The contribution of this work is a new flat-dispersion fiber operating at telecom wavelengths. The investigation of
chromatic dispersion in PCFs is implemented by the study of modified highly-nonlinear PCF with flattened dispersion.
Required dispersion properties, achieved by balancing material and waveguide dispersion contribution, should be done
for wide spectrum of wavelengths. Flat dispersion could be used for dispersion compensation purposes in systems with
wavelength division multiplex. The main attention is paid to photonic crystal fibers that exhibit unique properties, being
the result of selective doping of rings of holes in the considered structures. It is shown from numerical results that
flattened dispersion of -0.025 ps/nm/km from a wavelength of 1200 nm to 1700 nm is achieved using a highly nonlinear
photonic crystal fiber. The systematic study includes the description of mutual relations between fiber chromatic
dispersion and the structural or material parameters. The results are obtained by using the full-vectorial finite difference
frequency domain method.