Refractive microlenses, either individually or in high fill factor one and two dimensional arrays, can be used to provide high quality fibre launch and micro-laser divergence correction optics.
The microlens sag, formed by photoresist reflow, can be adjusted during fabrication to give a wide range of numerical apertures and working distances.
Diffractive microlenses, which are designed to operate at a single wavelength and focal length, are fabricated using a combination of photolithography and micro-etching techniques. A wide range of working distances and lens diameters can be created although due to the fabrication technologies used an f-number limit of 3 is necessary. The basic diffractive microlens has a standard quadratic phase profile although any aspheric profile can be created as either a single lens or as part of a 100% fill factor lens array (either uniform or with distinct individual lenses).
Both of the classes of microlens can be combined together to produce hybrid microlenses with, for example, two seperate focal planes one from the outer refractive zone and one from the inner diffractive zone.