Consistent with the present disclosure, data, in digital form, is received by a transmit node of an optical communication, and converted to analog signal by a digital-to-analog converter (DAC) to drive a modulator. The modulator, in turn, modulates light at one of a plurality of wavelengths in accordance with the received data forming a plurality of corresponding carriers. The plurality of carriers are then optically combined with a fixed spacing combiner to form a superchannel of a fixed capacity. Accordingly, the number of carriers are selected according to a modulation format and symbol rate to realize the fixed capacity, for example. The superchannel is then transmitted over an optical communication path to a receive node. At the receive node, the superchannel is optically demultiplexed from a plurality of other superchannels. The plurality of carriers are then supplied to a photodetector circuit, which receives additional light at one of the optical signal carrier wavelengths from a local oscillator laser. An analog-to-digital converter (ADC) is provided in the receive node to convert the electrical signals output from the photodetector into digital form. The output from the ADC is then filtered in the electrical domain, such that optical demultiplexing of the carriers is unnecessary.