Polymer waveguide Bragg gratings made by laser patterning technique

Abstract

Planar waveguide gratings are very useful components for planar optical structures in which they function as wavelength optical filters, demultiplexers or sensors. The Bragg gratings formed on planar optical waveguides in multimode propagation regime show multiple reflections, which can lead to enlargement of the envelope of the dip transmission spectral characteristic. This paper reports on the design and measurement of the two types multimode planar optical waveguides with diffraction Bragg grating (PWBG) made on the core or cladding layer of the structure. In the first monostructural design, PWBG was made from an optical epoxy polymer SU-8. The second hybrid PWBG design was based on ion exchange Ag⁺ ↔ Na⁺ glass waveguide. A grating was made in polymethylmethacrylate cladding layer covering the waveguide. The third-order polymer PWBGs with grating constant Λ _q−3 = 1.35 µm or Λ _q−3 = 1.2 µm were prepared by new laser-thermal patterning technique based on Marangoni effect. Based on experimental and theoretical results, the topological parameters of the structures were optimized to obtain maximum diffraction efficiency of the polymer PWBG. The beam propagation method and the rigorous coupled-wave analysis were used in theoretical modelling, simulation and evaluation of designed PWBG dimension parameters. The Bragg wavelengths transmission dips were measured in NIR optical band at λ = 1187 nm or λ = 1430 nm, respectively. The spectral transmission attenuation dips were 10 and 15 dB corresponding to 90 and 97 % diffraction efficiency of polymer PWBGs. The advantage of multimode PWBGs and its applications are discussed.