Presentation on theme: "Polarization of EM waves"— Presentation transcript:
1 Polarization of EM waves The polarization of a uniform plane wave refers to the time-varying behaviour of the electric field vector at fixed point in space.Consider, for example, a uniform plane wave travelling in the z-direction. With the E and H vectors lying in the x-y plane.Case 1:If Ey=0, and only Ex is present:The wave is said to be polarized in the x direction.If Ex=0, and only Ey is present:The wave is said to be polarized in the y direction.
2 If both Ex and Ey are present, and are in phase (=0, 2, 4 If both Ex and Ey are present, and are in phase (=0, 2, 4....) the resultant electric vector has a direction, dependent on the relative magnitude of Ex and Ey.The resultant vector will make the angle tan-1(Ey/Ex).In all the above cases the wave is said to be linearly polarized because the resultant vector is constant with time.Case 2:If both Ex and Ey are not in phase (=(2n+1)/2, n=0, 1, ), i.e. their maximum values (of amplitude) reach at different time, the direction of resultant electric vector will vary.
3 The locus of the end point of the resultant E will be an ellipse and the wave is said to be elliptically polarized.Case: 3When Ex and Ey have equal magnitudes and not in phase i.e.(=(2n+1)/2, n=0, 1, ), the locus of the resultant E will be an circle and the wave is said to be circularly polarized.
4 Equation (1) can be written as: Let the two plane polarized EM waves may superimpose. One has Electric vector, Ex in X direction and other has electric vector, Ey in Y direction, and both are propagating in Z direction.Where a and b are the amplitude of the waves and is the phase difference between them.Equation (1) can be written as:
5 From 2nd equation:From above equation we can find:Put these values in equation 3:oror
6 ororThis equation in general represents an ellipse. Therefore in this case the resultant will be elliptically polarised light. But actual nature of resultant wave can be given by following cases:Case I:n: integerthen
7 So equation 4 will be:orororWhich is the equation of a straight line. Thus emergent ray in this case will be plane polarised light.
8 Case II:thenSo equation 4 will be:Which is the equation of an ellipse. Thus emergent ray in this case will be elliptically polarised light.
9 Case III: with a=bSo equation 4 will be:Which is the equation of a circle of radius a. Thus emergent ray in this case will be circularly polarised light.