A photonics integrated circuit includes a semiconductor substrate; a buried insulator layer positioned over the semiconductor substrate; and a back-end-of-line (BEOL) insulator stack over a first portion of the buried insulator layer. In addition, the PIC includes a silicon nitride (SiN) waveguide edge coupler positioned in a first region over the buried insulator layer and at least partially under the BEOL insulator stack. An oxide layer extends over a side of the BEOL insulator stack. The SiN waveguide edge coupler provides better power handling and fabrication tolerance than silicon waveguide edge couplers, despite the location under various BEOL layers. The PIC can also include silicon waveguide edger coupler(s).