Considering that the switching speed of the Y-fed coupler Electro-Optic (EO) switch with two-section seperated reversed lumped electrodes is slow,through push-pull poling on the wavegides in the two EO regions,a bias-free high-speed travelling-wave line EO switch was designed.Design and optimization were performed on electrode parameters for obtaining low driving voltage,good impedance match and less-mismatch between optical index and microwave index.Besides,by using Fourier transformation on the applied square-wave switching signal,a novel analytical technique was presented to model and characterize the switching response.Numerical calculation results of the optimized device indicate that,under 1 550 nm central operation wavelength,the 3 dB state voltage is 0 V,and the upper-and lower-branch state voltages are -1.34 V and +1.34 V,respectively,indicating a switching voltage of 2.68 V.The insertion loss and crosstalk are less than 3.55 and -30 dB,respectively,and the 10%-90% rise time and fall time are both about 3.90 ps,indicating a cutoff switching frequency up to 128.2 GHz.The proposed high-speed device structre and numerical technique are of well meaning for the design and performance evaluation of a similar device based on Y-fed coupler structure.