Diffractive optical elements (DOEs) are available for demanding consumer and industrial applications. These lithographically patterned elements provide complete phase control of transmitted light without the limitations that refractive optics impose.
Diffractive elements are thin phase elements that operate through interference and diffraction to produce arbitrary distributions of light or help in designing optical systems. Binary elements can attain almost 80% efficiencies and usually cost-effective solutions when feature sizes are too small for analog fabrication and when the desired pattern has centrosymmetry. Below are the different diffractive elements that can be designed and manufactured:
Diffractive Lenses
These lenses can be used for reducing the number of elements in traditional lens systems and eliminating the need for exotic materials to correct chromatic aberrations. These thin diffractive optics elements are composed of a series of zones that tend to become finer towards the lens’ edge. Generally, they work best at a single wavelength. The efficiency and image contrast are decreased at any other wavelength. But, for applications where there is a particular number of discrete wavelengths, diffractive lens that shows 100 percent theoretical efficiency at every wavelength can be designed.
Beam Splitters (Spot Arrays)
A diffractive element is commonly used in splitting a laser beam into an array of spots. The element that produces a beam splitter is a grating with some complicated shape that generates the desired spots distribution. Binary and analog solutions are the basic approaches to produce a diffractive beam splitter. Some manufacturers produce analog diffractive solutions by using their laserwriting technique to produce a continuously-varying surface to yield the desired spot distribution. Analog design solutions can reach more than 90% theoretical efficiency; however, they require more sophisticated production techniques.
Diffractive Diffusers
These diffusers are used to offer controlled illumination for some specialized applications like lithographic illumination systems. When compared to refractive elements, diffractive diffusers have a sharp intensity fall-off that is as wide as the diffraction-limited spot that corresponds to the incident beam size at the operating wavelength. These diffusers can be implemented with analog or binary functions with around 90% to 95% and 80% efficiencies respectively.
Corrector Plates
Some applications require certain wavefront at some point in the optical system; however, the actual wavefront doesn’t show the desired form. When there is consistent and repeatable wavefront deviation, a corrector plate can be introduced to correct the wavefront. This is possible by inducing the appropriate phase delay at different points of the aperture to produce the desired wavefront.
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