An apparatus, comprising: an optical transmitter configured to selectively supply either a first plurality of optical signals or a second plurality of optical signals, each of the first plurality of optical signals being modulated in accordance with a first modulation format, and each of the second plurality of optical signals being modulated in accordance with a second modulation format, collectively, the first plurality of optical signals have an associated data rate being a collective date rate, and collectively, the second plurality of optical signals have the associated data rate; an optical combiner configured to receive the first plurality of optical signals and the second plurality of optical signals, the optical combiner combining either the first plurality of optical signals or the second plurality of optical signals and supplying either the first plurality of optical signals or the second plurality of optical signals to an optical communication path; and a signal processing circuitry (CB-1,..., CB-10) configured to provide the first plurality of optical signals at a first symbol rate and the second plurality of optical signals at a second symbol rate, and comprising a digital-to-analog converter (310, 312, 314, 316) that is configured to operate at a substantially constant clock sampling rate, wherein each of the first plurality of optical signals carry a series of first symbols at the first symbol rate and each of the second plurality of optical signals carry a series of second symbols at the second symbol rate, the first symbol rate being greater than the second symbol rate. an optical transmitter configured to selectively supply either a first plurality of optical signals or a second plurality of optical signals, each of the first plurality of optical signals being modulated in accordance with a first modulation format, and each of the second plurality of optical signals being modulated in accordance with a second modulation format, collectively, the first plurality of optical signals have an associated data rate being a collective date rate, and collectively, the second plurality of optical signals have the associated data rate; an optical combiner configured to receive the first plurality of optical signals and the second plurality of optical signals, the optical combiner combining either the first plurality of optical signals or the second plurality of optical signals and supplying either the first plurality of optical signals or the second plurality of optical signals to an optical communication path; and a signal processing circuitry (CB-1,..., CB-10) configured to provide the first plurality of optical signals at a first symbol rate and the second plurality of optical signals at a second symbol rate, and comprising a digital-to-analog converter (310, 312, 314, 316) that is configured to operate at a substantially constant clock sampling rate, wherein each of the first plurality of optical signals carry a series of first symbols at the first symbol rate and each of the second plurality of optical signals carry a series of second symbols at the second symbol rate, the first symbol rate being greater than the second symbol rate.