A travelling wave electro-optic modulator comprising a substrate ; first and second parallel spaced apart electrode strips arranged on the substrate ; first and second optical waveguides arranged on the substrate , the optical waveguides being positioned between the first and second electrode strips and extending parallel thereto; the first electrode strip comprising at least one portion extending proximate to the first optical waveguide ; the second electrode strip comprising at least one portion extending proximate to the second optical waveguide ; a semiconductive backplane layer arranged within the substrate and extending between the waveguides ; and, a matched termination connected to the first and second electrode strips , the matched termination comprising (a) a serpentine electrically conductive strip arranged on the substrate and connecting the first and second electrode strips together; and, (b) a semiconductive backplane matching element , the backplane matching element comprising a plurality of semiconductive backplane plates connected together by at least one semiconductive backplane arm , the plates and at least one backplane arm being arranged within the substrate , the plates being arranged proximate to the electrode strips such that each electrode strip is capacitively coupled to at least one backplane plate ; the serpentine electrically conductive strip being arranged such that at least a portion of its length is proximate to at least one backplane arm such that the two are electrically coupled together. a substrate ; first and second parallel spaced apart electrode strips arranged on the substrate ; first and second optical waveguides arranged on the substrate , the optical waveguides being positioned between the first and second electrode strips and extending parallel thereto; the first electrode strip comprising at least one portion extending proximate to the first optical waveguide ; the second electrode strip comprising at least one portion extending proximate to the second optical waveguide ; a semiconductive backplane layer arranged within the substrate and extending between the waveguides ; and, a matched termination connected to the first and second electrode strips , the matched termination comprising (a) a serpentine electrically conductive strip arranged on the substrate and connecting the first and second electrode strips together; and, (b) a semiconductive backplane matching element , the backplane matching element comprising a plurality of semiconductive backplane plates connected together by at least one semiconductive backplane arm , the plates and at least one backplane arm being arranged within the substrate , the plates being arranged proximate to the electrode strips such that each electrode strip is capacitively coupled to at least one backplane plate ; (a) a serpentine electrically conductive strip arranged on the substrate and connecting the first and second electrode strips together; and, (b) a semiconductive backplane matching element , the backplane matching element comprising a plurality of semiconductive backplane plates connected together by at least one semiconductive backplane arm , the plates and at least one backplane arm being arranged within the substrate , the plates being arranged proximate to the electrode strips such that each electrode strip is capacitively coupled to at least one backplane plate ; the serpentine electrically conductive strip being arranged such that at least a portion of its length is proximate to at least one backplane arm such that the two are electrically coupled together. <EOS>