Improvement of both bandwidth and driving voltage of polymer phase modulators using buried in-plane coupled micro-strip driving electrodes

International audienceA large performance improvement of polymer phase modulators is reported by using buried in-planecoupled microstrip (CMS) driving electrodes, instead of standard vertical Micro-Strip electrodes. Thein-plane CMS driving electrodes have both low radio frequency (RF) losses and high overlap integralbetween optical and RF waves compared to the vertical designs. Since the optical waveguide andCMS electrodes are located in the same plane, optical injection and microwave driving access cannotbe separated perpendicularly without intersection between them. A via-less transition betweengrounded coplanar waveguide access and CMS driving electrodes is introduced in order to providebroadband excitation of optical phase modulators and avoid the intersection of the optical core andthe electrical probe. Simulation and measurement results of the benzocyclobutene polymer as a claddingmaterial and the PMMI-CPO1 polymer as an optical core with an electro-optic coefficient of70pm/V demonstrate a broadband operation of 67GHz using travelling-wave driving electrodes witha half-wave voltage of 4.5 V, while satisfying its low RF losses and high overlap integral betweenoptical and RF waves of in-plane CMS electrode