Modeling of two core photonic crystal fiber modal interferometer for refractive index measurement by equalization wavelength

•Modified structure of two cores photonic crystal fiber is presented.•Phase constant of modes propagating through particular cores is simulated.•By suitable combinations of core parameters it observes an extreme in phase constant difference.•The wavelength of extreme shifts by the external refractive index.

We propose a modification structure model of in-fiber sensor based on intermodal interference in two core photonic crystal fiber for external refractive index measuring. Essential characteristics and influences of the structure are investigated. Formation of an extreme (equalization wavelength) in phase constant spectral dependence is presented and its using for simple external refractive index determination.