Diffractive elements operate through interference and diffraction to produce arbitrary distributions of light or aid in optical systems design. They can be designed in both binary and analog phase profiles. Binary elements reach 80% efficiencies and usually represent cost-effective solutions if feature sizes are too small for analog fabrication. Analog, continuous-phase diffractive optics attains more than 90 percent efficiencies and allow for the production of more general patterns. The following are some of the diffractive elements that can be designed and manufactured:
Diffractive Lenses
These lenses can be used for minimizing the number of elements in traditional lens systems and eliminating the need for exotic materials to correct chromatic aberrations. These very thin elements are composed of a series of zones that become finer toward the lens’ edge.
Corrector Plates
In a number of applications, the optical system requires a certain wavefront at some point. In case of a consistent, stationary, and repeatable wavefront deviation, a corrector plate can be introduced for correcting the wavefront. This is possible by inducing the appropriate phase delay at different aperture points to produce the desired wavefront. The corrector plate introduces a phase delay that complements the input wavefront to eradicate the undesirable variations. It is important to ensure the corrector plates are aligned with the incident wavefront.
Beam Splitters
Diffractive elements are commonly used to split a laser beam into an array of spots. In such a situation, a collimated beam incident on the element is separated into an array, which is either 1D or 2D. A grating that has complicated shape produces a beam splitter, generating the desired spots distribution. To produce a diffractive beam splitter, binary and analog design solutions are used. A binary solution is used to produce a beam splitter when the desired spot distribution is centrosymmetric. Meanwhile, an analog design solution is capable of reaching more than 90 percent theoretical efficiency, although it requires more sophisticated production techniques.
Diffractive Diffusers
Diffractive diffusers are meant to offer controlled illumination for some specialized applications like lithographic illumination systems. The sharp intensity fall-off makes the diffractive diffuser better than a refractive one. This advantage is as wide as the diffraction-limited spot that corresponds to the operating wavelength’s incident beam size. Binary or analog phase functions that have around 80% and 90% – 95% efficiencies respectively, can be used to implement diffractive diffusers. A binary phase function is deployed to implement diffractive circular diffuser.
