A method for transmitting a digital frame by an optical network unit in a digital communications network includes steps of arranging received data into a series of symbols, installing a primary cyclic prefix immediately preceding the series of symbols in time, and inserting individual ones of a plurality of secondary cyclic prefixes between each adjacent pair of symbols in the series of symbols. A length of each secondary cyclic prefix corresponds to a first duration shorter than an amount of time needed to turn on a laser of the optical network unit. The method further includes a step of providing to the optical network unit the digital frame. The digital frame includes the primary cyclic prefix, the plurality of secondary cyclic prefixes, and the series of symbols. The method further includes a step of modulating the provided digital frame by a laser of the optical network unit.