Steplens

Steplens is a term used to describe a class of optical lenses in which the optical power or phase is produced by discrete steps in either the surface contour or the refractive-index distribution, rather than by a perfectly continuous profile. This concept encompasses two common realizations: stepped-surface lenses, where the outer surface is formed by a sequence of small, stepped facets; and stepped-index or digital lenses, where the refractive index changes in a piecewise-constant fashion across the lens cross-section.

In stepped-surface lenses, the overall lens shape is approximated by a stack of flat or faceted steps. The number, height, and arrangement of steps determine focusing behavior and aberration characteristics. In stepped-index lenses, the material is composed of several layers or regions with different refractive indices, creating an effective gradient when light traverses the component. Such designs can approximate the focusing action of a continuous gradient index or be tailored for specific wavelength and angular performance.

Manufacturing methods vary with the type. Stepped-surface lenses can be produced by precise machining, micro-milling, lithographic patterning, or diamond turning to create the stepped geometry. Stepped-index lenses are often built from laminated materials, thin-film deposition, or multi-material additive manufacturing, where each layer or region has a distinct refractive index.

Applications include compact micro-optics, integrated photonics, and educational or research settings that explore gradient-like focusing without fully continuous index profiles. Challenges include step-induced scattering, surface roughness, and tighter tolerances required to manage aberrations and efficiency.