Analysis and Demonstration of Mach–Zehnder Polymer Modulators Using In-Plane Coplanar Waveguide Structure

Analysis, design, and experimental demonstration of polymer Mach-Zehnder (MZ) modulators with a newly proposed in-plane coplanar waveguide (CPW) electrode are presented in this paper. Compared to the conventional CPW electrode, the new in-plane CPW configuration significantly enhances the overlap factor between microwave and optical wave by 40% from the theoretical calculations. Different from polymer modulators using the traditional microstrip electrodes, this structure can suppress dc bias voltage drift and widen modulation bandwidth. Using CLD1/APC and AJL8/APC electrooptic polymers, MZ modulators using the in-plane CPW are fabricated and tested. The measured Vpi's of the MZ with 15-mum gap spacing and 2 cm electrode length are 5.4 and 9.5 V at 1.55 mum for the AJL8/APC and CLD1/APC devices, respectively. The evaluated Upsi
₃₃
's are 46 pm/V for the AJL8/APC and 26 pm/V for the CLD1/APC MZ. The dc bias stability is tested and compared for both the microstrip and the in-plane CPW electrode modulators. Experimental results show that the in-plane CPW modulator greatly improves the bias stability. From the microwave measurement, the microwave signal loss of the modulator using the in-plane CPW is much reduced to 0.2 dB/cmradicGHz, while 0.7 dB/cmradicGHz using the microstrip.