Diffractive Optical Elements

The use of light has proliferated in many commercial applications far beyond simple illumination. Many types of modern equipment use light in the form of lasers for various applications such as communications, printing, material processing, additive manufacturing, sensing, medical imaging or treatments, etc. Some of the mentioned applications require optics able to precisely manipulate laser beams in complex ways, often within a compact system. 

Diffractive optical elements (DOEs) are phase elements that can manipulate laser beams into various shapes and profiles, based on the phenomenon of optical diffraction. DOEs use custom designed micro-optic structures fabricated on a flat window, that spatially modulate the amplitude and phase of the laser beam propagated through it to achieve the desired shaping. They offer several key advantages over traditional refractive optical elements. DOEs are:

• Thin, planar and lightweight making them ideal for compact systems 
• Robust passive elements that, depending on the substrate material and coating, can last long under any environmental condition 
• Enablers of novel functionalities inconceivable using refractive optics 
• Highly precise optical elements with accurate output and negligible tolerances 

DOEs can be sub-divided into mainly three different categories according to their desired optical function:

1. Beam Shapers 
2. Beam Splitters 
3. Beam Foci 

Beam Splitters 

Beam splitter DOEs split a single incident laser beam into an array of out beams at predefined separation angles and energies, each retaining all other characteristics of the incident beam such as divergence and shape. The intensities and angles of propagation of the diffracted beams are defined by the microstructures in the beam splitter. Beam splitters can be customized for: 

• Any number of beams at predefined separation angles and arrangement
• Square or hexagonal packing, and even random packing of the spots is possible
• Any ratio of intensities of certain spots vs other spots.

Beam splitters are typically used in applications such as laser scribing, fibre coupling, medical devices, and LiDAR. 

Beam Shapers 

Beam shaper DOEs transform the incident laser beam into a spot with uniform intensity and with defined angular shape. By focusing the shaped beam, an output spot with a sharp edged,  well-defined intensity profile can be achieved at the focal plane. DOE beam shaping methods are determined by input beam quality and type:

• For Single mode lasers an Analytical beam shaper would be advised
• For Multi mode lasers the typical solution would be the Diffuser or Homogenizer

Beam shapers can be customized for: 

• Angular beam shaping or focal beam shaping 
• Any desired spot shape or size
• Any input beam diameter

Beam shapers are mainly used in applications such as cutting, welding, photolithography, medical devices, sensing and more. 

Beam Foci 

Beam Foci are DOEs that can manipulate the focal properties of the incident laser beam to produce an output beam with either increased depth of focus, multiple-focal planes or focusing of different  wavelengths to the same focal plane. Beam foci elements can be customized for: 

• Increased depth of focus (Bessel like beam created by elongated focus DOEs)
• Split incident beam into several foci with desired separation distance (Multi-focal DOEs) 
• Focus different wavelength or harmonies of a laser into a single focal plane (Diffractive achromat, dual wavelength lenses)

Beam Foci are typically used in applications involving transparent material processing such as glass cutting, spectroscopy, microscopy and metrology.

With all the aforementioned properties DOEs allows for efficiently shaping light and improving overall system performance within a compact optical system.