Design of a CMOS compatible dual polarization four-level optical modulator based on thermally-actuated phase transition of vanadium dioxide

Optical and electrical design of a CMOS compatible dual-polarization four-level amplitude modulator is proposed here. Thermally actuated phase transition of the Vanadium-Dioxide (VO2) through Joule-heating process is employed as the modulation mechanism. The modulator is in the form of two pairs of active waveguides that are coupled to a silicon access waveguide. Each pair of active waveguides passes one polarization (transverse electric or transverse magnetic) of incoming light and each pair is composed of two active waveguide sections that can introduce 3 dB and/or 6 dB propagation losses when their VO2 layer is set to its metallic phase. Considering the relatively slow transition time of the VO2, dual-polarization and multi-level modulation are employed to increase the achievable modulation bit-rate. Optical simulations show equally spaced output power level (with 3 dB separation) for both polarizations in the wide wavelength range of 1.5 mu m-1.57 mu m, while the insertion loss remains below 2.5 dB and 3.5 dB for the transverse electric and transverse magnetic polarization, respectively, in a structure with the overall length of 30 pm. Furthermore, according to the results of the thermal and electrical stimulations of the proposed modulator the required time and energy consumption for every bit modulation is found to be (similar to)21 ns and 0.22 nJ, respectively.