Chi-Hung Lee

Sub-wavelength gratings fabricated on a light bar by roll-to-roll UV embossing process

This research uses a roll-to-roll based ultraviolet (UV) resin process to make sub-wavelength gratings for display applications. Based on the rigorous coupling wave analysis (RCWA), we analyze the relationship between the first order transmission/reflection efficiency and the pitch of the grating for various shapes as rays pass through the sub-wavelength gratings, patterned with a backlight. The objective is to turn the R/G/B (620 nm, 520 nm, and 450 nm) incident rays into uniformly and normally output white light with high illuminance from the surface of a light guide.

Angularly positioned LED-based spatial-temporal color separation system.

A display method, two-field driving scheme based on angularly positioned color LEDs, is proposed for field sequential color liquid crystal displays (LCDs) without color filters. In each field, the angular rays of two colors from LEDs are collimated by a collimation lens, redirected by a light guide and converged by a cylindrical-lens array to map into corresponding sub-pixel positions for efficiently displaying color image.

An integrated optical pickup with roll-to-roll fabricated diffractive components

This work designed and fabricated an optical pickup system based on optical films using the roll-to-roll process. The design combined the advantages of the stacked and planar optical pickup system. Two blazed gratings were used as beam splitters for bending the optical path, while a cylindrical lens was used for astigmatic focus-error detection. The proposed design effectively reduces overall system configuration, component cost, and fabrication complexity.

Submicrometer grating light bar for a color-separation backlight

A light bar patterned using a submicrometer grating was designed to replace conventional dye color filters for color liquid crystal displays. The light bar generates color rays by transmitting them from side-lit color light-emitting diodes through the submicrometer grating. These angular color rays are then redirected by a V-grooved light guide, and then converged by a lens array and mapped to corresponding subpixel positions to efficiently display color images. The results show that 106% of the National Television System Committee (NTSC) color space in a blue-green-red-green (B-G-R-G) repeating pattern display pixel layout can be achieved.

Roll-to-Roll Process-Based Sub-Wavelength Grating for a Color-Separation Backlight

For this study, we designed a color-separation backlight to avoid the use of absorptive color filters in a conventional backlight. The module consists of sub-wavelength grating on a light-bar (SWG-LB) and a cylindrical lens array on a V-grooved light guide to display R/B/G images more efficiently. We designed the light bar to be a hexagon type in which partial total internal reflection (TIR) area is uniformly spaced between each SWG. The measurements showed that uniformity from the light bar and NTSC are 92.8% and 99%, respectively. The optical components including the sub-wavelength grating and the cylindrical lens array were mass produced, and the diamond turning was produced using a roll-to-roll process.

LED Collimation Module for Time Sequential Back Light System

Collimation lenses for light-emitting diode (LED) light sources have been widely used in lighting engineering. In this paper, a collimated LED light source was developed for a color liquid-crystal display backlight, which is driven using a two-field driving scheme to display color. A color-separation backlight that involves using the designed collimation modules possesses several advantages such as low volume, elimination of dye color filters, high feasibility with conventional ultra-precision machining processes, and a wide color gamut.

Progressive rear-view mirror for motorcycles

In this work, we present the design and fabrication of a progressive rear-view mirror for motorcycles. In the context of physiological and physical background knowledge, we first analyze the geometric relationships among the profile of the mirror, the blind spot, the field of view, and the reflected image size. On the basis of Walkers eye model, the binocular disparity is further calculated according to the image size on each retina. We present the polynomial expansion that specifies our progressive mirrors profile, as well as the fused deposition modeling process for fabricating physical mirrors. Compared with a conventional aspheric or flat mirror, this progressive mirror can achieve a wider horizontal viewing angle and shows a more stable image, thus enhancing riding safety.

Reconstruction of the optical system of personalized eye models by using magnetic resonance imaging

This study presents a practical method for reconstructing the optical system of personalized eye models by using magnetic resonance imaging (MRI). Monocular images were obtained from a young (20-year-old) healthy subject viewing at a near point (10 cm). Each magnetic resonance image was first analyzed using several commercial software to capture the profile of each optical element of the human eye except for the anterior lens surface, which could not be determined because it overlapped the ciliary muscle. The missing profile was substituted with a modified profile from a generic eye model. After the data-including the refractive indices from a generic model-were input in ZEMAX, we obtained a reasonable initial layout. By further considering the resolution of the MRI, the model was optimized to match the optical performance of a healthy eye. The main benefit of having a personalized eye model is the ability to quantitatively identify wide-angle ocular aberrations, which were corrected by the designed free-form spectacle lens.

LED collimation module for time sequential back light system

In this study, a collimated LED light source has been developed as a colorful liquid crystal display backlight, which is driven by a two-field driving scheme to display color. In each field, the angular rays of two colors from LEDs are collimated by a collimation lens, redirected by a light guide and converged by a cylindrical-lens array to map into corresponding sub-pixel positions for efficiently displaying color image. The simulation results of the backlight module and the corresponding experimental results will be discussed in detail.