Slow-wave electrode for use in compound semiconductor electrooptic modulators

A slow-wave electrode structure for integrated optic traveling-wave modulators in which the microwave´s effective refractive index is matched to the optical wave´s effective refractive index is described. The electrode structure is a capacitively loaded coplanar strip waveguide which can be formed in a single layer of metallization. Fabrication can be accomplished by a single photo-resist patterning, followed by an etching and a standard lift-off technique. Based on the use of gallium arsenide substrates and modern lithographic techniques allowing fabrication with micron scale resolution, slow-wave electrodes having a microwave effective refractive index of 3.5, as well as 50 and 75 Ω characteristic impedances are proposed. The theory of slow-wave electrodes is developed, and slow-wave electrodes have been designed, fabricated, and tested to verify the theory. Measurement results are found to agree well with the theory