GRINlenzen

GRINlenzen, or gradient-index lenses, are optical elements in which the refractive index varies gradually inside the material rather than remaining uniform. This spatial variation bends light smoothly as it propagates, enabling focusing, imaging, or beam shaping without the need for curved outer surfaces. GRIN lenses come in various geometries, including cylindrical rods, flat slabs, and more complex shapes, and are used to compactly couple light between fibers, integrate optical functions into tight spaces, or collimate and focus beams.

The guiding principle of a GRIN lens is a refractive-index profile that changes with position. A common, radially symmetric profile decreases from the center toward the edge, causing rays to bend toward the axis and produce focusing behavior. In some designs, the index also varies along the axis to achieve different focusing characteristics. The exact profile is chosen to produce the desired focal length, numerical aperture, and imaging performance for a given application.

Common applications include fiber-optic coupling (such as end-to-end connections between fiber and photonic devices), compact imaging and endoscopic systems, laser diode collimation, and integrated optical modules where space is at a premium. GRIN lenses offer advantages like a compact form factor, reduced surface reflections due to fewer curved interfaces, and the ability to tailor optical properties with a single element. They can be made from glass, polymer, or other transparent materials and fabricated using diffusion processes, ion exchange, or direct-write techniques to produce the gradient refractive index.

Limitations include dispersion-related chromatic effects and sensitivity to manufacturing tolerances of the index profile. Proper design and alignment remain important to achieve the intended optical performance.