Dipole orientation-dependent Purcell enhancement in silicon nitride dielectric waveguides using isotropic quantum dots and anisotropic nanoplatelets

We investigate the modification of spontaneous emission from quantum emitters positioned in the near field of silicon nitride dielectric waveguides. The role of dipole orientation is investigated through combined numerical simulations and experimental measurements by resolving normal, tangential, and parallel dipole components relative to the waveguide surface. The simulations reveal that emission enhancement depends strongly on the vectorial overlap between the emitter dipole and the guided-mode field components. Spherical quantum dots, exhibiting nearly isotropic dipole orientations with significant normal components, show higher ensemble-averaged Purcell enhancement, while anisotropic nanoplatelets, with predominantly in-plane dipole moments, display comparatively lower enhancement due to restricted coupling to the normal field component. Photoluminescence measurements and time-resolved studies are consistent with these trends, indicating orientation-dependent, cavity-free Purcell enhancement in integrated dielectric waveguides and establishing a qualitative framework for evaluating emitter orientation effects in waveguide-based quantum photonic platforms.