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A newly proposed electrode structure consisting of coupled microstrip-lines can achieve an efficient modulation by using the resonance of the odd propagation-mode. The modulator with the 1.2 mm-long electrode for 26 GHz operation was fabricated and its workability was experimentally confirmed.
Introduction: Waveguide electro-optic modulators using resonator electrodes can exhibit high modulation efficiency with band-operation for their short electrode length and this feature is promising for radio-on-fibre systems [1]. These modulators should be suitably applied especially for millimetre-wave or quasi-millimetre-wave signals because the direct modulation of semiconductor lasers is unavailable in such high frequencies.
Conventional resonator-type electro-optic modulators commonly use electrodes of the coplanar waveguide (CPW) structure, where hot and ground electrodes are closely placed on the substrate surface to induce high electric fields. In this Letter, we propose a novel structure of the electro-optic modulator using a resonator electrode of coupled micro- strip lines (CMLs), where the half wavelength resonance with the odd mode in propagation is used to induce a high electric field.
Some advantages are expected from using the microstrip-line (MSL) configuration for the modulation electrode compared with the CPW configuration. One advantage is that MSLs generally exhibit a lower transmission loss, which causes higher unloaded Q for the resonator electrodes. As the voltage in the resonant electrodes is enlarged by energy storage of the modulation signals, higher resonant Q cor- responds to higher modulation efficiency for short electrode length. Another advantage is that the potential level of the ground plane can be uniformly fixed by mounting the substrate on a metal fixture to directly contact the ground plane, prepared on the opposite surface of the substrate, with the fixture. Thereby, unexpected resonances caused by local fluctuation of the potential level of the ground plane, which should significantly degrade...