An electro-optical single-sideband modulator comprising: an electro-optical substrate; a bimodal optical waveguide structure formed in the substrate to support different optical modes having associated optical frequencies and optical propagation constants and comprising an optical input to receive an input optical carrier signal having an optical frequency, and a pair of optical outputs to output corresponding SSB modulated optical signals, each having an optical frequency spectrum with a single side lobe; and an electrode structure formed on the substrate to receive an input electrical modulating signal having an associated electrical frequency and electrical propagation constant, and to responsively apply an electrical field to the bimodal optical waveguide structure.