Photonic chip material refractive index extraction with a single photonic crystal micro-ring resonator

As co-packaged optics (CPO) integrates photonic chips and electronic dies together, accurate and non-destructive post-fabrication characterization of waveguide parameters—width, thickness, and the refractive indices of both core and cladding—becomes critical, because even minute index deviations are amplified in dense interconnects and directly impair the signal integrity and energy efficiency of CPO modules. We take the material refractive index as an example and demonstrate an effective approach for non-destructive parameter extraction of the as-fabricated optical waveguide with a single photonic crystal ring resonator. By lifting the degeneracy of the symmetric and anti-symmetric resonant peak, this single structure suffices to determine the core and clad indices rapidly with high precision. We successfully applied the extracted parameter of the refractive indices to validate the optical transmission of the index-sensitive wavelength division multiplexer device. Our approach has provided a facile solution for post-fabrication device parameter evaluation and is readily extendable to geometric parameters.