Observation of the thermal nonlinear optical effect in a microring resonator based on a small SU-8 polymer ridge optical waveguide

The thermal nonlinear optical effect is observed in a microring resonator (MRR) based on a small SU-8 polymer ridge optical waveguide. It is found that the resonant wavelength blue shifts almost linearly with a slope of about −0.8 pm/mW as the input power increases (which causes the increase in temperature and consequently the decrease of the refractive index). Both the strong light-confinement of the air-clad waveguide and the strong light-enhancement of the MRR cavity contribute to the significant nonlinearity. The absorption mechanism is analyzed in detail, and the absorbance of about 0.179 cm⁻¹ (around 1560 nm) is obtained.