Double-Sided Spectrally Splitting Contrast Grating for an Asymmetric Thermal Regulation Window

A window with tailored asymmetric thermal regulation can be achieved with thin film coupled gratings that demonstrate spectral splitting. The proposed double-sided contrast gratings can split the incoming beam between the solar wavelength and mid-infrared ranges. This study investigates grating and multilayer material configurations with selective and mixed transparency I the visible versus the infrared. Our computational methodology to build and stack successive grating structures with broadband spectral reflection and transmission is based on Bayesian optimization. The geometric parameters are optimized so that it allows directional transmission through 0th order and 1st order diffraction orders. The mechanism of the proposed stacks is achieved with zero contrast grating (ZCG) whose exit plane of the grating have no index gradient. As a result, the window rejects visible light through normal direction, while mid-infrared light passes through. Vice-versa, visible light exits the window in oblique angle. Without solar energy incoming directly normal to the window, it prevents direct heating of the medium in the normal direction underneath the window. Meanwhile, thermal radiative heat exchange with surroundings is only limited to the normal direction. This nano/microscale grating-based spectral beam splitting strategy can promote passive thermal regulation of automotive, home, and industrial environments.