Ultralow-birefringence measurement in optical fibers by the twist method

We describe a simple method for measuring ultralow birefringence in optical fibers. It allows one to measure birefringence in the range of 4 x 10(-6)-1.25 x 10(-8), which corresponds to the 0.25-80-m range of the polarization beat length at the wavelength of 1 mu m. A fiber section of a length shorter than the polarization beat length can be used for measurement. The measuring procedure involves measurement of the light intensity only and does not require an analysis of the light-polarization state. Experimental results for an optical fiber with a beat length of 1.9 m are presented. (C) 1997 Optical Society of America.