method for 400G optical modules.
The coherent scheme is an optical communication technology based on coherent signals. This technology is generally suitable for high-speed and long-distance optical modules. This scheme has the characteristics of high sensitivity, so the transmission distance is longer, but due to its complex technology, the cost is naturally high. Currently, coherent solutions are used in 400G and 800G long-distance transmission.
Common models of 400G optical modules are:
QSFP-DD 400GBASE-SR8, QSFP-DD 400GBASE-FR4, QSFP-DD 400GBASE-SR4, QSFP-DD 400GBASE-DR4, QSFP-DD 400GBASE-FR8, QSFP-DD 400GBASE-LR8, QSFP-DD 400GBASE-LR4, QSFP-DD 400GBASE-ER8, OSFP-RHS 400GBASE-SR4, OSFP 400GBASE-DR4, QSFP112 400GBASE-DR4.
400G optical modules will generate a certain amount of heat when working. The heat source is mainly near the PCB chip and optical devices (TOSA and ROSA). To solve the heat dissipation problem of optical modules, both heat conduction and heat dissipation must meet the conditions. If the heat dissipation is poor, it may affect the performance and life of the optical module. 400G optical modules usually use advanced thermal management technology. For example, OSFP optical modules have integrated heat sinks, which greatly improve the heat dissipation performance.
The transmission distance of 400G optical modules is mainly affected by three factors: light source, dispersion and loss. Different light sources have different light intensities, and the distance of light transmission is also different; dispersion is mainly determined by the type of optical fiber. The dispersion of single-mode optical fiber is less than that of multi-mode optical fiber. Single-mode optical fiber is suitable for medium and long-distance transmission, and multi-mode optical fiber is suitable for short-distance transmission; loss is mainly determined by the transmission distance. The longer the transmission distance, the more loss in the middle.
As can be seen from the high-performance computing network topology diagram, it is not only the storage capacity of the equipment for data that increases. The most critical thing is that the increase in the number of ports of both switches and network cards is an important reason for the realization of high-performance computing. Therefore, in the construction of high-performance computer rooms, the proportion of optical modules is gradually increasing, so customers will have more considerations on the cost of optical modules. The following is an analysis of the factors affecting the price of optical modules from several aspects:
For optical modules with the same transmission rate, the longer the transmission distance, the higher the price
Another important factor affecting the price of 400G optical modules is market demand. When the market demand is large, there will be a shortage of optical chips and price increases, and the price of the module will also fluctuate;
It can be determined that with the advancement of technology, the manufacturing process of 400G optical modules will become more mature, and the price of 400G optical modules will be greatly reduced while the production capacity is increased.