Fabrication of arbitrarily apodized fiber Bragg gratings with narrow bandwidth

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%.

RESEARCH ON COLOR CONSTANCY UNDER OPEN ILLUMINATION CONDITIONS

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).

Wide dynamic range CMOS image sensor with in-pixel double-exposure and synthesis

A wide-dynamic-range CMOS image sensor（CIS） based on synthesis of a long-time and a short-time exposure signal in the floating diffusion（FD） of a five-transistor active pixel is proposed.With optimized pixel operation,the response curve is compressed and a wide dynamic range image is obtained.A prototype wide-dynamic-range CMOS image sensor was developed with a 0.18μm CIS process.With the double exposure time 2.4 ms and 70 ns,the dynamic range of the proposed sensor is 80 dB with 30 frames per second（fps）.The proposed CMOS image sensor meets the demands of applications in security surveillance systems.

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

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.