Abstract

The optical Kerr effect in optical fibers has attracted considerable interest recently for high speed optical time division demultiplexing, sampling, and pulse shaping.¹ We have developed a new method to measure a small phase change induced by a low power pump light, by combining the differential interferometric technique² with a Sagnac interferometer. A rotational acceleration is applied on the fiber spool of the Sagnac interferometer to perform differential Sagnac interferometric measurements. This method was employed in the measurements of the nonlinear refractive indices of a polarization maintaining fiber for both polarization states of a 1.053-μm mode-locked Nd:YLF laser pump beam with respect to that of a 1.53-μm-DFB laser diode signal. We were able to measure the light induced phase modulation as low as 10^-2 radians. The cross-phase modulated nonlinear refractive indices measured with the pump beam’s polarization parallel and perpendicular to the signal beam’s polarization were 4.4 x 10^-16 and 1.5 x 10^-16 cm²/W, respectively. The ratio of the former value to the latter one is about 3, which is in a good agreement with theoretical calculation.³ Hence, the self-phase modulated nonlinear refractive index, n₂, of our polarization maintaining fiber turns out to be 2.2 x 10^-16 cm²/W.

© 1993 Optical Society of America