Design of an RGB tunable narrowband metalens using BaTiO₃ material with a high electro-optic coefficient

The narrowband metalens has high-quality resolution owing to the elimination of stray light interference in optic imaging processes. However, the operating wavelength of most of the existing schemes is fixed, which restricts the functional diversity and application range. Here, we propose an RGB tunable narrowband metalens by integrating metalens and bandpass filter composed of multilayer thin film based on an F-P resonator to simultaneously achieve focusing and filtering functions using BaTiO 3 material with high electro-optic coefficient. By applying external voltages on the BaTiO 3 thin film (BTOTF), the refractive index can be actively modified to switch the passband of the filter, therefore realizing the tunability of operational wavelengths. The results indicate that the device exhibits the switchable wavelength ability between red, green, and blue; meanwhile, near-diffraction-limited focusing is demonstrated at wavelengths of 488.2 nm (blue), 561.6 nm (green), and 611.3 nm (red) with corresponding FWHM of 1.2 µm, 1.46 µm, and 1.5 µm, respectively. The proposed RGB tunable narrowband metalens may be beneficial to promote the development of the fields of optical imaging and sensors.