Thermo-optic characterization of SU-8 at cryogenic temperature

We measured the optical transmission through an SU-8 microring resonator inside a cryostat and analyzed the shift of the resonant wavelengths to determine the thermo-optic behavior around a wavelength of 1600 nm. As the temperature was decreased from room temperature (RT) to 3K, the refractive index of crosslinked SU-8 was measured to increase from 1.571 to 1.584, while the thermo-optic coefficient decreased by two orders of magnitude.