New approach to the measurement of the nonlinear refractive index of short (<25 m) lengths of silica and erbium-doped fibers

The nonlinear refractive index n 2 of silica fiber (24 m) and erbium-doped fiber (10 m) is measured to within an accuracy of 5% by use of time-delayed photorefractive beam coupling of intense 53-ps, 1.064-μm pulses that experience self-phase modulation in the fibers. The resultant induced grating autocorrelation response yields a value of n 2 /A eff and a calibration standard for the fiber. A phase shift of the order of 0.19π can be detected and is limited only by laser amplitude fluctuations. A unique advantage of this technique is its ability to measure n 2 accurately in short lengths (z≤25 m) of fiber, whereas other approaches typically use much longer lengths of fiber (z≥100 m) .