Chun-Li Chang

Novel Image Polarization Method for Measurement of Lens Decentration

Tilt and decenter errors in lenses are usually caused by lens manufacturing processes: either injection or glass molding. This paper presents an image polarization method for measuring tilting and decentering of lenses. We placed a sample lens between two linear polarizers and passed either a focused or a divergent polarized beam through a half-wave or a full-wave plate. If any error were present in the shape of the lens, patterns and colors shown in the image of polarization would be altered. Finally, the degree of error in the shape of the lens can be computed using image processing software.

The pulse exciation of UV LED source for fluorescence detection

Fluorescence is widely used to detect the biochemical effect and some substance containing certain dye. In general, the formation of fluorescent reaction is that an organism or dye, excited by UV light (200–405 nm), emits a specific frequency of light; the light is usually a visible or near infrared light (405–900 nm) However, the object excited by continue UV light cannot provide the periodic response information and clear images for fluorescence analysis, and the fluorescence intensity of organism will decay with the time exposed to UV light. In this study, we use a tunable pulse control module to perform the fluorescence test of security organic dye, BL-ORT. When the BL-ORT is excited by the 30 ms/cycle pulsed UV-LED light, the most complete fluorescence datum can be obtained. Furthermore, the power consumption of pulsed exciting source can be down to 50 percent.

The design and fabrication of telecentric lens with large field of view

In ultra-precision (distortion < 0.5 %) vision inspection system, the accuracy of measurement depends on sharpness and distortion of image. The telecentric lens provides distortion-free and constant magnification (within depth of field) image, so it has become an indispensable key module in the amount of visual measuring system. The article presents a design and development of telecentric lens module for the wide range of vision inspection system (field-of-view > 100 mm). Based on the concept of equivalent design in optical tolerances, the lens module can be designed readily into a telecentric system, which consists of five spherical lenses and a glass molded aspheric lens. In order to correct image distortion, an aspheric lens would be added to the telecentric system. The experiment shows that the distortion can be reduced from 1.5 % to 0.34 % and the depth of field (DOF) is also improved up to 28.3 mm.

The image analysis of skin tissue irradiated with difference wavelengths of LED sources

Under the different light irradiation, the reflective and scattering intensity of skin image can be applied to evaluate many human health indices, such as oxygen saturation in blood, skin tissue aging or skin lesions (leukoplakia, turmoil cell, and so on). Due to the different absorption and scattering rate of skin illustrated by a variety of LED light source, we can perform the processing and analysis of skin surface images. Since the surface roughness is more sensitive to the shorter wavelength light source (430 nm and 470 nm LED), so the difference of reflective light image can be used to detect the skin roughness. In addition, the oxygenated hemoglobin (HbO2) in blood has a relatively high absorption rate at green (570 nm) and near-infrared (940 nm) light, so it can be used to compute the oxygen saturation. In this study, based on the different light absorption of HbO2 in blood, there are six light sources (deep blue, blue, green, deep red, NIR, white light) would be applied to the inspection of skin characteristics. The processed images provide better reference for the follow-up studies on the oxygen saturation of peripheral blood and skin aging.

A polarization image method for lens decentration measurement

the tilt and decenter error of lens is usually induced by lens manufacturing process, injection molding or glass molding. The paper presents a polarization image method for measuring the tilt and decenter of lens. At first, to put the lens under test between two linear polarizers, and then a focused or divergent polarized beam will pass through a half-wave plate, once the lens has a shape error, the polarization image pattern and color will be change. Finally, the lens shape error can be computed by image processing.

Near-field optical characterization of visible multiple quantum well semiconductor lasers

Both collection and excitation modes of scanning near-field optical microscopy (SNOM) were used to study a low power visible multiquantum-well laser diode (LD). Collection mode SNOM provides the near-field optical propagating intensity distribution at the facet of LD. Excitation mode SNOM gives local photoconductivity information of the structure of LD facet. Results show highly localized spatial correlation of LD structure and its optical performance at the facet. Different sizes of apertures were used in both modes, and results of near-field interactions can be quite different. Results show obvious difference of photocurrent distribution caused by the different sizes of apertures in excitation mode. Two wavelengths of 543.5 nm and 632.8 nm were used in excitation mode SNOM. It can be deduced from the two pump photon energies that there exists defect level in the energy range of 60 - 380 meV below the conduction band edge in the n-(Al0.7Ga0.3)0.5In0.5P cladding layer. In addition to the highly localized images of topography, optical output, and optical beam induced current at the facet of LD, local near- field optical spectroscopy was performed as well. Spatially resolved near-field optical spectra of both stimulated and spontaneous emissions were obtained at the facet of LD. Longitudinal modes of stimulated emission of LD were observed locally.

The development of automatic optometry instrument based on the ANSI/ISEA Z87.1 standard

In the past, the optometry instrument calibrated in diopter and astigmatism were usually performed by using human eyes. However, the larger uncertainty of measurement will be induced while observing the measuring patterns using human eyes. Therefore, based on the ANSI/ISEA Z87.1-2010 standard, this study presents the development of automatic optometry system, which comprises of the machine vision, image analysis and processing, and automatic focus technique without human operation. In addition, the astigmatism measurement can be well completed in the electric moving stage. The experimental results show the automatic optometry system has the high accuracy and good repeatability.

Development of telescope emulator system

The telescope emulator system comprises the binocular, gyroscope, encoder modular, mobile display, image processing module and computer, which is applied to stargazing, bird-watching teaching, big game player, military shooting, tower-view simulation and outdoor virtual reality, etc. Based on the orientation sensing of gyroscope by two gyroscopes and one encoder module and the message feedback to computer, the system can show the super large image in near-eyes display. Then the super large image will be segmented and distortion-corrected by the image processing module. Furthermore, the images shown on the micro-display module are projected into the eyes of observer by the near-eye system and telescope system. Finally, the image processing result will be shown on the mobile display. This paper presents the design and simulation of the telescope emulator.

A study on a portable fluorescence imaging system

The fluorescent reaction is that an organism or dye, excited by UV light (200-405 nm), emits a specific frequency of light; the light is usually a visible or near infrared light (405-900 nm). During the UV light irradiation, the photosensitive agent will be induced to start the photochemical reaction. In addition, the fluorescence image can be used for fluorescence diagnosis and then photodynamic therapy can be given to dental diseases and skin cancer, which has become a useful tool to provide scientific evidence in many biomedical researches. However, most of the methods on acquiring fluorescence biology traces are still stay in primitive stage, catching by naked eyes and researchers subjective judgment. This article presents a portable camera to obtain the fluorescence image and to make up a deficit from observer competence and subjective judgment. Furthermore, the portable camera offers the 375nm UV-LED exciting light source for user to record fluorescence image and makes the recorded image become persuasive scientific evidence. In addition, when the raising the rate between signal and noise, the signal processing module will not only amplify the fluorescence signal up to 70 %, but also decrease the noise significantly from environmental light on bill and nude mouse testing.