Fabrication of semiconductor Mach-Zehnder modulator

A method for manufacturing a semiconductor Mach-Zehnder modulator comprising the steps of forming a combination mesa structure overlying a substrate, said combination mesa structure including an input optical waveguide, first and second input branch optical waveguides branching off said input optical waveguide, first and second modulator arm waveguides optically coupled to said first and second input branch optical waveguides, respectively, first and second output branch optical waveguides optically coupled to said first and second modulator arm waveguides, respectively, an output optical waveguide optically coupled to both said first and second output branch optical waveguides, each of said waveguide having consecutively a first cladding layer of a first conductivity type, an optical guide layer, a second cladding layer of a second conductivity type, and forming a first electrode electrically connected to said second cladding layer of said first modulator arm waveguide, a second electrode connected to said first cladding layer of said first modulator arm waveguide and said second cladding layer of said second modulator arm waveguide, and a third electrode connected to said first cladding layer of said second modulator arm waveguide.