Modeling multifilament core fibers by effective index method

Multifilament core fibers (MCFs), a class of optical fibers whose core is made up of a number of strongly-coupled high-index rods surrounded by a low-index homogeneous cladding, can provide single mode operation and large mode area, desirable properties for high-power fiber lasers and amplifiers. We show that due to the low index contrast used in the fiber materials, an effective index method (EIM) can provide highly accurate results in modeling the mode properties of the MCFs such as the mode index and the normalized frequency V as compared with finite element calculation. The normalized frequency V can provide guidance for identifying the single mode regime of the MCFs. Furthermore, results based on the EIM also give good estimates of the mode area within a normalized wavelength range of 0.25–0.5. Thus, the EIM can be a simple yet accurate model for the design of MCFs.