Sang-Suk Kim

Fabrication and optical evaluation of aspheric glass lenses for 3 megapixel zoom camera phone module

The purpose of this study is to develop aspheric glass lenses 4mm in diameter by compression molding. The lens is intended for use as an optical design of 3 megapixel and 2.5 magnifications zoom in a camera phone module. Because of the excellent optical performance of glass and aspheric element, which minimize optical aberrations, the adoption of optical designs using of aspheric glass lenses is rapidly increasing with the progress of precision image forming optics. We fabricated the mold using ultra-precision processing of tungsten carbide (WC). The aspheric glass lens was precisely molded and then its characteristics were evaluated. The mechanical and optical properties of the molded lens were investigated and it showed 90–95% transcription ratio and 0:0655λ root-mean-square optical path difference (OPD-rms), which corresponds to a 0.844 Strehl ratio. Based on the optical performance using the Marechal criterion, we supposed that the molded lens is suitable for the optical design. It also means our fabrication process is available.

Re-Ir coating effect of molding core (WC) surface for aspheric glass lens

Recently, with increasing lightness and miniaturization of high resolution camera phones, the demand for aspheric glass lens has increased because plastic and spherical lenses are unable to satisfy the required performance. An aspheric glass lens is fabricated by high temperature and pressure molding using a tungsten carbide molding core, so precision grinding and coating technology for the molding core surface is required. In this paper, the optimal grinding condition of the tungsten carbide molding core was found after applying DOE to the development of the aspheric glass lens for the 3 mega pixel and 2.5 magnifications optical zoom for camera phone module. Also, the ultra precision grinding process was investigated under this condition by experiment. Rhenium-Iridium(Re-Ir) coating was applied on the ground surface of the tungsten carbide molding core. The influence of Re-Ir coating on the form accuracy and surface roughness was compared and evaluated. The form accuracy and surface roughness of the molding core were improved by application of Re-Ir coating on the surface of the tungsten carbide molding core. Aspheric lenses were also molded with the non-coated molding core and the Re-Ir coated molding core. Form accuracy(PV) and surface roughness(Ra) were measured. The form accuracy of the aspheric glass lens improved about 0.01 μm (aspheric surface) and the surface roughness by about 0.5 nm (aspheric surface).

Development of F-theta Lens for Laser Beam Printer

Global consumption of aspheric lens will expand rapidly due to golbal transformation of the electronics based industry to optics based mechatronics. Especially, F-Theta lens is one of important parts in Laser Scanning Unit(LSU) because it affects the optical performance of LSU dominantly. Non axisymmetric machine based processing techologies are required to obtain high accuracy in utlra-precision aspheric core, the most important component in plastic injection molded F-Theta lens assembly. In this study, the core with non-axisymmetric aspheric shape which is used to emit the F-Theta lens was processed using the ultra precision processing technology and the shape accuracy of the core was measured. And the results there of were evaluated and compared with the emitted shape accuracy of F-Theta lens.

Optical performance of F-Theta lens for laser scanning unit

Recently, the global applications of aspheric lens are expanding rapidly on the electronics, optical components, communications, aerospace, defense, and medical optics devices, etc. F-Theta lens, which is one of major applications of aspheric lens, is a core optical part in Laser Scanning Unit (LSU) because it mainly affects the optical performance of LSU. F-Theta lens is made of the plastic using the injection molding method because of its cost and weight. In this study, the mold core for F-Theta lens, which is consisting of two non-axisymmetric aspheric surfaces, was processed by fly-cutting method, and the form accuracy of the mold core was measured. The product of the F-Theta lens, which was fabricated by the injection molding method, was satisfied that can be applied to the actual specifications.

A Study on Pressing Conditions in the molding of Aspheric Glass Lenses for Phone Camera Module using Design of Experiments

This study investigated the pressing conditions in the molding of aspheric glass lenses for the mega pixel phone camera module using the DOE method. Tungsten carbide (WC; Japan, Everloy Co., 002K),which contained 0.5 w% cobalt (Co), was used to build the mold. The mold surface was ultra-precision ground and polished, and its form accuracy (PV) was 0.85um in aspheric surface. We selected four factors, pressing temperature, force and time of first step, and force of second step, respectively, as the parameters of the pressing process. in order to reduce the number of experiments, we applied fractional factorial design considering the main effects and two-way interactions. The analysis results indicate that the only two main effects, the pressing temperature and the time of pressing step 1, are available for the form accuracy (PV) of the molded lens. The analysis results indicated that the best combination of the factors for lowering the form accuracy(PV) value of molded lens was to have them at their low levels.

Study on pressing conditions in the molding of aspheric glass lenses for phone camera module using design of experiments

Recently, the application of aspheric glass lenses is rapidly expanding due to the availability of mass production employing the glass molding press(GMP) process. To date, the GMP process has been regarded as one of the reliable methods in fabrication of aspheric glass lenses. However, it has been found that there are some difficulties during the process to control many parameters (e.g. molding temperature, pressing time and pressing force, etc). Design of experiments (DOE) is one of the solutions to properly control these parameters and a useful tool in the process and analysis of complicated industrial design problems. This study investigated the pressing conditions in the molding of aspheric glass lenses for the mega pixel phone camera module using the DOE method. The fractional factorial design is applied and the form accuracy (PV) of the aspheric surface of the molded lens is employed as a response variable. The analysis results indicate that the only two main effects, the time of pressing step 2 and the force of pressing step 1, are available for the form accuracy (PV) of the molded lens. It is the optimum condition among the designed pressing conditions for lowering the form accuracy (PV) value that all factors are at their low levels. The form accuracies (PV) of the mold and molded lens under the optimum condition are 0.181 um and 0.22 um, respectively.

Optical Properties of Aspheric Glass Lens using DLC Coated Molding Core

In this research, the optimal grinding condition has been obtained by design of experiment (DOE) fur the development of aspheric lens for the 3 Mega Pixel, 2.5x optical zoom camera-phone module. Also, the tungsten carbide (WC) mold was processed by the method of ultra precision grinding under this optimal grinding condition. The influence of diamond-liked carbon (DLC) coating on form accuracy (PV) and surface roughness (Ra) of the mold was evaluated through measurements after DCL coating using ion plating on the ground mold. Also, aspheric glass lenses were molded, some before DLC coating of the mold and some after the DLC coating. The optical characteristics of each sample, molded by the different molds, were compared with each other.

A Study on Influence of PV and Ra with Re-Ir Coating of WC Core Surface for Glass Molding Lens

Aspheric glass lens have recently been used in camera phone module because they are more effective than spherical ones. In this paper, the grinding condition of the tungsten carbide molding core has been found after applying DOE to the development of the aspheric glass lens for the 3 Megapixel and 2.5x camera-phone module. Also, the ultra precision grinding process was investigated under this condition by experiment. Re-Ir coating was applied on the ground surface of the tungsten carbide molding core. The influence of Re-Ir coating on the form accuracy and surface roughness of molding core was compared and evaluated. The form accuracy and surface roughness of the molding core were improved by application of Re-Ir coating on the surface of the tungsten carbide molding core.

DLC Coating Effect of WC Core Surface for Glass Molding Lens

There have been intensive and continuous efforts in the field of DLC coating process because of their feature, like high hardness, high elasticity, abrasion resistance and chemical stability and have been applied widely the industrial areas. In this research, optimal grinding condition was investigated using Microlens Process Machine for the development of aspheric glass lens which is to be used for mobile phone module with 3 mega pixel and 2.5X optical zoom, and tungsten carbide(WC) mold cote was manufactured using high performance ultra precision machining and the effects of DLC coating on the form accuracy(PV) and surface roughness(Ra) of WC mold core was evaluated.