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The large refractive index of silicon enables sub-micron waveguide and high optical confinement. As a result, silicon photonic components could be made extremely compact, which is the foundation of the prosperous silicon photonics research. In the meantime, the large optical intensity within the waveguide, together with resonance structures, makes silicon photonics also an intriguing platform for studying phenomena involving high-order optical nonlinearities with low input power, such as two-photon absorption, four-wave mixing, stimulated Brillouin scattering, and free carrier absorption. Self-induced oscillation, also known as self-pulsing, is one of the phenomena induced by the interplay of multiple nonlinear processes. It happens when two or more contradict nonlinear effects interact and compete with each other. The oscillation theoretically can achieve >50 GHz frequency, but due to the heating caused by free carrier absorption, the reported oscillation speeds are limited to MHz level. Even excited with pulsed lasers to suppress the self-heating effect, the oscillation only achieves ~3 GHz. In this paper, we show that through infiltrating the subwavelength grating metamaterial ring resonator with materials of negative thermo-optic coefficient and high third-order nonlinearity, the strong, but slow, thermal effect can be suppressed and therefore ultrafast phenomena become eminent. In this experiment, DDMEBT is used which has third-order susceptibility three orders of magnitude larger than fused silica. Oscillations with about 27 GHz frequency are demonstrated experimentally simply by exciting the ring resonator with a continuous working laser. The oscillation frequency is more than one order of magnitude faster than the fastest self-oscillation effect that has been observed.
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