Improved performance of traveling wave directional coupler modulator based on electro-optic polymer

摘要

Polymer based electro-optic modulators have shown great potentials in highfrequency analog optical links. Existing commercial LiNibO3 Mach-Zehndermodulators have intrinsic drawbacks in linearity to provide high fidelitycommunication. In this paper, we present the design, fabrication andcharacterization of a traveling wave directional coupler modulator based onelectro-optic polymer, which is able to provide high linearity, high speed, andlow optical insertion loss. A silver ground electrode is used to reducewaveguide sidewall roughness due to the scattering of UV light inphotolithography process in addition to suppressing the RF loss. A 1-to-2multi-mode interference 3dB-splitter, a photobleached refractive index taperand a quasi-vertical taper are used to reduce the optical insertion loss of thedevice. The symmetric waveguide structure of the MMI-fed directional coupler isintrinsically bias-free, and the modulation is obtained at the 3-dB pointregardless of the ambient temperature. By achieving low RF loss, characteristicimpedance matching with 50{\Omega} load, and excellent velocity matchingbetween the RF wave and the optical wave, a travelling wave electrode isdesigned to function up to 62.5GHz. Domain-inversion poling with push-pullconfiguration is applied using alternating pulses on a 2-sectiondirectional-coupler to achieve a spurious free dynamic range of 110dB/Hz2/3.The 3-dB electrical bandwidth of device is measured to be 10GHz.