An optical fiber is kept along the z direction. The refractive indices for the electric fields along x and y directions in the fiber are n_x=1.5000 and n_y=1.5001 respectively (n_x≠n_y due to the imperfection in the fiber cross-section). The free space wavelength of a light wave propagating in the fiber is 1.5μm If the lightwave is circularly polarized at the input of the fiber, the minimum propagation distance after which it becomes linearly polarized. in centimetres, is