Photonic crystals in polymers by direct electron-beam lithography presenting a photonic band gap

Abstract

Direct lithography in electron-beam sensitive polymers was investigated to fabricate 2D-slab polymer-based photonic crystal structures. Polymethyl-methacrylate (PMMA) doped with azo dye Disperse Red 1 (DR1) chromophores was used as a test material to produce optimized low-index contrast photonic crystals presenting a photonic band gap for TE polarization. Extensive computational simulations of the full 3D-slab modes guided the design and fabrication strategy through optimization of the lattice structure, lattice parameter, hole size, and slab thickness. An exposure strategy that takes advantage of 100kV beam energy for deep lithography, and exposure control for multilevel pattern definition is presented, resulting in the high aspect ratio and verticality required to achieve a strong band gap effect. Finally, a method that enables a high-quality air-clad PMMA-DR1 to be fabricated and integrated with optical waveguides for characterization is presented, enabling successful observation of a photonic bandgap in a 2D-slab polymer photonic crystal.