High-NA achromatic diffractive lensing for arbitrary dual-wavelengths enabled by hybridized metal-insulator-metal cavities.

ABSTRACT

A new type of diffractive lens based on hybridized Fabry-Perot (FP) cavities with high-NA and achromatic features for arbitrary dual-wavelengths is theoretically proposed and demonstrated. We utilize the subwavelength-scale metal-insulator-metal nanocavity to form a Fresnel zone plate (MIM-FZP) that benefits from both spectral selectivity and high numerical aperture (NA > 0.9) to enable lensing functionality. By taking advantage of the different transmission orders from MIM, any arbitrary dual-wavelength achromatic focusing design is achieved. Using this approach, we merge two independent MIM-FZP designs and realize achromatic focusing performance at the selected dual-wavelength of 400/600 nm. Furthermore, the achromatic lens also exhibits a crucial potential for dynamically tuning of the operation wavelengths and focusing lengths as actively scaling the core layer thickness of MIM. The unique MIM-FZP design can be practically fabricated using a grayscale lithography technique. We believe such high-NA and achromatic optical devices enjoy great simplicity for structural design and can easily find applications including high-resolution imaging, new-generation integrated optoelectronic devices, confocal collimation, and achromatic lens, etc.