Most people are familiar with a classic optical lens (refractive lens), a curved piece of glass or plastic that focuses the light. However, the optics field includes various other optical components with enhanced performance – including diffractive lenses and diffractive lens design.
Diffractive optics offer new and powerful degrees of freedom for lens design and optimization of optical systems.
What Are Diffractive Optics?
Diffractive optics is a type of optics based on elements with operation principles that rely on the diffraction of light. This refers to a slight bending of light that occurs as it passes around the edge of an object, which depends on the size of the wavelength of light and the opening.
Diffractive optical elements can be combined with other optical components or be used on their own to achieve the desired performance for the project. This is often within the context of micro-optic elements, but it’s a highly versatile option for optical systems.
How Do Diffractive Elements Fit into Optics?
Optical engineers may need to control light through diffraction; this is diffractive optics. Distinguished from physical optics, this field describes the generation and control of light wavefronts by segmenting and redirecting them using interference and phase control.
Some of the different types of elements include:
- Diffractive optical elements which modify wavefronts by segmenting and redirecting them
- Fresnel lens, or a scale of zones without organized phasing
- Fresnel zone plate, which is a pattern that produces amplitude modulation
- Kinoform, which is a phased Fresnel lens for modulation in the surface relief
- Binary optics, which is an element with a discreet number of phase-controlling surfaces
- A holographic optical element is an element generated by the interference of two wavefronts to produce a component for an optical system
- Hybrid lens, or a refractive and diffractive lens with combined power
- Computer-generated hologram, which is a hologram made using computer calculations
With diffractive optics, optical engineers can:
- Create achromatic lenses using only a single optical material
- Create large aperture, lightweight optical elements
- Reduce the weight, complexity, and cost of optical systems
- Improve the performance of refractive systems
- Reduce the need for exotic materials
- Reduce the thermal lensing effects
- Achieve absolute accuracy in focal length
- Achieve diffractive micro-lens arrays with identical lens performance
The Fresnel Zone Plate
The Fresnel zone plate is one of the best-known examples of a diffractive lens. Unlike refractive lenses, the Fresnel zone plate features a flat window that is relatively thin to utilize light as a wave and achieve the diffractive effect. This occurs because the lens delays the light going through concentric rings on the surface – Fresnel Zones – to focus or diverge light like a refractive lens.
Diffractive Micro-Lenses
Another everyday use of diffractive lenses is micro-optic diffractive elements created as thin plates that build a spatial pattern of phase changes on the incident light beam – typically a laser beam. Some of these may be binary with only two different phase delays on the surface, while others have analog phase profiles.
Some micro-optic devices are designed with different diffraction patterns within a defined distribution of powers in other areas, such as diffractive beam splitters or beam combiners.
Diffractive Lens Design
A diffractive optical lens differs significantly from a refractive lens, but the design process is similar. It all begins with the design of the lens shape. Each area within this shape must be equivalent to a single wavelength of delay, and each Fresnel zone has a sharp change – the Kinoform phase.
During this phase, each Fresnel zone is adjusted to create equal height “steps” for production using semi-conductor fabrication methods and to ensure the right level of diffraction. Each angle must be exact, but the lens may integrate other designs, including toric lens design, spherization, and conic constant.
Depending on the project’s needs, various fabrication techniques have been developed for diffractive optical elements. Some can produce binary structures, while others can produce analog profiles.
Diffractive Lens Design at Apollo Optical Systems
Apollo Optical Systems has been at the forefront of innovation in diffractive optics technology for decades allowing us to bring diffractive lenses from laboratory settings to mass-produced commercial applications.
Our optical engineers made a breakthrough in diffractive lens fabrication in the 1990s using single-point diamond turning (SPDT) methods. This technology can achieve 97% to 99% efficiencies at the design wavelength with RMS-surface finishes of 1.5 nanometers. Our diffractive lenses can be fabricated using leading materials, including polymers and metals.
Discuss Your Diffractive Lens Project
With the unique combination of design, fabrication, and metrology, the team at Apollo Optical Systems can provide cutting-edge diffractive lens technology to provide leading optical components and systems. Contact us today to discuss your product requirements!