## Abstract

A method for measuring the effective refractive-index differences in a few-mode fiber by applying axial fiber stretching is described. This method represents a straightforward technique for characterization of few-mode fibers. Interference between LP_{01} and LP_{11} and in some cases also between LP_{11} and LP_{21} are observed in a fiber designed for support of LP_{01} and LP_{11}. The relative strength of the coupled modes depends on specific splicing characteristics, and in some cases only two modes are seen. The results agree well with theoretical predictions for the fiber under investigation.

© 2012 OSA

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### Equations (4)

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(1)
$$\Delta \beta (L)\cdot L\approx \Delta \beta ({L}_{0})\cdot {L}_{0}+\left[\frac{d\Delta \beta (L)}{dL}{|}_{{L}_{0}}\xb7L+\Delta \beta ({L}_{0})\right]\Delta L\text{\hspace{0.17em}}.$$
(2)
$$\Delta \beta (L)\cdot L\approx \Delta \beta ({L}_{0})\cdot {L}_{0}+\Delta \beta ({L}_{0})\cdot \Delta L\text{\hspace{0.17em}}.$$
(3)
$${L}_{B}=\frac{2\pi}{\Delta \beta ({L}_{0})}=\frac{{\lambda}_{0}}{\Delta {n}_{eff}}\text{\hspace{0.17em}}.$$
(4)
$$\Lambda =\frac{{\lambda}_{0}^{2}}{L(\text{\Delta}{n}_{eff}-{\text{\lambda}}_{0}\frac{\text{d\Delta}{n}_{eff}}{d\lambda})}=\frac{{\lambda}_{0}^{2}}{c\Delta {\tau}_{g}}\text{\hspace{0.17em}},$$