This work explores quick predictive methods for calculating potentially risky stresses in cemented doublets underdoing temperature change that agree well with finite element analysis. We also provide guidelines for avoiding stress concentrations.
With the ongoing advancements in aspheric manufacturing and metrology, companies have to overcome processing challenges and from time to time learn costly lessons along the way. Optimax Systems, Inc., a leader in quick delivery prototype optics, has been manufacturing aspheric lenses for over 20 years. Along the way, we have learned many lessons, some the hard way. In this paper, I will share a few stories of how aspheres have humbled us, how we overcame the problem, and provide takeaways for other manufactures and designers.
Optical designers assume a mathematically derived statistical distribution of the relevant design parameters for their Monte Carlo tolerancing simulations. However, there may be significant differences between the assumed distributions and the likely outcomes from manufacturing. Of particular interest for this study are the data analysis techniques and how they may be applied to optical and mechanical tolerance decisions. The effect of geometric factors and mechanical glass properties on lens manufacturability will be also be presented. Although the present work concerns lens grinding and polishing, some of the concepts and analysis techniques could also be applied to other processes such molding and single-point diamond turning.
Optical designers assume a mathematically derived statistical distribution of the relevant design parameters for their Monte Carlo tolerancing simulation. Presented are measured distributions using lens manufacturing data to better inform the decision-making process.
Freeform applications are growing and include helmet-mounted displays, conformal optics (e.g. windows integrated into airplane wings), and those requiring the extreme precision of EUV. These non-rotationally symmetric surfaces pose challenges to optical fabrication, mostly in the areas of polishing and metrology. The varying curvature of freeform surfaces drives the need for smaller, more “conformal”, tools for polishing and reference beams for interferometry. In this paper, we present fabrication results of a high-precision freeform surface. We will discuss the total manufacturing process, including generation, pre-polishing, MRF®, and metrology, highlighting the capabilities available in today’s optical fabrication companies.
In the manufacturing business, there is one product that matters, money. Whether making shoelaces or aircraft carriers a business that
doesn't also make a profit doesn't stay around long. Being able to predict operational expenses is critical to determining a product's
sale price. Priced too high a product won't sell, too low profit goes away. In the business of precision optics manufacturing,
predictability has been often impossible or had large error bars. Manufacturing unpredictability made setting price a challenge.
What if predictability could improve by changing the polishing process? Would a predictable, deterministic process lead to profit?
Optimax Systems has experienced exactly that. Incorporating Magnetorheological Finishing (MRF) into its finishing process, Optimax
saw parts categorized financially as "high risk" become a routine product of higher quality, delivered on time and within budget.
Using actual production figures, this presentation will show how much incorporating MRF reduced costs, improved output and increased
quality all at the same time.
For spherical lenses, 3D in-process metrology is rather simple. Surface form may be tested in reflection using a test plate or a tower
interferometer, and the polisher can rapidly assess the progress of the polishing process. For aspheric lenses 3D surface metrology is
not easy. It often requires expensive, long lead time holograms or diffractive optical elements, a powerful interferometer and labor
intensive setup by a skilled test technician. All of these factors combine into repeatability errors and suspect results. Looking deeper,
there are specific geometries where it may be advantageous to look THROUGH the lens rather than AT the lens. Testing and correcting
the aspheric lens as it is used, in transmission, addresses some of the shortcomings of traditional 3D surface metrology.
This presentation will compare and contrast transmission testing versus surface testing for aspheric lenses. It will list specific cases where Optimax Systems chose transmission testing over surface metrology and the reasons for the choice. Additionally it will touch on the techniques and results of this transmission testing.
Magnetorheological Finishing (MRF) offers an effective way for correcting transmitted wavefront of lenses. Traditional feedback based methods of polishing and testing a lens until it is tolerance made direct correction of transmitted wavefront difficult if not impossible. Being a feedforward, deterministic process, MRF makes direct targeting and correction of transmitted wavefront possible. The lens must have low spherical aberration, and full aperture metrology is required. The metrology will show the sum of all errors, and all errors are corrected simultaneously by fixing deterministically the transmitted wavefront. Optimax Systems uses this MRF process to correct aspheric lenses in transmission to subwavelength errors.
The optical axis of a spherical lens is the axis passing through the two centers of curvature of the optical surfaces. It is such a simple thing to describe. However, detecting where the axis is and positioning it can be as complex as the definition is simple. Make one or both of the surfaces aspheric and it gets even harder.