Page 50 - Optical Communications Essentials

The Behavior of Light

40 Chapter Three

Using n 1 1.48 for glass and n 2 1.00 for air, we get φ c 42°. This means that any
light in the glass incident on the interface at an angle φ 1 greater than 42° is totally
reflected back into the glass.

3.6. Polarization
Light is composed of one or more transverse electromagnetic waves that have
both an electric field (called an E field) and a magnetic field (called an H field)
component. As shown in Fig. 3.4, in a transverse wave the directions of the
vibrating electric and magnetic fields are perpendicular to each other and are at
right angles to the direction of propagation (denoted by the vector k) of the
wave. The wave shown in Fig. 3.4 is plane-polarized. This means that the vibra-
tions in the electric field are parallel to one another at all points in the wave, so
that the electric field forms a plane called the plane of vibration. Likewise all
points in the magnetic field component of the wave lie in a plane that is at right
angles to the electric field plane.

3.6.1. Unpolarized light
An ordinary light wave is made up of many transverse waves that vibrate in a
variety of directions (i.e., in more than one plane) and is referred to as unpo-
larized light. However, any arbitrary direction of vibration can be represented
as a combination of a parallel vibration and a perpendicular vibration, as shown
in Fig. 3.5. Therefore, unpolarized light can be viewed as consisting of two
orthogonal plane polarization components, one that lies in the plane of inci-
dence (the plane containing the incident and reflected rays) and the other that
lies in a plane perpendicular to the plane of incidence. These are denoted as
the parallel polarization and the perpendicular polarization components,

Figure 3.4. Electric and magnetic field distribu-
tions in a train of plane electromagnetic waves at
a given instant in time.

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