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(a) A schematic of the membrane GR. Scanning electron microscope images of a fabricated AlGaN GR: (b) perspective and (c) top views.
(a) A schematic of the microreflectance setup used to measure the reflectance spectrum of the GR. (b) Configuration diagram to show the relations between the iris opening (the spatially filtered area) in front of the spectrometer and the image of GR on the iris.
Reflectance spectra measured (thick solid line) and simulated (thin solid line): (a) TE polarization and (b) TM polarization. Oscillations appearing in the region of low reflectance are Fabry–Pérot modes. The mode spacing corresponds to the cavity length of , which matches well with the remaining buffer layer thickness. Reflectance for normal incidence measured at selected laser wavelengths (solid squares), together with simulated reflectance spectra (thin solid line): (c) TE polarization and (d) TM polarization.
Comparison between (a) the dispersion relation (calculated by FDTD) and (b) reflectance spectrum (calculated by RCWA) of the AlGaN GR for TE polarization (, , , and ). Here we assume an ideal GR that is suspended in the air with no underlying structure.
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