DOE optics in a nutshell
A Diffractive Optical Element (DOE), also known as Diffractive Optical Lens or Computer-Generated Hologram (CGH), is an optical component that utilized the wave characteristics of light to achieve its function.
Typically, the DOE is a micro relief structure on the face of an optical window, with the structures diffracting the light in a pre-designed pattern (various substrate materials can be used depending on application requirements). These micro structures heights are tailored to create a desired phase delay for a certain design wavelength. Thus, a DOE is typically designed to perform a specific optical function on a specific wavelength, i.e. – to be used in laser systems where the light is monochromatic.
The power of DOE Diffractive Optical Elements
DOE are used in various applications to perform complicated mathematical functions on the phase of the input beam to generate various shapes and structures of output beam or beams, and thus improve systems performances.
When using diffractive beam splitters for example, one may generate multiple beams with similar characteristics to the input beam at predefined separations from one another. The diffractive beam splitter is widely used in applications demanding parallel processing to improve the process throughput.
Another common example for a diffractive optical element is the diffractive beam shaper or diffractive diffuser used to generate a flat top profile of the beam with a very sharp “drop” of the energy outside the flat area. This energy profile enables system manufacturers to almost perfectly exploit the energy at hand that their source provides them, as the flat region is design to the exact energy level required for the process threshold and thus, no energy is being wasted by surpassing that threshold. The flat top diffractive beam shaper is typically used in high-power material processing applications where the energy cost is a substantial component and high precision of the process is required.
Other DOE diffractive optical elements may include diffractive axicons, diffractive vortex lenses and more. One may even combine two or more optical functions on a single custom DOE optical surface, to create a highly compact optical system or sub-system generating the exact required function.
Looking to the future – Diffractive Optics is becoming the “go-to” solution in many laser applications
Diffractive optical elements have several advantages over traditional refractive optics:
- DOE are flat, thin and lightweight making them the perfect solution in systems where compactness is valued.
- DOE are passive components, and depending on the substrate material can be extremely robust, thus preform perfectly over time in any system and environmental conditions, including very high-power systems of up to hundreds of KW.
- DOE have perfect angular accuracy with almost no tolerances on shaping or splitting angles due to the high production precision. The DOE diffractive optical element production process includes lithography and etching, same as semiconductors fabrication, making feature tolerances negligible (<10-5 of angles typically) When you use a DOE in your system you know that the first DOE, the second, the one-hundredth or the one-thousandth DOE – they will all give exactly the same angles or shape sizes.
Diffractive optical elements have made their way into industrial applications well over 20 years ago, and are rapidly becoming the “go-to” solution in many medical, industrial and research applications. This is a trend that is growing more and more observed with laser power cost decreases over the past few years.
TL; DR – Q&A
Q: What are Diffractive Optical Elements?
A: Diffractive Optical Elements are phase relief elements that use micro-structures fabricated onto an optical window substrate to alter the phase of light propagated through it and thus to create various complex optical functions.
Q: What differentiates Diffractive Optics from regular refractive optics?
A: Diffractive Optics enables complex optical functions that cannot be obtained with a single optical component otherwise, with accurate and constant properties. Unlike refractive optics, diffractive optics is designed to operate at a single wavelength.
Q: When is it beneficial to use Diffractive Optical Elements?
A: When trying to improve laser system’s performance in an application with a high cost source, when trying to achieve a specific complex output energy distribution, and when designing a compact optical system based on a single wavelength source, Diffractive Optical Elements have absolutely no competition.
Q: What applications use Diffractive Optical Elements?
A: Diffractive Optical Elements are used in various applications including medical, material processing, research and 3D sensing applications.
