Experimental demonstration of wideband multimodule serial reflectors

We demonstrate unpolarized wideband reflectors fashioned with orthogonal serial resonant reflectors. Unpolarized incident light generates internal TM- and TE-polarized reflections that are made to cooperate to extend the bandwidth of the composite spectral reflectance. The experimental results presented show ~42% band extension by a two-grating module. In addition, good angular tolerance is found because the orthogonal arrangement simultaneously supports classical and fully conic mountings at oblique angles. The resulting spectra form contiguous zero-order reflectance across wide spectral/angular regions. Furthermore, using a multimodule device with serial reflectors fabricated with silicon-on-quartz wafers with different device layer thicknesses, extreme band extension is achieved providing ~56% fractional bandwidth with reflectance exceeding 98%. These results imply potential for developing lossless unpolarized mirrors operating in diverse spectral regions of practical interest.