Fabrication of Freeforms Optimax has developed a robust freeform optical fabrication CNC process that includes generation, high speed VIBE polishing, sub-aperture figure correction, surface smoothing and testing of freeform surfaces.
Optimax excels at grinding, polishing and coating precision optics quickly and reliably. We can deliver high precision optics in as little as one week.
Customers trust Optimax to create high-quality optics and deliver them fast, and our custom aspheres are no exception. Designing with aspheres reduces the size and weight of your system. Optimax produces aspheres from glass, fused silica, crystals and ceramics for UV, Visible and IR applications using proprietary “grind and shine” techniques for low scatter surfaces.
About Aspheric Lens Manufacturing
Aspheres have one or more optical surfaces of non-constant curvature. They are used to manage aberrations inherent to spherical lens systems, and to reduce system size and weight. Aspheric lenses have enabled a leap forward in capabilities for medical devices and defense and security.
Manufacturing and metrology of complex aspheres is an emerging science for optical fabricators: Optimax leads the way in our investment in cutting edge equipment and testing, research and training, and track record of performance on customer programs.
We’ll walk you through the process, and invite you to visit the Resource Library for technical resources at every step.
Specifying an asphere begins with a custom aspheric form, often fit to the Forbes Q Polynomial (Figure 1) or the Even Aspheric Equation (Figure 2). Describing form involves specifying Vertex Radius (I/C). Conic Constant (k) and applicable Aspheric Coefficients (a). Including a Sag Table (Figure 3) provides reference information to check correct data entry for each manufacturing or metrology tool used.
Forbes Q Polynomial
Figure 1
Even Aspheric Equation
Sag Table
Figure 2
Optimax places tolerances on vertex radius and form error, without tolerances on conic constant or aspheric coefficients. Even aspheric coefficients are preferred.
Need to spec or quote an asphere? Contact us or browse our technical resources:
Looking for the most advanced manufacturing and metrology technology in North America? Optimax utilizes deterministic CNC machine tools for predictable removal rates and adherence to tight tolerances. To control centration, precision tools maintain the optical axis.
Need to spec or quote an asphere? Contact us or browse our technical resources:
Coatings can make or break an asphere’s performance. Optimax offers integrated coating services to reduce the risk and time delay in coating your optics. Our clean environment thin film coating lab has the capability to coat from UV through IR wavelengths. Featuring multiple chambers with deposition sources, including electron-beam and ion assist, Optimax can offer a wide variety of coating options including BBAR, V-coat and mirror coatings. Custom coatings are also available. Coating verification is supported by Perkin-Elmer spectrophotometers.
Coatings Data Sheet.
Testing Aspheres
Optimax inspects 100% of all optics. Test data is provided with prototype orders.
Our metrology must match the sophistication of our manufacturing technology. Optimax offers state-of-the-art metrology, including surface profilers and interferometers to verify that parts meet the form error specification. Testing options are form-specific lenses with mild departure from a best-fit sphere that has the highest potential for fractional wave precision.
Optimax manufactures a wide variety of optical components. When on-time delivery is crucial, Optimax offers an expedited delivery option with a money back guarantee.
Continued Innovation
Optimax’s R&D department is continuously looking for ways to improve our fabrication process and produce higher quality optics. Our current research projects are designed to meet future market needs, such as:
This represents a general list of soft limits and is intended for reference only.
As requirements move closer to a min or max shown the more challenging the part will be.
Certain combinations may not be possible – Choosing Max Sag and Min Diameter on concave surfaces for example.
Interferometric testing of aspheres is extremely case specific. The slower the onset of departure, the more likely interferometric testing is possible.
During manufacturing the lens is oversized in diameter. Be aware, forms well behaved within clear aperture may turn exotic or undefined just beyond final diameter.
Manufacturing Limits for Aspheric Surfaces
Based on Form Error Tolerance
Form Error > 2μm Lower Resolution Profilometry (2-D)1
Attribute
Minimum
Maximum
Diameter (mm)
3
250
Local Radius (mm)
-8 (Concave)
∞
Sag (mm)
0
502
Departure (mm)
0.01
20
Included Angle (°)
0
120
Form Error 0.5 – 2μm Higher Resolution Profilometry (2-D)1
Attribute
Minimum
Maximum
Diameter (mm)3
3
250
Local Radius (mm)
-12 (Concave)
∞
Sag (mm)
0
252
Departure (mm)
0.01
20
Included Angle (°)
0
150
Form Error < 0.5μm Interferometry with Stitching (3-D)
Attribute
Minimum
Maximum
Diameter (mm)3
3
250
Local Radius (mm)
-13 (Concave)
∞
Sag (mm)
0
252,4
Departure (mm)
0.002
1
Included Angle (°)
0
120+5
1Typical metrology is Zygo MetroPro plots for interferometry
2For concave surfaces the maximum may be smaller, limited by tool clearance first. Short radii have lower maximums
3Larger diameters can be accommodated using multiscan fusion
4Total sag allowed is a function of diameter, determined by fringe resolution of the interferometer
5Very basic forms (paraboloid, ellipsoid) can have higher included angles
This represents a general list of soft limits and is intended for reference only.
As requirements move closer to a min or max shown, the more challenging the part will be.
During manufacturing, the lens is over-sized in diameter.
Manufacturing Limits for Spherical Surfaces
Based on Form Error Tolerance
Attribute
Minimum
Maximum
Diameter (mm)
3
400
Radius (mm)
±1
∞2
Aspect Ratio (Diameter/Center Thickness)
<1:1
30:1
Included Angle (°)
0
2103
1Limited by machine envelope
2Metrology dependent. Avoid 3-10 meter radii when possible, choosing to stay plano instead. It will be less expensive too.
3This represents highest values possible. Actual value possible depends on finished and metrology options available plus tolerance range available for a given part.
This represents a general list of soft limits and is intended for reference only.
As requirements move closer to a min or max shown, the more challenging the part will be.
Manufacturing Limits for
Prism Surfaces
Attribute
Minimum
Maximum
Diameter (mm)
3
300
Thickness
1
150
Aspect Ratio1
1
502
1Diameter divided by thickness
2This represents highest values obtained. When at maximum other minimums (irregularity) may not be possible. Will be smaller with less well behaved materials.
3This is for the most well behaved materials. More difficult materials (CaF2, Ohara S-FPL, etc.) will need larger tolerance ranges.
4Of full aperture (FA)
5In addition to irregularity
6This represents lowest values obtained. Will grow with diameter. Will be larger with less well-behaved materials.
7Typical metrology is Zygo MetroPro plot for interferometry.
8This represents lowest values obtained. Will grow with diameter. Will be larger with less well-behaved materials.
9Also known as parallelism or pyramidal error in prism manufacture.
10Tighter specification is possible but can be extremely expensive. For a more economical limit, please consider using 0.005mm.
11Subject to measurement uncertainty
12Crystals and reflective materials will receive 40W inspection
13This represents lowest values obtained. Actual values for crystalline materials, especially polycrystalline, will be higher.
Here are manufacturing limits and tolerances specific to optical aspheres, prisms, cylinders and spheres. For more detailed information on any attribute, please contact sales@optimaxsi.com.