Biophotonics_Concepts_to_Applications

These types of components typically incorporate polarization-sensitive birefringent
crystalline materials such as calcite, lithium niobate, rutile, and yttrium vanadate.
Light consists oftransverse electromagnetic wavesthat have both electricfield
(Efield) and magneticfield (Hfield) components. The directions of the vibrating
electric and magneticfields in a transverse wave are perpendicular to each other and
are orthogonal (at right angles) to the direction of propagation of the wave, as
Fig.2.4shows. The waves are moving in the direction indicated by thewave vector
k. The magnitude of the wave vectorkis k = 2π/λ, which is known as thewave
propagation constantwithλbeing the wavelength of the light. Based on Maxwell’s
equations, it can be shown that E and H are both perpendicular to the direction of
propagation. This condition defines aplane wave; that is, the vibrations in the
electricfield are parallel to each other at all points in the wave. Thus, the electric
field forms a plane called theplane of vibration. An identical situation holds for the
magneticfield component, so that all vibrations in the magneticfield wave lie in
another plane. Furthermore,EandHare mutually perpendicular, so thatE,H, and
kform a set of orthogonal vectors.
An ordinary lightwave is made up of many transverse waves that vibrate in a
variety of directions (i.e., in more than one plane), which is calledunpolarized light.
However any arbitrary direction of vibration of a specific transverse wave can be
represented as a combination of two orthogonal plane polarization components. As
described in Sect.2.4and in Chap. 3 , this concept is important when examining the
reflection and refraction of lightwaves at the interface of two different media, and
when examining the propagation of light along an opticalfiber. In the case when all
the electricfield planes of the different transverse waves are aligned parallel to each
other, then the lightwave islinearly polarized. This describes the simplest type of
polarization.

z

Magnetic

field

Electric field

Direction

of wave

propagation

Wave

vector

y

x

H

H

E

E

k

k

Fig. 2.4 Electric and
magneticfield distributions in
a train of plane
electromagnetic waves at a
given instant in time

30 2 Basic Principles of Light