400G Transceivers Test - How Does It Ensure the Quality of Optical Modules?
Updated at Dec 18th 20241 min read
With the growing demand for higher bandwidth and faster data transmission, 400G transceivers have emerged as essential components of modern networks. Ensuring their performance and reliability is crucial, and this is achieved through rigorous and comprehensive testing procedures. This article explores the key tests that ensure 400G transceivers' optimal performance, helping you understand how they deliver better performance and enable reliable connectivity.
Key Items in 400G Transceiver Test
For transceiver vendors, product quality is fundamental to establishing reliable trust with customers. Let's have a look at the key items in the 400G transceiver test.
ER Performance and OMA Optical Power Tests
The extinction ratio (ER) indicates the minimum ratio of the average optical power during the transmission of all signal 1s (emits light) to the average optical power during the transmission of all signal 0s (does not emit light) under complete modulation mode, is an important indicator to measure the performance of 400G optical transceivers.
Based on these two parameters, the ER indicates the capability of distinguish between signal 0 and signal 1. Therefore, it serves as a measure of the laser operating efficiency. OMA (outer optical modulation amplitude) can measure the power differences when the transceiver laser turns on and off, testing 400G transceivers' performance in another aspect. Both the ER and the average power can be measured by mainstream optical oscilloscopes.
Optical Spectrum Test
The optical spectrum test is mainly divided into three parts: center wavelength, side mode suppression ratio (SMSR), and spectrum width of the 400G transceivers. All of these three parameters are essential for keeping a high-quality transmission and performance of the modules. The larger the value of the side mode suppression ratio, the better the performance of the laser of the module. Watch the following video to see how FS tests the optical spectrum for 400G QSFP-DD transceivers.
Forwarding Performance Tests
400G transceivers have a more complicated integration compared with the existing 40G/56G and 100G modules, which puts higher requirements for the test of its forwarding performance. RFC 2544 defines the following baseline performance test indicator for networks and devices: throughput, delay, and packet loss rate. In this test procedure, the electrical and optical interfaces will be tested and make sure the signal quality they transmitted and received will not get distortion.
Eye Diagram Test
Different from the single eye diagram of NRZ modulation in 100G optical transceivers, the PAM4 eye diagram has three eyes. And PAM4 doubles the bit bearing efficiency compared with NRZ, but it still has noise, linearity, and sensitivity problems. IEEE proposes using PRBS13Q to test the PAM4 optical eye diagram. The main test indicators are eye height and width. By checking the eye height and width in the test result, technicians can tell if the signal linearity quality of the 400G transceiver is good or not.
Jitter Test
The jitter test is mainly designed to measure transmitters' output jitter and receivers' jitter tolerance. Jitter, including random and deterministic jitter, causes bit errors, interferences with clock recovery, and reduces system performance. Effectively performing jitter tests enables consistency verification and supports debugging tasks, such as modifying the PCB, replacing components or connectors, and adjusting chip parameters or software. In real-world test environments, the jitter test is operated with the eye diagram test to check the 400G transceivers' performance.
Bit Error Rate Test
The electrical interfaces of 400G transceivers use 8x 50Gb/s PAM4, or 4x 100Gb/s PAM4 modulation. The higher lane speed and the utilization of PAM4 (4-Level Pulse Amplitude Modulation) in 400G electrical interfaces do bring higher transmission efficiency and lower network deployment costs but also results in more noise (also known as a decrease in signal-to-noise ratio) during signal transmission. This increased noise causes to a higher bit error rates (BER).
The BER is a key metric for describing the reliability of data transmission that measures the number of lost data packets and is subjected to data criticalness. Low BER can contribute to information preservation, system stability, and signal stabilization, effectively improving data transmission accuracy and integrity. The following video demonstrates how FS tests the BER of 400G QSFP-DD modules to ensure transmission stability and reliability.
Compatibility Test
Real device testing, conducted with advanced equipment and a rigorous qualification process, guarantees high-quality 400G transceivers with 100% compatibility. The FS laboratory features 400G devices from leading brands, including Cisco, Dell, Arista, Juniper, and Mellanox. To ensure compatibility, all 400G transceivers are tested in targeted switches for superior performance, quality, and reliability before shipping.
Temperature Test
Compared to NRZ (Non-Return-to-Zero), PAM4 generates higher energy consumption during long-distance data transmission to maintain signal stability and accuracy, leading to increased heat dissipation requirement. However, each 400G transceiver module has its operating temperature range defined by its supplier. If the temperature exceeds this range, modules may fail to function properly, even causing delays or network breakdowns. So the temperature test is essential to ensure the transmission performance and reliability of high-speed 400G transceivers in communication networks and data centers.
Conclusion
With its higher transmission rate, larger bandwidth, and better scalability, 400G Ethernet has enormous market potential. Many optical module vendors and networking solution providers have promoted their own 400G product solutions to the market. Hence, 400G transceiver tests are crucial for ensuring 400G modules have more stable data transmission, lower latency, and packet loss rate, which can enhance product performance, provide high-quality products, and improve user satisfaction and user stickiness.