Wideband capacitively coupled silicon modulator with barium titanate cladding

Abstract Standard silicon modulators rely on the interaction between an optical signal and an electrical signal exploiting the plasma dispersion effect. Optical modes in such modulators are confined exploiting high refractive index contrast rib waveguides and, the electrical signals are usually coupled to the optical waveguide through doped silicon ohmic regions. Thus, these modulators are fundamentally bandwidth-limited due to resistor–capacitor time constant. In this paper, we showed a method to overcome this limitation by capacitive coupling of the electrical signal to the waveguide region replacing the ohmic contacts. Our modulator combines a silicon strip waveguide with lateral a PN diode with a high-dielectric constant (high-k) material, barium titanate cladding. We demonstrated a Mach-Zehnder interferometer based silicon modulator with series push-pull configuration. For a 2 mm long device we generate sidebands up to 67 GHz and observe a flat frequency response. Moreover, the modulator achieves a phase shift of 0.014 radians for a C-band optical wave when subjected to a 15 GHz radio-frequency modulation signal with an amplitude of 2.44 V.