• Journal of the Korean Society of Food Science and Nutrition
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• v.34 no.9
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• pp.1330-1335
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• 2005

Red brownish p-pheylenediamine (PPD) has been widely used hair dye for women. The dye was known to cause systemic anaphylaxis, dermatitis and bladder cancer. But the effect of PPD toxicity with oxygen free radical has not been studied. This study investigated the degree of skin injury by PPD. PPD ($2.5\%$ PPD in $2\%\;NH_{4}OH$) was applied to the rat skin ($25 mg/16.5\;cm^2$) 3 or 5 times every other day. Histopathological findings demonstrated the proliferation of epithelial cells and the increased keratinization by PPD. The activities of glucose 6-phosphatase (G6Pase) was decreased and acid phosphatase (ACP) was increased in PPD-applied rat skin. Groups in which PPD was applied 5 times were more damaged than groups applied 3 times. To examine the relationship between tissue damage and oxygen free radicals, effect of PPD on xanthine oxidase (XO) activity was measured and XO activity was more significantly increased in the group treated with PPD 5 times than 3 times. However, reduced glutathione (GSH) content, and the activities of catalase (CAT), super-oxide dismutase (SOD) and glutathione S -transferase (GST) were more decreased in PPD-applied groups than in controls. Even though the activities of XOD was not changed in the group treated with PPD 3 times, the decreased activities of oxygen free radical system and the damaged skin tissue were observed. This result might be caused by the production of toxic PPD metabolites in rat skin. In conclusion, topical PPD application led to skin injury in a dose-dependent manner, probably due to the generation rate of oxygen free radical.

• Korean Journal of Optics and Photonics
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• v.18 no.6
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• pp.383-388
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• 2007

A color filter was demonstrated incorporating a patterned metal grating in a quartz substrate. The filter is created in a metal layer perforated with a symmetric two-dimensional array of circular holes, with the pitch smaller than the wavelength of the visible light. A finite-difference time-domain simulation was performed to analyze the device by investigating the effect of structural parameters like the grating height, the period, the hole size, and the refractive index of the hole-filling material on its performance. The device performance was especially optimized by controlling the refractive index of the material comprising the holes of the grating. And two different devices were fabricated by means of the e-beam direct writing with the following design parameters: the grating height of 50 nm, the two pitches of 340 nm for the red color and 260 nm for the green color. For the prepared device with the period of 340 nm, the center wavelength was 680 nm and the peak transmission 57%. And for the other device with the pitch of 260 nm, the center wavelength was 550 nm and the peak transmission was 50%. The filling of the hole with a material whose refractive index is matched to that of the substrate has led to an increase of ${\sim}15%$ in the transmission efficiency.

• Korean Journal of Optics and Photonics
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• v.25 no.1
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• pp.38-43
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• 2014

An external cavity laser supporting two wavelengths is demonstrated by incorporating polymer waveguide Bragg reflectors and a superluminescent light-emitting diode. An oversized rib waveguide structure and Bragg gratings are designed by using the effective-index and transmission-matrix methods. Bragg gratings with different periods are inscribed on a polymer waveguide through double-exposure laser interferometry. In order to tune the cavity loss affected by the reflectivity of Bragg gratings, a Bragg reflectors with varying length is incorporated. Two-wavelength-mode lasing is achieved for the device consisting of 2-mm long, 537-nm period gratings and 2.2-mm long, 540-nm period gratings; the lasing wavelengths are 1554 nm and 1564 nm, with an output power close to 0 dBm, a 20-dB bandwidth of 0.2 nm, and a side-mode suppression ratio of 45 dB.

• Korean Journal of Optics and Photonics
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• v.32 no.4
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• pp.163-171
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• 2021

Conventional white light-emitting diodes (LEDs) for lighting applications consist of blue LEDs and yellow phosphors, the spectrum of which lacks deep red. To improve the color-rendering characteristics of white LEDs, a red quantum-dot film was applied to the diffuser plate of LED lighting. The mean free paths of the quantum dots and the concentration of the TiO₂ particles in the diffuser plate were adjusted to optimize the optical structure of the lighting. The color-rendering index (CRI) was greater than 90 for most conditions, which demonstrates that adoption of the red quantum-dot film is an effective way for improving the color-rendering properties of conventional white LEDs. The angular dispersion of color coordinates could be removed by utilizing the optical cavity formed between the diffuser plate and the reflector on the bottom of the lighting, where multiple passages of the light through the quantum-dot film reduced the differences in optical path length depending on the viewing angle.

• Korean Journal of Optics and Photonics
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• v.27 no.1
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• pp.1-17
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• 2016

Over the past two decades, fiber-based lasers have made remarkable progress, now having reached power levels exceeding kilowatts and drawing a huge amount of attention from academy and industry as a replacement technology for bulk lasers. In this paper we review the significant factors that have led to the progress of fiber lasers, such as gain-fiber regimes based on ytterbium-doped silica, optical pumping schemes through the combination of laser diodes and double-clad fiber geometries, and tandem schemes for minimizing quantum defects. Furthermore, we discuss various power-limitation issues that are expected to incur with respect to the ultimate power scaling of fiber lasers, such as efficiency degradation, thermal hazard, and system-instability growth in fiber lasers, and various relevant methods to alleviate the aforementioned issues. This discussion includes fiber nonlinear effects, fiber damage, and modal-instability issues, which become more significant as the power level is scaled up. In addition, we also review beam-combining techniques, which are currently receiving a lot of attention as an alternative solution to the power-scaling limitation of high-power fiber lasers. In particular, we focus more on the discussion of the schematics of a spectral beam-combining system and their individual requirements. Finally, we discuss prospects for the future development of fiber laser technologies, for them to leap forward from where they are now, and to continue to advance in terms of their power scalability.