We presented the digital holography (DH) system with enhanced image quality. While conventional DH uses highcoherence laser for illuminations, the speckle noise included in the image degrades the quality of the reconstructed data. To reduce the noise regards to the light source, lower-coherence light source could be applied in DH system. In this paper, the quantum dot (QD) based wavelength converter is utilized as the light source. Compared with light-emitting diode (LED), QD-based light source could be applied to versatile system, including dual-wavelength DH. Due to the low coherence both temporally and spatially, spatial filtering and collimation is presented. Also, numerical processes including noise reduction and aberration compensation is described to enhance the quality of the image. By experimental verifications, the proposed DH system shows better quality compared with conventional system, which is enough to utilize the quantitative measurement.
There are many proposals and studies for the high density optical data storages with a data capacity over 150GB. Multi-layer recording is consider as one of the best candidates for the next generation optical data storage since it can be realized with an addition of a few optical components in the current Blu-ray (BD) optical pickup. Of course, it is required to compensate the spherical aberration between the recording layers in the multi-layer disk. A novel liquid crystal (LC) lens is proposed and designed to compensate the spherical aberration occurred by the difference of substrate thickness. New structure of liquid crystal (LC) lens includes both concave and convex surfaces which can compensate the spherical aberration with a relatively long range. Since previously developed LC panel showed very low tolerance to the shift of objective lens, new design was proposed with a special LC lens structure to improve both characteristics of the shift tolerance and compensation range. The refractive index of LC lens is changed by applying a voltage on the ITO electrodes prepared with a curvature surface. Therefore, a focal point of the transmitted light can be changed with a careful control of applied voltage, resulting in a compensation of the spherical aberration. Several types of LC lens, including spherical and aspherical surfaces, were designed and their performance was simulated theoretically. With an optimized curvature control with the spherical LC lens, the aberration of BD optical pickup can be kept under 0.018λRMS even for the thickness variation of ±25μm.
New optical memory system is urgently required to realize high memory capacity and fast data transfer rate in the coming high-speed internet era. To overcome the current capacity barrier of far-field techniques, a novel near-field optical memory using near-field optics has been proposed using vertical cavity surface emitting laser (VCSEL) microprobe array. Arrays of up to 625 microprobes were prepared successfully using newly developed micro-fabrication process, which includes the photolithography and dry etching by ion-milling method. Since etching rate depends on the incident angle of ion beam to etching surface, it is possible to realize higher etching rate for metal layer deposited on top surface compared to side plane by adjusting the angle of ion beam to both surfaces. In case of GaP microprobes, the relative etching rate of top surface to side plane shows maximum value when top surface is exposed to ion beam with 25 degree. After forming apertures on top surface, GaP probe shows triangle surface of around 200 nm in each edge, which strongly depends on its original size of flat-tip surface before the aperture formation. We believe that ion-milling method developed in this research is very effective to prepare all apertures simultaneously in the array system and can be applied to other microprobes prepared in batch process.