Diffractive White-Light Diffuser with Subwavelength Structure

Diffractive diffusers have some desirable characteristics, whereas they have a large dependence on wavelengths. For their application over a wide wavelength range, achromatization is planned for diffractive-type optical diffusers. A diffracted pattern can be achromatized by fixing the ratio of each optical path area and optimizing the multiwavelength diffracted patterns simultaneously. Subwavelength pillar structures are used for multilevel optical path regions. We fabricated test pieces to demonstrate this method. Patterns were formed by KrF and ArF stepper lithography and dry etching, and then replicated to resin by UV nanoimprint. Simulations and measurements gave similar results, which suggests that these methods for achromatization work well. Diffractive white-light diffusers will be realized when elements with subwavelength high-aspect-ratio pillar structures are fabricated precisely as designed.