Tellurite glass defect-core spiral photonic crystal fiber with low loss and large negative flattened dispersion over S + C + L + U wavelength bands.

A defected-core spiral photonic crystal fiber is proposed to achieve very large negative flattened dispersion and small confinement loss. Simulation results reveal that the designed structure exhibits very large flattened dispersion over S+C+L+U wavelength bands and an average dispersion of about -720.7  ps nm(-1) km(-1) with an absolute dispersion variation of 12.7  ps nm(-1)  km(-1) over the wavelength ranging from 1.45 to 1.65 μm. The proposed fiber has five air-hole rings in the cladding leading to very small confinement loss of 0.00111  dB/km at the excitation wavelength of 1.55 μm. The tolerance of the fiber dispersion of ±2% changing in the structural parameters is investigated for practical conditions.