Ho-Seop Jeong

Fabrication of phone-camera module using wafer-scale UV embossing process

We have developed a compact and cost-effective camera module on the basis of wafer-scale-replica processing. A multiple-layered structure of several aspheric lenses in a mobile-phone camera module is first assembled by bonding multiple glass-wafers on which 2-dimensional replica arrays of identical aspheric lenses are UV-embossed, followed by dicing the stacked wafers and packaging them with image sensor chips. This wafer-scale processing leads to at least 95% yield in mass-production, and potentially to a very slim phone with camera-module less than 2 mm in thickness. We have demonstrated a VGA camera module fabricated by the wafer-scale-replica processing with various UV-curable polymers having refractive indices between 1.4 and 1.6, and with three different glass-wafers of which both surfaces are embossed as aspheric lenses having 230 μm sag-height and aspheric-coefficients of lens polynomials up to tenth-order. We have found that precise compensation in material shrinkage of the polymer materials is one of the most technical challenges, in order to achieve a higher resolution in wafer-scaled lenses for mobile-phone camera modules.

Mode propagation in optical nanowaveguides with dielectric cores and surrounding metal layers

The mode spectrum in an optical nanowaveguide consisting of a dielectric-core layer surrounded by two identical metal layers is investigated. A simple model based on mode matching to predict the properties of mode propagation in such optical nanowaveguides is proposed. It is shown that quasi-TM00 and quasi-TM10 modes supported by an optical microstrip line do not have a cutoff frequency, regardless of the size of the metal strips, the thickness of the dielectric slab, and the cross-sectional shape. The transverse size of the TM00 mode supported by a nanosized microstrip line was found to be approximately equal to the transverse dimension of the microstrip line. In closed rectangular and elliptical nanowaveguides, i.e., in which all dielectric surfaces are covered with metal films, the cross-sectional shape of the waveguide should be stretched along one side to produce propagation conditions for the fundamental mode.

High efficiency trichromatic LED backlight for mobile LCDs

Trichromatic LED backlights render higher color gamut and panel transmittance to the liquid crystal displays (LCDs) than yellow phosphor-converted white LED backlights can possibly do at their best. In realization, however, several technical challenges arise, such as color mixing, minimizing the total number of chips, and maintaining the color balance. We designed and demonstrated a backlight unit for 2.2 inch TFT LCD using two RGB 3-chip LEDs to assess the feasibility and the technical hurdles to overcome. The average brightness of the backlight is 2509cd/m2 at the input power of 200mW. The power efficiency is lower than but comparable to commercially available white LED backlights. The color gamut of the LC panel is increased from 53% to 78% when its conventional white LED backlight is replaced by the trichromatic LED backlight. Panel transmittance is expected to be enhanced as well by about 8%. The ambient temperature change was found to be the most significant cause of the color shift of the trichromatic LED backlight. The forward bias voltage can be used in the feedback, since it changes linearly with temperature.

Camera Imaging Lens Fabrication using Wafer-Scale UV Embossing Process

We have developed a compact and cost-effective camera module on the basis of wafer-scale-replica processing. A multiple-layered structure of several aspheric lenses in a mobile-phone camera module is first assembled by bonding multiple glass-wafers on which 2-dimensional replica arrays of identical aspheric lenses are UV-embossed, followed by dicing the stacked wafers and packaging them with image sensor chips. This wafer-scale processing leads to at least 95% yield in mass-production, and potentially to a very slim phone with camera-module less than 2 mm in thickness. We have demonstrated a VGA camera module fabricated by the wafer-scale-replica processing with various UV-curable polymers having refractive indices between 1.4 and 1.6, and with three different glass-wafers of which both surfaces are embossed as aspheric lenses having

Miniaturized Optical Pickup and Mechanism for Mobile Optical Disc Drive

230{\mu}m

Low-profile optic design for mobile camera using dual freeform reflective lenses

sag-height and aspheric-coefficients of lens polynomials up to tenth-order. We have found that precise compensation in material shrinkage of the polymer materials is one of the most technical challenges, in orderto achieve a higher resolution in wafer-scaled lenses for mobile-phone camera modules.

Blu-ray Disc/Digital Versatile Disc Recording and Reproducing Compatible Use Technology in the 2nd Generation Pick Up for Blu-ray Disc

Recently, the market for portable instruments has been increasing markedly. If a very small optical disc drive can be realized, it is expected that a new market for memories will be created, because the running cost of an optical disc is very low. The main issues in such realization are miniaturization of a loading mechanism with a disc cartridge and recording density growth. In this paper, we propose a miniaturized optical pickup and mechanism that realizes a 5-mm-high drive usable with a cartridge disc. An optical axis shift using a prism pair is introduced for using conventional optical parts. A plano-concave lens and a hologram lens are used to compensate for achromatic aberration. Finally, signals reproduced by the miniaturized pickup are showed. Data-to-clock jitter was 6.3% for Blu-ray Disc (BD) storage density.

An image quality evaluation method for DOE-based camera lenses

Aspherical glass or plastic lenses are usually adapted in the camera module of handheld phone. Recently, slimmer cameras are required according to reducing thickness of handheld phone. In this paper, we present an ultra slim camera module using multiple freeform off-axis imaging lenses. New optical concept of multiple lens system introduces the planar optics with freeform shaped aspherical lens surface on the wafer, which can achieve the thickness of 50% compared to the conventional symmetric lens system. In order to achieve the resolution specification, we separate the field of view in camera module. As the result, two inverted images are produced on a same imaging sensor and the acquired inverted images are processed by photo stitching algorithm so as to combine them. Finally, in order to verify the new imaging system, we manufacture the new slim lens through the UV embossing replication process. We found the new imaging system is feasible for VGA resolution and it can be expandable to the high resolution system.

Design of liquid crystal lens for the compensation of spherical aberration in the Blu-ray optical pickup

We developed a 2nd generation pick up for the Blu-ray disc (BD), which makes possible recording and reproducing on both BD and digital versatile disc (DVD), and has a size for audio and visual (AV) and personal computer (PC) applications. These properties are realized by a single objective lens and a newly developed hologram element. The next generation optical disc system, which is expected to enable over 15 GB recording and reproducing on an optical disc, is also expected to record and reproduce on DVD or compact disc (CD), using one pick up. In order to satisfy such demand, we have developed an objective lens with a long working distance and proposed a BD/DVD/CD compatible use technology. This paper reports the details of how we achieved a proper sized AV/PC for common use, BD/DVD recording and reproducing compatible use and the dual layer disc in the 2nd generation pick up for BD.

Low-Cost Hologram Module for Optical Pickup by Adjusting Photodiode Package

A novel image quality evaluation method, which is based on combination of the rigorous grating diffraction theory and the ray-optic method, is proposed. It is applied for design optimization and tolerance analysis of optical imaging systems implementing diffractive optical elements (DOE). The evaluation method can predict the quality and resolution of the image on the image sensor plane through the optical imaging system. Especially, we can simulate the effect of diffraction efficiencies of DOE in the camera lenses module, which is very effective for predicting different color sense and MTF performance. Using this method, we can effectively determine the fabrication tolerances of diffractive and refractive optical elements such as the variations in profile thickness, and the shoulder of the DOE, as well as conventional parameters such as decenter and tilt in optical-surface alignments. A DOE-based 2M-resolution camera lens module designed by the optimization process based on the proposed image quality evaluation method shows ~15% MTF improvement compared with a design without such an optimization.