This PDF file contains the front matter associated with SPIE Proceedings Volume 11889, including the Title Page, Copyright information, and Table of Contents.

Blazed and slanted gratings present particularly interesting optical properties in that they can diffract light predominantly into one side of the diffraction plane (m≤0 or m≥0). This is useful in a variety of applications, especially for augmented reality (AR) display combiners, where slanted gratings are commonly used to reduce ghosts and improve efficiency. However, angled gratings are difficult to manufacture in volume. Nanoimprint lithography (NIL) has been explored as a route to mass manufacture AR waveguides with slanted structures. Nonetheless, NIL presents several challenges associated with the process of molding and releasing angled features, which result in a constrained process window and the possibility to imprint grating with low aspect ratio and slant angle. An additional challenge of NIL is the choice of imprinted material, which should have the right mechanical and optical properties and the highest desired refractive index. A technology solution to manufacture diffractive optics in volume with large slant angles (>45°) and a high refractive index is necessary in order to have products such as AR glasses reach the consumer market. In this paper we report a series of breakthroughs that our Optics and Display Research team at Facebook Reality Labs (FRL) has achieved, which allow for replication of gratings with a slant angle up to 60° and an aspect ratio of 10:1 in a material with refractive index of 1.90 (RI). A study of the replication process, optimization of materials and processes will be presented. Pattern fidelity, RI uniformity and repeatability of the grating optical response are tracked as function of imprint number. To the best of our knowledge, these results are the first public demonstration of a scalable process to manufacture AR combiners with highly slanted structures in a material with a refractive index of 1.90.

Freeform optics and metasurfaces are two emerging optical technologies that show promise for addressing the needs of modern consumer devices like augmented and virtual reality (AR/VR) displays and mobile cameras. Recent advances in fabrication and testing have been critical to the success of freeform optics. In parallel, various methods for metasurface fabrication, including electron-beam lithography (EBL), have been researched and well established in the last decade but have been limited to fabrication on flat substrates. Metaform is a new optical component that consists of a metasurface conformed to a freeform substrate. We will explore the advances in nodal aberration theory, freeform design methodology, nanofabrication, and metrology necessary to make metaform optics a reality. To validate the developed processes and highlight the advantages of metaforms, we will examine a compact metaform imager inspired by the needs of AR displays. By leveraging the benefits of both metasurfaces and freeform optics, metaforms can thus be used to navigate critical design tradeoffs between optical performance, system volume, and form factor.

The battlefield requires weapon guidance, threat detection, recognition and optical targeting and imaging systems that operate in hard-to-distinguish threat environments, in all conditions, day or night. Since ultraviolet, visible, and infrared optical systems remain the ultimate solution for many systems requirements, high precision optics are pervasive in the military. Systems in development, such as Directed Energy (DE) Weapons and hypersonic missiles impose new optics manufacturing demands. Affordable U.S. manufactured advanced optics are needed to meet these new requirements, and the development of advanced, cutting edge optics design and manufacturing technology is needed to provide superior systems that will enhance the combat capabilities of the warfighter. The American Center for Optics Manufacturing (AmeriCOM) was established by optics manufacturers essential to the defense industrial base in partnership with the Defense Department. The AmeriCOM mission is a three-pronged national effort: • Develop workforce training programs specifically targeted to support the increasing complexity and growing manufacturing requirements of the nation’s optics and photonics industry. • Develop advanced optics manufacturing technologies, testing equipment, and the specialized materials required to support scalable manufacturing in order to strengthen the defense precision optics industrial base. • Successfully transition the mission-critical optics and photonics technologies developed, to production manufacturing operations — the most important measure of success.

A well-established solution for measurement of aspheric surfaces relies on translating the test part along the optical axis of a precision laser Fizeau interferometer while collecting interference fringes from areas of low slope relative to a spherical reference surface. The data are assembled into a final surface profile using the instrument geometry and scan history. This principle has been the foundation of a commercial instrument for nearly two decades. Here we report on several key advances for this instrument: 1. Optical configuration management for improved automated alignment for flats, spheres, aspheres, and torics. 2. Upfront and re-callable distortion and magnification calibrations for each transmission sphere/zoom combination. 3. Job-centric user interface with improved ease-of-use, including importing of asphere definitions directly from standard lens design software files. We give an overview of the new system, show measurement examples, and discuss how the improvements mentioned above affect the metrology and the user experience.

The demand for large coated flat and curved optics is growing for applications in automotive (windshields, LIDAR windows) or space (spectrally resolved imaging, FSO Lasercom). Their large size leading to high Transmitted wavefront error (TWE) and their sensitivity to wavelength require new metrology instruments. We propose measuring the TWE of such optics with a quadriwave lateral shearing interferometer (QLSI) based wave front sensor, in a double-pass configuration. We present the instrument ability to measure optics in their full transmission spectral band. We also discuss the best strategy to characterize large TWE optics in dynamic ranges exceeding tens of microns.

The NMF600 S non-contact measurement machine for freeform optics by Dutch United Instruments (DUI) was used to measure a large concave surface with a polygon outside contour with typical diagonal of 250 mm. The surface is a higher order freeform off-axis surface, which was measured centered on the table. The total non-rotationally symmetric freeform departure during this measurement was 3.5 mm PV. Moreover, the surface has an anti-reflective coating. Depending on the pointspacing and measurement aperture, the measurements take between 7 and 23 minutes. They show a repeatability of well below 5 nm rms on a total form error after 6DOF fitting of 1.53 um rms. The pointspacing of 0.1 mm clearly shows the mid-spatial errors and raster polishing residuals.

This presentation will examine the case study of a 3x zoom lens that was optimized to work in the MWIR and the LWIR wavelength region and the challenges that come with working in such a wide waveband.

Despite the strong demand for high-precision Modulation Transfer Function (MTF) measurements for industrial and scientific applications, currently there is a lack of MTF calibration services traceable to national standards. Trioptics GmbH, in cooperation with the National Metrology Institute in Germany (PTB), is establishing an accredited laboratory for traceable MTF measurements of optical lenses aiming at an expanded uncertainty of 𝑈_MTF = 0.01 for coverage factor 𝑘 = 2. To reach this goal, influences of misalignment and mechanical stage positioning errors need to be considered. We present an experimental approach to investigate the influence of the detector’s positioning accuracy on the MTF measurement uncertainty depending on the imaging properties of individual lenses under test. For samples with different optical properties (effective focal length and aperture), the MTF is measured at various positions in a 2D grid spanned over image field and focusing direction. At each position, the derivatives of MTF in field and focusing direction are calculated. Knowing the overall mechanical uncertainty of the detector, this data can be used to determine local uncertainties of the measured MTF. In contrast to the classical way of defining measurement uncertainty only by benchmarking the accuracy of the measurement equipment, we now include MTF-sensitivity of the sample under test. Hereby, a more precise and application-oriented analysis of the MTF accuracy for a measurement system can be achieved.

We describe high-precision measurements of the transmitted wavefront error and refractive index homogeneity of glass plates using a low-coherence interferometer in a downward-looking configuration. With the low-coherence illumination there are no spurious interference fringes even for a plane-parallel sample. Unbiased results are obtained by using a combination of four different measurement steps. The measurement performance and repeatability are shown for the lowcoherence interferometer OptoFlat with a special fixture incorporating sample holder and return mirror. Its ease of handling and supporting software-based user guidance through the measurement steps greatly facilitate wavefront and homogeneity measurements in the optics shop.

We present a straightforward approach to making sensitive fluorescence measurements using a chopped laser and phase-lock detection scheme. By using high-quality optical filters in the excitation and detection paths, the trade-off between spectral information and ultimate sensitivity is controlled by the choice of filter edge locations and bandwidths. Using this approach, we demonstrate a sensitivity of ~1 pW optical power of detected fluorescence over a bandwidth of ~125 nm centered at 505 nm using a 405 nm diode laser as an excitation source. We present the details of the measurement technique and discuss its value in selection of optical materials for fluorescence-based analytical systems.

The need to detect defects in optical glass during IQC, post cleaning, post coating and final QC has become of paramount importance. Optical glass is very high value-added and must be defect-free. Throughout the industry, legions of inspectors perform manual inspection. Manual inspection adds significant cost, reduces yield and becomes the production bottleneck. In-line 100% automatic defect detection can augment or replace manual inspection and delivers a host of benefits including increased throughput, improved yield, scrap reduction, reduced labor cost and maximum customer satisfaction. Solid-State Laser Reflection (SSLR) technology has been successfully applied to this challenge; defect detection to 1µm has been achieved.

Air turbulence is a major environmental factor that degrades the precision of optical part interferometric metrology. For large optics with a long cavity, turbulence effects become critical. Reducing those effects by protecting the cavity with mechanical means is necessary, though not sufficient. Averaging wavefronts is a simple, classic, and efficient remedy. However averaging leaves unanswered the following issues: How many wavefronts should be averaged? What is the resulting uncertainty on the parameters of interest (RMS, PTV...)? What is the risk for a parameter to be over tolerance? For addressing those issues, the Xonox X-fringe® interferometry software is fitted with an advanced "Average Statistics" function. Reading a given number of phase data maps, the function computes the average phase map and estimates the significant statistical characteristics of the turbulence, namely its space and time auto-correlation function (ACF), as well as the ACF of the sample average. The latter provides a covariance matrix, applied to Monte-Carlo random trial simulations. On each of those random trials, a parameter of interest is computed. For a high number of trials, the frequency histogram of this parameter tends towards its probability density. Finally, this density yields confidence intervals of the parameter (i.e., uncertainty with a confidence level), and above all, the risk that the parameter could be over tolerance. The user can create templates defining, for a given set of Zernike, the parameter of interest (PTV, RMS, Strehl), or that of the residual wavefront. The software evaluates the signal-to-noise ratio and the measurement reliability.

Smartphones, AR/VR and ADAS optics are challenging to qualify due to their short focal length, high chief ray angle and numerical aperture. Wave front sensing measures the optical aberration and the associated Zernike coefficients, which are used to understand manufacturing errors. In this paper, we propose to use a quadriwave lateral shearing wave front sensor, which is able to characterize such samples without any intermediate optics. This configuration makes the qualification process comprehensive and fast. We will present examples of commercial and calibrated optics with CRA larger than 35°.

The use of high-power continuous wave (CW) lasers in the emerging directed energy (DE) market has put greater emphasis on the quality of optical coatings. These coatings (both high reflectance and anti-reflection) require high damage thresholds for use at irradiances up to and greater than 1 MW/cm². The challenge in the coating process is to minimize the number of coating defects that can contribute to absorption and eventual coating failure. The industry lacks standardized testing to detect possible defects at the required irradiances for DE optics. To aid in the development of coating designs and production techniques for DE related optics, we have constructed a high-irradiance Ytterbium fiber laser-based scanning metrology system to detect absorbing defects in DE optical coatings. Defects are detected by their localized thermal heating creating a hot-spot. The goal of this work is to continually improve the coating, increase the laser damage threshold, and contribute to a standard for the testing and validation of directed energy optical coatings.

Many free space optical systems can be fiberized, enabling advantages in function, size and weight. Implementations include fiber-based lasers, interferometers, polarimeters, spectrometers, endoscopic probes, and pigtailed detectors. Interference filters can be integrated into a fiberized system by depositing the filters on fiber tips. Omega has deposited a variety of interference stacks on fiber tips. One can think of fiber tips as miniaturized substrates – the ultimate small part configuration. This article reviews optical fibers and fiber tips, coating fiber tips, testing the coated tips, as well as the performance and applications of the coated tips.

With more than 40 years of experience in ALD and thin film deposition technology, Beneq has developed a new-generation ALD technology that revolutionizes high volume manufacturing of plasma-enhanced thin films: the spatial ALD. In spatial ALD, the substrate is rotated across successive process zones to achieve ultra-fast and high-precision thin film deposition. In this work, we present the latest results obtained with the novel Beneq C2R spatial ALD system, including the fabrication of SiO2, Ta2O5 and Al2O3 with deposition rates reaching > 1 µm/h on 200 mm wafers. Ultimately, our technology overcomes the challenges of traditional ALD and paves the way for the large volume production of optical components on the most challenging surfaces found in the industry.

ZERODUR® glass ceramic is a material well established in stability-critical industrial markets. While ZERODUR®’s chemical formulation has been unchanged for over 50 years, its thermal attributes can be tailored for specific temperature ranges. Especially, its near-zero thermal expansion, its homogeneous properties and its extensive characterization are favorable for applications requiring heightened dimensional stability performance. SCHOTT invested extensively into both comprehensive material characteristic studies, and into a newly dedicated highly capable machining and metrology facility. We will describe the capabilities of SCHOTT’s newly-build ZERODUR® competence center focusing on CNC machining and precise characterization of monolithic lightweight mirrors through 4-meter sizes. Beside the production of various light-weighted designs, any optical form on a mirror’s specular surface can be generated. This is done by precision grinding while, at the same time, minimizing the sub-surface damage. Subsequently, the optical finishers can expect a better starting point and the utility to the telescope designer becomes evident. Latest results on optimizing the front figure tolerance for different mirror substrate diameters are presented. We will emphasize the capabilities of the precisely controlled 5-m coordinate measurement equipment. These refined manufacturing methods support the design of better, more affordable, higher performance future optical assemblies and enable design-to-cost approaches for cost-critical projects.

In 1884 Otto Schott, Ernst Abbe and Carl and Roderich Zeiss founded the SCHOTT & Associates Glass Technology laboratory in Jena, Germany. Otto Schott’s target was to develop new glasses on optical positions defined by Ernst Abbe and high reproducible quality that would tremendously improve the image quality of Carl Zeiss microscopes and optical instruments. Prior to 1880, optical components were made from simple crown and flint glasses. The crown glasses were soda-lime silicates with low refractive indices and moderate Abbe numbers. The flint glasses were lead silicates with relatively low Abbe Numbers. By 1884 already two dozen flint and crown glasses were available for optical system designs. Still today photonics industry relies heavily on optical glasses to realize tightest optical design requirements of today photonics applications. The difference between today and the past is that the designer can choose from a variety of more than 120 optical glasses with differences in optical position, transmittance and very specific dispersion requirements.

The Research and Development group at Rochester Precision Optics LLC (RPO) is conducting a years-long survey of the optical properties of glasses in the Ge-As-Se family. The goal of this survey is to find compositions in this ternary space that are more appropriately suited to demanding DoD and advanced R&D needs. This talk will focus only on the As-Se binary tie line of the full family but will illustrate glass compositions and measurements never before achieved even in this simple system. In particular, the refractive index of each composition is measured using a minimum deviation system from 850 nm to 14 μm. By parameterizing the fits of these dispersion curves, we achieve a deterministic model for designing custom compositions over this tie line. We also discuss the completely novel As80Se20 glass, who’s properties have not been previously reported in literature.

Freeform optics are gaining popularity and the industry is adapting to meet the challenges. Datum surfaces are generally required for proper tolerancing of freeform surfaces due to the possible lack of symmetry. Complex rotationally symmetric surfaces such as high departure aspheres are becoming more commonplace. Metrology systems must now be able to handle large spherical departures, curvature inflections, vertical or steep datum features, and varying surface texture. The UltraSurf was created to address many of these challenges. It is a 5-axis non-contact metrology system. It employs various optical point sensors that can handle rough surface textures such as ground glass as well as highly reflective optical and surfaces. The combination of five motion axes allow for the scanning of standard aspheric optical shapes as well as freeform optics and associated datum structures. UltraSurf can scan freeform windows to gather form error on both primary surfaces as well as thickness and wedge when paired with a low-coherence interferometry probe. UltraSurf was designed from the ground up to have flexible software that can enable a user to input these complex freeform surfaces and address the upcoming challenges. Examples of freeform and steep complex surface metrology will be presented along with how the UltraSurf can streamline the process.

Freeform optics are becoming more widely used in the optics industry to expand the capabilities of systems while reducing the package size and number of elements required in the system. The complexity of freeform designs introduces new challenges to the manufacturing flow compared to rotationally symmetric optics. New manufacturing techniques have been developed to solve these new challenges. In addition, as tolerances tighten on freeform surfaces, the methods used to address these challenges can be the difference between the part being inside or outside of tolerance. Successful manufacturing starts when designing the freeform part and choosing the proper datum structure. When moving to processing, choosing the right fixture is a key component of efficient manufacturing. Part measurements are critical to both perform error map driven figure corrections and to determine if the part is within tolerance. An easily oriented error map is a simple way to improve the surface while avoiding inducing new mid-spatial signatures into the part surface. This paper will present common challenges of manufacturing freeform optics and the best practices in designing, manufacturing, and measuring that will ensure the greatest chance of making a freeform optic that meets its specifications.

An additive manufacturing platform, including nanocomposite materials and 3D printing, is presented that allows 3D-freeform gradient index (GRIN) functions to be fabricated within planar or surfaced lens elements. The degrees of design freedom allow for realization of complex optical functions that reduce optical system size and weight.

Freeform optics are becoming more prevalent in the optics industry as designers recognize their ability to expand system capability while also reducing the number of optics required and its package size. While there are increased system capability benefits, freeform optics are more challenging to manufacture. The same machine can often be used for manufacturing rotationally symmetric and freeform optics, but new software is required for the complex freeform geometries. The computer aided manufacturing (CAM) software used by the metal working industry has similar flexibility, but often lacks the critical features needed to achieve the required tolerances for optics, including metrology driven figure corrections. To address the challenges and requirements for manufacturing freeform optics, OptiPro has developed PROSurf, a CAM package developed specifically for manufacturing freeform optics. With flexibility in mind, PROSurf was designed to support the custom tooling used in optics manufacturing, a wide range of input surface definition types, and many of the industry standard file types for error maps. The software can generate tool paths for both grinding and polishing and adjust those paths based on surface measurements to improve the form error of the surface, converging towards the desired surface tolerance. This paper will highlight PROSurf’s capabilities for manufacturing freeform optics.

Traditionally a rotary table is used for optical centering because the table creates an axis as a reference. We showed, previously, that a Bessel beam also creates an axis useful for centering. The Bessel beam axis and a center of curvature of a surface makes it possible to center an optic simultaneously in tilt and decenter. Now we show that simultaneously sampling two arbitrary points along the Bessel beam also permits full adjustment of tilt and decenter of a powered optic. This makes centering possible without either a rotary table or a precision linear stage.

This work builds on prior work that developed a methodology for evaluating thermal stress in cemented doublets. The prior studies were limited by a paucity of actual test data, particularly from thermally tested cemented doublets. This follow-on study uses the existing methodology to estimate stresses in cemented doublets that have been tested for a temperature range from –40°C to 85°C and establishes safe stress levels using actual data. We also discuss limitations and concerns that we need to address to improve our understanding of cemented doublet failure.

The 5D-alignment of multi-element assemblies within a single barrel by adhesive bonding represents a powerful alternative to the so-called “poker-chip assembly” where the barrel is populated with sub-cells. This way, the single element’s lateral and axial position can be precisely controlled. The described process allows for production of mounted lenses with an outstanding alignment precision below 1 µm in all dimensions in less than 3 minutes per lens element. The fully automated process greatly simplifies the transfer of existing, conventional optomechanical designs to higher performance and allows for smaller and lighter barrel designs compared to the established poker chip assembly.

Alignment turning is an efficient process to streamline the production of mounted objective lenses. By machining the mount with respect to the optical axis, the objective lens can be assembled to high precision without further adjustment. High precision objective lenses can be built by drop-in assembly. But even four decades since inception, there are challenging applications. Aspheric lenses, large lenses and single micron tolerances require suitable pre- and post-processes to use this technology efficiently in mid- and large-scale production. This paper presents different manufacturing processes tailored for microscope and semiconductor markets. Challenges in the opto-mechanical design are analyzed and modern solutions are presented.

With labor shortages and difficulty in getting experienced technicians, automation provides an opportunity to increase production and efficiency with a dwindling labor pool. Repetitive tasks such as machine tending, and cleaning parts are easily automated with a robot to free up technicians to perform other more demanding tasks. These repetitive tasks can be boring, fatiguing, menial, and can lead to worker burnout. Automating these tasks can improve working conditions and worker morale. Automation increases production rate and productivity. By communicating directly with the machines, a robot can reduce reaction time between processes, reducing downtime. Automation provides consistency and opportunity to run lights out, 3 shifts or over weekends, without breaks, increasing machine up time and throughput. It also reduces labor cost by reducing the number of employees required to hit production numbers. This labor savings results in a quicker return on investment. To help customers automate, OptiPro offers an “off the shelf” Pro-loader solution, as well as customized solutions to meet any required demands. The Pro-loader is a rollup automation cart that connects to OptiPro machines for easy setup. OptiPro has integrated the robot into the machine software to allow it to mimic an operator’s keystrokes and run programs the same way an operator would. This also gives flexibility in running many part geometries that the machine can produce. OptiPro has also developed cells which combine multiple machines such as a generator, polisher, cleaning stations, and even metrology to produce completed part surfaces.

Quality Control requires the measurement of all dimensions and specifications for which a supplier is contractually bound to deliver but does not add intrinsic value to the parts that are to be inspected. Therefore, streamlining QC activities provides important savings by reducing overhead costs. QC activities aid in process development, and when combined with Statistical Process Control (SPC) methods, can alert users to trends that would result in products failing specifications before those failures occur. In addition, the ability to collect and analyze a comprehensive data set consisting of the as manufactured, measured values for the parameters of interest can be utilized by system integrators. To serve the needs of the optical manufacturing community and system integrators alike, XONOX has developed an integrated system that allows lens manufacturers and lens consumers to efficiently check all aspects of traditional lens elements. Through the use of innovative job planning and reporting software, devices designed for efficient series inspection, and a process that ensures traceability and consistency, XONOX IQC provides a turn-key solution that meets demanding production, inspection and regulatory requirements.

Spatially-varying features with uniform depths in large areas are challenging to achieve with etching based lithography. Here we propose an additive lithographic fabrication process to realize simultaneous presence of micrometer and millimeter features with low surface roughness. The etching step is replaced by sputter deposition and bi-layer lift-off to form the microstructures. Instead of removing materials, our method grows materials onto the substrate. We demonstrate its effectiveness with a reflective Tilt-Gaussian-Vortex mask with aluminum deposited on a fused silica substrate. The center has a diameter of 130 microns with minimum spacing of 2 microns, and the background pattern is 3 mm by 3 mm, with the largest flat region spanning 1.5 mm. A preliminary 4-level prototype has been tested in the Gemini Planet Imaging calibration unit upgrading project, and an improved 16-level sample has been measured. The results show uniform depth and surface roughness control in the whole area.

An important challenge in infrared imaging today consists in addressing the SWaP problem (Size, Weight and Power), for example by simplifying as much as possible the optical system before the sensor. The work presented in this paper takes advantage of recent techniques in femtosecond laser direct writing to imprint optical systems. This work aims at merging a lens array with a filter array by writing gradient index lenses with a femtosecond laser inside a dedicated glass substrate. A classical gradient index lens requires a huge refractive index variation, which cannot be reached today with femtosecond laser processing (Δ𝑛_𝑚𝑎𝑥 ~ 0,05). So, we decided to turn towards writing a gradient index Fresnel lens. A first-order Fresnel lens was designed with a Δ𝑛_𝑚𝑎𝑥 < 5.10⁻² discretised into 8 index levels to guarantee a diffraction efficiency of 85% on the overall spectral bandwidth of the filters. We studied a chalcogenide glass because of his good properties in mid-IR optics. We compared the different laser responses of the material: threshold of permanent changes, quantitative phase and index variation. Finally, we showed that reaching a phase variation of π radians with femtosecond laser writing is possible even for a huge scanning speed (0,01 mm/s up to 25 mm/s). By overlapping the written lines, we were able to implement a maximum phase variation of 8 radians (with only one written layer), demonstrating the possibility to write quickly a GRIN Fresnel lens with a diameter of some millimeters.

This effort evaluates laser processing for one of the more simplistic laser functionalities, utilizing the absorption of the laser for surface heating, and relying on the surface tension of the material as a function of temperature to leave a polished surface. The laser polishing is investigated across different materials: oxide optical glass, non-oxide chalcogenide optical glass, and optical polymer. A continuous wave visible wavelength laser is used for the chalcogenide glass, while a pulsed 10.6µm laser is used for the oxide glass and the optical polymer. The laser polishing results are compared to a hot forced-air local surface heating technique and traditional polishing methods.

We investigate the use of an innovative fixed abrasive diamond fine grinding pad, Squadro-G, for the fine grinding of various glass types. Through continuous development of the diamond abrasive matrix, grain size and concentration, we have found significant pathways to improve the process performance of the fine grinding operation. For the various glass types used in the investigation the process performance was monitored based on materials removal rates, surface quality, run-to-run consistency and Squadro-G pad lifetime. Data shows the use of Squadro-G fixed abrasive grinding pads can enable efficient processing of various types of glass and tool configurations. Ultimate flexibility is gained via the availability of different grit sizes, dedicated pad configurations with respect to given glass types, and east mounting and dismounting.

This paper reports on the possibility of single point diamond turning (SPDT) of an axisymmetric convex aspherical fused silica lens. Due to the relatively abrupt tool wear during SPDT of fused silica, generally the process is not considered to be commercially acceptable. Surfaces created with SPDT are very rough and of no optical functionality. That said the SPDT can be a very convenient method in production of fused silica asphere and freeform optics should the process be amenable to producing relatively smooth surfaces. In this article it is shown that a lens fabricated via conventional fine grinding processes can be SPDT'ed to roughness values below 100 nm RMS and surface form better than 800 nm PV.

This paper investigates the impact of diamond crystal type on single point diamond turning of single crystal silicon oriented at the <111< direction. The sample has a diameter of 85 mm with a concave base radius of curvature of 291 mm. The tools are made of single crystal diamond formed naturally (hereby referred to as natural diamond) and under lab controlled highpressure high-temperature conditions (hereby referred to as synthetic diamond). The tools have similar geometries of 0.5 mm nose radius, -25° rake angle. The natural diamond is oriented such that the top face of the diamond stone is a {100} plane and the cutting occur in the <110> direction relative to the stone. The synthetic diamond stone is oriented in the {100} plane with the cutting happening in the <100> direction. It is seen that, on average, the synthetic tool can cut approximately 38.5% longer distances without inducing significant brittle fracture on the surface.

We report on the latest developments in fast tool servo technology for cutting freeform surfaces and lenslet arrays. Fast tool servo cutting performance is examined and contrasted to micro-milling and XZC turning for low spatial frequency surfaces and high spatial frequency surfaces (e.g. lens arrays). The influences of servo bandwidth, positioning resolution, and vibration level are examined in terms of their effect on form accuracy, mid-spatial frequency errors, surface finish and cutting time.

There is an ever-increasing demand for small optical systems, applications such as cell phone camera lenses, Infrared night vision sensors, and medical devices continue to grow. For these applications, a new compact ultra-precision diamond turning machine offering the highest precision for making both lenses and mold inserts has been developed. A small footprint ideally suited for limited lab space combined with the ability to add a Fast Tool system, optical metrology and automated loading and unloading makes for a versatile yet highly capable machine for precise freeform manufacturing. Unique hardware and software designs yield the highest accuracy on the market.

Hard ceramic and glass material with tough mechanical properties and complex geometries can present a significant challenge in manufacturing. Slower processing times, excessive tool wear, and increased setup times are common with these materials and geometries. To overcome these challenges OptiPro has developed OptiSonic, an ultrasonic assisted machining technology. OptiSonic utilizes a custom tool holder that is designed to produce oscillations, in microns of amplitude, when loaded into a rotating spindle. A software package, IntelliSonic is used for setting up and controlling the ultrasonic motion during operation. Initially, the software is used to characterize each tool to find its optimal resonant peak to operate. Then, while grinding, IntelliSonic continuously adjusts the frequency to maintain optimal grinding efficiency during the operation. OptiSonic has shown, through testing, a reduction of force while machining. The combination of OptiSonic, kinematics, and RTCP (rotating tool center point) allows for full 5-axis simultaneous motion for grinding which allows operators to keep a more consistent wear band on the tool and aid in setup, operation, and part quality. After machine kinematic alignment is completed, the RTCP in the CNC control can make compensations without having to generate new tool paths. Also, the same tool paths can be shared between machines that have kinematics enabled. This can lead to a significant time reduction in setting up and adjusting tool paths.

As freeform optics become more prevalent, it is important for manufacturers to have flexibility when fabricating such optics. Traditionally, QED's Magnetorheological Finishing (MRF™) machines have used a raster toolpath to polish optics that lack rotational symmetry in either their aperture shape or surface form. However, a spiral toolpath may be desirable for a variety of reasons: to achieve a tighter edge exclusion, to correct rotationally-symmetric features, or to polish high- NA optics that may exceed the half-angle limits of raster polishing. In this paper we present a new spiral toolpath polishing capability for surfaces that have circular apertures but have a surface form that lacks rotational symmetry. This enables rotationally polishing freeform optics, such as off-axis parabolas (OAPs) and toroids, in addition to tilted plano surfaces or wedged (non-centered) spheres. We will explain the capabilities of this new polishing mode and present initial polishing results.

To achieve optimal polishing convergence results, the removal function of the tool should be accurately characterized. This removal function is termed a “spot” in Magnetorheological Finishing (MRF), and for best results the spot should be characterized with nanometer-level accuracy. Such precise results have typically been obtained with an interferometer, which can provide the necessary accuracy as well as good lateral spatial resolution. However, interferometers are often in high demand during optical fabrication, have limited slope capture range (complicating measurement of especially high removal rates or small spots), and aren’t always ideal for the “shop floor” environment. QED has developed a measurement method for spots to address these shortcomings. It is more compact, potentially less expensive, less environmentally sensitive, and has more slope capture range compared to a typical interferometer. Used in conjunction with QED’s spot morphing algorithm, only plano optical substrates are needed to measure material specific removal function characteristics, which can then be applied to a wide range of part geometries of the same material type. Spots characterized with the new method are shown to provide excellent polishing convergence and are highly consistent with interferometric data. In conclusion, the new method is ideal for conveniently and cost-effectively measuring spots on the shop floor.

Freeform optics offer great flexibility in design parameters, but the subaperture techniques required for manufacture often result in mid-spatial frequency (MSF) errors that can impact final performance. These errors must be removed, but the options to do so, often requiring hand-smoothing by a skilled artisan, are costly and time-consuming. Optimax has developed the HERMES (High End Robotic MSF Elimination System) a robotic platform that uses a machine learning algorithm to smooth parts. Preliminary research indicated promising results, but the process had not yet been compared to the “gold standard” of human smoothing. Results indicate that HERMES fared well compared to smoothing results of a highly skilled artisan. Future directions for work are discussed.

Magnetorheological Finishing (MRF) is a well-established process for precision optical finishing. The primary benefits of MRF are its determinism, ability to finish complex surface shapes and good removal rate. Higher removal rates can be desirable to reduce cycle times or increase the amount of material removal. Cases include but are not limited to aspherization, harder materials, correcting higher error amplitudes, polishing very large aperture optics, and subsurface damage removal. Novel developments have been made with the fluid nozzle, magnetic field, and wheel geometry to increase the removal rate. Custom nozzle shapes are used to create a very wide MRF ribbon resulting in a much wider removal function (spot). The increase in ribbon width requires the use of higher volumetric flow rates. The magnetic field must be shaped to ensure that the field passes through this wider ribbon. Radius of curvature of the MRF wheel parallel to the axis of rotation is increased to achieve a wider spot. Results show an order of magnitude increase in volumetric removal rate due to a much wider and longer spot. Spot width increases of 3x, and spot length increases of 2x, as compared to a traditional MRF spot, were achieved. Polishing shape corrections were conducted with these spots which resulted in convergence rates over 80%. This development allows MRF to be used in applications previously limited by cycle time

We present unique optomechanical designs allowing precise fabrication and alignment of diamond-turned aluminum image slicers through preformed monolithic blocks and, most importantly, sub-group assemblies. This last approach reduces manufacturing time and risks while resulting in more alignment flexibility when compared to the traditional monolithic slicer build. We describe all optomechanical parts included in the process, as well as the selection of tooling and machining parameters to obtain good surface quality results on the first groups of slices for the GIRMOS (Gemini InfraRed Multi-Object Spectrograph) instrument image slicer.

Modern optical fabrication techniques have grown progressively more complex to reflect the broadening design space of optical systems. Rotationally symmetric aspheric surfaces have been joined by off-axis and freeform designs, and the demands made of the “simpler” designs are continuously pushing the limits of the current “state of the art.” As a result the metrology needed to support the fabrication of such components has become increasingly complex. Both in-process testing and final performance certification require metrology that can report surface performance as a function of alignment to reference datums. The metrology requirements for the various process steps are often differentiated by the resolution requirements. As the processing progresses away from full aperture tooling, the opportunity to address and/or impart higher order content increases. The resolution of the test setup must correspondingly increase to provide a way to measure and mitigate any of this content deemed undesirable. Simply specifying a low-order figure tolerance is no longer sufficient. As system requirements have changed designers have become more aware of the issues associated with these higher order errors. Surface error specifications now often span a specific range of spatial frequencies and therefore require a corresponding range of instruments to characterize as well. This paper will compare the various metrology techniques employed by the team at QED Optics and discuss how they enable specific aspects of the manufacturing process.

Wave Front Phase Imaging (WFPI) is used to measure the stria on an artificial, transparent plate made of Schott N-BK7® glass material by accurately measuring the Optical Path Difference (OPD) map. WFPI is a new technique capable of reconstructing an accurate high resolution wave front phase map by capturing two intensity images at different propagation distances. An incoherent light source generated by a light emitting diode (LED) is collimated and transmitted through the sample. The resultant light beam carries the wave front information regarding the refraction index changes inside the sample¹. Using this information, WFPI solves the Transport Intensity Equation (TIE) to obtain the wave front phase map. Topography of reflective surfaces can also be studied with a different arrangement where the collimated light beam is reflected and carrying the wave front phase, which again is proportional to the surface topography. Three Schott N-BK7® glass block samples were measured, each marked in which location the wave front phase measurement will be performed². Although WFPI output is an OPD map, knowing the value of refractive index of the material at the wavelength used in the measurements will lead to also knowing the thickness variations of the plate.

We will present a new approach of linearized focal plane technique (LIFT), formerly developed by ONERA, which results in an improvement of a factor of 16 (4x4) of the spatial resolution. This technology is based on the combination of standard SH technology with phase retrieval algorithms applied on all spots of the microlens array that provides information on high spatial frequencies. We will show some measurements performed on extremely complex wavefronts. This technology presents very promising perspectives for optical and freeform metrology and can advantageously replace, at lower cost and better usability, Fizeau interferometry : insensitivity to vibrations, multi-wavelengths compatibility, lambda/100 accuracy and a wide dynamic range are, in fact, intrinsic characteristics of this technology.

Spectrally Controlled Interferometry measures surface form and radius in one measurement. Earlier results demonstrated ~30 PPM uncertainty, which rivals the standard DMI radius measurement, from a simple proof-of-concept test without careful compensation for the ambient environment. Results showing improved uncertainty through better calibration including environmental compensation are presented.

The demand for chalcogenide material is steadily increasing. Optical designers are seeing the advantages of the material in their optical designs. On the other side, lens manufacturers have to process this “new” material and often have trouble because chalcogenide glass behaves differently than traditional IR materials like Ge or ZnS. The talk will give you an overview on the improvements on chalcogenide production in terms of internal quality, measurements processes and production technologies.