This paper reviews recent advances in the generation, detection and transmission of orthogonal-frequency-division-multiplexing (OFDM) based superchannels, enabled by efficient and powerful digital signal processors. The use of OFDM to form a superchannel can be (1) at the modulation stage by naturally realizing a square-like signal spectral shape to allow close packing of multiple modulated signals, and/or (2) at the optical multiplexing stage by seamlessly multiplexing these modulated signals. This paper reviews recent advances in this field. Several OFDM-based superchannel architectures are described and compared.