Indium Tin Oxide Based Dual-Polarization Electro-Optic Intensity Modulator on a Single Silicon Waveguide

For high-speed optical transmission, polarization-division-multiplexing (PDM) is a promising technic to double the link capacity. However, most of on-chip PDM systems include a polarization beam splitter, a polarization rotator, and two modulators, which are costly and complex for integration. In this study, a novel dual-polarization electro-optic intensity modulator is proposed that is based on a single silicon waveguide with indium tin oxide (ITO) cladding. The design is validated by numerical simulation with commercial software Lumerical Solution. Based on the epsilon-near-zero effect of ITO, the device, on a single waveguide, manages to modulate simultaneously transverse electric (TE) and transverse magnetic (TM) modes with independent electrical driving signals. With a 75 μ m-long silicon rib waveguide, the extinction ratios (ERs) of both TE and TM modes can be around 15 dB, and the nonuniformity is around 0.5 dB. The 3 dB modulation bandwidths are 57.8 GHz and 65.9 GHz for TE and TM modulation, respectively. Within 1 dB ER nonuniformity, the device can operate at E-, S-, and C-band, which distinguishes itself by achieving wavelength-division-multiplexing compatible PDM and with only one single waveguide. To our best knowledge, the concept of independent and simultaneous dual-polarization modulation on a single waveguide is proposed for the first time. The modulator offers various merits including ultracompact size, high speed, and complementary metal oxide semiconductor (CMOS) compatibility.