Transcript Photonics Engineering Prof. Hosoeng Kim Optical Signal & Laser Application Lab. Chung-Ang University

Photonics Engineering
Prof. Hosoeng Kim
Chung-Ang University
Optical Signal & Laser Application Lab.
광응용공학 (PHOTONICS ENGINEERING)
담당교수 (Instructor) 김호성 (Kim Hoseong) 5292 http://prof.cau.ac.kr/~laser 010-2514-5292
강의시간/강의실 (Room/Time) 207관(봅스트홀) 604 강의실 월5,6 / 수6
상담가능시간 (Office Hour for Advice) 월 10-11 E-mail [email protected]
과목 개요 (Course Description)
This course introduces light applications such as optical communication and Flat Panel Display to un
derstand these applications, this course covers properties of light, lenses , optical systems, light sourc
es including lasers, Detectors and Fiber optics.
수업 목표 (Course Goals)
Understanding the optical engineering and improve design skill.
강의 진행 방식
Power Point, Demonstration, Design Project (optical receiver design and simulation)
학습 평가 방법 Homework 10%, Midterm 25%, Project 30%, Final 35%
기타 안내 사항
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.
교재: Optics Hecht, Optoelectronics and Photonics Kasap (2001)
주별강의 내용/과제 (Weekly Course Schedule/Assignments)
1주차 강의내용 (1 week Topic(s)) 1.Propagation of light.
2주차 강의내용 (2 week Topic(s)) 1.Propagation of light.
3주차 강의내용 (3 week Topic(s)) 2.Lenses and aberrations
4주차 강의내용 (4 week Topic(s)) 2.Lenses and aberrations
5주차 강의내용 (5 week Topic(s)) 3.Simple optical instruments.
6주차 강의내용 (6 week Topic(s)) 4.Detectors.
7주차 강의내용 (7 week Topic(s)) 5.Light modulators.
8주차 강의내용 (8 week Topic(s)) 6.Illuminators and condensers.
9주차 강의내용 (9 week Topic(s)) 7.Lasers.
10주차 강의내용 (10 week Topic(s)) 7.Lasers.
11주차 강의내용 (11 week Topic(s)) 8.Diffraction theory.
12주차 강의내용 (12 week Topic(s)) 9.Interference.
13주차 강의내용 (13 week Topic(s)) 10. Optical communication
14주차 강의내용 (14 week Topic(s)) 11. Displays
15주차 강의내용 (15 week Topic(s)) 12. Holography, and 3D Display
16주차 강의내용 (16 week Topic(s)) Exam
Prof. Hosoeng Kim(1)
• 1976년 2월 경복고등학교 졸업(마지막 고교입시)
• 1976년 3월 서울대학교 전기공학과 입학
English Discussion 동아리
• 1977년 겨울방학 AFKN 받아 쓰기
• 1978년 9월 English Discussion 동아리 회장
• 1979년 3월 서울시 성수동에서 노동 야학
10월 박정희 서거
운동권? 취업? 진학? 군입대?
• 1980년 2월 동 대학 전기공학과 학사
3월 동 대학 전기공학과 대학원 입학
5월 광주사태, 휴교령
9월 개학, 공부에 몰두함
박사 및 교수를 목표로 함
• 1982년 2월 동 대학 전기공학과 석사
Prof. Hosoeng Kim(2)
• 1982년 3월-8월
석사장교 소위 임관 및 전역
• 1983년 3월-1983년 8월 서울대 박사과정
• 1983년 9월 - 1986년 8월
금성전기기술연구소 주임연구원(연구소장 권유)
3년 후 유학보장
Low Noise Amplifier and downconvertor for satellite communication
• 1984년 4월 결혼, 86년 장녀 출생
• 1986년 9월 - 1988년 8월 (새로운 학문을, 내 돈으로…)
State University of NY at Buffalo 공학석사
• 1988년 9월 - 1992년 8월 동 대학 공학박사
“Laser Applications to Superconducting Thin Film Deposition and
Laser Drilling”
• 1993년 3월 - 현재
중앙대학교 전자전기공학부 교수
• Laser Applications : Laser Metrology, MOEMS, Light
sensors, Optical system design, circuits…..
What One’s Future Will Be
• 성공은 능력이 아니라 의지에 달려 있다.
• 4학년의 고민
- 진로: 취업(중앙대생이라면 언제라도 가능)
진학: 본교, 유학, 석사, 박사?
(돈, 머리, 체력. 의지는 기본)
• 꿈은 이루어진다!!!
• 배우자 고르기 (controllable, observable)
• CEO되기: 지성인? 지식인 인가?
너 자신을 알라!!!
Laser
Light Amplification
by Stimulated Emission of Radiation
(lase (v))
Features
Monochromatism
Coherence
Small divergence
Ultra short pulse
Monochromatism
(single frequency or color)
• Very narrow bandwidth (linewidth)
ex) stabilized HeNe laser: λ=632.8 nm f=4.74x1014 Hz
∆λ= 10-6(nm), ∆f=1 MHz
• Very high quality factor: ~108
• Immune to chromatic aberration
Blue
• Very small focus: a few micrometer diameter
• Application to Interferometer.
Red
Coherence(可干涉性, 결맞음)
• 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.
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.
θ
• 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
Ultra Short Pulse
• ∆t = 10 fs ~ us
- λ=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 > 1012 W/cm2
• Laser drilling, cutting, welding
• Laser Weapon
- SDI (Strategic Defense Initiative), MD
Chapter 1
Basic Properties of Light
Light is described using 3 pictures.
Waves
Rays
Photons
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!)
2

Example: E  Eaˆ x cos 
z  2 ft 
 

 2

H  Haˆ y cos 
z  2 ft 
 

E(V/m)
∙∙∙∙∙∙
A T0 T1 T2 T3 T4 T5
O
Z(m)
-A
• 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.
Another way to draw the plane wave is
“wave-fronts” surface of constant “phase” or
“phase-fronts”
• The wavefront advances by a distance λ, in a time 1/f.
So the velocity is υ = distance/time = λf.
One of the many remarkable properties of light is it’s universal, constant speed:
• The physics of electromagnetic (EM) wave propagation is valid for arbitrary λ, f. On Earth,
we can generate, manipulate and/or detect EM waves with wavelength from ~100 km all the
way down to ~ 10-6Ǻ. 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,
γ -ray.
Index of Refraction
• When light travels in materials, the speed is modified:

c
f
n
Usually n ≥ 1. (It can be < 1)
• The reason is that the electric field shakes the electrons, which tends to drag the field.
 2

• Plane wave still has the same form: E  Eaˆ x cos 
z  2 ft 
 

But the effective wavelength becomes modified by n.
c vac



.
If we define the vacuum wavelength, λ vac=c/f , then in the material,
nf
n
The wavelength becomes shorter, if n ≥ 1.
Dispersion
The index of refraction in most materials depends on wavelength:
Blue
In air – the index depends also on air pressure, humidity, and
temperature which leads to many beautiful atmospheric effects.
Red
- 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: 4000~7000 Ǻ, 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
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.
 2

cos 
r  2 ft 
 

For spherical waves, we have E  E0
r
 2

cf . plane wave E  Eaˆ x cos 
z  2 ft 
 

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).
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 = hν,
ν : frequency in Hz
h = 6.62 × 10-34 J-s : plank’s constant
1 W = 1 J per second
For 2 eV visible photons,
1 W = 6.3 × 1018 eV/s
= 3.15 × 1018 photons/sec
Photoelectric Effect
Novel Prize to Einstein
1
m 2  eV0
2
h 
1
m 2  
2
h 0  
eV0  h(  0 )
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.
2
∆E = hv
∆E = hv
1
Spontaneous emission
• random phase, polarization
Stimulated absorption
∆E = hv
Stimulated emission
• Same Phase
• Same polarization
• Laser!!
• Photons are not point particles. They have a wave-like property.
A useful picture is the wave-packet.
Many photon packets can be
thought of as superimposing to
make up a plane wave, spherical
wave or any other
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,
1eV= 1.6 ×10-19 J
Typical visible photon energy : 1.2 ~ 2.3 eV
Reflection and Refraction, Snell’s 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
If n1 > n2, then we can have
The refracted ray disappears! The light is totally
reflected. This usually occurs inside a prism , and is
called total internal reflection. θC = “critical angle”.
For a typical glass with n = 1.5, the critical angle is:
θC = 20.9o
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 θ1 = 0,
2
 n n 
Rs  R p   2 1  : Fresnel Loss
 n2  n1 
4n1n2
Ts  Tp 
2
 n2  n1 
If 1   2   / 2, tan  , and R p  0
No reflection for p-polarization wave!
1  n2 
1   B  tan  
Brewster angle or Polarizing angle. [Hecht 8.6]
 n1 
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
Polarization State
• The e-field oscillates in time at a given point in space
• For light wave propagating in z-direction, let’s 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

E ( z , t )  ax E10 cos(t  kz )  a y E20 cos(t  kz  ).
2
E (0, t )  ax E1 (0, t )  a y E2 (0, t )
- Set z=0,
 ax E10 cos(t )  a y E20 sin(t ).
- Analytically,
cos(t ) 
E1 (0, t )
,
E10
sin(t ) 
E2 (0, t )
,
E20
y
- Which leads to the following equation for an ellipse:
2
2
 E1 (0, t ) 
 E2 (0, t ) 




  1.
 E10 
 E20 
E(0,t)
ω
E2
0
α
E1
x
E ( z )  ax E1 ( z )  a y E2 ( z )  ax E10e jkz  a y jE20e  jkz ,
- Circularly polarized if E10  E20
- Elliptically polarized if E10  E20
<Circular polarization>
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
• Polarizing beamsplitter
polarization state)
• Polaroid sunglasses are filter out the light of which E-field is parallel to the ground since
R  Rs
1
R  Rp
R
B

2
i
Rs  R p
R  R .