Everything You Need to Know About Complex Optical Modulation
2018-10-23 | 3 min read
New data centers are being built across the globe, while today’s CPUs and RAM ensure latencies so low that it is no problem to map immense amounts of data spread over several servers within a fraction of a second. The most critical question, is whether or not the rest of the infrastructure can keep pace. The cloud revolution and the resulting data avalanche is becoming an enormous challenge for the existing infrastructure. To avoid bottlenecks in the near future, the bit-rate efficiency needs to increase at every stage of the data journey.
Traditional non-return-to-zero (NRZ) data transmission is facing its limits. This is where complex optical (also referred to as coherent optical) modulation comes into the game and demonstrates its huge potential. It is spectrally more efficient than any direct transmission format.
Instead of transmitting a binary data stream, several bits can be coded to a new symbol, and a stream of these symbols can then be transmitted. The figure below illustrates the concept for two bits being coded to one new symbol. With this method, twice the amount of data can be accommodated in the same bandwidth.
One of the big advantages of coherent modulation schemes is that they can encode even many more bits in a single symbol.
In practice, they play a role especially for longer distances and higher data rates. However, even in shorter distances such as metro data center interconnects (DCI) where they are already used and inside the data centers, the traditional direct transmission formats are partly abandoned for coherent modulation.
But what are these complex modulation schemes in detail? How are they used in practice? What does their implementation technically imply?
Complex optical modulation may literally be complex but it is easy to understand with Keysight’s new guide to the essentials of complex optical modulation in theory and practical implementation.