An optical coupling adaptor (10) couples an optical fiber to a photonic integrated circuit (PIC) chip (40). The adaptor (10) once connected to the PIC chip (40) forms a chip-adaptor assembly. The photonic integrated circuit (PIC) chip (40) has a plurality of inverted taper waveguides having an enlarged optical mode. The optical coupling adaptor (10) has a first section (20) having a plurality of ridge waveguides (24) between layers of cladding and also separated laterally by cladding and a second section (30) abutting the first section (20), the second section (30) having a plurality of trenches (34) each filled with an optical polymer that once cured has a refractive index that matches that of the ridge waveguides (24). The optical coupling adaptor (10) is adhered to the PIC chip (40) using the optical polymer as an adhesive such that the optical polymer in the trenches (34) once cured form polymer waveguides that confine the enlarged mode of the inverted taper waveguides.
