Breaking polarisation-bandwidth trade-off in dielectric metasurface for unpolarised white light

Optical metasurfaces have gained attention due to their considerable prospects, which can benefit consumers and industries in terms of virtual reality devices and digital displays in various multimedia and entertainment-related applications. To date, most of the metasurface optimisation strategies involving isotropic or anisotropic nanoantennas encounter a trade-off between polarisation insensitivity and operating bandwidth under unpolarised white light, which is a fundamental requirement for many applications in digital displays. We presented a novel technique to break the trade-off between polarisation insensitivity and bandwidth by engineering the displacement dependent phase delay of the adjacent parallel and perpendicular anisotropic nanoantennas in a dielectric metasurface. As a result, we numerically demonstrate a highly efficient metasurface operating at an almost entire visible domain (wavelength of 450 nm-650 nm) while maintaining a constant phase modulation under all polarisation states, thus enabling the polarisation-insensitive metadevices for unpolarised white light.