Low-loss silica on silicon integrated waveguides

Low-loss waveguides integrated on a silicon substrate are essential components in the design and fabrication of photonic circuits. For this application, a wide operational bandwidth - from visible to infrared wavelengths - is critical. Previous research has yielded waveguides made with various materials and geometries. Several of these devices have achieved low, <0.1dB/cm loss in either the visible or the near-IR. However, to obtain effective confinement of light from the visible through the near-IR, it is necessary to develop waveguides which have near-constant loss and minimal non-linear effects across the entire wavelength range. To overcome this challenge, we have developed novel silica on silicon waveguides fabricated using conventional lithographic techniques and CO2 laser reflow. The entire waveguide is elevated above the higher refractive index silicon substrate, creating an isolated, air-clad waveguide. The cylindrical waveguide's loss was determined by coupling light from 658nm, 980nm, and 1550nm lasers into the waveguide using lensed optical fibers. Due to the inherently low material loss of silica and the isolation from the silicon substrate, the device has low optical loss (0.7-0.9dB/cm) and linear behavior across the entire wavelength, polarization, and input power ranges studied. These on-chip waveguides will benefit many applications, including biodetection and integrated photonics.