Due to the improving manufacturing processes, freeform surfaces become a serious option within the optical design process. The work presented here was done within the German Regional Growth Core fo+ and involves all steps from optical design to manufacturing and testing. Two approaches for monolithic freeform systems solving the same optical task will be compared with respect to their manufacturability. For this not only surface form deviation but also surface positioning tolerances play an important role. Thus, this will give important hints to what type of optical system is better suited for serial production. The results of this analysis will be presented.
Other than for spheres the decenter of an aspheric surface cannot be compensated for by further tilting. During tolerancing process of an optical system it is usually assumed that the surface form deviation, the wedge and tilt of a surface have the same origin of coordinates. When manufacturing a lens, the surface form deviation is measured with different machines than the wedge and decenter. Measuring the surface form, the software applies piston, tilt and decenter that differs from the wedge and decenter of the lens. The results of testing this effect with different measurement set-ups and a possible solution will be presented.
Successful fabrication of aspheres requires all parts of the process chain including design, production, and measurements. Aspheres now are well-established and accepted as an equal optical element, when done properly. Research and industry have now started to focus efforts to develop the next element that propels the field forward in capability, namely the optical freeform surface. An essential factor enabling wide use of freeforms is communicating requirements. This paper discusses form description and tolerancing additions to ISO 10110 to accommodate freeform surfaces. Information stating how ISO 10110 and related standards documents such as ISO 14999-4 are being continually developed to meet the requirements for specifying freeform surfaces is also provided. This paper further provides an example monolithic freeform element using the recently updated relevant parts of ISO 10110. The first manufacturing of this component has been successful, and this paper shows the role the ISO standard has played in success. Definitions for toleranced parameters, such as surface registration (centration) and form deviation (irregularity, slope, Zernike, PV, and PVr), are also indicated. The monolithic example also shows how to use the defined data and definitions for metrology and data handling. Metrology results for the freeform surface are given.
Manufacturing optical components relies on good measurements and specifications. One of the most precise
measurements routinely required is the form accuracy. In practice, form deviation from the ideal surface is effectively
low frequency errors, where the form error most often accounts for no more than a few undulations across a surface.
These types of errors are measured in a variety of ways including interferometry and tactile methods like profilometry,
with the latter often being employed for aspheres and general surface shapes such as freeforms. This paper provides a
basis for a correct description of power and radius of curvature tolerances, including best practices and calculating the
power value with respect to the radius deviation (and vice versa) of the surface form. A consistent definition of the
sagitta is presented, along with different cases in manufacturing that are of interest to fabricators and designers. The
results make clear how the definitions and results should be documented, for all measurement setups. Relationships
between power and radius of curvature are shown that allow specifying the preferred metric based on final accuracy and
measurement method. Results shown include all necessary equations for conversion to give optical designers and
manufacturers a consistent and robust basis for decision-making. The paper also gives guidance on preferred methods for
different scenarios for surface types, accuracy required, and metrology methods employed.
For 10 years there has been the asphere as one of the new products to be accepted by the market. All parts of the chain design, production and measurement needed to learn how to treat the asphere and what it is helpful for. The aspheric optical element now is established and accepted as an equal optical element between other as a fast growing part of all the optical elements. Now we are focusing onto the next new element with a lot of potential, the optical freeform surface. Manufacturing results will be shown for fully tolerance optic including manufacturing, setup and optics configurations including measurement setup. The element itself is a monolith consisting of several optical surfaces that have to be aligned properly to each other. The freeform surface is measured for surface form tolerance (irregularity, slope, Zernike, PV).
In the last 10 years aspheres have readily gone from new products and specialized components to wide acceptance in the market. Successful fabrication of aspheres requires all parts of the process chain including design, production, and measurements. Aspheres now are well-established and accepted as an equal optical element, when done properly. This segment has been the fastest growing market of all optical elements. Research and industry have now started to focus efforts to develop the next new element that propels the field forward in capability, namely the optical freeform surface. An essential factor enabling wide use of freeforms is communicating requirements. This manuscript provides an example monolithic freeform element using the recently updated relevant parts of ISO 10110. The first manufacturing of this component has been successful, and this manuscript shows the role the ISO standard has played in success. Specifically the description of the complex freeform element, as well as definitions for toleranced parameters such as surface registration (centration) and form deviation (irregularity, slope, Zernike, pv, and pvr), are indicated. The provided example also shows how to use the defined datums and definitions for metrology and data handling.
For a lot of applications like spectrometer and high power laser roughness as an important parameter has been discussed over and over again. Especially for high power systems the surface quality is crucial for determining the damage threshold and therefore the field of application. Above that, it has often been difficult to compare roughness measurements because of different measurement methods and the usage of filters and surface fits. Measurement results differ significantly depending on filters and especially on the measured surface size. Insights will be given how values behave depending on the quality of surface and the size of measured area.
Many applications require a high quality of roughness in order to reduce scattering. Some of them in order to prevent from damage like high power laser applications. Others like spectrometers seek to increase the signal-to-noise ratio. Most of them have already been built with spherical surfaces. With higher demands on efficiency and more sophisticated versions aspherical surfaces need to be employed. Therefore, the high requirement in roughness known from spherical surfaces is also needed on aspherical surfaces. For one thing, the constant change of curvature of an aspherical surface accounts for the superior performance, for another thing, it prevents from using classical polishing technics, which guarantied this low roughness. New methods need to be qualified. In addition, also results of a new manufacturing process will be shown allowing low roughness on aspheric even with remarkable departure from the best fit sphere.
In recent years, freeform surfaces have become increasingly important. This paper introduces new form description and tolerancing additions to ISO 10110 to accommodate freeform surfaces. Information stating how ISO 10110 and related standards documents such as ISO 14999-4 are being continually developed to meet the requirements for specifying freeform surfaces is also provided. The manuscript includes examples illustrating the increased features of the standard.
Standards provide a conduit for understanding and communication in the global optics industry. Proper use and knowledge of standards is beneficial to global commerce and increases productivity. In this paper the design utility and efficiency afforded by standards is shown with examples that are congruent with current ANSI and ISO published documents.
Highly efficient beam splitters are important for a variety of high power laser applications. We prove different approaches like aperture and amplitude splitting for practicability for single- and multimode laser sources. Combining of micro- and macro-optical fabrication technologies allows novel monolithic free form splitting components with implemented segmented or stepless diffractive optical surfaces. The monolithic components are robust, compact and low weight and easy in handling. Here, we present two monolithic components: a segmented free form 1-to-17 beam splitter for fibre coupled lasers and a diffractive 1-to-11 beam splitter for single mode lasers with peak-to-peak pitch of 1.25mm and 0.8mm, respectively. The optical designs, the manufacturing of the prototypes as well as surface and performance measurements are reported. The prototypes from Fused Silica and Calcium Fluoride are designed for 532nm and 1064nm wavelength. Simulations show efficiencies larger than 98% and peak-to-peak non-uniformity below±3.2%. First laboratory results confirm efficiencies of < 95% and peak-to-peak non-uniformity of less than ±5%.
A scheme for using as-produced surface irregularity data from asphere production for numerical statistical tolerance
analysis is presented with this paper.
Interferometric precision measurements are being modeled in Zernike space and then used for monte carlo
tolerancing analysis. We show that low Zernike frequencies dominate the image distortion behavior of the irregularities
found in the specific asphere production process. Very good agreement between model representation
and measured data effect is found.
Silicon lenses are widely used for infrared applications. Especially for portable devices the size and weight of the optical
system are very important factors. The use of aspherical silicon lenses instead of spherical silicon lenses results in a
significant reduction of weight and size.
The manufacture of silicon lenses is more challenging than the manufacture of standard glass lenses. Typically
conventional methods like diamond turning, grinding and polishing are used. However, due to the high hardness of
silicon, diamond turning is very difficult and requires a lot of experience. To achieve surfaces of a high quality a
polishing step is mandatory within the manufacturing process. Nevertheless, the required surface form accuracy cannot
be achieved through the use of conventional polishing methods because of the unpredictable behavior of the polishing
tools, which leads to an unstable removal rate.
To overcome these disadvantages a method called Ion Beam Figuring can be used to manufacture silicon lenses with
high surface form accuracies. The general advantage of the Ion Beam Figuring technology is a contactless polishing
process without any aging effects of the tool. Due to this an excellent stability of the removal rate without any
mechanical surface damage is achieved. The related physical process - called sputtering - can be applied to any material
and is therefore also applicable to materials of high hardness like Silicon (SiC, WC).
The process is realized through the commercially available ion beam figuring system IonScan 3D. During the process,
the substrate is moved in front of a focused broad ion beam. The local milling rate is controlled via a modulated velocity
profile, which is calculated specifically for each surface topology in order to mill the material at the associated positions
to the target geometry.
The authors will present aspherical silicon lenses with very high surface form accuracies compared to conventionally
The success of many advanced technologies increasingly depends on the precision of the optical
lenses used. Therefore the demand for high precision optical elements in more common devices and
instruments is increasing as well. Concurrently the need to make devices smaller and lighter weight
is also driving the demand for precision optical elements. Therefore, the use of aspherical glass
lenses is growing tremendously and has become the standard for many applications.
So far most methods for manufacturing aspherical glass surfaces use grinding and polishing. Very
sophisticated methods such as Ion Beam Figuring have not been used for common precision optics.
The reasons for this might be perceptions of high costs, doubt about the ablation rate and limited
knowledge about the technique within the optical industry.
Now Asphericon has set up its first ion beam correction system for precision aspherical optics (asphericon
ION-Finish). This presentation will show how the ion beam technology has matured and
become affordable enough for common precision applications. In some examples we will show how
ion beam systems are used to correct aspheres to precisions of better than lambda/60 rms (10nm).
Together with a flexible measurement technique, the manufacturing of aspherical glass lenses becomes
very fast and cost-efficient. Furthermore, advantages and disadvantages will be discussed. In
connection with that the required quality of the pre-polishing will be addressed too. Finally it will be
shown how fast the correction process can be and how flexibly the size of the tool can be changed.
Recently and upcoming optical applications depend more and more on the precision of the optical elements used. The
last is especially driven by shorter wavelength, higher flux densities and imaging close to the diffraction limit. Therefore
a dramatically increasing demand on high precision and high quality optical components in leading edge equipment as
well as common devices and instruments is observed.
So far a few methods have been introduced to provide an adequate manufacturing performance using mechanical grinding
and polishing techniques. Up to now the very sophisticated ion beam figuring (IBF) has not been used for common
optics. The reasons for this might be the perception of higher costs and less knowledge about the technique in the industry.
Now an affordable ion beam figuring technique has been developed to address precision aspherical optics applications.
This paper introduces ion beam figuring technology based on equipment which is widely used in semiconductor mass
production for ultra precise film thickness trimming.
Ion beam figuring works by raster-scanning a focused broad ion beam across an optical surface with variable velocity
and dwell time in order to precisely and locally trim away surface contour errors.
As a new and cost effective approach the ion beam figuring system used in this presentation applies a 3 axis movement
system only (compared to expensive 5-axis movements in other applications). X-and y-axes are used for the areal scan,
and the z-axis is used for focus adjustment due to the surface contour of the optical element. The system was intentionally
designed without the 2 additional tilt axes for incident angle adjustment and cleverly reduces the complexity and size
of the system.
It is shown that curved spherical or aspherical surfaces can be corrected down to λ/50 or better by using the state of the
art 3-axes trimming system. Even with high spatial frequency parts final processing qualities better than λ/10 are
Within the past ten years a variety of CNC manufacturers for aspherical surfaces have been established. The field of
applications they are working for are very different. The way CNC manufacturers measure surfaces as well as the way
they characterize the surface form deviation differs even more.
Furthermore, there are a lot of customers being interested in using aspherical surfaces in their applications. In fact,
aspherical lenses are not established as standard optical elements yet which is due to the fact that many users are not
familiar with the implications of the use of aspherical surfaces with respect to the tolerancing of the optical system. Only
few know how to specify an asphere, moreover, they differ about how to do that.
The paper will give an insight in what is possible in aspherical manufacturing in terms of accuracy, efficiency, number of
pieces per design and surface forms. An important issue is the development of deviation of form and slope in connection
to prepolishing and correction polishing. Based on experiences of the manufacture of more than 500 different aspherical designs with diameters ranging from 3 - 200 mm, the paper is going to give an insight into production practices. Finally, there will be a general overview on what could be done and what needs to be done in order to unify the different ways of tolerancing of aspherical surfaces.
There are different ways to design and build beam shapers; generally, it is based on diffractive or refractive optical elements. Both solutions have different kinds of advantages and disadvantages. Diffractive designs are very sensitive to parameters like wavelength, nevertheless, they are in general easier to manufacture. The refractive design offers more flexibility in terms of wavelength. In general, there are two possibilities for manufacturing such refractive beam shapers, either on basis of spheres or on basis of aspheres. Concerning the production of aspheres there have always been strong limitations either in terms of the surface form - only a small deviation from best fit sphere/plano surface is possible - and/or in terms of surface accuracy. As fully discussed in literature it is necessary to increase form accuracy in case of using aspherical forms with small aspherical departures. In other words, the quality of the beam shaper does not necessarily improve by using aspherical forms with small aspherical departures. On the contrary, one has to increase the form accuracy of the beam shaper element in order to keep beam quality standards.
Based on ten years of experience a technology has been developed that allows us manufacturing of optical surfaces in almost all kinds of forms, shapes and sizes. By now it is possible to produce aspherical forms both concave and convex, with strong departures from the best fit sphere as well as with inflection points from 4 to 200 mm in diameter.
By now it is possible to manufacture aspherical surfaces with big departures while securing high accuracies. It is the purpose of this paper to give an understanding of how the refractive approach can be applied for the fabrication of aspherical beam shapers.