Mesoporous sol-gel silica cladding for hybrid TiO₂/electro-optic polymer waveguide modulators

We report the efficient poling of an electro-optic (EO) polymer in a hybrid TiO₂/electro-optic polymer multilayer waveguide modulator on mesoporous sol-gel silica cladding. The mesoporous sol-gel silica has nanometer-sized pores and a low refractive index of 1.24, which improves mode confinement in the 400-nm-thick EO polymer film in the modulators and prevents optical absorption from the lower Au electrode, thereby resulting in a lower half-wave voltage of the modulators. The half-wave voltage (V_π ) of the hybrid modulator fabricated on the mesoporous sol-gel silica cladding is 6.0 V for an electrode length (L_ℓ ) of 5 mm at a wavelength of 1550 nm (V_πℓ  product of 3.0 V·cm) using a low-index guest-host EO polymer (in-device EO coefficient of 75 pm/V).