Under condition that a non-circularity ratio is 5% or lower and a thermal expansion coefficient of a glass which forms the core is .alpha.1 and a thermal expansion of a glass which forms the cladding is .alpha.2, the difference of coefficients is controlled such that a formula -2.5.times.10.sup.-7/.degree. C..ltoreq..alpha.1 -.alpha.2.ltoreq.1.0.times.10.sup.-7/.degree. C. is satisfied so as to maintain a polarization mode dispersion to be 0.03 ps/km.sup.0.5 or lower. The difference of coefficients is further controlled such that a formula -1.5.times.10.sup.-7/.degree. C..ltoreq..alpha.1-.alpha.2.ltoreq.0/.degree. C. is satisfied so as to maintain a polarization mode dispersion to be 0.015 ps/km.sup.0.5 or lower. By doing this, birefringence is reduced by adjusting the thermal expansion coefficient in a core and a cladding; thus providing an optical fiber, and an optical transmission path using the optical fiber, having preferable PMD for high speed transmission.