The fabrication of index-modulated grating coupler in a polymeric waveguide using two-photon initiated photopolymerization

A simple process suitable for fabrication of volume phase grating coupler in planar optical waveguide by two-photon initiated polymerization is presented. The volume phase grating has been written by scanning femtosecond laser pulses directly on the polymeric thin-film through a high numerical aperture lens. The areas of the index-modulated grating without morphology are 1.5 mm × 1.5 mm. The microstructure feature of coupling grating was illustrated. The corresponding index modulation reaches 0.03. We demonstrated the implementation of input coupling by this grating into the polymeric waveguide film. The measured coupling efficiency was about 11%.