400G Technology Info Graphics
High Speed Meets Bandwidth
Download now our 400G Technology Info Graphics and get an overview of the bandwidth of optical networks in time, interesting facts about optical transceiver modules and the advantages and technical specifications of PAM4. Ideal for looking up and printing.
Development of Bandwidth
The global demand for higher bandwidth and the constant increase regarding the needed volume of data requires new technologies in order to be able to follow this trend. Wheras 1G was the benchmark in 1999, 21 years later we have reached 400 times this data volume. In order to meet the requirements of applications such as 5G, Internet of Things (IoT) or cloud data centres, the new 400G technology is the next level to keep pace with this development.
QSFP-DD – One Form Factor, Many Possible Uses
Among the 400G modules, the QSFP-DD has prevailed as the most popular form factor against the CFP8 and OSFP modules. It is characterized by its small size and above all by its low power consumption of a maximum of 15 Watts.
There are different variants to cover certain applications or to support the different types of fibres. The following table shows an overview of the different QSFP-DD modules and their different characteristics:
PAM4 - Pulse Amplitude Modulation
Due to the constantly growing demand for higher data rates the NRZ coding (Non Return to Zero) which has been the norm up to now reached its limits. Pulse Amplitude Modulation or in short PAM4, is therefore used in 400G modules.
Comparison of NRZ & PAM4
With the NRZ coding there are only two discrete amplitude values. The signal can be either “High” or “Low”. As a result, only one information bit can be transmitted per symbol. In contrast, with Pulse Amplitude Modulation, 4 discrete amplitude values can be used. This means that with PAM4 coding twice the number of information bits can be transmitted per time unit.
Signal Methods: Eye Diagram
By using Pulse Amplitude Modulation, the limits of Non Return to Zero coding can be overcome. As described, the decisive difference lies in the different amplitude values of the PAM4 coding. When looking at the signals of the two types of modulation on the oscilloscope, the difference can be made clear easily. This leads to the formation of the so-called eye patterns:
If we are looking at the signals of the NRZ Modulation, we see the characteristic formation of a single eye opening with 2 fixed amplitude values and one rising and one falling edge for each symbol.
In comparison, there are 3 characteristic features in PAM4 Eye openings with 4 discrete amplitude values. This allows 2 bits per symbol and thus twice the data rate per time unit.
