Molded Lenses Research Articles

Ni–Nb–Zr–Ti amorphous alloys for glass lens molding die materials

Mold materials for glass lenses with microstructures, such as gratings, require not only excellent mechanical properties, high thermal stability and oxidation resistance, but also sufficient machinability by Single-Point Diamond Turning (SPDT). Our research on Ni–Nb–Zr alloys has shown that one amorphous alloy composition (Ni35Nb40Zr25 at.%) met almost all the requirements for glass lens mold materials. Unfortunately, when fabricating gratings on the mold, the immense wear on the bit, which may be caused by the high hardness of the alloy (more than 10GPa by the nano-indentation method), made it impossible to cut precise gratings. Consequently, the addition of a fourth element was considered to decrease the hardness. After several experiments, the addition of Ti was found to decrease the hardness. At first, Ti was added to substitute 10% Zr, to give Ni35Nb40Zr15Ti10 at.%. Although this alloy had a lower hardness (9.5GPa) than Ni35Nb40Zr25 at.%, it still cannot be micro-cut by SPDT. It was then decided to substitute Ti for Ni–Nb instead of Zr. Three samples: Ni30Nb35Zr25Ti10 at.%, Ni28Nb32Zr25Ti15 at.% and Ni25Nb30Zr25Ti20 at.%, were fabricated for evaluation. Finally, the Ni28Nb32Zr25Ti15 at.% and Ni25Nb30Zr25Ti20 at.% were found to have a low enough hardness to allow for precision machining.

Fabrication of a microball lens array for OLEDs fabricated using a monolayer microsphere template

We report on a method for fabricating microball lens arrays with high outcoupling efficiency based on the replica molding process, which involves casting liquid polymethylmethacrylate (PMMA) into concave microball lens molds. Concave microball lens molds were fabricated by casting a poly-dimethyl-siloxane (PDMS) mixture onto a monolayer microsphere template, which was prepared by spin-coating an aqueous suspension of polystyrene spheres. Microball lenses were fabricated using microspheres with a diameter of 90 µm. After attaching the microball lens array to organic light-emitting diodes (OLEDs), the luminance was enhanced by approximately 108%.

Processing Optimization of Optical Lens in the Injection Molding

The processing conditions during the manufacturing have critical effects on the optical performances of the molded lenses including the refractive index, isochromatic fringe order, and the fringed pattern. The objective of this work is to investigate numerically some effects of the molding conditions on the residual stresses of injection molded lenses, and then to optimal the processing parameters for reducing the residual stresses using the Taguchi method. The results show the optimal method is able to improve the residual stress and to produce a good fringed pattern.

Simulation and measurement of optical aberrations of injection molded progressive addition lenses

Injection molding is an important mass-production tool in the optical industry. In this research our aim is to develop a process of combining ultraprecision diamond turning and injection molding to create a unique low-cost manufacturing process for progressive addition lenses (PALs). In industry, it is a well-known fact that refractive index variation and geometric deformation of injection molded lenses due to the rheological properties of polymers will distort their optical performance. To address this problem, we developed a method for determining the optical aberrations of the injection molded PALs. This method involves reconstructing the wavefront pattern in the presence of uneven refractive index distribution and surface warpage using a finite element method. In addition to numerical modeling, a measurement system based on a Shack-Hartmann wavefront sensor was used to verify the modeling results. The measured spherocylindrical powers and aberrations of the PALs were in good agreement with the model. Consequently, the optical aberrations of injection molded PALs were successfully predicted by finite element modeling. In summary, it was demonstrated in this study that numerically based optimization for PAL manufacturing is feasible.

Laser Scanning Unit용 FΘ 렌즈 개발

Ftheta Lens, whose image height is proportional to its field view angle, is one of the most important parts in Laser Scanning Unit(LSU). In this paper lens design, mold production and modification method of lens design and mold are introduced. Lens design was carried out with Zemax and Special Toric surfaces were applied for lens surfaces to minimize distortion both in main and sub scanning directions. And a high precision machine with 1nm resolution was used to fabricate lens mold cores. After injection the lens was evaluated and the difference from design was examined. This difference was compensated by modifying lens design and new lens mold cores were made according to modified lens design to obtain the quality of original design.

Discussions on on-machine measurement of aspheric lens-mold surface

At present, regarding to the machining of aspheric lens mold, there are two major methods to carry out the on-machine measurement (OMM) — contacting method (CM) and non-contacting method (NCM). Here such two methods are reviewed in detail. CM is mainly based on the contacting probe which is scratching aspheric surface of lens mold to achieve profile data. To be efficient, an idea with 45° tilt of probe is proposed for OMM of lens mold by Suzuki. But generally speaking, the contacting OMM is not so efficient and can only deal with axisymmetric aspheric lens mold. On the contrary, NCM mostly uses laser to achieve aspheric profile without any contact. On ultra-precision lathe, laser scanning system or laser interferometer is mounted on the frame of lathe and transfers measurement data to machining system efficiently. However, most NCMs need stable environment and low working noise except instantaneous phase-shifting shearing interferometry (IPSSI). Therefore, a new idea about IPSSI is proposed in this paper to realize OMM of lens molds. Unfortunately, it's also difficult to test the high numerical aperture aspheric or free-form lens molds. By comparison, the newly-developed fringe reflection (FR) method is becoming the promising method because it features the high efficiency and high accuracy. However, this method has not been used for OMM system yet. Much research should be conducted for FR OMM technology.

The implementation and performance evaluation of a silicon-based LED packaging module with lens configuration

This study develops a transfer molding with flexible master for a silicon-based light emitting diode packaging with an aspherical lens and a microlens array using microelectromechanical systems technology. By transferring the pattern from wafer to wafer, the precise alignment of the lens configuration and the reflector of the silicon substrate can be achieved; batch processing can be used to reduce the costs. The size of the packaging element can be further reduced to allow more applications. For evaluating the packaging performance, the transfer of the pattern of various lens profiles is accomplished successfully using silicone gel and electroplating nickel as the lens molds, and experiments to determine the mechanical reliability are conducted. The experimental results show that the lens profiles of the silicone gel and nickel masters are exactly transferred onto the surfaces of epoxy and silicone gel encapsulations, respectively, without any damage to the material surface. The brightness of the packaging elements with a single aspherical lens profile and high fill factor microlens array are increased by 26 and 16 %, respectively, as compared with optical encapsulation with a smooth curved surface. The light uniformity is greatly improved for a 100 % fill factor microlens array. The proposed packaging solution satisfies the requirements of pattern transfer in a wafer level and improves lighting performance.

FEM Analysis of Glass Lens Molding Press

Glass molding press is an efficient and promising process for glass lens manufacturing. Molding temperature and velocity are crucial factors for pressing, and the annealing rate directly influences the residual stress and volume change of the final lens. The research contributes to studying the key factors that influence the quality of the molded lens. In the paper, by incorporating stress relaxation and structural relaxation of the viscoelastic material, numerical simulation is undertaken to determine the proper process parameters. Furthermore, the whole process of a spherical lens molding is simulated to predict the final residual stress and volume change, also the influence of different annealing rates is estimated.

Reducing Refractive Index Variations in Compression Molded Lenses by Annealing

Compression molding of glass optics is gradually becoming a viable fabrication technique for high precision optical lenses. However, refractive index variation was observed in compression molded glass lenses, which would contribute to image quality degradation. In this research, annealing experiments were applied to control the refractive index variation in molded glass lenses. The refractive index variations pre and post annealing experiment in molded lenses were measured by an experiment setup based on Mach-Zehnder interferometer. The experimental results showed that the refractive index variation can be controlled providing that a proper cooling process is applied during cooling.

Evaluation of Demolding Force by Parallel Mold Press for Glass Imprint

Measurement method of compressive or tensile forces during glass imptrint was developed by improving a lens mold press machine. Deformation and demolding behaviors could be quantified under the pressing using a glassy carbon and a tungsten carbide mold. After the pressing of a glass at slightly above the deformation temperature followed by the cooling of the glass and mold under applying a small tensile force, an abrupt demolding was observed below the glass transition temperature, which was affected by the pressing temperature and the glass compositions. This measurement method should be useful for the characterization of deformation and demolding behaviors of wide variety of glasses not only for optical lens but also for nanostructured optical components.

707 回転工具による非球面金型研磨の特性(OS7 オーガナイズドセッション《精密/微細加工と評価》)

707 回転工具による非球面金型研磨の特性(OS7 オーガナイズドセッション《精密/微細加工と評価》)

Fabricating of polymer aspherical lens mold using ELID grinding

Fabricating of polymer aspherical lens mold using ELID grinding

Lighting molded optics: Design and manufacturing

Proper design and manufacturing of glass molded lenses need to be performed in several steps. The whole process from customer requirements to f nal functional product is shown on two examples - a lens for street light and a lens for spot light with narrow lighting angle.

핫 프레스 성형용 EL-Max 소재 초정밀 연삭 가공에 관한 연구

Demand for optical glass device used for lighting could increase rapidly because of LED lighting market growth. The optical glass devices that have been formed by hot press molding process the desired optical performance without being subjected to mechanical processing such as curve generation or grinding. EL-Max material has been used for many engineering applications because of their high wear resistance, high compressive strength, corrosion resistant and very good dimensional stability. EL-Max is very useful for a glass lens mold especially at high temperature and pressure. The performance and reliability of optical components are strongly influenced by the surface damage of EL-Max during grinding process. Therefore, the severe process condition optimization shall be necessary for the highly qualified EL-Max glass lens mold. To get the required qualified surface of EL-Max, the selection of type of the diamond wheel is also important. In this paper, we report best grinding conditions of ultra-precision grinding machining. The grinding machining results of the form accuracy and surface roughness have been analyzed by using Form Talysurf and NanoScan.

Run-to-run process control of magnetic abrasive finishing using bonded abrasive particles

In this study, magnetic abrasive finishing, a polishing method using novel bonded magnetic abrasive particles, is implemented in the nanometer-scale surface polishing of STAVAX (S136) die steel workpieces, which are widely used for precision lens molds. With the aid of run-to-run control, a process control method, nanometer-scale mold surface quality is achieved and maintained over multiple runs. A specially designed magnetic quill equipped with an electromagnet was connected to a computer numerical control machining center to construct the polishing setup. Based on Preston’s equation and a set of preliminary experiments, design of experiment and analysis of variance were used to select and evaluate the relevant control parameters for the process. The finishing results show that the magnetic abrasive finishing has a nanometer-scale finishing capability (down to 8 nm surface roughness). Under run-to-run control with the selected parameters, the surface roughness values were successfully maintained below the target values (10 and 50 nm for Ra and Rmax, respectively), which shows that the proposed magnetic abrasive finishing scheme is readily adaptable to ultraprecision polishing applications, which are subject to disturbances for a relatively long period of time.

Microlenticular lens replication by the combination of gas-assisted imprint technology and LIGA-like process

A mold used in creating diffractive optical elements significantly affects the quality of these devices. In this study, we improved traditional microlens fabrication processes, which have shortcomings, mainly by combining gas-assisted imprint technology and the lithographie galvanoformung abformung (LIGA)-like process. This combination resulted in the production of high-quality optical components with high replication rates, high uniformity, large areas and high flexibility. Given the pixel size of the panel used, the optimal viewing distance, the film thickness and the glass thickness in the formula, we could determine the radius of curvature and the thickness of the lens. By the use of U-groove machining, precise electroforming and embossing to produce polydimethylsiloxane (PDMS) molds, lens film elements can be produced via an ultraviolet (UV)-cured molding process that converts microlenses into flexible polyethylene terephthalate films. In this study, the microlenticular lens mold is fabricated by U-groove machining, Ni electroforming and PDMS casting. Then, the PDMS mold with microlenticular lens structure is used in the gas-assisted UV imprint process and the PET film with microlenticular lens array is obtained. The lenticular lens had a radius of curvature and height of 228 and 18 µm, respectively. A 3D confocal laser microscope was used to measure the radius of curvature and the spacing of the metal molds, nickel (Ni) molds, PDMS molds and the finished thin-film products. The geometry of the final microlenticular lens was very close to the design values. All geometric errors were below 5%, the surface roughness reached the optical level (with all Ra values less than 10 nm) and the replication rate was 95%. The results demonstrate that this process can be used to fabricate gapless, lenticular-shaped, high-precision microlens arrays with a unitary curvature.

Runner design to improve quality of plastic optical lens

Although the layout of multicavity molds is a geometrically balanced design, when the melt flows into the runner, the shear-induced partial changes in material properties will result in intracavity imbalance. This study placed a rectangular flow restrictor within the tertiary runner of a precision optical lens mold to create melt turbulence through flow blocking. Due to polymer rheological characteristics, uniform melt temperature distribution in the runner channel could be obtained, making the temperature distribution inside the cavity more uniform, and reducing the thermal residual stress and warpage of injection molded parts. The optimal runner restrictor design is placing 5 mm away from the secondary runner centerline, making both the depth and the width of the block 3 mm. A relatively uniform melt temperature distribution with a maximum temperature difference of 1.1 °C can be achieved. Injection molds were fabricated according to the optimized restrictor design, and experimental verification was performed. The contour accuracy of a lens parallel to injection direction was improved from 10.44 to 5.03 μm. Therefore, this runner restrictor design can be applied to high-precision optical molds due to the ease of machining and the capability of improving the quality of optical lens.

Fabrication of molded chalcogenide-glass lens for thermal imaging applications

With the recent development of less costly uncooled detector technology, expensive optics are among the remaining significant cost drivers. As a potential solution to this problem, the fabrication of IR lenses using chalcogenide glass has been studied in recent years. We report on the fabrication of a molded chalcogenide-glass lens for car night vision and on the evaluation of the lens. The moldability of chalcogenide glass was characterized through transcription properties of the mold's surface. In addition, both IR transmittance and x-ray diffraction patterns of the molded chalcogenide-glass lens were evaluated to verify the compositional and structural stability of the glass material under the given molding conditions.

기구학적 커플링으로 구성된 3자유도 병렬 메커니즘 해석 및 설계

This paper presents a high-speed automatic micro-alignment system that is a part of an inspection machine for small-sized molded lenses of mobile phones, palm-top computers, and so on. This work was motivated by the shortcomings of existing highest-grade commercial machine. A simple tip/tilt/Z parallel mechanism is designed based on kinematic couplings, which is a 3-degree-of-freedom (3-DOF) moderate-cost alignment stage. It is used to automatically adjust the posture of each lens on the tray, which is impossible by the conventional instrument. Amplified piezoelectric actuators are used to ensure the accuracy and dynamic response. Forward kinematic analysis and simulation show that the parasitic motion is small enough compared to the actuator stroke. From the workspace analysis of the moving platform, it is clear that the output motion range satisfies the design requirements.

High Precision Grinding of Large Fresnel Lens Mold

Demand for glass Fresnel lenses is increasing in solar panel manufacture in order to increase power efficiency. Glass lenses are usually moulded using a glass moulding method with tungsten carbide moulds. In this study, large Fresnel lens moulds made of tungsten carbide are tested to be ground by a simultaneous 2-axis (Y, Z) controlled grinding method. The resinoid bonded diamond wheel is trued with a rare metal truer to increase the sharpness of the wheel edge. In the grinding test of the tungsten carbide mould, a form accuracy of less than 0.8 μm P-V and surface roughness of 18 nm Rz are obtained, and it is clarified that the proposed grinding method is useful for Fresnel grinding.