A proposal for the new modified W type optical fiber structure with ultra high effective area and small dispersion as well as dispersion slope is presented. For the proposed structure, all these features are achieved due to placing extra depressed cladding layers, which is the key to achieve higher effective area and flat dispersion curve compared with the conventional W structures. Meanwhile, the suggested design method is based on the Genetic Algorithm optimization technique to choose optimal value for the structural parameters. Also, our calculation for extracting optical properties of the proposed structure is evaluated analytically. The designed dispersion flattened single mode fiber has dispersion and its slope respectively within [0.1741-0.9282] ps/km/nm and [(-0.011)-(0.0035)] ps/km/nm2 in the spectral range of [1.46-1.625] μm (S+C+L bands) which are noticeably smaller than the reported value for ultra-low dispersion slope fibers . The designed fiber has ultrahigh effective area from 103.56 to 232.26 μm2 in the above wavelength interval. Meanwhile, we show that there is a breakthrough in the quality factor of the ultra-low, ultra-flattened chromatic dispersion single mode optical fiber.
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