Athermal silicon nitride ring resonator by photobleaching of Disperse Red 1-doped poly(methyl methacrylate) polymer

To fabricate athermal silicon nitride waveguides, the dimensions of both the core and cladding, refractive index, and thermo-optic coefficients must be controlled precisely. We present a simple and effective method for the postfabrication trimming of silicon nitride ring resonators that overcomes the highly demanding fabrication. In order to manipulate the polymer's refractive index and thermo-optic coefficient, we bleached the Disperse Red 1-doped poly(methyl methacrylate) (DR1/PMMA) top cladding using UV irradiation. After a suitable bleaching time, the temperature-dependent wavelength shift of the ring resonator was reduced from -9.8 to -0.018 pm/°C, which is the lowest shift that we are aware of for an athermal waveguide realized by overlaying a polymer cladding to date.