(a) Schematic of an all-pass microring resonator constructed by PUA-cladding silicon nitride slotted waveguide. (b) The corresponding waveguide cross section. (c) Second-order dispersion versus wavelength for different waveguide. (d) Effective refractive index of the waveguide versus temperature. The red, blue, and green curves represent strip waveguide, slot waveguide with SiO₂ cladding, and slot waveguide with PUA cladding, respectively.