PFI:AIR - TT: Demonstration of parametrically robust wideband resonant reflectors

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This PFI: AIR Technology Translation project focuses on translating research discoveries associated with a new class of wideband reflectors to fill the need for new photonic components in a broad variety of applications including laser manufacturing and infrared imaging systems. This innovation is important as new fundamental physical effects will be applied to enable solutions not attainable with current competing technology. The project will result in new designs and prototype reflectors that will be tested in detail for operation in important frequency bands. The proposed reflectors will have the following unique features: high degree of parametric stability, large spectral bandwidth, compact size, and high-yield manufacturing. These features provide advantages including high efficiency, low loss, economy in fabrication, and robustness in applications. These single-layer devices can be fabricated on substrates or as membranes. They avoid the multiple interfaces and associated issues in commercial thin-film multilayer reflectors; thus, thermal expansion effects and adhesion problems are minimized. These reflectors can be applied in spectral regions for which the deposition of thin-film multilayers is impractical or impossible. Therefore, this innovation provides new solutions and is likely to compete effectively in a sizeable market space. This project addresses the following technology gaps as it translates from research discovery toward commercial application: (1) verification of the utility of the proposed fundamental resonance effect in this context, and (2) verification that practical prototype reflectors with high-efficiency wideband spectra can be fabricated. The proposed resonant reflectors are designed with gratings in which the grating ridges match to an identical material, thereby avoiding local reflections and phase changes. As this critical interface possesses zero refractive-index contrast, we call them "zero-contrast gratings." For simple gratings with two-part periods, we use numerical calculations to show that zero-contrast gratings provide extremely large flattop bandwidths and parametrically stable spectra; this project aims to demonstrate these devices experimentally. In summary, the main goals are to fabricate reflector prototypes operating in the ~1.2- to 12- micron spectral region; verify bandwidths of ~600-1100 nm with reflectance exceeding 99%; verify the predicted parametric stability; demonstrate polarized and unpolarized reflectors; and verify theoretical predictions of 99.99% reflectance for ~10- to 100-nm bandwidths. These devices are designed using powerful electromagnetic optimization algorithms, and they are made using standard nanofabrication methods including thin-film deposition, lithographic patterning, and etching. They are characterized by spectral analysis in the ~1- to 12- micron wavelength band. Hence, the project delivers compact, robust, polarized and unpolarized resonant reflectors that work within a broad spectral application space where classical methods fail to deliver effective solutions. In addition, personnel involved in this project, including undergraduate and graduate students, will receive entrepreneurial experiences, including business planning, by enrolling in "Engineering Entrepreneurship" that is taught by the PI on a regular basis.