Aspheric Glass Lenses Research Articles

Release characteristics of a high-hardness DLC coating on an aspherical glass lens mold

In this paper, we investigated the changes in the shape precision of a diamond-like carbon (DLC)-coated surface of an aspherical glass lens mold. The press molding process of the experiment involved placing a bulk material made of glass in an ultra-precision mold and applying cylinder pressure at a high temperature. Thermally stable tungsten carbide was used as the mold material. DTM grinding with a resolution of 0.1 [Formula: see text]m was performed to precisely process the tungsten carbide aspherical lens mold. HiPIMS–DLC and ta-C DLC coatings having excellent anti-stiction and hardness were applied on the polished mold. The hardness of the thin film was measured using nanoindentation. For the composition of the DLC, the [Formula: see text]/[Formula: see text] peak values were detected through Raman spectroscopy. Furthermore, the friction coefficient of the DLC thin film was measured using a tribology tester, and the friction coefficients of HiPIMS–DLC and ta-C were 0.018 and 0.014. Using FTS measurements, we confirmed that the precision of the aspherical lens shape (Peak to Valley) of the aspherical lens was 1.5 [Formula: see text]m and 0.5 [Formula: see text]m, respectively.

High-precision molding simulation prediction of glass lens profile for a new lanthanide optical glass

Precision glass lens molding (PGLM) is a recently developed method for fabricating glass optical components with high precision in large volumes. Lanthanum optical glasses are extensively used as optical materials owing to their superior optical properties, such as high refractive index, low dispersion, and high transparency. However, the transformation temperature of currently available high refractive index glass is generally above 650 °C and poses a challenge in manufacturing ultra-hard molds, durable coatings, and high-temperature molding equipment using PGLM. In this study, a preparation method for obtaining high refractive index, low -melting -point lanthanide optical glass (B-ZLaT198) used in PGLM was developed to reduce the transformation temperature. The developed method also characterizes the glass refractive indices and thermal-mechanical properties. To achieve the high-precision prediction of a molding shape in a simulation, a viscoelastic constitutive model of glass was established based on a micro-deformation uniaxial compression creep test. Moreover, by solving the Tool-Narayanasway-Moynihan model parameters based on the specific heat capacity fitting of optical glass at different heating and cooling rates, the input parameters of the structural relaxation model (SRM) for simulation prediction of aspheric glass lens profile deviation in the annealing stage were obtained. Finally, the profile deviation of the aspheric lens was predicted using a finite element model simulation. The results showed that the simulation’s predicted profile of an aspheric lens using the SRM model was in good agreement with that of experimental molding profile. In addition, using the SRM provided a higher prediction accuracy than that of the thermal expansion model in the annealing stage. Adopting the SRM was necessary for the annealing simulations of molding pressing and also verified the accuracy of the proposed viscoelastic characterization method for calculating the thermomechanical parameters of optical glasses.

軸対称非球面研削における研削条件の最適化

With the recent increase in the size and image quality of optical equipment, there is a strong demand for higher precision aspherical lenses. Generally, an aspherical glass lens or its mold is formed by grinding and then finished by polishing. Since the shape accuracy deteriorates in this polishing process, it is necessary to keep the polishing amount small. Therefore, it is desirable to optimize the grinding conditions and reduce the grinding surface roughness. In this paper, to optimize the grinding conditions of axisymmetric aspherical surface, maximum height roughness of axisymmetric aspherical ground surface is analyzed theoretically utilizing the statistical grinding theory. From the view point of relationship between the grain cutting direction and workpiece feed direction, grinding can be classified into parallel grinding and cross grinding. And it is found that the parallel grinding is suited to axisymmetric aspherical grinding.

Development of an intelligent grinding system for fabricating aspheric glass lenses

Precision optical systems, such as lithographic projection lens or cameras for satellites, typically composed of glass or ceramics optical components. In the manufacturing processes of glass and ceramics components, grinding is a key technique for curvature generation (CG) of optical surface. However, dimension errors and sub-surface damage (SSD) of components occur during the CG process. High material removal rates during the CG leads to deeper SSD on optical surface. The SSD must be removed by subsequent lapping and polishing processes to ensure high optical surface quality. However, these processes are complex, and a precise process to remove SSD from the aspheric surfaces with tens or hundreds of microns of departure from best fit sphere (BFS) is required. Thus, an efficient precision lens fabrication method can reduce the depth of SSD and help to control the dimension error during the CG process. We developed a five-axis grinding system with intelligent machining techniques to improve the quality of CG process. The intelligent grinding system based on the Tongtai five-axis machine (GT-630) was combined with two measurement modules of the Renishaw measurement probe. A customized computer-aided manufacturing software was developed and applied to this grinding system. Spherical and aspherical components with a maximum diameter of 600 mm can be fabricated using the grinding system. To improve the grinding efficiency, an ultrasonic-assisted module was combined with the BBT 40 tool arbor. The frequency range, amplitude, and power of the ultrasonic device were 15–40 kHz, 0.2–2 μm, and 1000 W, respectively. The intelligent grinding system included several vibration, temperature, and acoustic emission sensors and a microphone to monitor the dynamic status of machine during the grinding process and help to quality control. The wear of the diamond grinding wheel could be predicted immediately by analyzing the collected data in this system. A five-axis machine was applied to an intelligent grinding system for large glass lenses. The fabrication time of 200 mm diameter aspheric lenses reduced about 3 weeks by using this intelligent grinding system to integrate aspherization processes into curvature generation to become an aspheric curvature generation step.

A MEMS lens scanner based on serpentine electrothermal bimorph actuators for large axial tuning.

Confocal microscopes and two-photon microscopes are powerful tools for early cancer diagnosis because of their high-resolution 3D imaging capability, but applying them for clinical use in internal organs is hindered by the lack of axially tunable lens modules with small size, high image quality and large tuning range. This paper reports a compact MEMS lens scanner that has the potential to overcome this limitation. The MEMS lens scanner consists of a MEMS microstage and a microlens. The MEMS microstage is based on a unique serpentine inverted-series-connected (ISC) electrothermal bimorph actuator design. The microlens is an aspheric glass lens to ensure optical quality. The MEMS microstage has been fabricated and the lens scanner has been successfully assembled. The entire lens scanner is circular with an outer diameter of 4.4 mm and a clear optical aperture of 1.8 mm. Experiments show that the tunable range reaches over 200 µm at only 10.5 V and the stiffness of the microstage is 6.2 N/m. Depth scan imaging by the MEMS lens scanner has also been demonstrated with a 2.2 µm resolution, only limited by the available resolution target.

Numerical Simulation of Glass molding Process for Large Diameter Aspherical Glass Lens

In order to obtain the approximate precision molding process parameters of large diameter aspheric glass lens and predict the residual stress of the lens, a thermodynamic coupling model was established by using FEM software—ABAQUS. Meanwhile, we obtained the filling ratios of large diameter aspheric glass lens at different temperatures and pressures. Furthermore, the work analyzed the different process parameters effecting distribution of residual stress. In the large aspherical glass molding process, the annealing rate has a great influence on residual stress, and the molding velocity and pressure effect the stress inside glass in the forming stage. The more important, mathematical optimization of the temperature of molding and annealing for different glasses can improve the production efficiency. It is expected that the simulation of large diameter aspherical glass lens is a meaningful way to investigate the isothermal glass molding process.

A Study on the Performance Improvement of ta-C Thin Films Coating on Tungsten Carbide(WC) Surface for Aspherical Glass Lens by FCVA Method Compared with Ir-Re coating

A Study on the Performance Improvement of ta-C Thin Films Coating on Tungsten Carbide(WC) Surface for Aspherical Glass Lens by FCVA Method Compared with Ir-Re coating

A Study on the Molding Process of an Optical Communication Aspherical Glass Lens Using the Weight Molding Method

A Study on the Molding Process of an Optical Communication Aspherical Glass Lens Using the Weight Molding Method

冷却间隙对小口径双非球面硫系玻璃镜片模压成型质量的影响

冷却间隙对小口径双非球面硫系玻璃镜片模压成型质量的影响

Review of small aspheric glass lens molding technologies

Aspheric lens can eliminate spherical aberrations, coma, astigmatism, field distortions, and other adverse factors. This type of lens can also reduce the loss of light energy and obtain high-quality images and optical characteristics. The demand for aspheric lens has increased in recent years because of its advantageous use in the electronics industry, particularly for compact, portable devices and high-performance products. As an advanced manufacturing technology, the glass lens molding process has been recognized as a low-cost and high-efficiency manufacturing technology for machining small-diameter aspheric lens for industrial production. However, the residual stress and profile deviation of the glass lens are greatly affected by various key technologies for glass lens molding, including glass and mold-die material forming, mold-die machining, and lens molding. These key technical factors, which affect the quality of the glass lens molding process, are systematically discussed and reviewed to solve the existing technical bottlenecks and problems, as well as to predict the potential applicability of glass lens molding in the future.

Efficient dielectric metasurface collimating lenses for mid-infrared quantum cascade lasers.

Light emitted from single-mode semiconductor lasers generally has large divergence angles, and high numerical aperture lenses are required for beam collimation. Visible and near infrared lasers are collimated using aspheric glass or plastic lenses, yet collimation of mid-infrared quantum cascade lasers typically requires more costly aspheric lenses made of germanium, chalcogenide compounds, or other infrared-transparent materials. Here we report mid-infrared dielectric metasurface flat lenses that efficiently collimate the output beam of single-mode quantum cascade lasers. The metasurface lenses are composed of amorphous silicon posts on a flat sapphire substrate and can be fabricated at low cost using a single step conventional UV binary lithography. Mid-infrared radiation from a 4.8 μm distributed-feedback quantum cascade laser is collimated using a polarization insensitive metasurface lens with 0.86 numerical aperture and 79% transmission efficiency. The collimated beam has a half divergence angle of 0.36° and beam quality factor of M2=1.02.

Numerical Modeling of Cooling Stage of Glass Molding Process Assisted by CFD and Measurement of Residual Birefringence

Process parameters of Precision Glass Molding (PGM) are often sought by Finite Element (FE) simulation. Mechanical as well as thermal boundary conditions (BCs) are necessary for FE simulation in which mechanical BCs are usually known or easily determinable. However, most of the thermal BCs are generally assumed in the FE simulation as they cannot be measured directly. The focus of this article is to propose a novel method for evaluating the thermal BC of glass–N2 gas. FE simulations as well as thermal cycling experiments are carried out for a glass disk specimen for three different cooling rates. CFD analysis of N2 flow in the PGM machine is performed to understand the heat extraction mechanism. Based on this, adhoc values for equivalent heat transfer coefficient (heqv) are obtained by lumped system analysis. A novel methodology is then proposed for obtaining accurate heqv values by measurement of integrated residual birefringence in glass using digital photoelasticity. FE simulation is repeated for different values of heqv until the integrated birefringence based on simulation matches with that of the experiment. For the same cooling rates, two aspherical glass lenses are molded and their residual birefringence is measured and compared with the glass disk specimen.

A Study of Micro-Grinding and Inspection for Aspheric Glass Lens

This study discussed abrasive machining of aspheric glass lens, with the aim to increase the aspheric lens machining efficiency and reduce the back-end polishing process. The discussions covered "optical lens design", "Taguchi method optimization", "grinding force measurement", and "on-line real-time inspection". A window interface was designed by using Borland C++ Builder for optical glass design. The aspheric design parameters were substituted in it to obtain the machining path. In terms of Taguchi method optimization, the performance of electroformed grinding rod was compared with that of resin grinding rod. Taguchi method was used to look for optimization, and the quality characteristic was surface roughness. After experimental analysis, the optimization results were: using a resin binder grinding rod, the optimum parameter of 50,000 (rpm), forward grinding, feeding at 10 mm/min, grinding depth at 0.02mm, and aspheric lens surface roughness of 0.03μm. In terms of grinding force measurement, an eight-ring strain gage dynamometer was designed to measure the optimum grinding force. The measurement result showed that the grinding force in vertical direction was 3.2kg, and that in horizontal direction is 4kg. In terms of visual inspection, a CCD camera was mounted on the machine, which takes the image of workpiece immediately after it is machined. The form was inspected, and the dismounting error was reduced.

Thermal deformation compensation in the molding of aspheric glass lenses

Generally, aspheric glass lenses are manufactured using a glass molding press (GMP) method and a tungsten carbide mold core. This study analyzes the thermal deformation that occurs during the GMP process, and the results were applied to compensate an aspheric glass lens. After the compensation process, the form accuracy of aspheric glass lenses improved from ∼3.7 to ∼0.35 μm. The compensated lens complied with the actual specifications. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or repro- duction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10.1117/1.OE.53.6.065106)

Quantitatively measurement and analysis of residual stresses in molded aspherical glass lenses

Residual stresses are important criteria for evaluating precision compression molded glass lenses. In this research, residual stresses inside a molded aspherical glass lens were investigated using both experimental and numerical methods. Specifically, residual stresses were calculated from optical measurements obtained by the use of a circular polariscope. From the measurements, both the magnitude and distribution of residual stresses in the aspherical glass lens were obtained. The residual stresses were also calculated using the structural relaxation model implemented in the finite element method software, and the results were compared to the measurements in experiments that were performed using matching molding conditions. In addition, residual stresses under different cooling rates were investigated in simulation and the impact of the cooling rate on the aspherical surface deviation was also discussed.

Precision Glass Molding of High Filling Factor Micro Lens Arrays

Glass micro lens arrays (GMLAs) have several advantages such as a high transmission rate, anti-environment, and can be used for special wavelength applications. Precision glass molding (PGM) has been used to mass produce high-accuracy aspherical glass lenses. Ultra-precision diamond grinding (UPDG) is a fundamental part of the precision glass molding process. Using UPDG, grinding spherical and aspherical to sub-micrometer form and nanometer surface roughness is simple. However, asymmetrical surface MLAs are difficult to generate using the UPDG process. UPDG, together with the wheel-forming method and a strategy used to separate the entire surface generation process into several grinding loops, were studied and developed to generate high filling factor MLAs on the mold surface. The GMLA material used was K-CSK120, made by Sumita Inc., Japan. Finally, GMLAs with an approximately 100% filling factor were generated using PGM with form accuracy and surface roughness that were respectively less than 0.3 μm and 10 nm. The tolerance of each single micro lens figure was greater than 95%.

Fabrication of a Hybrid Aspheric Lens Using Glass and Thermosetting Polymer Molding Technique

This study developed a precise hybrid optical lens (PHOL) that included polymer and glass materials. Although glass offers superior anti-thermal, anti-environmental, anti-scraped corrosion resistance and optical properties than polymer materials, it is difficult to fabricate glass materials. Therefore, it is difficult to obtain a high-accuracy aspheric glass lens. This paper presents the fabrication of a PHOL that combined aspheric polymer and glass bases using a glass-molding technique. The PHOL can be used to reduce aberration errors in optical systems using two materials. The PHOL maintains the advantages of glass materials, and the cost of aspheric polymer is lower than that of the aspheric glass layer. Thermosetting polymer was used as the aspheric part in this study. Compared to UV-curable polymer, thermosetting polymer has higher thermal stability, and the molds are not limited by glass materials, which must be transmissible by UV light. First, a glass sphere lens was used as a base of the PHOL. Subsequently, the ultra-precise diamond turning technique was used to fabricate the mold with an aspheric profile. During the molding process, the thermosetting polymer was formed into an aspheric layer and covered on the glass base. The PHOL of 11.2 mm in diameter was obtained using controlled cooling. Finally, the surface accuracy (PV) of the PHOL was less than 0.5μm, has been successfully fabricated in this study.

Annealing of Compression Molded Aspherical Glass Lenses

Residual stresses and refractive index of molded glass lenses are important quality indicators of their optical performance. In this research, the control of residual stresses and refractive index variation of molded glass lenses were experimentally investigated by postmolding annealing. Residual stresses were quantitatively measured using a circular polariscope. Refractive index was reconstructed and calculated by an optical setup based on Mach–Zehnder interferometer. In addition, geometry of the aspherical surface of lens was also evaluated before and after annealing. The comparison between the measured results before and after annealing showed that residual stresses and refractive index variation were well controlled and the shape of the aspherical surface was largely retained. This comprehensive experimental study demonstrated a suggestion to improve quality of the compression molded glass lens by postmolding annealing for high-precision optical applications.

An integrated solution for mold shape modification in precision glass molding to compensate refractive index change and geometric deviation

In precision glass molding, refractive index change and geometric deviation (or curve change as often referred to in industry) occurred during molding process can result in substantial amount of aberrations. Previously, refractive index change and geometric deviation were investigated in separate studies by the authors. However, optical performance of a molded glass lens depends on both refractive index and geometry. In order to mold lenses with optimal performance, both refractive index change and geometric deviation have to be taken into consideration simultaneously and compensated. This paper presented an integrated compensation procedure for modifying molds to compensate both refractive index change and geometric deviation. Group refractive index change predicted by the finite element method simulation was used to provide a modified geometry design for a desired lens. Geometric deviations of molded glass lenses with the modified design were analyzed with a previously developed numerical simulation approach, which is used to modify the mold shape. This procedure was validated by molding a generic aspherical glass lens. Both geometry and optical measurement results confirmed that the molded lens performed as specified by the original design. It also demonstrated that finite element method assisted compensation procedure can be used to predict the final optical performance of compression molded glass components. This research provided an opportunity for optics manufacturers to achieve better performance lens while maintaining lower cost and a shorter cycle time.

非球面光学玻璃透镜的模压仿真研究

非球面光学玻璃透镜的模压仿真研究