effect in a fiber span the pmd emulator of the present invention comprises at least two sections of polarization maintaining fiber each having a predetermined pmd value mechanical twisting means which twist one of neighboring ones among the pm fiber sections a single mode fiber spliced in between neighboring pm fiber sections wherein the single mode fiber has a small pmd value negligible compared to any of the pm fiber sections according to the present invention pmd effect can easily be replicated in the field of experiments studying pmd effect of a real fiber span application_number US 48815904 A description accordingly it is an object of the present invention to provide a pmd emulator including components that have comparatively small control parameters and can generate the desired pmd value precisely it is an object of the present invention to provide a pmd emulator having a small optical loss it is an object of the present invention to provide a pmd emulator that is easy to control and generates a specific pmd value easily it is another object of the present invention to provide a pmd emulator having distribution similar to the maxwellian distribution that is a distribution on the pmd of the real optical fiber transmission system to accomplish the above objects there is provided polarization mode dispersion pmd emulator the pmd emulator includes at least two polarization maintaining pm fiber sections each having a predetermined pmd value mechanical rotating means for rotating one of two neighboring pm fiber sections among the pm fiber sections relative to the other one.