Optical Glass Lenses Research Articles

An error compensation method for single point oblique axis grinding considering the grinding wheel wear

With the increasing amount of high quality optical products, the manufacturing requirement for the high-precision optical glass lenses is on the rise. Grinding is typically the main manufacturing process for the optical mold. The degree of wheel wear has a direct impact on the precision of the grinding process. In this paper, the wear rule of grinding wheel in the grinding process of optical aspheric surface is studied with the in-site wear measurement system. A new image processing method and a wear degree evaluation method are proposed. The wear prediction model for the grinding wheel is established. Then a modified compensation method of optical aspheric surface considering grinding wheel wear is proposed. The optical aspheric surface is then compensated using a modified multinomial equation considering grinding wheel wear. The results demonstrate that the profile error of optical aspheric surface can be reduced to less than 150 nm. The proposed compensation method that takes into account the grinding wheel wear can highly improve the grinding precision and efficiency of optical aspheric surface as compared with the conventional compensation method.

Development of mid-infrared glass lens based on TeO2-ZnO-La2O3 glass system

Investigation on thermal, mechanical and optical properties is of utmost importance in designing optical glass for the development of mid-infrared camera module. In this study, two tellurite glass systems, namely the ternary TeO2 −ZnO−La2O3 (TZL) system modified with various concentrations of ZnO and the quaternary TeO2 −ZnO−La2O3 −MoO3 (TZL-Mo) system incorporated with various concentrations of MoO3, were fabricated using the melt-quenching method for mid-infrared optical glass lens. The effects of ZnO and MoO3 contents on characteristic properties of the glasses were investigated. The thermal stabilities were found to be > 117 °C in both the glass systems. The coefficients of thermal expansion decreased from 14.26 to 12.6 and 13.91–13.08 (×10−6/K) with increasing the ZnO and MoO3 contents in the TZL and TZL-Mo glass systems, respectively. Notably, the thermal stability and coefficient of thermal expansion were improved considerably with the addition of MoO3 to the ternary TeO2 −ZnO−La2O3 (TZL) tellurite glass composition. The Knoop hardness values increased from 339 to 384 and 326–371 kgf/mm2 with increasing the contents of ZnO and MoO3, respectively. The glass composition of 60TeO2 − 30ZnO− 7La2O3 − 3MoO3 was selected to produce molded glass lens using the glass molding process because of its attractive thermal and optical characteristics. The average transmittance of the glass in the range of 3–5 µm was found to be 91% after the anti-reflection coating process. Finally, the TZL-Mo3 aspherical lens was developed with diameter of 22 mm for mid-IR camera module.

A controllable interface design and manufacturing strategy for embossed glass hierarchical nano-lens

Constructing nanostructured surfaces on the macro/micro-scale optical lens is of great importance in the improvement of light transmittance, reflection, and surface functionality of optical devices. In this paper, a flexible and novel material interface design and manufacturing method for hierarchical macro/nano optical glass lenses is proposed. To verify the feasibility of the presented manufacturing strategy, the deformation history and flow driving mechanism of multiscale structured surfaces during second hot embossing were studied by simulations and experiments. The results showed that solid-like glass preform exhibits a higher nanoscale deformation resistance and elastic recovery, which can reduce the distortion levels of the nanostructured surface. At small scales, molecular confinement greatly reduces the tectonic deformation of nanostructured surface at relatively low applied heat and pressure. However, beyond a specific thermal energy threshold, nanostructured convex surfaces are easily compressed into a smooth flattened surface. By collaborative control of embossing conditions, the nano-surface integrity of multiscale structured surface can be ensured during second hot embossing. Compared to the smooth macroscale optical lens, the hierarchical macro/nano glass lens exhibited better optical transmittance and antireflection properties. The proposed design and manufacturing strategy provides a facile and flexible solution for building the hierarchical macro/micro/nanostructure functional optics.

Large size optical glass lens polishing based on ultrasonic vibration

Large size optical glass lens polishing based on ultrasonic vibration

Slurry Conditions for Reaction-Induced Slurry-Assisted Grinding of Optical Glass Lens

The demand for optical glass lenses is rising owing to the increase in image resolution. Optical glass is a hard and brittle material. Thus, an efficient and precise grinding method is required for optical glass to improve lens quality and productivity. There are a few methods of producing crack-free machined surfaces; however, they provide only limited grinding efficiency. To resolve this issue, the authors’ group has proposed the reaction-induced slurry-assisted (RISA) grinding method, which expands the range of ductile-regime grinding by utilizing the chemical–mechanical action of a cerium oxide slurry. In this study, the grinding performance of RISA grinding is experimentally evaluated for different pH levels. The results are compared using Tukey’s test, where surface roughness is considered as the characteristic value and the pH value as the analyzed factor. The result shows that RISA grinding efficiently produces a high-quality surface when the slurry is alkaline. The adhesion of cerium oxide abrasives to the wheel in RISA grinding follows the same mechanism as slurry aggregation. In addition, adhesion is more likely to occur when the alkalization of the slurry promotes aggregation. The tank in the slurry supply unit is replaced with a rotating tank to ensure stable RISA grinding with a highly aggregable slurry while preventing aggregation. The performance evaluation shows that a high-quality surface with a surface roughness of less than 10 nm in most parts is obtained. Moreover, the critical depth of cut stably increases by a factor of 5.8.

Fabrication of optical glass lenses using laser slicing technology (Stress formation and crack propagation mechanism in internal laser processing)

Fabrication of optical glass lenses using laser slicing technology (Stress formation and crack propagation mechanism in internal laser processing)

Development of surrogate models of clamp configuration for optical glass lens centering through finite element analysis and machine learning

Development of surrogate models of clamp configuration for optical glass lens centering through finite element analysis and machine learning

Prediction model of residual stress during precision glass molding of optical lenses.

Precision glass molding (PGM) is an important processing technology for aspheric lenses that has the advantages of low complexity, high precision, and short processing time. The key problem in the PGM process is to accurately predict the residual stress of aspheric lenses. In this paper, we examine the residual stress relaxation model for aspheric lenses, including a creep experiment of D-K9 glass, calculating shear relaxation function, and predicting residual stress of aspheric lenses with the finite element method. Validations of the proposed model are conducted for three different process parameters, including molding temperature, molding pressure, and molding rate. The experimental and simulation results show that the errors of the residual stresses of the three process parameters are within 0.358 Mpa, which proves the validity of the model. The model can be used to predict the residual stress of the optical glass lens fabricated by PGM and analyze the processing parameters.

Analysis of the optical quartz lens centering process based on acoustic emission signal processing and the support vector machine

A method was proposed for analyzing the optical glass lens centering process, and experiments on biplane quartz lenses were performed to determine the material removal rate (MRR) for the hard, brittle material. This study used acoustic emission–sensing technology to monitor the MRR and reconstruct the original shape of the lens. The MRR was evaluated, and an error of 17.87% was obtained. A Taguchi experiment was combined with signal analysis to optimize the process parameters, and a support-vector machine was trained to classify the quality of the grinding wheel; the model had accuracy 98.8%. By using the proposed analysis method, workpiece quality was controlled to an edge surface roughness of < 2 μm, a lens circularity error of < 0.01 mm, a crack length of < E0.1, and an optical axis error of < 150 μrad.

An Open Labelled Comparative Clinical Study to Evaluate the Effect of Go-Ghrita Tarpana and Triphala-Ghrita Tarpana on Antero-Posterior Diameter in Axial-Myopia

Background and Objective: Axial-myopia is characterized by blurriness of vision for distance caused by increased in A-P diameter. Usual treatment for myopia is optical correction by optical glass and contact lens. To restore distance vision, surgical intervention like, LASIK is adopted, which has complications like dry eye syndrome and astigmatism. The Ayurvedic approach of the disease mainly concentrates on treating the disease and preventing the progression of the disease. There are many hypothetical theories regarding mode of action of Tarpana on Myopia and Timira. In this study, an attempt is made to observe the effect of Tarpana on A-P diameter of eyeball and to know the difference between Tarpana by plain Go-Ghrita and Triphala Ghrita. Materials and Methods: 20 patients of Group A, were treated with Go-Ghrita Tarpana (two sittings of 7 days each, with the gap of 14 days) and in Group B, 20 patients were treated with Triphala-Ghrita Tarpana (two sittings of 7 days each, with the gap of 14 days). Results: The data of both the groups were collected according to the objective and subjective parameters and analyzed using the most appropriate statistical test (repeated measures of ANOVA, Bonferroni Test and Mann- Whitney U Test). The efficacy is statistically significant within the group at P &lt;0.001and statistically insignificant between the groups at P &gt;0.05 among all the parameters. Interpretation and Conclusion: On comparison of Go-Ghrita Tarpana with Triphala-Ghrita Tarpana, both have an equal effectiveness on distant vision, Optical correction and A-P diameter.

Analysis of lens fracture in precision glass molding with the finite element method.

Precision glass molding (PGM) technology has recently emerged as a promising fabrication method for mass-fabricating optical glass lenses with complex surfaces. However, lens fracture as a common problem has not been analyzed in detail. In this paper, the divergent cone cracks in the molded lens were analyzed using the finite element method, because crack propagation cannot be seen in the molding process. A three-dimensional model was established in MSC Marc software for analyzing the temperature, stress components, and principal stress of the glass in different molding stages. The crack paths were analyzed using the simulation results and the fracture basis. Based on the analysis, PGM experiments with different processing parameters were carried out. The appearance of the molded lenses demonstrated the rationality and correctness of the analysis. Thus, analyses of other types of lens fractures can use the analysis method proposed in this paper rather than relying on trial and error.

Quality improvement of collimating lens produced by precision glass molding according to performance evaluation.

Precision glass molding technology is one of the most important approaches to produce optical glass lenses. However, the high fidelity and repeatability of optical performance be sometimes achieved even though the lenses meet the requirements of geometric assessments. The surface errorform errors transferred from mold surface with a complicated combination of components of different spatial-frequencies greatly influence the optical lenses performance. An optical model is built to investigate the impact of form errors with various frequencies on the optical performance of the lens. The mid-spatial frequency error is proved to be the factor that results in the most serious surrounding circle phenomenon. Based on the diffraction theory of the sinusoidal grating, numerical calculation is carried out to analyze their relationship. Experiments are conducted to validate the analysis and a mold polishing procedure is provided as a method to improve the quality of lenses according to performance evaluation.

Ultra-precision grinding of optical glass lenses with La-doped CeO2 slurry

Higher accuracy and more efficient production of large aperture glass lenses is increasingly required for high-resolution imaging devices. These glass lenses are typically manufactured by both ultra-precision grinding and polishing. However, prolonged polishing deteriorates the lens shape accuracy and diminishes productivity. In order to reduce the required amount of polishing or even obtain a polish-free fine surface, chemical action-assisted ultra-precision grinding using La-doped CeO2 slurry is proposed and its effectiveness is experimentally evaluated. The results show that the proposed grinding method successfully provides a high-quality surface comparable to a polished surface and results in five times higher productively than conventional grinding.

Evaluation of surface quality by using servo information in ultra-precision grinding of optical glass lenses

Evaluation of surface quality by using servo information in ultra-precision grinding of optical glass lenses

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

The study of ultrasonic vibration assisted polishing optical glass lens with ultrasonic atomizing liquid

In this paper, our study is ultrasonic vibration assisted polishing optical glass lens with ultrasonic atomizing liquid. The ultrasonic vibration is applied to the axial direction of the main shaft, which can make abundant grains to impact the workpiece with the high-frequency reciprocating style. And the ultrasonic atomizing liquid is applied to the nozzle in order to make grains more homogeneous and decrease clustering phenomenon, which can improve the surface quality. The material removal rate model of single and multiple grains in the holes and micro-peaks of the polishing head are established by analyzing the removal mechanism of ultrasonic vibration assisted polishing for optical glass lens with ultrasonic atomizing liquid. Several sets of experiments were designed and the optical glass lenses were polished through contrast experiment. The contrast experiment results show that the material removal rate of ultrasonic assisted polishing of optical glass lens with ultrasonic atomizing liquid is better than that of one-dimensional ultrasonic assisted polishing and common polishing. And the surface roughness of ultrasonic vibration assisted polishing with ultrasonic atomizing liquid can reach 2 nm. And the results of experiments can be seen that the removal rate of the material is related to the abrasive grain diameter, the rotational speed and the feed rate of polishing head, and the ultrasonic amplitude. The experimental results are basically consistent with the prediction model.

Experimental research on temperature field distributions for optical lenses irradiated by femtosecond laser

The infrared thermal imaging system was used in order to investigate the temperature field distributions for optical glass lenses irradiated by femtosecond pulsed laser. The experimental research of the temperature field distributions on the surface of the H-K9L optical glass lenses with anti-reflection film and film free have been accomplished by this system combining with the irradiation at different frequencies and actuation duration by the femtosecond pulsed laser. The angle between the normal direction of the mirror surface and the laser output was 45 degrees. Experimental results showed that the coating of the lens on surface increases the distortion of the heat-affected zone and the temperature field, the penetration time increases as well as the temperature gradient decreases at the same time, which was caused by the reflection reducing coating on the surface of the lenses and this kind of coating has a certain protective effect to the optical lenses. The output frequencies of the laser presented a positive correlation linearly to the maximum surface temperatures of the lens in a certain range when the output energy of single laser pulse was constant. The spectral of temperature field was dominated by low frequency signals, the higher the laser output frequency was, the larger the amplitude of the spectrum signals was. The evolutionary processes of temperature for feature points at the edge of heat-affected zone were basically the same, therefore the laser irradiation in a small angle less than 45 degrees had little influence on the distributions and the evolutionary processes of the surface temperature fields in the heat-affected zone for thin targets.

Influence of servo characteristics on crack generation in ultra-precision grinding of optical glass lenses

Generally, manufacturing process of optical glass lenses, which are used for single lens reflex cameras, is classified into grinding and polishing for removing cracks generated by grinding. Thus, it is desired not to generate the cracks in grinding as much as possible. Because grinding condition with cracks differs depending on the material properties of the workpiece, suitable grinding condition needs to be selected based on a lot of experimental verifications. In addition, the controller’s gain of the tool spindle with grinding wheel may be intentionally set to low value in ultra-precision grinding. Thus, the spindle speed may decrease even under servo control because of grinding load. In this study, the influence of servo characteristics on crack generation is evaluated in ultra-precision grinding of optical glass lenses. Concretely, an optical glass lens was machined using an ultra-precision 5-axis grinding machine and servo information of tool spindle was monitored during the process. Comparison of the obtained servo information and the surface observation of the workpiece revealed that the spindle speed decreased and the number of the cracks increased at the outside of the workpiece. The experimental results suggested the possibility of estimating the grinding load and predicting the surface quality by monitoring the variation in the spindle speed.

Polishing of Tungsten Carbide by Combination of Anodizing and Silica Slurry Polishing

Sintered tungsten carbide (WC) is widely used in precision molding of optical glass lenses, and is considered as a critical mold material for optical industry, due to its high hot hardness and low thermal expansion ratio. However, WC is also a well-known difficult-to-polish material owing to its high hardness and strong chemical inertness. In an effort to realize the high-quality and highly efficient polishing of WC, a two-step polishing process combining anodizing and soft abrasive polishing was developed. Experimental studies of the anodizing step and the slurry polishing step were conducted. Anodizing has been found to be able to quickly soften WC and realized a drastic decrease of its surface hardness from 22.1 GPa to below 2.0 GPa, which allows us to polish the substrate surface using soft silica abrasives. In the polishing step using silica slurry, the oxide layer was removed and it has been revealed that the surface quality of polished WC was greatly affected by the duration of anodizing and the type of polishing pad. A scratch-free, pit-free and smooth WC surface can be obtained by combination of 10 min of anodizing and 30 min of silica slurry polishing using a suede type polishing pad. This research offers a new method for achieving high-quality finishing of WC with high efficiency.

Basic Study on Ductile-Mode Grinding of Optical Glass Lenses with Rubber Bonded Diamond Wheels

Large aperture lenses with high surface quality are demanded for professional imaging products such as single-lens reflex cameras and astronomical telescopes. Large aperture optical lenses are shaped by ultra-precision grinding and finished by prolonged polishing. However, the prolonged polishing process leads to deterioration of the form accuracy. In order to reduce the amount of polishing, ductile-mode ultra-precision grinding is demanded. In this study, a rubber bonded wheel, which has a low elastic modulus, is used for grinding of spherical glass BK7, and influence of the hardness of the rubber bonded wheel and abrasive chip thickness on brittle fracture and surface roughness are experimentally investigated.