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.
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.
A receiver structure referred to as piecewise maximum likelihood (PML) is proposed in order to reduce the complexity of the PRML receiver. A channel response of optical disk is used for the performance evaluation. The channel distortion such as tangential tilt effect of optical disk also considered. The hardware implementation complexity between the PML and adaptive PRML is compared.
For a dual layer structure, the effect of different physical geometries is studied using 0.65 and 0.85 of numerical aperture(NA), and this result gives an incitation for making a physical format for rewritable high density disc.
An experimental result of QPSK wobble addressing method is presented. The wobble address signal which is formed on groove track in BPSK method can be read back on land track as well. The performance of wobble addressing method is explained by its CNR characteristics and corresponding BER
We report certain diffraction effects that are pertinent to the operation of double-layer optical recording media. The diffraction of light from the out-of-focus layer and the resulting distribution on the in-focus layer are studied using computer simulations. The findings are then verified by direct measurements. We also describe a technique for analyzing (by computer simulation) the focus-error signa, FES, in systems that use the astigmatic method in conjunction with the double-layer disk. The results of our computer simulations of the FES are compared with those measured in an actual disk drive; good agreement between computation and measurement is obtained.
In an optical pick-up for high areal density recording using Nd:YAG SHG (second harmonic generation) green laser, the stability of a servo mechanism may be deteriorated easily due to many optical elements and long optical path. We propose a new stable servo method employing a differential critical-angle prism. This method showed one order of higher stability than conventional astigmatic servo method to the chief ray tilt. We obtained more than a CNR of 48dB even in case of the large chief ray tilt with 0.5 micrometers mark length on MO recording layer, which is close to the case of no chief ray tilt.
High density magneto-optical recording was realized with the combination of a compact green laser and a very sensitive NdTbFeCo/TbFeCo MO disk for the wavelength of 532 nm. This media has a high Kerr rotation angle at 532 nm and maintains a stable recording domain. With an objective lens of 0.6 NA, CNR of 48 dB and jitter of 3.0 nsec by mark edge recording was obtained for a mark length of 0.45 micrometers (0.34 micrometers /bit) at a writing power of 4.5 mW.