By logically superimposing three base one dimensional (1D) photonic crystals, the broadband slow light with low dispersion is obtained. The slow light pass band is smoothed by adjusting the period ratio of three base structures, period number of new photonic crystal (PC) and the filling factor. In the optimized structure, the minimum of transmission (T) arrives at 0.5902, the full width half maximum (FWHM) is 55nm, the group velocity is in the range from 0.08326c to 0.2912c, and the group velocity dispersion (GVD) parameter D maximum is 14.65 ps2/nm·mm. Moreover, by material optimization, adjusting the refractive index of na and nb, the slow light properties can be improved further. With suitable materials, the T minimum increases to 0.6485, the group velocity decreases to the range from 0.08014c to 0.2592c, and GVD parameter D maximum decreases to 13.98 ps2/nm·mm with FWHM 52nm.
This paper presents a new visible watermarking solution for CMOS image sensor which can enhance secure
features of captured images. Visible watermarks are embedded in the Bayer format image data and can be transferred by
the subsequent interpolation process. A piecewise function is setup based on the gray scale resolution characteristics of
human eyes. Watermark stretch factor can be adaptively chosen according to the gray value of the current pixel. The
advantage of this algorithm is that the watermark has the same visibility in different image brightness region. A number
of color images have been used to test the method. In order to check the robustness of watermarked images, we
conducted adding noise and filtering experiments, results show that the visibility of watermark is also good after the
experiments. The approach allows a digital watermark to be embedded in an image immediately upon its capture, before
leaving the imaging chip.