30Oct, 2023
    Exploring 400G Optical Module Typical Applications

    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.

    Table 1, Comparison of different types of data centers

    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.

    Table 2, Bandwidth requirement of optical modules in 5G Metro 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.

    21Sep, 2023
    Optical Modules FAQs — Part 2

    In the dynamic realm of optical networking, real-world challenges often test the capabilities of both original equipment manufacturer (OEM) and third-party modules. These challenges encompass issues like unresponsive ports, fluctuating links, CRC errors, packet loss, module failures, and sudden downtimes. To assist and enlighten our community, we’ve compiled essential answers to these common queries:

    Q1: High Prices of OEM Modules — Are They Justifiable? Do You Really Need Them?

    A1: The soaring prices of OEM modules may raise eyebrows, with a part of the cost aimed at providing assurance, and another part for profit. Yet, OEM modules indeed guarantee superior quality and compatibility, potentially avoiding disruptive issues. Juggling various third-party modules based on cost alone can lead to complications. Some third-party optical modules maintain robust quality control and compatibility testing. The choice depends on your priorities and operational capabilities.

    Q2: Manufacturer Size — Does Bigger Mean Better Quality?

    A2: For well-established modules, the difference between large and small manufacturers is subtle, mostly evident in extreme cases. Regardless of size, it’s crucial that both manufacturers ensure compatibility with your specific equipment.

    Q3: AOC Compatibility Troubles — Whose Responsibility Is It?

    A3: When AOC (Active Optical Cable) connections between different manufacturers don’t function as expected, both parties share the responsibility. To avoid such scenarios, clarify the type of equipment on the other end and whether pre-coding is necessary before procuring AOC/DAC (Direct Attach Cable).

    Q4: Deciphering Optical Module Transmission Distance

    A4: Optical module and AOC transmission distances are primarily determined by the modules themselves, with equipment playing a smaller role. However, for modules that support Forward Error Correction (FEC), both the module and the equipment must be FEC-compatible to achieve extended distances. For example, without FEC, some 40G single-mode modules can only transmit up to 30km, but with FEC support, they can reach 40km.

    Q5: Critical Parameters for Long-Distance Single-Mode Optical Modules

    A5: When purchasing 40km/80km optical modules, don’t solely rely on the advertised distance or actual fiber length. Consider both the claimed receiving sensitivity and real-world line attenuation to ensure that the specified 80km optical module indeed performs as expected.

    Q6: Demystifying the 1-to-4 Cable

    A6: Nearly all 40G QSFP+ ports can be configured to split one 40G connection into four 10G links. Similarly, most modern 100G QSFP28 ports support configuration to split one 100G into either four 10G or four 25G connections. The two types of 1-to-4 cables are DAC and AOC, alongside modules and separate fiber optics.

    Q7: Compatibility Codes and Model Differences

    A7: Some module compatibility issues may arise due to changes in compatibility code verification mechanisms between different models. Model 2 network cards may necessitate compatibility codes, while Model 1 did not.

    Q8: Third-Party Modules and Device Compatibility

    A8: Issues with third-party modules not functioning on specific devices may stem from the modules being compatibility-tested with other devices but not the one in question. Compatibility extends beyond coding to various signal specifications.

    Q9: Unilateral UP Status — Is This Normal?

    A9: It’s common for one end to be UP while the other remains unresponsive. Transmit and receive functions operate independently.

    Q10: Tackling Packet Loss and CRC Errors

    A10: When encountering packet loss and CRC errors, it’s essential to note that ports receiving CRC errors are receiving them from the other end. Investigate the equipment on the opposite side and the line, particularly if third-party devices are involved.

    Q11: Diagnosing Unresponsive Ports

    A11: Unresponsive ports can result from various factors such as mismatched auto-negotiation settings, temperature fluctuations, compatibility issues between modules and equipment, incompatibility at either end of the equipment, optical fiber problems, coding discrepancies, FEC settings, excessive optical attenuation, and device-specific behaviors like loop protection and link jitter protection.