A new method of measuring optical nonlinearity for resonant nonlinear optical fibers is proposed. A long-period fiber grating (LPG) pair was used to measure the nonlinear refractive index n<sub>2</sub> of a Yb<sup>3+</sup>/Al <sup>3+</sup> codoped optical fiber, which was spliced between the two LPGs, as the fiber was pumped with a laser diode. The nonlinear refractive index of the Yb<sup>3+</sup>/Al <sup>3+</sup> codoped fiber near 1580 nm depended on the pump power. As the pump power increased, the nonlinear refractive index decreased. At launched pump powers of 2–8 mW, the nonlinear refractive index of the Yb<sup>3+</sup>/Al <sup>3+</sup> codoped fiber near 1580 nm was ~7.5×10<sup>-15</sup>m <sup>2</sup>/W .
© 2002 Optical Society of America
(060.2300) Fiber optics and optical communications : Fiber measurements
(160.5690) Materials : Rare-earth-doped materials
(190.4370) Nonlinear optics : Nonlinear optics, fibers
(350.2770) Other areas of optics : Gratings
Y. H. Kim, B. H. Lee, Y. Chung, U. C. Paek, and W.-T. Han, "Resonant optical nonlinearity measurement of Yb3+ / Al3+ codoped optical fibers by use of a long-period fiber grating pair," Opt. Lett. 27, 580-582 (2002)