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An optimized design of a dual-core photonic crystal fiber coupler

An optical fiber coupler is a very important component in realizing all-fiber communication system. The appearance of dual-core photonic crystal fibers (PCFs) has enabled a new method of designing fiber coupler. Directional coupler based on the dual-core PCFs was investigated and shows intriguing properties, e.g., broadband coupling, the shorter coupling length, and polarized-mode coupling. However, the coupling bandwidth is the one of the most key properties due to the wavelength dependent of coupling efficiency for optical fiber coupler. In order to obtain the wavelength flattened response coupler with insensitive to deformation of air holes, in this paper an asymmetry dual-core PCF coupler with depressed-doped core is proposed and its coupling characteristics are also investigated by full-vector beam propagation method (BPM) in detail. The result of simulation shows that the coupling coefficient of 50%± 0.5% over a wide wavelength from 1.3μm to 1.7μm. Its coupling length is about 394μm, which is much shorter than that of other dual-core PCF couplers reported in literature. The fluctuation of coupling ratio is smaller than 5% with variation of the coupling length of 10%. We also demonstrate it could be more robust caused from the shorter coupling length. Furthermore, the mode field of the coupler is Gaussian-shape which means that additional insertion loss will not be introduced.