Ultra-high-speed compound semiconductor polarization/mode converter using slow-wave coplanar electrodes

Recent progress made toward the development of ultra-high-speed, wide-band, electro-optic modulators, fabricated in compound semiconductors, is described. Specifically, integrated-optic polarization converters, a typical application being TE = TM mode conversion, which can be fabricated in compound semiconductors are discussed. These devices use slow-wave, coplanar strip electrodes to achieve the velocity-match condition between a modulating microwave signal and a modulated optical signal. The paper describes the slow-wave electrodes and the theory of operation, the design, and the fabrication of the integrated-optic polarization converters that use them. Electrical measurements for the slow-wave electrodes showing them to be low-loss, below 0.4 Np/cm, and to be able to meet the velocity-match condition, having effective indices ∼ 3.4, have been made for frequencies up to 40 GHz. Also, optical measurements for the polarization converters showing no appreciable drop in optical modulation have been made for frequencies up to 20 GHz. Finally, design improvements that will aid in the development of such devices having low drive power requirements and optical bandwidths above 100 GHz are discussed.