Coherent Optical Module Compatibility

Many different forms of optical modulation and multiplexing have been employed in coherent optical modules. Some coherent optical modules can fall back to older, simpler modulation techniques such as (NRZ) and/or with 4 levels (PAM-4) when appropriate. This is used, for example, when it is discovered that the module on the other end of the link does not support coherent. [pdf]