Supercontinuum generation in amorphous TiO2 waveguides

CMOS-compatible waveguide platforms e.g. silicon (Si) and silicon nitride (SiN) for nonlinear applications are attracting increasing attention due to the capability of scalable manufacturing and integrating multiple functions on one chip. However, nonlinear effects in Si waveguides are limited by the strong two-photon absorption (TPA) of Si in near infrared and are energy inefficient in SiN waveguides due to low linear and nonlinear refractive indices (RIs) of SiN.

Alternatively, titanium dioxide (TiO2) waveguides, thanks to the high linear and nonlinear RIs, a TPA-free bandgap and a broad transparency window of TiO2 material, evolve as a promising platform for nonlinear processes including key ones like the supercontinuum generation (SCG). Recently, both amorphous and anatase TiO2 waveguides have been demonstrated for four-wave mixing, self-phase modulation, third-harmonic generation.

Specifically, SCG has been also achieved in the anatase TiO2 waveguides. Generally, amorphous TiO2 is preferred for nonlinear applications due to the lower loss, since many nonlinear processes, like the SCG, are very sensitive to the optical intensity and thus the waveguide loss. Here we report a supercontinuum generated in an amorphous TiO2 ridge waveguide, which has a size of 360nm by 950nm and exhibits a loss of 3~4 dB/cm.

An erbium-doped femtosecond fiber laser (100fs) with a center wavelength of 1555nm is used to pump the waveguide. An estimated average power of 5mW, corresponding to 555 W peak power, is coupled into the waveguide by a C-coated aspherical lens, producing a spectral broadening from 938nm to at least (limited by the OSA) 1750nm