Optical communication systems are widely used today for data communication. Optical communication systems may employ optical fibers as the transmission medium to support high data rates in long distance transmissions (e.g. long haul optical systems). Continuous demands for increased optical network capacities provide challenges for current and future network designs. Flexible and adaptive networks equipped with flexible transceivers and network elements that can adapt to traffic needs may meet these challenges. In a flexible optical transceiver, an optical transmitter and receiver may be software-programmable, which may allow various transmission schemes or modulation formats, data rates, forward-error correction (FEC) protocols, and number of subcarriers to be configured. The optical transmitter and receiver may be set up to make the best use of the available channel bandwidth. This may mean trading capacity for reach based on modifying the amount of information placed on a carrier. Accordingly, flexible transceivers may be useful subsystem elements for current and future optical networks.
In development of optical communication networks or systems, flexible grid (flex-grid) and flexible rate (flex-rate) are two industrial trends for realizing flexible optical networks. Compared to the flex-grid approach that may need network structural changes, the flex-rate approach on a fixed-grid network may sometimes be more attractive. Existing flex-rate techniques may be based on modulation format changes that have limited granularity, that is, the minimal adjustable data rate of an optical signal may be relatively big. Thus, it may be desirable to improve the granularity to obtain more operable data rates.