Study on multiple waveguide platforms for waveguide integrated Raman spectroscopy

Abstract

Waveguide Raman spectroscopy uses the evanescent field outside a waveguide to probe the analyte on the surface of the chip, permitting to selectively study thin films or nanostructures on top of the waveguide while benefiting from the long iteration path of the excitation with the analyte. Both the polarization of the excitation mode as well as the refractive index contrast of the waveguide platform play an important role in the Raman excitation process as well as the coupling efficiency of the generated Raman signal back into the waveguide. In this article, we characterize three waveguide platforms of different refractive index contrasts for waveguide Raman, namely Al2O3, Si3N4 and TiO2 on SiO2. Toluene was used as a test analyte. Both background and analyte were measured for quasi- transverse electric (quasi-TE) and quasi- transverse magnetic (quasi-TM) modes. TM modes generate less background than TE modes due to less confinement of the mode in the waveguide core materials. A combination of Si3N4 and quasi-TM polarization led to the highest SNR in this study.