We present the design of retrodiffraction gratings that utilize total internal reflection (TIR) in a lamellar configuration to achieve high performance for both TE and TM polarized light and polarization-sensitive performance for gratings behaving as polarizer filters; the design was based on rigorous coupled wave analysis (RCWA) and the Taguchi method. The components can thus be fabricated from a single dielectric material and do not have to be coated with a metallic or dielectric film layer to enhance the reflectance. The effects of the structural and optical parameters of lamellar gratings were investigated, and the TIR gratings in a lamellar configuration were structurally and optically optimized in terms of the signal-to-noise ratio (S/N) and a statistical analysis of variance (ANOVA) of the refractive index, grating period, filling factor, and grating depth as control factors and the estimated efficiency by RCWA as a noise factor. For more accurate robustness, a two-step optimization process was used for each purpose. For TIR gratings designed to perform similarly for TE and TM incident polarization, the -1st-order efficiencies were estimated to be up to 92.0% and 88.5% for TE and TM polarization, respectively. Also, for the TIR gratings designed to achieve polarization-sensitive performance when behaving as a polarizer filters, the -1st-order diffraction efficiencies for TE and TM polarization were estimated to be up to 95.5% and 2.7%, respectively. From these analysis results, it was confirmed that the Taguchi method shows feasibility for an optimization approach to a technique for designing optical devices.
This paper presents scalar and vector analyses of sawtooth gratings with a period of 2.0 µm in terms of Fourier transformation and rigorous coupled wave analysis (RCWA) and its fabrication on a slanted silicon substrate by a newly proposed fast atom beam (FAB) etching method. First, the optical and geometrical properties of sawtooth gratings were investigated and optimized under the phase-matching requirement, and the 1st diffraction efficiency for TM polarization and the scalar approximation, 73.0% and 100%, were estimated, respectively. Second, sawtooth gratings optimized by two diffraction analysis methods were successfully fabricated by the FAB etching method. Last, by a hot-embossing process suitable for mass production, 100 µm thick poly-methyl methacrylate (PMMA) material was replicated from a sawtooth-patterned silicon substrate, and its 1st diffraction efficiency for TM polarization, 63.0%, was measured from optical testing.
This paper presents the experimental investigation of the optimal hot embossing replication to prevent the nanoscale thermal deformation of microstructures replicated from the electroless Ni mold fabricated by the diamond tool-interfered scribing process. The fabricated microstructures have the blazed profile with a period of 2.0 ㎛ and a depth of 0.2 ㎛ and a thermoplastic material PMMA as the replica was used. The hot embossing molding was carried out under the several experimental conditions. In terms of a quality of surface smoothness, profile, sharp blaze edge, surface roughness, peak to valley Ry and optical performance of the replica, the PMMA microstructures replicated under the optimal conditions, were ideally identical with those in the mold in dimension, and it was found that the demolding temperature is the most important factor for replication. From optical testing, diffraction efficiency of the replica was measured, 87.6%, similar to that of the calculated value 89.6%, and the replica molded in other conditions showed the noticeable efficiency drop due to molding error.
This paper presents optimization of phase reflection sawtooth gratings with a period of 2.0 μm and a depth of 0.2 μm based on the Fourier transformation (FT) and the rigorous coupled wave analysis (RCWA). And its fabrication on oxygen free Cu and electroless Ni-coated surfaces by using diamond cutting in a shaping process whose toolpath is interfered to provide smaller period. The diffraction efficiencies were estimated 100% for FT, 83.0% and 79.0% for TE and TM polarization of the incident light at a depth of 0.2 μm. It was found that electroless Ni-coated surface had better performance in terms of machining and optical functionality. From optical testing, the diffraction efficiencies were measured 84.0% and 84.4% for TE and TM polarization, respectively.
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