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In this paper the guiding properties of photonic crystal fibers with a square lattice of air-holes in a silica matrix have been studied for the first time. The dispersion curves of fibers with different hole-to-hole spacing and air-hole diameter have been accurately calculated. Negative values of the dispersion parameter and the dispersion slope have been obtained with a hole-to-hole spacing of 1 microm. A comparison between fibers with square and triangular lattice has been also performed, taking into account the dispersion properties and the effective area in the wavelength range between 1200 nm and 1600 nm.

The modal cutoff of square-lattice photonic crystal fibers with a finite number of air-hole rings has been accurately investigated to our knowledge for the first time. By analyzing the leaky behavior of the second-order mode, we have obtained a phase diagram that describes the regions of single-mode and multimode operation as well as the endlessly single-mode regime. Furthermore, starting from these results, we have obtained the cutoff normalized frequency according to two different formulations of the V parameter previously adopted for fibers with a triangular lattice. A final comparison of the cutoff properties of fibers characterized by a square lattice and a triangular lattice has been carried out.

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