Briefly describe the two types of polarization in a waveguid

Briefly describe the two types of polarization in a waveguide.

Solution

Polarization (also polarisation) is a parameter applying to waves that specifies the geometrical orientation of the oscillation.Electromagnetic waves such as light exhibit multiple polarizations, as do many other types of waves such as gravitational waves[1] and sound waves in solids. On the other hand,sound waves in a gas or liquid only oscillate in the wave\'s direction of propagation, and the oscillation of ocean waves is always in the vertical direction. In these cases one doesn\'t normally speak of \"polarization\" since the oscillation\'s direction is not in question.

In an electromagnetic wave, both the electric field and magnetic field are oscillating but in different directions; by convention the \"polarization\" of light refers to the polarization of the electric field. Light which can be approximated as a plane wave in free space or in an isotropic medium propagates as atransverse wave—both the electric and magnetic fields are perpendicular to the wave\'s direction of travel. The oscillation of these fields may be in a single direction (linear polarization), or the field may rotate at the optical frequency (circular or elliptical polarization). In that case the direction of the fields\' rotation, and thus the specified polarization, may be either clockwise or counter clockwise; this is referred to as the wave\'s chirality or handedness.

Wave propagation and polarizationEdit

Most sources of light are classified as incoherent and unpolarized (or only \"partially polarized\") because they consist of a random mixture of waves having different spatial characteristics, frequencies (wavelengths), phases, and polarization states. However, for understanding electromagnetic waves and polarization in particular, it is easiest to just consider coherent plane waves; these are sinusoidal waves of one particular direction (or wavevector), frequency, phase, and polarization state. Characterizing an optical system in relation to a plane wave with those given parameters can then be used to predict its response to a more general case, since a wave with any specified spatial structure can be decomposed into a combination of plane waves (its so-called angular spectrum). And incoherent states can be modeledstochastically as a weighted combination of such uncorrelated waves with somedistribution of frequencies (its spectrum), phases, and polarizations.

Transverse electromagnetic wavesEdit

A \"vertically polarized\" electromagnetic wave of wavelength has its electric field vector E (red) oscillating in the vertical direction. The magnetic field B(or H) is always at right angles to it (blue), and both are perpendicular to the direction of propagation (z).

Electromagnetic waves (such as light), traveling in free space or anotherhomogeneous isotropic non-attenuatingmedium, are properly described as transverse waves, meaning that a plane wave\'s electric field vector E and magnetic field H are in directions perpendicular to (or \"transverse\" to) the direction of wave propagation; E and H are also perpendicular to each other. Considering a monochromatic plane wave of optical frequency f (light of vacuum wavelength has a frequency of f = c/ where c is the speed of light), let us take the direction of propagation as the z axis. Being a transverse wave the Eand H fields must then contain components only in the x and y directions whereasEz=Hz=0.

Non-transverse polarizationEdit

In addition to transverse waves, there are many wave motions where the oscillation is not limited to directions perpendicular to the direction of propagation. These cases are beyond the scope of the current article which concentrates on transverse waves (such as most electromagnetic waves in bulk media), however one should be aware of cases where the polarization of a coherent wave cannot be described simply using a Jones vector, as we have just done.

Just considering electromagnetic waves, we note that the preceding discussion strictly applies to plane waves in a homogeneous isotropic non-attenuating medium, whereas in an anisotropic medium (such as birefringent crystals as discussed below) the electric or magnetic field may have longitudinal as well as transverse components. In those cases theelectric displacement D and magnetic flux density B[clarification needed] still obey the above geometry but due to anisotropy in the electric susceptibility (or in the magnetic permeability), now given by a tensor, the direction of E (or H) may differ from that of D(or B). Even in isotropic media, so-calledinhomogeneous waves can be launched into a medium whose refractive index has a significant imaginary part (or \"extinction coefficient\") such as metals;[clarification needed]these fields are also not strictly transverse.[