Transcript 总复习

考试时间和注意事项
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考试时间和注意事项
 Simple question (answer briefly)， calculation
 Notes: in English
 Chapter 1、2 （15％）
 Chapter 3 (15%)
 Chapter 4 (20%)
 Chapter 5 (10%)
 Chapter 6 (10%)
 Chapter 7 (20%)
10%
第一、二章主要内容
Description of homogeneous light
波动方程：最基本的传输方程
Goos-hänchen shift
Three especial incidence angles
TIR
Resonator
Description of homogeneous light
The simplest traveling wave: a sinusoidal wave for z propagation
----a monochromatic plane wave
E( x, z, t )  E0  x  cos t   z  0 
横向：驻波， E0(x)表
示一种光场分布；
纵向：行波特性，用
传播常数描述。
复数形式：
E ( x, z, t )  E0  x   exp  j t   z  0  
电磁场理论分析光波导
Maxwell’s equation
2 E  k 2n2 E  0
Helmhotz equation
General solution for
field distribution
2 H  k 2n2 H  0
Continuous for
tangential components
Eigenvalue equation + filed distribution
波动方程：最基本的传输方程
2 E  k 2n2 E  0
 H k n H 0
2
2 2
---Helmhotz equation
Wave equation in linear, isotropic, noconducting, nonmagnetic,
homogeneous dielectric medium
Goos-hänchen shift
Penetration depth of the ray, denoted by ys
Virtual reflecting plane
B
y
ys  zs cot i
n2
Penetration depth
i
A
r
n1>n2
z
2zs
Incident wave
lateral shift
Reflected wave
P32:Goos-hänchen shift
Ex ( y, z, t )  $xE  y   cos t  kn1 sin i z  0 
$x
k
2

c
n1    r
v
c
d
V p  , Vg 
n1
d
Three especial incidence angles
 normal incidence： i＝0
 Brewster angle
 Critical angle
n2
R||  0  tan  p 
n1

n2
T  0  t   sin  c 
2
n1
TIR----transmitted wave
Total internal reflection (TIR): there is no transmitted wave but
only a reflected wave when i > c. (P15)
What happens the transmitted wave when i > c. (P21)
E t ( y, z , t )  Et ( y )e
 2 y
 exp  j t  kn1 sin i z  
Notes: (1) 发生全反射时，第二媒质中并不是丝毫没有电磁
场，只不过是不再有能量流过界面。
(2) 透射波是一个非均匀波，它沿着入射面的媒质边界（即
z方向）传播，但波的振幅则按规律exp(-ay)随离开界面的
距离（y方向）而作指数式的衰减
TIR---Phase shift in TIR
For i   c , Er (TIR wave's phase shift without amplitude change)
for TE modes: Er ,  Ei ,e
for TM modes: Hr ,  H i , e
i
 i||
Waveguide Conditon
A short-duration light pulse is launched into the dielectric waveguide
 the light emerging from the other end is a broadened light pulse.
High o rder mode
Light pulse
Low order mode
Broadened
light pulse
Cladding
Core
Intensity
Intensity
Axial
0
Spread, 
t
t
Schematic illustration of light propagation in a slab dielectric waveguide. Light pulse
entering the waveguide breaks up into various modes which then propagate at different
group velocities down the guide. At the end of the guide, the modes combine to
constitute the output light pulse which is broader than the input light pulse.
?1999 S.O. Kasap, Optoelectronics (Prentice Hall)
Figure 2.7
Waveguide Conditon
First Three Modes
y
n2
E(y)
Cladding
m=1
m=0
Core
n1
n2
m=2
2a
Cladding
The electric field patterns of the first three modes (m = 0, 1, 2)
traveling wave along the guide. Notice different extents of field
penetration into the cladding.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
Figure 2.6
Chapter 3 semiconductor science and light emitting diodes
1. Principles（ LED的基本工作原理）
LED的定义：利用半导体pn结自发辐射发光的器件的总称。
Example: pn+ junction
Electronenergy
p
Ec
EF
Ev
n+
p
Eg
n+
eVo
Ec
EF
eVo
Ev
Eg
hu Eg
V
Electron in CB
Hole in VB
(b) With forward bias V
(a) Without any bias
Chapter 3 semiconductor science and light emitting diodes
2. LED characteristics:
spontaneous emission
 The emitted photons are in random directions
 The wavelength of the emitted light
1.2396
h  Eg     m  
Eg  eV 
hc
 Peak emission:
 E g  k BT

 Energy spread: (h)
 linewidth  (nm)
relation between  with energy distribution (h)?
Chapter 3 semiconductor science and light emitting diodes
3. External and internal efficiency
optical power output
external =
Electrical power input
internal
rate of radiative recombinatuion

total rate of recombination  radiative and nonradiative 
区别：从发光区产生的光
透射到外部介质的光
Chapter 3 semiconductor science and light emitting diodes
4. DH LED
Example NpP: AlGaAs-GaAs-AlGaAs
n+
AlGaAs
p1
GaAs
p2
AlGaAs
可以对少数载流子和光波起双重限制作用！
注入效率和发光效率大大提高！
Chapter 3 semiconductor science and light emitting diodes
5. Surface emitting LED (SLED) and Edge emitting LED (ELED)
Light
Light
DH
(a) Surface emitting LED
(b) Edge emitting LED
Chapter 4 stimulated emission devices lasers
1. Three transition process（光和物质相互作用三种跃迁过程）
 spontaneous emission
 Stimulated emission
 Stimulated absorption
2. Conditions for obtaining stimulated emission
 Population inversion
 pumping
 three energy levels at least
ground state, pump energy level, long-lived state
Chapter 4 stimulated emission devices lasers
3. Einstein relationship
R21  stim 
c3

  h 
3
R21  spon  8 h
R21  stim 
N
 2
R12  absorp  N1
(9)
(10)
(1) R21(stim) >R12(absorp)N2>N1 population inversion
(2) R21(stim) >R21(spon) need a large photon concentration
Notes:
From (1) The laser principle is based on non-thermal equilibrium
From (2) an optical cavity needed to contain the photons
Chapter 4 stimulated emission devices lasers
4. Structure of laser
 lasing medium：supply the transition energy level
 Optical cavity ：acts as an optical resonator to supply the
positive feedback to build up the intensity of stimulated
emissions and finish frequency selection
 pumping energy: to achieve population inversion
5. Conditions for achieving a continuous wave lasing emission
 Threshold gain
G op  Pf / Pi  1  g th
 Phase condition roundtrip  m  2   resonator frequency
Where Gop is the net round-trip optical gain, m is an integer
Chapter 4 stimulated emission devices lasers
6. Linewidth and modes within the linewidth of the
optical gain curve
(FWHM) :  1/ 2 or 1/ 2
2 L 2 L 2 L 02
m  m1  m 

 2
m 1 m m
2L
 m 
c
m 1
c
c
c
c




2L
2L 2L
m
m 1 m
1/ 2
linewidth of spectrum
modes=

separation of two modes m
Chapter 4 stimulated emission devices lasers
7. Optical resonator
(1) 光学谐振腔在激光器中的作用
 提供正反馈,相当于提高激光工作物质的光放大作用距离
 使激光能沿着一个固定方向传播
 使腔内模式有限,使光能量集中在有限的模式中.(选频)
(2) 光学谐振腔结构：开腔
(3) 光学谐振腔的模式:具有稳定的场分布
相位谐振条件：一个来回光的相位变化为2的整数倍
2

 nr  L  m  2
 m is an integer 
Chapter 4 stimulated emission devices lasers
8. Optical gain coefficient g and absorption coefficient 
x
P
P+ P
x
P
g
P  x
or  P   P   P  exp  gx 
If there is loss:  P   P   P  exp   x 
Chapter 4 stimulated emission devices lasers
9. Simplified description of a laser oscillator
(N  N ) and P
o
2 1
N N
2
1
Po = Lasing output power
(N  N )
2 1 th
Threshold population
inversion
Pump rate
Threshold pump rate
Figure 4.12
Chapter 4 stimulated emission devices lasers
10. laser modes
激光器的输出光谱由许多独立的频率分量所组成。这些独立的频率分量便
称为模式。
准确地讲：模式是指能在腔内存在的、稳定的光波基本形式
确定的频率、振幅和相位在空间的分布是确定的，不随时间改变
TEMpqm mode:
P、q表征模式在垂至于腔轴的平面内的振幅分布情况，横模阶数
p: number of nodes in the field distribution along y;
q: number of nodes in the field distribution along z;
m: 模式在光腔轴向形成的驻波节点数目，纵模阶数
number of nodes along the cavity axis x, is very large (~106 in
gas lasers)
Chapter 4 stimulated emission devices lasers
11. Working process of the semiconductor laser
 Population inversion when degenerately doped pn
junction is forward biased by a voltage V greater than
the bandgap
 An incoming photon come emission (from
spontaneous emission of the excited atoms) cause
stimulated emission
 Optical resonator build up the intensity of stimulated
emissions
12. Heterostructure laser diodes---reduce the threshold current
 Carrier confinement
 Photon confinement
Chapter 4 stimulated emission devices lasers
12. Output spectrum of the laser diode
Po (mW)
10
0C
25C
8
50C
6
4
2
I (mA)
0
0
20
40
60
80
Chapter 4 stimulated emission devices lasers
13. parameters of laser diode
(1)P-I曲线的斜率：slope
P0

I  I th
每安培注入电流有多少瓦的激光输出
(2)external quantum efficiency（外量子效率）
number of output photons from the diode (per unit second)
EQE =
number of injected electrons into the diode (per unit second)
(3)external differential quantum efficiency（外微分量子效率）
increase in number of output photons from the diode (per unit second)
EDQE =
increase in number of injected electrons into the diode (per unit second)
Chapter 5 photodetectors
1. definition of photodetectors
Convert a light signal to an electrical signal such as a
voltage or current
2. Principe of the pn junction photodiode
3. Characteristics of pn junction photodiode
(1) Ramo’s theorem
1.24
λg  μm  =
Eg  eV 
(2) Upper cut-off wavelength:
(3) Optical Absorption Coefficient
At at a distance x from the surface:
I  x  = I0 exp   x 
Chapter 5 photodetectors
(4) Quantum efficiency and responsivity

I ph /e
P0 /hν
, R
Relation with  and R:
I ph
P0
e
e
R 
=
h
hc
4. structure of photodiodes
(1) Pn junction:

Annular electrode
 Antireflection coating
 p+ side very thin
 Normally reverse biased
Chapter 5 photodetectors
(2) Pin photodiode:在pn结的耗尽区域内具有本征区域（i层）
i层作用：扩大携带电信号的光生载流子的产生空间；降低与响
应频率有关的pn结电容。(提高灵敏度和响即应度)
(3) Avalanche photodiode (APD)
avalanche region, absorption and photogeneration region
Reverse biased: widen the depletion region to the  layer
(4) (SAM)APD and (SAGM) APD
 SAM APD:
Allow the multiplication to be initiated by one type of carrier
 SAGM APD:
Make easier for the carrier to pass to the multiplication layer
Chapter 6 photovoltaic devices
1. Principle of photovoltaic devices
2. I-V characteristics of the solar cell
(1) Short circuit current
(2) Open circuit voltage
(3) fill factor
(4) Cell efficiency
3. equivalent circuit of a solar cell---maximum power point
(1) Solar cell in parallel
(2) Solar cell in series