PYL560

Applied Optics
Course Coordinator
Anurag Sharma

Optics and Photonics Centre

and Physics Department
IIT Delhi
 Optics
is the science of light

Photonics
is the applied science and
technology based on light
 Light
• From the Sun is the source of all energy
on earth (except nuclear energy).
• It sustains all life forms on earth through
photosynthesis.
 Light
• From the Sun is the source of all energy
on earth (except nuclear energy).
• It sustains all life forms on earth through
photosynthesis.
• Most important sensory organ is the eye
which is sensitive to light and enables us
see around.
• Eye is the primary optical “instrument”
provided to us by the nature.
 Optical Instruments
• The first optical instrument, the spectacles,
appeared only in the 13th C.
• It took two centuries to realize that two
spectacle lenses, one behind the other
would give a large magnification.
• This realization led to the development of
microscopes and telescopes in which
Galileo played an important role.
• Little later, Newton split the white light into
colors through a prism.
 Optical Instruments
• Have played an enabling, but crucial role in
the development of science and technology.
 Optical Instruments
• Have played an enabling, but crucial role in
the development of science and technology.
• Can you think of astronomy and
astrophysics without a telescope?
 Optical Instruments
• Have played an enabling, but crucial role in
the development of science and technology.
• Can you think of astronomy and
astrophysics without a telescope?
• Where would be biology and medicine
without a microscope?
 Optical Instruments
• Have played an enabling, but crucial role in
the development of science and technology.
• Can you think of astronomy and
astrophysics without a telescope?
• Where would be biology and medicine
without a microscope?
• Without spectroscopy, the atomic and
molecular properties could not be known
and chemistry and material science would
not have reached where it is today.
 Optical Instruments
• In modern times, the connectivity for social
and educational platforms is provided by
fiber optics.
 Optical Instruments
• In modern times, the connectivity for social
and educational platforms is provided by
fiber optics.
• Solar cells are provided energy solutions.
• LEDs, cheap and versatile, are providing
energy efficient solutions to lighting.
 Optical Instruments
• In modern times, the connectivity for social
and educational platforms is provided by
fiber optics.
• Solar cells are provided energy solutions.
• LEDs, cheap and versatile, are providing
energy efficient solutions to lighting.
• Lasers are wonder sources and are being
increasingly employed in defence,
manufacturing, medicine, etc.
 Optics and Photonics
are providing innovative solutions
to a variety of problems
in diverse area.
 Optics and Photonics
are providing innovative solutions
to a variety of problems
in diverse area.

It is widely expected that this

century will have photonics play a
similar role as played by electronics
in the last century.
 Light
• Light has fascinated mankind ever since
man could observe.
• The mechanism of “seeing” has been
under study since the time of early
philosophers.
• In the last 4 centuries, major strides
have been made in the understanding
of light and in its uses.
 Light
• It was only half a decade back that the
world acknowledged the due
importance of light.
 Light
• It was only half a decade back that the
world acknowledged the due
importance of light.
• UNESCO declared 2015
as the Year of Light and
Light Based Technologies
 Light
• It was only half a decade back that the
world acknowledged the due
importance of light.
• UNESCO declared 2015
as the Year of Light and
Light Based Technologies
• To perpetuate this, May 16
is now declared as the
International Day of Light
 Breakthroughs In Optics
How do we see? BC
 Breakthroughs In Optics
How do we see? BC
Light propagate? Newton 17th
Light has colors Newton 17th
 Breakthroughs In Optics
How do we see? BC
Light propagate? Newton 17th
Light has colors Newton 17th
Light is a wave Huygens 17th
Young 18th
 Breakthroughs In Optics
How do we see? BC
Light propagate? Newton 17th
Light has colors Newton 17th
Light is a wave Huygens 17th
Young 18th
Light is an EM Wave Maxwell 19th
Hertz 19th
 Breakthroughs In Optics
How do we see? BC
Light propagate? Newton 17th
Light has colors Newton 17th
Light is a wave Huygens 17th
Young 18th
Light is an EM Wave Maxwell 19th
Hertz 19th
Light Quantum Planck 19th
Einstein 20th
 Breakthroughs In Optics
How do we see? BC
Light propagate? Newton 17th
Light has colors Newton 17th
Light is a wave Huygens 17th
Young 18th
Light is an EM Wave Maxwell 19th
Hertz 19th
Light Quantum Planck 19th
Einstein 20th
Maser/Laser Einstein 20th
Townes 20th
Maiman 20th
 Nobel Prizes
In Optics Related Areas
 19 in Physics (33 Scientists)
 1 in Chemistry (3 Scientists)
 1 in Medicine (1 Scientist)
 In 2014, both in Physics and in
Chemistry, the Prizes went to
Optics related subjects.
Approximations in
Theory of Optics
 Theories of Optics
• Paraxial Optics
• Geometrical Optics
• Wave Optics
• Electromagnetic Theory of Optics
• Quantum Optics
 Theories of Optics
• Paraxial Optics
• Geometrical Optics
• Wave Optics
• Electromagnetic Theory of Optics
• Quantum Optics
 Theories of Optics
• Geometrical Optics
The main law is Snell’s Law:

The main principle is

Fermat’s principle

Based on concepts of
rays and wavefronts
 Theories of Optics
• Paraxial Optics

Close to the axis, all wavefronts are spherical

and all rays converge to the centre the sphere.
Paraxial
Optics
Paraxial
Optics

Stretch in the transverse

direction
Paraxial
Optics

Stretch in the transverse

direction
Paraxial
Optics
Paraxial
Optics

Stretch further
Paraxial
Optics
Wavefronts

Lens surfaces

Stretch in the transverse direction

 Paraxial Optics

Close to the axis, all wavefronts are spherical and all

rays converge to the centre the sphere.
 Paraxial Optics

Close to the axis, all wavefronts are spherical and all

rays converge to the centre the sphere.
All rays from a point object create a spherical
wavefront which after passing through a lens system
remains a spherical wavefront and hence converges
to or appear to diverge from a point image.
 Paraxial Optics

Close to the axis, all wavefronts are spherical and all

rays converge to the centre the sphere.
All rays from a point object create a spherical
wavefront which after passing through a lens system
remains a spherical wavefront and hence converges
to or appear to diverge from a point image.

Thus, perfect images are formed.

 Paraxial Optics

In paraxial optics, all rays are close to the axis and

hence make very small angles with the axis.
 Paraxial Optics

In paraxial optics, all rays are close to the axis and

hence make very small angles with the axis.
All surfaces are nearly normal to the axis and hence,
the angle of incidence on the surface is very small.
After refraction also, the angle remains small.
 Paraxial Optics

In paraxial optics, all rays are close to the axis and

hence make very small angles with the axis.
All surfaces are nearly normal to the axis and hence,
the angle of incidence on the surface is very small.
After refraction also, the angle remains small.
Therefore under paraxial approximation, Snell’s law
reduces to
which is a linear relationship in angles. This is
responsible for perfect imaging in optical system.
 Paraxial Optics

In paraxial optics, all rays are close to the axis and

hence make very small angles with the axis.
All surfaces are nearly normal to the axis and hence,
the angle of incidence on the surface is very small.
After refraction also, the angle remains small.
Therefore under paraxial approximation, Snell’s law
reduces to
which is a linear relationship in angles. This is
responsible for perfect imaging in optical system.
Lens and mirror imaging formulae and lens makers’
formula are all under paraxial optics.
 Geometrical Optics
The main law is Snell’s Law:

As the angle increases beyond paraxial region,

higher order terms in the expansion of sin start
appearing.
 Geometrical Optics
The main law is Snell’s Law:

As the angle increases beyond paraxial region,

higher order terms in the expansion of sin start
appearing.
The wavefront after going through the system
does not remain spherical and image is not a
point but a spot, spread of points.
 Geometrical Optics
The main law is Snell’s Law:

As the angle increases beyond paraxial region,

higher order terms in the expansion of sin start
appearing.
The wavefront after going through the system
does not remain spherical and image is not a
point but a spot, spread of points.
Images now have aberrations. The first to
appear are 3rd order aberrations.
Geometrical Optics
The term in the expansion of is
responsible for the 3rd order aberrations.
Geometrical Optics
The term in the expansion of is
responsible for the 3rd order aberrations.
In the 3rd order, there are five aberrations:
• Spherical aberration
• Coma
• Astigmatism
• Field Curvature
• Distortion
At larger angles higher order aberrations
also become important.
 Theories of Optics
Paraxial Optics Optical system design,
Geometrical Optics instrument design
Wave Optics Interference, diffraction
Electromagnetic Nature of light,
Theory of Optics Polarization, Interaction
with matter
Quantum Optics Concept of photon,
quantum nature of light,
interaction with matter,
generation/detection of
light
 Theories of Optics
Paraxial Optics Optical system design,
Geometrical Optics instrument design
Wave Optics Interference, diffraction
Electromagnetic Nature of light,
Theory of Optics Polarization, Interaction
with matter
Quantum Optics Concept of photon,
quantum nature of light,
interaction with matter,
generation/detection of
light
 This course
1 Introduction
2 Electromagnetic waves in a medium: review of Maxwell’s equations and
3 propagation of electromagnetic waves, various states of polarization and
their analysis.
4 Anisotropic media, plane waves in anisotropic media, uniaxial crystals,
some polarization devices.
5 Diffraction: scalar waves, the diffraction integral, Fresnel and Fraunhofer
diffraction, diffraction of a Gaussian beam, diffraction grating.
6 Fourier optics and holography: spatial frequency and transmittance
function, Fourier transform by diffraction and by lens, spatial-frequency
filtering, phase-contrast microscope. Holography: on-axis and off-axis
hologram recording and reconstruction, types of hologram and some
applications.
7 Coherence and Interferometry: Spatial and temporal coherence, fringe
visibility, Michelson stellar interferometer, optical beats, multiple beam
interference, Fourier transform spectroscopy.
8 Guided wave optics: Modes of a planar waveguide, optical fibers: step-
index and graded index fibers, waveguide theory and quantum
mechanics, applications of optical fibers in communication and sensing.
Electromagnetic Waves
Maxwell’s Equations
 Electromagnetic Waves
Maxwell’s Equations

Variation ϵ and the geometry of the problem

dictate the solutions. New solutions are still
being obtained after over 155 years.
 Solutions of Maxwell’s Equations
In a homogeneous and isotropic medium
devoid of any source, the solutions are plane
waves.
x
k
n

54
 Solutions of Maxwell’s Equations
At an interface between two homogeneous
and isotropic media the solutions lead to
reflection and transmission
x

qi
qr

ni
z
Interface
qt

nt
 Solutions of Maxwell’s Equations
At 3-layer dielectric structure, we obtain
interference
x

ni
z
Interface
nf
 Solutions of Maxwell’s Equations
At 3-layer dielectric structure, we obtain
interference
x

ni
z
Interface
nf

nt
 Solutions of Maxwell’s Equations
At 3-layer dielectric structure, we obtain
interference Superposition
x leading to
Interference

ni
z
Interface
nf

nt
 Solutions of Maxwell’s Equations
Restricting the size of a wave by placing
apertures in its path.
 Solutions of Maxwell’s Equations
Restricting the size of a wave by placing
apertures in its path.
 Solutions of Maxwell’s Equations
Restricting the size of a wave by placing
apertures in its path.

Leads to
Diffraction
 Solutions of Maxwell’s Equations
So far we have considered homogeneous and
isotropic medium: vacuum, air, water and glass
would be such media.
 Solutions of Maxwell’s Equations
So far we have considered homogeneous and
isotropic medium: vacuum, air, water and glass
would be such media.
However, if we consider a crystal, like quartz, in
which the arrangement of atoms is not identical
in all directions, the medium would not be
isotropic although it would be homogeneous.
 Solutions of Maxwell’s Equations
So far we have considered homogeneous and
isotropic medium: vacuum, air, water and glass
would be such media.
However, if we consider a crystal, like quartz, in
which the arrangement of atoms is not identical
in all directions, the medium would not be
isotropic although it would be homogeneous.
In such cases, a wave incident on the medium,
in general, splits into two waves and we get two
refracted waves.
 Solutions of Maxwell’s Equations
Thus, in an anisotropic medium (such as crystals),
we have double refraction or birefringence.
 Solutions of Maxwell’s Equations
Thus, in an anisotropic medium (such as crystals),
we have double refraction or birefringence.
This leads, in general, to double image formation
through a crystal.

A
 Solutions of Maxwell’s Equations
Thus, in an anisotropic medium (such as crystals),
we have double refraction or birefringence.
This leads, in general, to double image formation
through a crystal.

AA
A
Crystal
 Solutions of Maxwell’s Equations
So far, we mainly considered plane waves under
various medium properties. However, optics
deals with images which are two dimensional
distribution of intensities.
 Solutions of Maxwell’s Equations
So far, we mainly considered plane waves under
various medium properties. However, optics
deals with images which are two dimensional
distribution of intensities.
These images can be considered as two
dimensional signals which are processed through
various imaging systems which are linear.
 Solutions of Maxwell’s Equations
So far, we mainly considered plane waves under
various medium properties. However, optics
deals with images which are two dimensional
distribution of intensities.
These images can be considered as two
dimensional signals which are processed through
various imaging systems which are linear.
This can be done through Fourier analysis of
signal and system properties.
 Solutions of Maxwell’s Equations
Fourier Optics deals with optical processing of
two-dimensional signals (images).
 Solutions of Maxwell’s Equations
Fourier Optics deals with optical processing of
two-dimensional signals (images).
This has many applications and is closely
connected with Holography which is a technique
to record and produce 3-D images.
 Solutions of Maxwell’s Equations
Fourier Optics deals with optical processing of
two-dimensional signals (images).
This has many applications and is closely
connected with Holography which is a technique
to record and produce 3-D images.

Guided wave optics – Fiber Optics/Integrated

Optics – deals with guidance of light. Light can be
propagated over hundreds of kilometers and still
be detected reliably. Fibers are the backbone of
all internet that we have today.
 This course
1 Introduction
2 Electromagnetic waves in a medium: review of Maxwell’s equations and
3 propagation of electromagnetic waves, various states of polarization and
their analysis.
4 Anisotropic media, plane waves in anisotropic media, uniaxial crystals,
some polarization devices.
5 Diffraction: scalar waves, the diffraction integral, Fresnel and Fraunhofer
diffraction, diffraction of a Gaussian beam, diffraction grating.
6 Fourier optics and holography: spatial frequency and transmittance
function, Fourier transform by diffraction and by lens, spatial-frequency
filtering, phase-contrast microscope. Holography: on-axis and off-axis
hologram recording and reconstruction, types of hologram and some
applications.
7 Coherence and Interferometry: Spatial and temporal coherence, fringe
visibility, Michelson stellar interferometer, optical beats, multiple beam
interference, Fourier transform spectroscopy.
8 Guided wave optics: Modes of a planar waveguide, optical fibers: step-
index and graded index fibers, waveguide theory and quantum
mechanics, applications of optical fibers in communication and sensing.