We introduce a new prototype instrument for measuring the 2D spatially resolved distribution of spectral reflectance based on new spectral imaging technique. The instrument captures digital spectral images of a test sample using a pulsed LED-based monochromatic source and a scientific grade CCD array and special data acquisition algorithm is used to extract the useful image data corresponding to the target application. In earlier version of this instrument, we used a commercial CCD camera with 8-bit ADC without any cooling stages which has many drawbacks. In this work, we have modified our setup by introducing a new scientific grade CCD; deep-cooled interline transfer sensor with 16-bit ADC and electronic shutter. With this new instrument we could achieve a higher accuracy, higher spatially resolved measurements, higher dynamic range, mush better sensitivity and lower uncertainty and we could avoid many sources of errors in the old setup. With one wavelength scan, one can get the full reflectance data of the sample under test which saves a lot of time in comparison with conventional methods. This new instrument is promising with a potential of applications in the field of optical material testing.
We constructed a standard measurement setup for polarization mode dispersion (PMD) based on Jones matrix eigen-analysis method. We measured a differential group delay of a 1 m-long polarization maintaining fiber (PMF) and evaluated the measurement uncertainty to be less than 0.6 %. As a transfer standard for PMD, we fabricated mode-coupled PMD artifacts by concatenating the 50 PMF sections with random birefringent axis orientation. Using the standard setup, we certificated the PMD values of the three PMD artifacts to be 0.0884 ps, 0.977 ps, 1.541 ps with the standard uncertainty of 0.4 fs, 16 fs, 23 fs, respectively.
This work presents an alternative approach for preparing photometric standard LEDs, which is based on a novel functional seasoning method. The main idea of our seasoning method is simultaneously monitoring the light output and the junction voltage to obtain quantitative information on the temperature dependence and the aging effect of the LED emission. We suggested a general model describing the seasoning process by taking junction temperature variation and aging effect into account and implemented a fully automated seasoning facility, which is capable of seasoning 12 LEDs at the same time. By independent measurements of the temperature dependence, we confirmed the discrepancy of the theoretical model to be less than 0.5 % and evaluate the uncertainty contribution of the functional seasoning to be less than 0.5 % for all the seasoned samples. To demonstrate assigning the reference value to a standard LED, the CIE averaged LED intensity (ALI) of the seasoned LEDs was measured with a spectroradiometer-based instrument and the measurement uncertainty was analyzed. The expanded uncertainty of the standard LED prepared by the new approach amounts to be 4 % ~ 5 % (k=2) depending on color without correction of spectral stray light in the spectroradiometer.
Providing marine signal lanterns, Fresnel lens has been adopted to transfer the beam from the lanterns up to 10 nautical miles (18.53 km). The Fresnel lens with diameters of 250 mm was designed by a ray tracing program and optimized by adjusting the groove parameters of the lens. Each optical sag element which is a part of a lens was independently designed by using the analytical method. The angular luminous intensity distributions (ALID) of this lens were calculated by the illumination analysis program considering the ALID of a light bulb. The ALID of a C-8 type bulb (24 W) was measured with a goniophotometer and its luminous flux was measured by an integrating sphere to be 397 lm. At the best alignment of the bulb, the maximum luminous intensity of the lantern was more than 1000 cd for the 250 mm lens. The ALID was investigated as a function of distance from the lens focus to determine the tolerance margin of the alignment. Horizontal deviations of the light bulb from the focus along the optical axis widened the angular FWHM of the vertical ALID. However, vertical deviations caused shifts of the vertical ALID without spreading the angular FWHM. The designed 250 mm aspherical lens of marine signal lantern was made by the injection molding with single peace acryl. We measured the luminous intensity distribution of acryl lens and found that the MLI of the lens was 827 cd. And the full width at half maximum of the diverging angle of the diverging beam was 3.5 deg. Although the measured MLI was 83% of the calculated result, it would be increased with surface polishing of prototype molding pattern.
The analysis of the polychromatic modulation transfer function (PMTF) for evaluating the image quality of the color LCD monitor is presented. The PMTF is easily calculated from the values of the MTF weighted by the overall spectral response of the system. To obtain the spectral response of the monitor, the chromaticity (x, y) and luminance are measured with a spectroradiometer. The variations of the luminance, chromaticity (x, y), and MTF of the color CRT and LCD monitors for different viewing angles are measured. We designed a synthetic equipment that could obtain the chromaticity (x, y), luminance, and MTF of the color monitor simultaneously. The experimental results of several color monitors made in Korea are presented.