A polymer directional coupler （DC） electro-optic switch with push-pull electrodes and rib waveguides is designed based on the conformal transforming method, image method, coupled mode theory, and electro-optic modulation theory. Its structure and principle are described, the design and optimization are performed, and the characteristics are analyzed, including the coupling length, switching voltage, output power, insertion loss, and crosstalk. To realize normal switching function,the fabrication tolerance,wavelength shift, and coupling loss between a single mode fiber （SMF） and the waveguide are discussed. Simulation results show that the coupling length is 3082μm; the push-pull switching voltage is 2.14V;and the insertion loss and crosstalk are less than 1.14 and -30dB,respectively. The proposed analytical technique on waveguides and electrodes is proven to be accurate and computationally efficient when compared with the beam propa- gation method （BPM） and the experimental results.
By using the proposed 3-D mode propagation analysis method and point-matching method, a polymer multimode interference (MMI) Mach-Zehnder interferometer (MZI) electro-optic (EO) switch is designed and optimized for enhancing the EO modulating efficiency and matching the impedance and the velocity. The designed switch possesses low driving voltages of ±1.375 V with a short EO active region length of 5 mm under 1550 nm wavelength, and the estimated cutoff switching frequency is up to 263 GHz due to the less mismatch between the lightwave velocity and microwave velocity. The 3-dB lightwave bandwidth is 60 nm, and within the wavelength range of 1520-1580 nm, the insertion loss and crosstalk are less than 6.71 and -30 dB, respectively.
