With the maturity of industry standards and the continuous growth of network demands, 400G optical module technology has become a vital engine driving the upgrade of the Information and Communications Technology (ICT) industry. It has gained increasing attention and widespread application. It has vast prospects in various application scenarios, including data center networks, metropolitan transport networks, and long-distance high-capacity transmission networks. This article will provide a detailed perspective on 400G optical modules in three typical application scenarios: data center networks, metropolitan transport networks, and long-distance high-capacity transmission networks.

400G Optical Module Application in Data Center Interconnection Background

Rapid Growth of East-West Traffic According to IDC data, it is expected that by 2025, nearly 80% of global data traffic will be stored in core and edge servers. Simultaneously, the growth rate of east-west traffic within data centers will be significantly higher than that of north-south traffic and inter-data center traffic. Traditional data centers are gradually being replaced by cloud data centers, driven largely by the popularity of cloud computing, which has stimulated the industry’s demand for 400G optical modules.

Trends: Reduction in Cost per Bit and Power Consumption

In general, customer demands adjust in response to changes in application scenarios. For long-distance WDM transmission, module performance is a key factor as customers seek higher capacity and longer transmission distances. In contrast, in short-distance transmission scenarios within data centers, cost is of greater importance to customers.

To achieve higher capacity, there are three main ways in which 400G optical modules reduce the cost per bit:

1. PAM4 Technology: PAM4 technology effectively improves bandwidth utilization. Under the same bit rate conditions, PAM4 signals have twice the bit rate of NRZ signals, thus increasing transmission efficiency while reducing costs.
2. Multi-Channel: An 8-channel transmission solution is more advantageous in terms of balancing cost and power consumption compared to 4-channel transmission.
3. Higher-Rate Optical Chips: These optical chips can increase transmission speed without affecting the transmission distance. Various 25G-rate optical chips (DML, EML, VSCEL) are gradually upgrading to 56G-rate optical chips.

400G optical modules find extensive applications in data centers. For instance, the 400G QSFP-DD XDR4 optical module can be used in 4x100G breakout scenarios for QSFP28-FR-100G. For data center interconnection applications, the 400G QSFP-DD FR4 optical module can support 2km single-mode fiber transmission. The 400G QSFP-DD LR8 and 400G QSFP-DD LR4 optical modules, on the other hand, support link lengths of up to 10km by transmitting 4 CWDM wavelengths. Additionally, the 400G QSFP-DD ER8 optical module, suitable for long-distance transmission, can cover 40km of G.652 single-mode fiber links.

Applications of 400G Optical Modules in Metropolitan Area Carrier Networks

Background: Traffic Growth Driven by New Technologies in the 5G Era

Carrier networks are experiencing growing demands in the 5G era, including ultra-high bandwidth, massive connections, ultra-low power consumption latency, and high reliability. Existing urban networks’ 100G ports can no longer meet the transmission requirements for core and aggregation layers. Therefore, 400G optical module solutions play a significant role in 5G carrier networks.

Trend: Reducing the Unit Bit Transmission Cost to Improve Reliability and Transmission Distance

Due to the anticipated high volume of optical modules in 5G base stations, network operators urgently need to lower the optical module costs in network construction investments. Furthermore, in the telecom carrier network, where optical modules have a lifespan of over 10 years and can transmit over 80km, there are higher demands for reliability and performance in metropolitan carrier network applications.

Metropolitan Carrier Network Applications

To achieve higher transmission rates and lower production costs, 400G optical modules used for integrated metropolitan carrier networks employ similar technologies to those in data center network scenarios:

• High-Reliability Optical Modules: Utilizing sealed packaging to meet the 10-year lifespan and operating temperature range of 0~70°C requirements.
• High-Performance LWDM Transmitters: Low dispersion costs and outstanding transmission performance.
• High-Performance APD Receivers: Enhancing reception sensitivity.
• Coherent Technology: To enable transmission distances beyond 80km, 400G optical module solutions employ coherent technology. Simultaneously, with the development of SiP and INP integration technologies and the continuous evolution of CMOS technology, coherent optical modules are becoming smaller and more power-efficient. The advantages of low power consumption and compact size in 400G ZR optical modules are expected to be widely applied in metropolitan network edge access scenarios.

400G Optical Module Applications in Long-Distance High-Capacity Transmission Networks

Background: Increasing Bandwidth Pressure for Long-Distance Data Transmission due to Traffic Growth

The growth in network traffic has increased the bandwidth pressure on transmission networks. For long-distance and high-bandwidth transmission, the use of coherent transmission technology in 400G optical modules with wave division multiplexing (WDM) provides an optimal solution.

With the introduction of flexible modulation and grid technologies, dense wave division multiplexing (DWDM) enhances spectral efficiency and transmission capacity by selecting the most suitable coding methods and channel widths for each port’s capacity and transmission distance.

Trend: Improved Spectral Efficiency

Coherent optical modules are advancing in three aspects:

1. Spectral Efficiency: Progress in oDSP algorithms enhances spectral efficiency and single-fiber capacity.
2. Bit Rate: Increasing the single-wavelength bit rate to achieve higher single-port bandwidth, thereby reducing unit bit cost and power consumption.
3. Smaller Size and Lower Power Consumption: Using integrated optoelectronic components, advanced manufacturing processes, and specialized oDSP algorithms to reduce the size and power consumption of 400G optical modules.

Conclusion

Currently, mainstream 400G optical modules are widely used in various network scenarios, including data center networks, metropolitan carrier networks, and long-distance high-capacity transmission networks. The demand for higher capacity, lower unit bit cost, and lower power consumption is driving optical modules towards higher data rates.