A NOVEL, WIDE-BAND, LITHIUM-NIOBATE ELECTROOPTIC MODULATOR

A set of floating electrodes and a relatively thick buffer layer of lo w-dielectric constant is Interspaced between the coplanar RF transmiss ion line and the LiNbO3 substrate containing the optical wave-guide st ructure, The composite structure is designed to feature a 50-Ohm chara cteristic impedance, to have an effective dielectric constant equal to that of the optical wave for close velocity match, and to have a 3 dB bandwidth of 40 GHz., The purpose of the floating electrodes is to op timize the modulation sensitivity resulting in an improvement of about 6 dB, As a result, the RF power required for full modulation is lower than heretofore reported changing over the range from below 2 GHz to 20 GHz, from 44 mW to less than 70 mW, The close agreement between the theoretical and experimental values of the design parameters demonstr ates the usefulness of the quasistatic assumption in the analysis of t he composite structure.