POLARIZATION NOISE SUPPRESSING OPTICAL FIBER

PROBLEM TO BE SOLVED: To provide a polarization noise suppressing optical fiber which can improve the degree of freedom of selection of a signal frequency when applied to a polarization plane modulation optical communication system. SOLUTION: A core 3 is coated with a clad 4, whose external diameter is varied in stages like R7 , R2 , and R10 to form the polarization noise suppressing optical fiber 8. The clad external diameter mean of the overall length of this optical fiber is about 125μm, the width of variation in the clad external diameter is more than about ±10% of the clad external diameter mean, and the totals ΣL7 , ΣL2 , ΣL10 ... of the lengths of optical fiber positions A7 , A2 , A10 ... having mutually different clad external diameters R7 , R2 , R10 ... are nearly equalized within a previously given permissible range.