13 March 2015 Design and fabrication of sub-wavelength athermal resonant waveguide replicated gratings on different polymer substrates
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We demonstrated the design, fabrication and characterization of three Resonant Waveguide Gratings (RWGs) with different polymer substrate materials [polycarbonate (PC), cyclic-olefin-copolymer (COC) and Ormocomps). The RWGs are designed by Fourier Modal Method and fabricated by Electron Beam Lithography, Nanoimprinting and Atomic Layer Deposition. RWGs are investigated for athermal filtering device operation over a wide range of temperatures. Spectral shifts of RWGs are described in terms of thermal expansion and thermo-optic coefficients of the selected substrate and waveguide materials. Furthermore, the spectral shifts are explained on the basis of shrinkage strains, frozen-in stresses and the molecular chain orientation in polymeric materials. The thermal spectral stability of these filters was compared by theoretical calculations and experimental measurements. For PC gratings, there is a good agreement between calculated and measured results with a net spectral shift of 0.8 nm over 75 °C wide temperature range. Optical spectral characterization of COC and Ormocomp gratings showed larger red spectral shifts than predicted by theoretical calculations. The deviation (0–1.5 nm) for the COC grating may result in by high modulus and inherent stresses which were relaxed during heating and accompanied with the predominance of the thermal expansion coefficient. The Ormocomps gratings were subjected to UV-irradiation, causing the generation of compressive (shrinkage) strains, which were relieved on heating with a net result of expansion of material, demonstrated by thermal spectral shifts towards longer wavelengths (0–2.5 nm). The spectral shifts might also be caused partially by the reorientation and reconfiguration of the polymer chains.
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Muhammad Rizwan Saleem, Muhammad Rizwan Saleem, Rizwan Ali, Rizwan Ali, Seppo Honkanen, Seppo Honkanen, Jari Turunen, Jari Turunen, } "Design and fabrication of sub-wavelength athermal resonant waveguide replicated gratings on different polymer substrates", Proc. SPIE 9374, Advanced Fabrication Technologies for Micro/Nano Optics and Photonics VIII, 93740W (13 March 2015); doi: 10.1117/12.2076873; https://doi.org/10.1117/12.2076873

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