thanks Suresh for your reply ,you directly copied from A field Guide by Collete. From reading statement i have already arise the questions.. what about the initial phases of electric field and magnetic field they are still uncertain..instead we measure the polarization parameters??? 

The reason is that polarization is a random phenomenon in terms of time. 

Elliptical polarization means that electrical (and magnetic) vectror rotates with changing of length so that its end describes an ellipse. The period of rotation is the period of wave (reverse to the frequency). Initial phase is not importatnt and you hardly can determine the initial phase in case of lightwave. All else depends on what you want to measure.