Photonics Engineering

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Photonics Engineering

• Prof. Hosoeng Kim

Optical Signal Laser Application Lab.
Chung-Ang University
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????? (PHOTONICS ENGINEERING) ???? (Instructor)
??? (Kim Hoseong) 5292 http//prof.cau.ac.kr/lase
r 010-2514-5292 ????/??? (Room/Time) 207?(????)
604 ??? ?5,6 / ?6 ?????? (Office Hour for Advice)
? 10-11 E-mail hkim_at_cau.ac.kr
?? ?? (Course
Description) This course introduces light
applications such as optical communication and
Flat Panel Display to understand these
applications, this course covers properties of
light, lenses , optical systems, light sources
including lasers, Detectors and Fiber optics.
??
?? (Course Goals) Understanding the optical
engineering and improve design skill.
?? ?? ?? Power
Point, Demonstration, Design Project (optical
receiver design and simulation) ?? ?? ??
Homework 10, Midterm 25, Project 30, Final 35
?? ?? ?? It is not necessary to buy two text
books but it is recommended strongly to buy one
of two. Slides of PowerPoint can be dowloaded
from my homepage. ?? Optics Hecht,
Optoelectronics and Photonics Kasap (2001)
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???? ??/?? (Weekly Course Schedule/Assignments)
1?? ???? (1 week Topic(s)) 1.Propagation of
light. 2?? ???? (2 week Topic(s)) 1.Propagation
of light. 3?? ???? (3 week Topic(s)) 2.Lenses
and aberrations 4?? ???? (4 week Topic(s))
2.Lenses and aberrations 5?? ???? (5 week
Topic(s)) 3.Simple optical instruments. 6?? ????
(6 week Topic(s)) 4.Detectors. 7?? ???? (7 week
Topic(s)) 5.Light modulators. 8?? ???? (8 week
Topic(s)) 6.Illuminators and condensers. 9??
???? (9 week Topic(s)) 7.Lasers. 10?? ???? (10
week Topic(s)) 7.Lasers. 11?? ???? (11 week
Topic(s)) 8.Diffraction theory. 12?? ???? (12
week Topic(s)) 9.Interference. 13?? ???? (13
week Topic(s)) 10. Optical communication 14??
???? (14 week Topic(s)) 11. Displays 15?? ????
(15 week Topic(s)) 12. Holography, and 3D Display
16?? ???? (16 week Topic(s)) Exam
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Prof. Hosoeng Kim(1)

• 1976? 2?    ?????? ??(??? ????)
• 1976? 3? ????? ????? ??
• English Discussion ???
• 1977? ???? AFKN ?? ??
• 1978? 9? English Discussion ??? ??
• 1979? 3? ??? ????? ?? ??
• 10? ??? ??
• ???? ??? ??? ????
• 1980? 2?    ? ?? ????? ??
• 3? ? ?? ????? ??? ??
• 5? ????, ???
• 9? ??, ??? ???
• ?? ? ??? ??? ?
• 1982? 2?    ? ?? ????? ??

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Prof. Hosoeng Kim(2)

• 1982? 3?-8? ???? ?? ?? ? ??
• 1983? 3?-1983? 8? ??? ????
• 1983? 9? - 1986? 8? 
• ????????? ?????(???? ??)
• 3? ? ????
• Low Noise Amplifier and downconvertor for
  satellite communication
• 1984? 4? ??, 86? ?? ??
• 1986? 9? - 1988? 8?  (??? ???, ? ???)
• State University of NY at Buffalo ????
• 1988? 9? - 1992? 8?   ? ?? ????
• Laser Applications to Superconducting Thin Film
  Deposition and Laser Drilling
• 1993? 3? - ??       
•   ????? ??????? ??
• Laser Applications Laser Metrology, MOEMS,
  Light sensors, Optical system design, circuits..

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What Ones Future Will Be

• ??? ??? ??? ??? ?? ??.
• 4??? ??
• - ?? ??(??????? ???? ??)
• ?? ??, ??, ??, ???
• (?, ??, ??. ??? ??)
• ?? ?????!!!
• ??? ??? (controllable, observable)
• CEO?? ???? ??? ???
• ? ??? ??!!!

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Laser

• Light Amplification
• by Stimulated Emission of Radiation
• (lase (v))
• Features
• Monochromatism
• Coherence
• Small divergence
• Ultra short pulse

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Monochromatism (single frequency or color)

• Very narrow bandwidth (linewidth)
• ex) stabilized HeNe laser ?632.8 nm
  f4.74x1014 Hz
• ?? 10-6(nm), ?f1 MHz
• Very high quality factor 108
• Immune to chromatic aberration
• Very small focus a few micrometer diameter
• Application to Interferometer.

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Coherence(????, ???)

• The spatial and temporal phase variation of the
  electric field of the two waves are the same.
• Characteristics of stimulated emission.
• Spatial coherence, temporal coherence

• Holography, Interference, Speckles.

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Small Divergence

• Divergence The bending of rays away from each
  other or the spreading of a laser beam with
  increased distance from the exit aperture.

• Divergence angle of typical HeNe laser
• 1 mr 0.0573o

• Alignment, distance measurements (earth to moon)
• Weapon guiding Gulf War
• Tight focusing

• 800 m in diameter on the moon (400,000 km from
  earth) Apollo 11

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Ultra Short Pulse

• ?t 10 fs us
• - ?3 x 108 x 10 x 10-15 3 x 10-6 m 3 µm
• - Diameter of human hair 100 µm
• Ultra high intensity(power density W/cm2)
• -1 mJ, 10 ps, on 10-4 cm2 I gt 1012
  W/cm2
• Laser drilling, cutting, welding
• Laser Weapon
• - SDI (Strategic Defense Initiative), MD

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(No Transcript)
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Chapter 1 Basic Properties of Light
Light is described using 3 pictures.
Waves
Photons
Rays
seemingly contradictory!
Waves
Reading Assignment Hecht, Chapter 2 (most of
this should be review), 3.2, 3.3, 3.4.4, 3.5, 3.6
A propagating disturbance in electric and
magnetic field (simultaneously!)
Example
At a fixed point in space, the electric field
oscillates in time. At a fixed point in time, we
see a wave train frozen.
This is called a plane-wave because the field
is constant everywhere in the x-y plane at a
given z.
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Another way to draw the plane wave is
wave-fronts surface of constant phase
or phase-fronts
The wavefront advances by a distance ?, in a
time 1/f.
So the velocity is ? distance/time ?f.
One of the many remarkable properties of light is
its universal, constant speed
The physics of electromagnetic (EM) wave
propagation is valid for arbitrary ?, f. On
Earth, we can generate, manipulate and/or detect
EM waves with wavelength from 100 km all the way
down to 10-6?. Usually we describe light by
wavelength rather then frequency, except in the
microwave and radio regions.
The electromagnetic spectrum encompasses the
complete range of frequency/wavelength. Different
regions have different names. Radio, microwave,
infrared, visible, ultraviolet, x-ray, ? -ray.
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Index of Refraction
When light travels in materials, the speed is
modified
Usually n 1. (It can be lt 1)
The reason is that the electric field shakes
the electrons, which tends to drag the field.
Plane wave still has the same form
But the effective wavelength becomes modified by
n.
If we define the vacuum wavelength, ? vacc/f ,
then in the material,
The wavelength becomes shorter, if n 1.
Dispersion
The index of refraction in most materials depends
on wavelength
In air the index depends also on air pressure,
humidity, and temperature which leads to many
beautiful atmospheric effects.
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- All information-bearing signals consist of a
band of frequencies.
- Waves of the component frequencies travel with
different velocities, causing a distortion in the
signal wave shape.
- This phenomenon is called dispersion.
Wavelength units (length)
Visible light 40007000 ?, 400 700 nm, 0.4 0.7
µm
Old New Frequency Ranges (GHz)
Ka K 26.5-40
K K 20-26.5
K J 18-20
Ku J 12.4-18
X J 10-12.4
X I 8-10
C H 6-8
C G 4-6
S F 3-4
S E 2-3
L D 1-2
UHF C 0.5-1
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Spherical Waves
Another type of ideal light wave. Constant phase
fronts are circular, emanating from a point
source. Far away from the source, the radius of
the circle becomes so large that we can
approximate the wave as a plane wave.
For spherical waves, we have
Huygens Principle
Very useful model for wave propagation.
Every point on a wavefront is regarded as a
secondary point source generating a spherical
wavelet.
The advance of the wave front is found at the
envelope of all these wavelets.
Generally, this seems to give parallel
wavefronts. But things get interesting at edges.
This leads to diffraction (more later).
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Rays
Follow a point on the wavefront. As the
wavefront advances the point traces a straight
line. This is a ray of light.
For many cases, we can forget the waves and
just trace rays in optical systems. This allows a
vast simplification of our analysis and design
processes. Virtually all optical design is done
with rays. Highly sophisticated optical design
CAD programs are available for ray tracing.
Photons (light particles)
This picture has light represented by tiny
bundles of energy (or quanta), following straight
line paths along the rays.
The coexistence of electromagnetic wave physics
and photon physics is the central paradox of
quantum mechanics.
One photon has an energy given by
E h?, ? frequency in Hz
For 2 eV visible photons,
h 6.62 10-34 J-s planks constant
1 W 6.3 1018 eV/s 3.15 1018
photons/sec
1 W 1 J per second
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Photoelectric Effect
Novel Prize to Einstein
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Interaction of Radiation and Matters
Atoms have energy states corresponding to
electron orbits.
One atom jumps from a higher energy state to
a lower energy state and emits one photon.
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?E hv
?E hv
1

• Spontaneous emission
• random phase, polarization

Stimulated absorption
Stimulated emission
?E hv

• Same Phase
• Same polarization
• Laser!!

Photons are not point particles. They have a
wave-like property. A useful picture is the
wave-packet.
The typical photon energy unit is the
electron-Volt. This is defined as the energy
required to push one electron across a one-Volt
potential,
Many photon packets can be thought of as
superimposing to make up a plane wave, spherical
wave or any other
1eV 1.6 10-19 J
Typical visible photon energy 1.2 2.3 eV
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Reflection and Refraction, Snells Law
Reading assignment Hecht 4.3, 4.4, 4.7
An important element of optics is the interface
between two materials with different index of
refraction.
Total Reflection
The refracted ray disappears! The light is
totally reflected. This usually occurs inside a
prism , and is called total internal reflection.
?C critical angle. For a typical glass with n
1.5, the critical angle is
If n1 gt n2, then we can have
?C 20.9o
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Light Impinging at a Surface Cheng p411,
8-10.2,8-10.3
The plane containing the light ray propagation
vector and the surface normal is called the
plane of incidence
For a general polarization state incident on a
surface, we choose s and p directions to
decompose the polarization effects.
Fresnel Reflection Coefficients
Near ?1 0,
Fresnel Loss
No reflection for p-polarization wave!
Brewster angle or Polarizing angle. Hecht 8.6
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Polarization Cheng p364, Hecht 8.1, 8.2
Light waves have transverse polarization.
The electric field vector points in a direction
perpendicular to the propagation direction (ray
direction).
The magnetic field vector is orthogonal to
propagation direction. Generally, we can ignore
the magnetic field.
The E-field vector can lie anywhere in
transverse plane
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Polarization State
The e-field oscillates in time at a given point
in space
For light wave propagating in z-direction,
lets look in the x-y plane.
AM linear polarization, with E field
perpendicular to the ground TV linear
polarization, with E field parallel to the ground
FM circular polarization with the surface
perpendicular to the ground
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- Set z0,
- Analytically,
- Which leads to the following equation for an
ellipse
E(0,t)
?
E2
E1
0
- Circularly polarized if
ltCircular polarizationgt
- Elliptically polarized if
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Polarizers are devices which select one
polarization.
Polarizing sheet has an allowed direction
transmits polarization component of incident
light along the allowed direction transmitted
light is linearly polarized
(can be used to analyze input polarization state)
Polarizing beamsplitter
Polaroid sunglasses are filter out the light of
which E-field is parallel to the ground since