Extracting the core and cladding contributions to fluorescence and Raman emission in integrated photonic waveguides

Minimizing background optical emission originating from waveguides is critical for achieving high-sensitivity performance in integrated photonic platforms, particularly for applications in biosensing, chemical detection, environmental monitoring, and quantum sensors. These background signals, often stemming from intrinsic fluorescence (also known as autofluorescence or photoluminescence) or Raman scattering in the waveguide core or cladding, can obscure weak optical signals and limit the accuracy of integrated photonic sensors. In this work, we introduce a novel parameter-extraction technique that quantitatively separates waveguide losses and background-generation efficiency, and identifies the individual contributions of the waveguide core and cladding to the total background signal. Our method utilizes only standard photonic waveguides and requires no specialized sample preparation or auxiliary test wafers. We validate our technique experimentally by characterizing silicon-nitride waveguides across nine wafers fabricated in a 300-mm-wafer platform developed at AIM Photonics. Applying our parameter-extraction method, we demonstrate its utility in showing a clear correlation between waveguide propagation loss and fluorescence, and its sensitivity in resolving material-specific differences in Raman spectra between wafers fabricated using different processes, including those arising from hydrogen-related impurities in non-annealed cores. This work provides a practical and comprehensive tool for quantifying, diagnosing, and reducing material-specific propagation loss and background signals in integrated photonic waveguides, ultimately enabling more effective development of low-noise and low-loss photonics platforms.