Differential derivative method for highly accurate calculation of fiber refractive index curves.

• A differential derivation method is demonstrated to accurately calculate the refractive index curves by enhancing the mode tracking ability. • For either the incomplete or the complete coupling situations, the mode evolution can be tracked with high accuracy. • The characteristics of dispersion, birefringence, and attenuation for each mode are closely related to the refractive index curves. An accurate calculation of the fiber's refractive index will benefit the development of fiber communication and fiber sensors. The refractive index of an optical fiber is an important parameter, which is closely related to the characteristics of dispersion, birefringence, and attenuation. It is vital to accurately calculate the refractive index in designing special optical fibers. However, the refractive index curves for different transmission modes of an optical fiber may be crossed or closed at some specific wavelengths, where the calculator may easily be tricked. A differential derivation method (DDM) is demonstrated to accurately calculate the refractive index curves by enhancing the mode tracking ability. The effectiveness is verified in the calculations of the refractive index curves for the HE 11 , HE 12 , TE 01 , and EH 11 modes of a custom-designed fiber. [ABSTRACT FROM AUTHOR]