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Center for Freeform Optics (CeFO)

University of North Carolina-Charlotte

University of Rochester

Last Reviewed: 12/26/2019

Our vision is that compact, affordable, and high-performance optical systems based on freeform optics will permeate precision technologies of the future.

Center Mission and Rationale

The mission of the Center for Freeform Optics is advancing research and education on the science, engineering and applications of freeform optics through a dedicated, continuing industrial partnership. 

This Center has been created to launch the permanent introduction of freeform surfaces into the manufacturing infrastructure for optical systems worldwide. Its catalyst is the recognition of the advance of promising new fabrication possibilities such as, on one hand, Slow/Fast Tool Servo Technology and High-speed Diamond Machining community and, on the other hand, emerging technologies such as Laser Polishing and 3D Printing. We also anticipate that advances in grinding and computer-controlled polishing, ion beam finishing, and MRF with appropriate control of mid-spatial frequencies will enable freeform optics for the leading generation of ultra-precise EUV optics, an area of strong expertise within the team supporting this center. Freeform optics has the potential to impact across a broad wavelength range from IR surveillance to EUV lithography.

Fundamentally, the ability to manufacture freeform surfaces changes the game for optical system design. Prior to the emergence of these new capabilities, optical systems involved surfaces that were either rotationally symmetric or sections out of rotationally symmetric surfaces.  Other than an occasional toroid or similar anamorphic surface, there have been very few other shapes in imaging optical systems.  Significantly, there are three specific types of aberrations in an imaging optical system (ignoring for the moment field curvature, which is more of a fundamental property), spherical aberration, coma, and astigmatism.  Here, the latter two arise when an ideal converging spherical wavefront encounters an offset section of a spherical surface. As a result, these two field-dependent aberrations are directly affected by the spherical surface.  The outcome of introducing freeform surfaces is that until this most recent decade there has been no means to independently introduce coma into an optical system.  For an off-axis or unobscured system, this situation has severely limited the optical system performance.  The Center for Freeform Optics has been leading the development of optical aberrations for freeform surfaces and systems as well a the development of design methods and processes to bridge design to manufacture.

The ability to design and manufacture optical systems with freeform surfaces has received great interest from industry and governmental institutions in recent years because it has been proven to yield an order of magnitude performance increase with no increase in physical size.

The main benefits of freeform optics can be summarized as follows:

  1. Increased compactness: 5X in volume has been demonstrated.
  2. Advanced performance:  Up to a 100 fold increase has been demonstrated.
  3. Lighter weight:  Weight scales with the cube of a linear dimension.
  4. New solution space.

 

This center is uniting three perceptually mature research technologies: optical design, optical fabrication, and optical testing. Two of these areas are in the midst of a true revolution and the third is being challenged to bring the science of optical systems to an entirely new, unexplored region of solutions. In the process, completely new applications for optical systems are emerging. This center provides the synergistic, collaborative working space to bring freeform optical surfaces into the mainstream of optical systems.
 

Research program

Three main thrust areas:

  1. Fundamentals of Freeform Optics: mathematical descriptions of freeform surfaces, aberration theory of systems that depart from rotational symmetry and leverage freeform surfaces, light propagation through freeform optical systems, optical design methods and tools to bridge design to manufacture.
  2. Advanced Materials for Fabrication and Manufacturing of Freeform Optics:  emerging technologies such as fast-tool servo diamond turning, ultra-precision grinding, and high precision molding require many refinements for low cost, optimal optical quality, and speed of material removal. The approaches must also solve long-standing problems with manufacturing-induced defects and surface artifacts. Emerging technologies such as laser polishing and 3D printing are poised to transform freeform optics manufacturing, including for mass production.
  3. Optical Testing for Freeform Optics:  Optical fabrication is limited by optical metrology.  Freeform optics presents a grand challenge in optical testing to achieve both nanometer accuracy and speed for cost-effective manufacturing.

Special Activities

As the Center grows and diversifies, it is necessary to develop standards and guidelines to help companies with the least expertise in freeform optics to adopt and implement it. The Center will pursue the realization of standards with regards to the development, evaluation, implementation, and use of freeform surfaces in devices and equipment.

Facilities and Laboratory

CeFO Facilities: A Summary

The Center for Freeform Optics has extensive experimental facilities on two campuses, with the addition of a third campus, to be used to support the wide range of research activities that are part of the Center for Freeform Optics.       

At the University of Rochester, our major facilities are grouped under manufacturing and characterization. In manufacturing, we have both full-aperture and sub-aperture grinding and finishing platforms, the Optipro SX-50 and the QED Q22-XE MRF and the Optipro UltraForm Finishing (UFF) platform.  The Optipro SX-50 is a CNC manufacturing full-aperture platform that can be used for the manufacturing of flat and spherical surfaces using bound abrasive tools. The QED Q22-XE MRF platform is also CNC and uses magnetorheological finishing for sub-aperture finishing, figure correction, both for aspheres and mild freeform optics. The Optipro UltraForm Finishing platform is also a CNC platform for sub-aperture finishing and figure correction using a novel belt abrasive technology. The Optical Fabrication Shop at the Laboratory for Laser Energetics has polishing capabilities for optics up to 300 mm in diameter. We also have a dedicated magnetorheological spot-taking-machine (STM) for process research and development.

Characterization facilities include SEM, AFM, nanoindenters, an x-ray diffractometer, and various white-light and monochromatic interferometers and profilometers for metrology of optical surfaces, including surface roughness measurement. Examples are an Optikos MTF testing system, Zygo New View interferometer, and a ThorLabs polarimeter, as well as diverse microscopes (optical, Nomarski, polarizing, and IR) and spectrometers. The NANO-UR nanofabrication facility has extensive nano-manufacturing platforms (atomic layer deposition, sputtering, evaporators, lithography bench, AFM, reactive ion etcher, etc.). Finally, in 2017, an UltraSurf Freeform metrology capability from Optipro was added to our facilities.

The UNC Charlotte facilities include extensive manufacturing and metrology platforms, equipment and resources. These resources are located in several adjacent departments and centers (Mechanical Engineering and Engineering Sciences (MEES); Physics and Optical Science (POS));the Center for Precision Metrology-CPM, a previous NSF I/UCRC; and the Center for Optoelectronics and Optical Communications (the Optics Center)). 

The available equipment allows for a wide range of fabrication and characterization activities. Some of our equipment is uncommon and well suited to state-of-the-art freeform optics research. Examples for fabrication include an ABB IRB140 Six-Axis Polishing Robot, Makino A51 and A55 Machining Centers, Moore Nanotech 350FG and 650FG 5-axis Ultraprecision Machining Centers, a QED Q22-XE Magnetorheological Finishing Machine, a Raith 150 E-beam Lithography System, and a Nanoscribe Professional GT Nano 3D Printer. 

Unique equipment for characterization includes a ZygoNewView 5000 Scanning White Light Interferometer, a Zygo Verifire HD 100 mm Aperture at 633 nm, a Zeiss F25 Micro Coordinate Measuring Machine, a Mahr MarSurf LD 260 profilometer, a Zygo FTPSI 100 mm Aperture Wavelength Scanning Interferometer at 1550 nm, a custom Twyman-Green interferometer at 10.6 microns, a tunable THz Laser, a VASE Woolam Spectroscopic Ellipsometer, an Olympus OLS4000 LEXT 3D Measuring Laser Microscope, and a CASI scattering facility for BSDF and BRDF measurements from 633 nm to 10.6 ┬Ám.

Locations

University of Rochester

275 Hutchison Rd

Rochester, New York, 4627

United States

University of North Carolina-Charlotte

9201 University City Blvd

Charlotte, North Carolina, 28223

United States

(704) 687-8159