Tech focus: Freeform optics

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A look at the commercial offerings of the main players in freeform optics.

Freeform optics are optical shapes or surfaces that are designed with little to no symmetry constraints. This means  they allow for the combination of several optical elements in a single component, which would usually require the use of several components. In turn, this places them ideally for device miniaturisation, for example. They can also be manufactured to be lightweight and compact.

These freeform optics can be customised for each application and their surface structure optimised for the desired properties of an individual use case. They have been used in non-imaging and illumination optics since around the 1990s, but the benefits of design freedom and compact size have become increasingly recognised elsewhere in recent years. In particular, they have seen more widespread use in applications such as augmented and virtual reality (AR/VR), automotive lidar, military optical systems, medical technologies, aerospace, computer science and electronics.

In terms of manufacturing process, the manufacture of a freeform optic is similar to that of a highly complex aspheric lens, where the surface form and local slope can have an influence on the complexity of the shape and the manufacturing process used to create it. It is also important when it comes to the manufacture of freeform optics to achieve high precision and accuracy in optical surface generation.

Historically, the design and processing difficulty of some of these components have limited their even wider application potential. But in more recent years, techniques such as diamond turning have been used as an efficient method of processing these optical freeform surfaces, leading to more widespread use and market growth.

 

Synopsys: Featured product

Today’s optical designers are often tasked with finding ways to correct more aberrations and use fewer surfaces, and do so in more compact geometries that must fit within anything from smaller medical instruments to more wearable augmented reality (AR) systems. Setting up compact geometry, with multiple reflecting or refracting surfaces, can be challenging when there are numerous folded surfaces or complex optical path constraints. To help support this type of design work, CODE V and LightTools optical design software offer unique and powerful freeform design and optimisation tools.

www.synopsys.com/optical-solutions 

Spectrum Scientific: Featured product

Freeform mirrors Spectrum Scientific’s freeform mirrors offer significant benefits, including a single surface giving compound compensation, redistribution of tolerances and additional aberration correction coupled to fewer optics to align and a reduction in optical volume.

www.ssioptics.com/product-category/precision-mirrors/ freeform-mirrors

 

Commercial products

Vendors of freeform optics and related products and solutions include Asphericon, which manufactures unconventional shapes in a number of materials. Available are lenses, mirrors and monolithical elements with diameters up to 300mm. The company’s freeform systems are based on Alvarez lenses with compact freeform optical design. Thanks to the surface shape it is possible to vary an optical function infinitely. Examples are the dynamic change of the focal length of a system, the compensation of divergence of laser beams, as well as the creation of square top-hat profiles. Asphericon also offers optical design consulting for production-optimised system designs

Fresnel Technologies manufactures moulded plastic optics, Fresnel lenses, IR transmitting materials and conventional and freeform optics. It also offers design help, tooling and production, and diamond machining.

Greenlight Optics has developed advanced design and modelling capability, a workflow process to manufacture freeform lenses. It has also developed metrology to analyse the freeform surfaces. The company’s capabilities include in-house optical and mechanical design, diamond turning, CNC machining, plastic optics moulding, metrology, and assembly and testing.

Jenoptik produces polymer optics that are not rotationally symmetrical. These are compact to help improve applications. It uses its Slow Tool Servo technology to produce high-precision, freeform optics with diameters ranging from 1 to 350mm. A modified diamond turning procedure is used, with a controlled rotation axis and two linear axes. The part of the freeform optics that is not rotationally symmetrical is achieved by means of a dynamic movement of the tool toward the optical axis. The process is ideal for diamond processing of polymers and metals.

Kong Optics specialises in the volume fabrication of high-precision and ultra-smooth aspheres, including freeform optics. Its products have been used in performance-critical systems in astronomy, aerospace, defence and semiconductor equipment.

Lambda Research Corporation’s TracePro is a 3D solid, modelling-based optical analysis software programme that is built on an existing CAD kernel, allowing for file exchange with all CAD software. Originally developed for NASA for stray light analysis of space telescopes and remote sensing systems, TracePro is a multi-threaded programme, which means it can use as many processors or as many cores as the user has available, allowing for fast ray traces and speedy iteration and checking of designs. For freeform optics, the software has a 3D optimiser built in to help design out some of the complexity associated with the freedom of freeform optics in illumination applications.

LightPath Technologies has decades of experience in precision moulding of lenses, upon which it expanded in 2021 to begin producing high-volume, precision moulded freeform optics. These can be produced from a range of materials in the visible, NIR, SWIR, MWIR and LWIR wavelengths. The company also developed the metrology necessary to test new lenses using computer-generated holograms (CGH) to accurately measure freeform optics in production volume, as well as contact profilometry methods to ensure consistent quality and performance.

LightTrans offers its optical design software, VirtualLab Fusion, to support light shaping by freeform surfaces, diffractive beam splitters and pattern generators, diffusers and general arrays of micro-optical components, including, but not limited to, micro-lens arrays. The emphasis of the software package is on the use of lens arrays, diffractive optical elements and cell arrays consisting of gratings, mirrors and prisms. For the designed components, fabrication data can be exported in several formats, including STL and GDSII; the interaction with SLMs is also supported. Fast physical optics simulation and optimisation algorithms enable the design of these optical elements.

LT Ultra manufactures a range of freeform precision optical surfaces out of steel without polishing. It uses ultrasonic assisted diamond turning on steel parts. Its range includes pyramidal mirrors, ellipsoids, masters, toroids of all types, roof mirrors, conical mirrors, bifocal paraboloidal mirrors, waxicons and axicons, stepped mirrors, chopper blades, scraper mirrors and cylindrical mirrors. Other special shapes are available on special order.

Millpond ApS is a manufacturer of custom mirrors and inserts for injection moulding tools. The company specialises in freeform and aspheric shapes, providing tailor-made optical devices in various metallic substrates by applying high-precision diamond turning and/or milling technology.

Optimax Systems supplies high-precision optics. The company is a prototype and custom optics manufacturer that produces aspheres, cylinders, prisms, spheres, freeform optics and coatings. Optimax offers small volume, high-quality products on a fast turnaround.

As well as spectroscopy accessories and applications, Pike Technologies manufactures customised optics including mirrors, lenses, optical mounts and IR microscope objectives. In addition to optical design and prototyping, PIKE offers metrology measurement services, diamond turning, optical thin-film coating, freeform optics and spherical grinding and polishing. Its core infrastructure for optical manufacturing features four diamond turning lathes, precision metrology instrumentation and more. Pike products are used in the petrochemical, food, forensic, pharmaceutical, semiconductor, agriculture, government and the material science industries, as well as in many academic institutions around the world. They can be used for the analysis of organic and inorganic materials by FTIR, NIR, Raman and 
UV-VIS spectroscopy.

Shanghai Optics uses advanced manufacturing techniques, such as CNC machine tools and single point diamond turning, to create high-quality freeform optics and state-of-the-art metrology. Its metrology options include surface profilers, interferometers, and computer-generated holograms, which are used to verify the optical components.

Spaceoptix is a supplier of high-performance metal optical components and systems for applications in space, astronomy, science and industry. The portfolio includes the development, fabrication and testing of customised mirror and freeform optics, as well as engineering and manufacturing services.

Spectrum Scientific (SSI) has been manufacturing high-volume flat, aspheric and freeform reflective optics, hollow retroreflectors and holographic diffraction gratings since 2004. The company primarily use the optical replication process in its manufacturing, allowing for the supply of high fidelity, high-specification precision optics at a competitive cost.

Synopsys provides solutions for designing and verifying advanced silicon chips, and for designing the next-generation processes and models required to manufacture those chips. As part of this, the company’s CODE V and LightTools optical design software are designed as powerful optimisation tools for freeform design.

Vertex Optics employs all the latest optical fabrication solutions to manufacture freeform optics cost-effectively. The company uses CNC optical grinding and sub-aperture polishing machines with five-axis capability to produce almost any freeform optical surface.

This is not an exhaustive list. If you provide products and solutions for freeform optics and would like to be included, please let us know at editor.electro@europascience.com

For complex surfaces such as freeform optics, precise metrology plays a key role in providing essential quality control and feedback during the fabrication process. Laser interferometers and 3D optical profilers from Zygo ensure quality and process monitoring during manufacturing by characterising and quantifying critical surface parameters such as form errors, waviness, defects, and surface roughness.