Diffractive Optics: Why Hybrid Lenses are Beneficial

Diffractive Optics: Why Hybrid Lenses are Beneficial

Diffractive optics offers new and exciting degrees of freedom in designing and optimizing optical systems. The use of this technology allows the achromatization of optical systems with one economical refractive material like acrylic plastic or common crown glass. It allows the creation of aspheric wavefronts without aspheric surfaces. With the use of these optics, there is no need for exotic and expensive flint-type materials.

Diffractive Optical Elements Fabrication

The use of diffractive optical elements (DOEs) has been limited by the impacts linked to scattered light. Structured scattering takes place when light is distributed into unwanted diffractive orders. Statistical scattering refers to random scattering due to surface roughness.

Producing a surface-relief DOE involves the fabrication and use of a precision surface-relief master element to create huge quantities of replicas. A suitable process allows the manufacture of tens of thousands of elements based on one master.

To produce high-quality DOEs, manufacturers shape or micromachine the required surface profile into some substrate material. Achieving high diffraction efficiency is possible by ensuring the edging step of every zone boundary is quite shape and the surface profile within every zone is smoothly shaped or blazed. This is necessary to avoid statistical scattering.

Benefits of Hybrid Lenses

A traditional refractive achromat is composed of crown and flint glass, which bring two wavelengths to a common focal point. Typically, the constitutive crown and flint elements have powers that are 1.5 to 2.5 times greater than that of the combination, which indicates steep surface curvatures and makes it hard to produce low-f-number achromats.

Essentially, it is possible to use a diffractive lens as a replacement to the flint-glass materials in most broadband optical systems. For instance, its use can let designers achromatize an optical system that has a single kind of glass or plastic. This hybrid refractive/diffractive lens provides a better performance than traditional doublets while showing all the benefits of diffractive optics.

Unlike traditional achromats, both the diffractive and refractive lens elements have the optical power that reduces the refractive element’s surface curvature and enabling the production of low-f-number achromats. Additionally, a hybrid achromat’s weight is often just 1/2 to 1/3 that of the corresponding traditional achromat. The ability to eliminate expensive and hard-to-work flint-type materials from the system and use a single, low-cost crown-type glass for the lens’s refractive portions makes a hybrid lens a great option for cost savings. Also, it is possible to fabricate the diffractive lens directly onto the refractive element’s surface, simplifying mounting and assembly requirements and offering extra cost savings.