UC Berkeley

Nonlinear silicon photonics offers on-chip wavelength converters and light emitters based on nonlinear optical effects such as self-phase modulation, four-wave mixing, supercontinuum generation, and stimulated Raman scattering. However, the efficient second harmonic generation has not been demonstrated by silicon-based optical components since group IV materials are centrosymmetric crystals in which the second-order nonlinearity is absent. To solve the problem, we proposed “bimodal phase-matching” for second harmonic generation. A plasmonic particle emits second harmonic radiation, which can be controlled by the shape of the particle. Hence, the plasmonic particle was designed to match the radiation pattern with the higher mode of the waveguide at the wavelength of the second harmonic emission. Besides, the fundamental mode of the waveguide at fundamental wavelength was also matched with the higher order mode of the waveguide at the wavelength of second harmonic. This concept was confirmed by observing built up second harmonic light in suspended silicon nitride waveguides.

Another challenge in silicon photonics is the demonstration of optical components operating at mid-infrared wavelength. Although mid-infrared silicon photonics is a promising technology for spectroscopy and ultrafast optical telecommunications, the absorption in the buried oxide layer and the dispersion of the waveguide restrict the performance of the mid-infrared optical devices on a silicon chip. Here, we demonstrated mid-infrared supercontinuum generation from a suspended silicon waveguide. The device improved the transmission in the mid-infrared range because the oxide layer was etched and the waveguide was suspended. Furthermore, the waveguide was engineered to have a flat dispersion in the anomalous regime. We fabricated suspended silicon waveguides and measured octave-spanning supercontinuum spectra in the mid-infrared range from the waveguide. The mid-infrared light converter on a silicon chip will pave the way for next generation communication devices and new sensing devices.