Presentation on theme: "Polarization of EM waves"— Presentation transcript:
1Polarization 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.
2If 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.
3The 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.
4Equation (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:
5From 2nd equation:From above equation we can find:Put these values in equation 3:oror
6ororThis 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
7So equation 4 will be:orororWhich is the equation of a straight line. Thus emergent ray in this case will be plane polarised light.
8Case II:thenSo equation 4 will be:Which is the equation of an ellipse. Thus emergent ray in this case will be elliptically polarised light.
9Case 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.