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RESEARCH ON COLOR CONSTANCY UNDER OPEN ILLUMINATION CONDITIONS

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Journal of Electronics(China) 2009年第5期26卷 681-686页

作者： Xu Xiaozhao Zhuo Li Zhang Jing Shen Lansun Signal ＆ Information Processing Lab Beijing University of Technology Beijing 100124 China

Color information plays a key role in the research fields of object recognition and image retrieval. However, the actual color varies by the conditions of illumination, especially the open natural daylight. Four different color constancy schemes are proposed in the paper to minimize the effects of open illumination conditions. (1) The color constancy scheme based on the image statistics is proposed, which includes the color cast detection and removal. (2) The color constancy scheme based on the color temperature curve is proposed, which combines Gaussian model with linear fitting to estimate color temperature curve. (3) The color constancy scheme based on the double exposure theory is proposed, which is able to reproduce a color image under typical illumination. (4) According to the concepts of supervised learning, the supervised color constancy scheme is proposed. The transformation of color values from unknown illumination to typical illumination is solved by improved Support Vector Regression (SVR).

关键词： Image statistics Color temperature curve double exposure Supervised color constancy

Fabrication of arbitrarily apodized fiber Bragg gratings with narrow bandwidth

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Journal of Southeast University(English Edition) 2009年第1期25卷 23-25页

作者：吕昌贵恽斌峰崔一平东南大学先进光子学中心南京210096

A double-exposure fabrication method without any intensity shadow mask to fabricate arbitrarily apodized fiber Bragg gratings（ FBGs） with narrow bandwidth is demonstrated by controlling the total ultra violet （UV） irradiation along the grating by varying the speed of a translation stage. The UV source used is a stable continuous intracavity frequency-doubled argonion laser. The parameters （such as length, apodization profile, average index change）of FBGs can be easily changed with this method. The total UV irradiation is kept constant in the doubleexposure process because of the precise control of the exposure time, which ensures that the apodized FBG＇s bandwidth can be extremely narrow. The full width at half maximum （FWHM） bandwidth of the 2-cm-long apodized FBG fabricated by this method is 0. 15 nm with a maximum reflectivity of more than 95%.

关键词： fiber Bragg grating apodization double exposure

Dispersion Compensation of 180-km 10-Gb/s Transmission System Using Chirped Fiber Grating

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Tsinghua Science and Technology 2002年第3期7卷 305-308页

作者：孙成城曹京李春赟 Department of Electronic Engineering Tsinghua University Beijing 100084 China

Many methods have been suggested to reduce dispersion in optical fiber communication. Among these methods, chirped fiber grating (CFG) is a promising scheme. This paper describes a linearly chirped fiber grating with 95% reflectivity and 0.3 nm bandwidth written using a double exposure method with a uniform phase mask. The CFG resonant wavelength is 1554.5 nm and dispersion is 1700 ps/nm. Dispersion compensation in a 10-Gb/s optical transmission system has been demonstrated using this chirped fiber grating. The power penalty induced by the dispersion compensation after 180-km transmission is 1 dB. This is the first report describing dispersion compensation of 180 km at 10-Gb/s optical transmission now-return to zero (NRZ) system in China.

关键词： chirped fiber grating dispersion compensation double exposure