An apparatus and method for tunably delaying a signal and using that delayed signal in a duobinary transmitter is described. The transmitted duobinary signal is representative of the binary signal, and is formed by, among other things, introducing into a copy of the binary signal a delay that may be adjusted to be greater than or less than the bit period of the signal. Once the binary signal has been converted into a duobinary signal, it may then be converted into an optical duobinary signal. Alternatively, the conversion from binary to duobinary in accordance with the invention may be performed in the optical domain.