A
microlens is a small
lens, generally with a
diameter less than a
millimetre (mm) and often as small as 10 micrometres (µm). The small sizes of the lenses means that a simple design can give good optical quality but sometimes unwanted effects arise due to optical
diffraction at the small features. A typical microlens may be a single element with one plane surface and one spherical convex surface to
refract the light. Because microlenses are so small, the substrate that supports them is usually thicker than the lens and this has to be taken into account in the design. More sophisticated lenses may use
aspherical surfaces and others may use several layers of optical material to achieve their design performance.