Advanced Optical Modulation Formats

Since the publication of the fourth volume of the book series Optical Fiber Telecommunications in 2002, high-speed opt transmission systems have increasingly been building on techniques that are well established in radio-frequency (RF) communication systems. and in particular in wireless communication. Examples are advanced modulation formats, line coding, enhanced forward error correction (FEC), and digital signal processing at transmitter and receiver. The adoption and extension of these techniques from the Mb/s regime into the multi-Gb/s realm is driven by the desire to steadily lower the cost per end-to-end networked information bit in an environment of continuously increasing data traffic. This is being done by extending the regeneration-free reach of optical line systems at the highest possible per-fiber transmission capacities, while at the same time allowing for optical wavelength routing in optically transparent mesh networks. In this context, communication engineering techniques are now supplementing established methods from optical physics to increase transmission reach, system capacity, and network flexibility. Today, research and commercial implementation of digital optical communication techniques fall into two main areas, distinguished by the per-wavelength symbol rates they operate at: