Polymer based electro-optic modulators have shown great potentials in high frequency analog optical links. Existing
commercial LiNibO3 Mach-Zehnder modulators have intrinsic drawbacks in linearity to provide high fidelity
communication. In this paper, we present the design, fabrication and characterization of a traveling wave directional
coupler modulator based on electro-optic polymer, which is able to provide high linearity, high speed, and low optical
insertion loss. A silver ground electrode is used to reduce waveguide sidewall roughness due to the scattering of UV
light in photolithography process in addition to suppressing the RF loss. A 1x2 multi-mode interference 3dB-splitter, a
photobleached refractive index taper and a quasi-vertical taper are used to reduce the optical insertion loss of the device.
The symmetric waveguide structure of the MMI-fed directional coupler is intrinsically bias-free, and the modulation is
obtained at the 3-dB point regardless of the ambient temperature. By achieving low RF loss, characteristic impedance
matching with 50Ω load, and excellent velocity matching between the RF wave and the optical wave, a travelling wave
electrode is designed to function up to 62.5GHz. Domain-inversion poling with push-pull configuration is applied using
alternating pulses on a 2-section directional-coupler to achieve a spurious free dynamic range of 110dB/Hz2/3. The 3-dB
electrical bandwidth of device is measured to be 10GHz.