2.1 The Nature of Light
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phase. Generally, one draws wave fronts passing through either the maxima or the
minima of the wave, such as the peak or trough of a sine wave, for example. Thus
the wave fronts (also called phase fronts) are separated by one wavelength.
When the wavelength of the light is much smaller than the object (or opening)
that it encounters, the wave fronts appear as straight lines to this object or opening.
In this case, the light wave can be represented as a plane wave, and its direction of
travel can be indicated by a light ray, which is drawn perpendicular to the phase
front, as shown in Fig. 2.1. The light-ray concept allows large-scale optical effects
such as reflection and refraction to be analyzed by the simple geometrical process
of ray tracing. This view of optics is referred to as ray or geometrical optics. The
concept of light rays is very useful because the rays show the direction of energy
flow in the light beam.
2.1.1 Polarization
Light emitted by the sun or by an incandescent lamp is created by electromagnetic
waves that vibrate in a variety of directions. This type of light is called unpolarized light. Lightwaves in which the vibrations occur in a single plane are known as
polarized light. The process of transforming unpolarized light into polarized light is
known as polarization. The polarization characteristics of lightwaves are important
when examining the behavior of components such as optical isolators and filters.
Polarization-sensitive devices include light signal modulators, polarization filters,
Faraday rotators, beam splitters, and beam displacers. Birefringent crystals such
as calcite, lithium niobate, rutile, and yttrium vanadate are polarization-sensitive
materials used in such components.
Light is composed of one or more transverse electromagnetic waves that have
both an electric field (called E field) and a magnetic field (called H field) component
[2]. 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
of the wave, as Fig. 2.2 shows. The waves are moving in the direction indicated by
the wave vector k. The magnitude of the wave vector k is k = 2π/λ, which is known
as the wave propagation constant with λ being 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 a plane wave; that is, the vibrations
in the electric field are parallel to each other at all points in the wave. Thus, the
electric field forms a plane called the plane of vibration. Likewise all points in the
magnetic field component of the wave lie in another plane of vibration. Furthermore,
E and H are mutually perpendicular, so that E, H, and k form 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) and is referred to as unpolarized
light. However any arbitrary direction of vibration of a specific transverse wave can
be represented as a combination of two orthogonal plane polarization components.
33
phase. Generally, one draws wave fronts passing through either the maxima or the
minima of the wave, such as the peak or trough of a sine wave, for example. Thus
the wave fronts (also called phase fronts) are separated by one wavelength.
When the wavelength of the light is much smaller than the object (or opening)
that it encounters, the wave fronts appear as straight lines to this object or opening.
In this case, the light wave can be represented as a plane wave, and its direction of
travel can be indicated by a light ray, which is drawn perpendicular to the phase
front, as shown in Fig. 2.1. The light-ray concept allows large-scale optical effects
such as reflection and refraction to be analyzed by the simple geometrical process
of ray tracing. This view of optics is referred to as ray or geometrical optics. The
concept of light rays is very useful because the rays show the direction of energy
flow in the light beam.
2.1.1 Polarization
Light emitted by the sun or by an incandescent lamp is created by electromagnetic
waves that vibrate in a variety of directions. This type of light is called unpolarized light. Lightwaves in which the vibrations occur in a single plane are known as
polarized light. The process of transforming unpolarized light into polarized light is
known as polarization. The polarization characteristics of lightwaves are important
when examining the behavior of components such as optical isolators and filters.
Polarization-sensitive devices include light signal modulators, polarization filters,
Faraday rotators, beam splitters, and beam displacers. Birefringent crystals such
as calcite, lithium niobate, rutile, and yttrium vanadate are polarization-sensitive
materials used in such components.
Light is composed of one or more transverse electromagnetic waves that have
both an electric field (called E field) and a magnetic field (called H field) component
[2]. 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
of the wave, as Fig. 2.2 shows. The waves are moving in the direction indicated by
the wave vector k. The magnitude of the wave vector k is k = 2π/λ, which is known
as the wave propagation constant with λ being 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 a plane wave; that is, the vibrations
in the electric field are parallel to each other at all points in the wave. Thus, the
electric field forms a plane called the plane of vibration. Likewise all points in the
magnetic field component of the wave lie in another plane of vibration. Furthermore,
E and H are mutually perpendicular, so that E, H, and k form 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) and is referred to as unpolarized
light. However any arbitrary direction of vibration of a specific transverse wave can
be represented as a combination of two orthogonal plane polarization components.