An apparatus comprises: a CDR sub-system comprising: an FFE; a decision component coupled to the FFE; a subtractor coupled to the FFE and the decision component; and a tap weight updater coupled to the subtractor and the FFE; and a PR-MLSE component coupled to the CDR sub-system. A method comprises: converting an optical signal with a first modulation format to an analog electrical signal; converting the analog electrical signal to a first digital signal; equalizing the first digital signal into a second digital signal with a second modulation format, wherein the second modulation format has more levels than the first modulation format; and performing CDR on the second digital signal.