Low-Cost, High-Volume Diffractive Lens Array for Optical Document Security

Advances in optical security technologies are crucial in combating counterfeiting, particularly for government issued documents and banknotes. A recent development in this field is the creation of a high-numerical-aperture (NA) multilevel diffractive microlens array (MLA) that operates across multiple wavelengths ¹.

The MLA features a high NA of 0.88 (f/0.27) and is engineered to focus light at wavelengths of 480 nm, 550 nm, and 650 nm. Each microlens in the array has a diameter of 70 µm and a focal length of 19 µm in air, arranged in a closely packed configuration. The fabrication process involves UV casting on a polymer film, positioning the focal plane of the MLA at the under surface of the film. This method ensures that each microlens can focus light into a spot with an estimated full-width at half-maximum (FWHM) of approximately 310 nm.