Microelectronic assemblies, related devices and methods, are disclosed herein. In some embodiments, a photonic assembly may include a substrate having a core with a surface, wherein a material of the core includes glass; and a dielectric material on a portion of the surface of the core, the dielectric material including conductive pathways; a photonic integrated circuit (PIC) electrically coupled to the conductive pathways in the dielectric material; a first optical component between the PIC and the surface of the core, wherein the first optical component is coupled to the surface of the core by optical glue or by fusion bonding; and a second optical component coupled to the core, wherein the second optical component is optically coupled to the PIC by an optical pathway through the core and the first optical component.