Transcript No Slide Title

Plane of polarization
y
E
x
^
y
Ey
^
^
x
xEx
Ex
E
z
(a)
(b)
^
yE
y
E
(c)
(a) A linearly polarized wave has its elect ric field oscillat ions defined along a line
perpendicular t o t he direct ion of propagation,z. The field vector E and z define a plane of
polarization. (b) The E-field oscillat ions are cont ained in t he plane of polarizat ion. (c) A
linearly polarized light at any inst ant can be represented by t he superposit ion of t wo fieldsEx
and Ey with the right magnit ude and phase.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
z
Ey
 = kz
E
z
E
z
Ex
A right circularly polarized light. The field vector E is always at right
angles to z , rotates clockwise around z with time, and traces out a full
circle over one wavelength of distance propagated.
© 1999 S.O. Kasap,Optoelectronics(Prentice Hall)
y
y
(a)
y
(b)
(c)
=0
=1
 =0
(d)
E
x
x
Exo
Eyo
y
=1
=1
 =0
Exo
Eyo
=1
=1
 = /2
Exo
Eyo
x
E
=1
=1
 = /2
Exo
Eyo
Examples of linearly, (a) and (b), and circularly polarized light (c) and (d); (c) is
right circularly and (d) is left circularly polarized light (as seen when the wave
directly approaches a viewer)
© 1999 S.O. Kasap,Optoelectronics(Prentice Hall)
x
y
y
(a)
(b)
y
=1
=2
=0
E
x
x
Exo
Eyo
(c)
E
=1
=2
 = /4
Exo
Eyo
x
=1
=2
 = /2
Exo
Eyo
(a) Linearly polarized light with E yo = 2Exo and  = 0. (b) When  = /4 (45), the light is
right elliptically polarized with a tilted major axis. (c) When  = /2 (90), the light is
right elliptically polarized. If E xo and E yo were equal, this would be right circularly
polarized light.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
Ecos
Linearly
polarized light
E

TA2
Light det ector
TA1
Polarizer 2 = Analyzer
Polarizer 1
Unpolarized light
Randomly polarized light is incident on a Polarizer 1 with a transmission axis TA 1. Light
emerging from Polarizer 1 is linearly p olarized with E along TA 1, and becomes incident
on Polarizer 2 (called "analy zer") with a transmission axis TA 2 at an angle to TA1. A
detector measures the intensity of the incident light. TA1 and TA2 are normal to the light
direction.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
T wo polaroid analyzers are placed wit h their t ransmission axes, along
the long edges, at right angles t o each other. T he ordinary ray,
undeflected, goes through the left polarizer whereas the extraordinary
wave, deflected, goes t hrough the right polarizer. T he t wo waves
therefore have orthogonal polarizations.
P
x
k
n1

B
n3
O
n2
A
O
z
A
B
z
Optic
axis
y
(a) Fresn el's ellipsoid
(b) An EM wave pro pagat ing alongOP at an
angle  to opt ic axis.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
x
x
n o = n1
(a)
Eo
y
z
n o = n1
(b)
Eo
ne (0) = n2 = n1
y
Ee
n e (90) = n 3
z = Optic axis
Ee
z = Optic axis
z = Optic axis
Eo = Eo-w ave and Ee = Ee-w ave (a) Wave propagation along the op tic axis. (b)
Wave propagation normal to optic axis
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
kz Optic axis
Ee
e-wave
o-wave
S e = P ower flow
ke
Ee
Q
ke
ke
O
Eo
P
kx
ko
E oscillationst o paper
E oscillations // to paper
(a)
Wavefront s (const ant phase fronts)
(b)
(a) Wavevector surface cuts in the xz plane for o- and e-waves. (b) An extraordinary
wave in an anisotropic crystal with a k e at an angle to the optic axis. The electric field
is not normal to k e. The energy flow (group velocity) is along Se which is different
than k e.
© 1999 S.O. Kasap,Optoelectronics(Prent ice Hall)
Optic axis
Principal section
Principal section
Incident ray
E//
e-wave
e-ray
o-ray
Incident wave
A calcite rhomb
E
o-wave
Optic axis
(in plane of paper)
An EM wave that is off the optic axis of a calcite crystal splits into two waves called
ordinary and extraordinary waves. These waves have orthogonal polarizations and
travel with different velocities. The o-wave has a polarization that is always
perpendicular to the optical axis.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
z , ne
x , no
Optic axis
Ee-wave
E
Ee-wave
y
z
Eo-wave
(a)
x , no
Eo-wave
(b)
Optic axis
y , no
(a) A birefringent crystal plate with the optic axis parallel to the plate surfaces. (b) A
birefringent crystal plate with the optic axis perpendicular to the plate surfaces.
© 1999 S.O. Kasap,Optoelectronics(Prent ice Hall)
z = Slow axis
Optic axis
E //

E //
E
ne = n3

y
E
E
no
LL
x = Fast axis
A retarder plate. The optic axis is parallel to the plate face. The o- and e-waves travel
in the same direction but at different speeds.
© 1999 S.O. Kasap,Optoelectronics(Prent ice Hall)
Half wavelength plate: 
=š
Optic axis

Quarter wavelength plate: 
z
z
E
Input

x
 = arbitrary
E
45
x
x
 < 45
 = 45
z
z
= š/2
z

Output
x
(a)
E
E
x
(b)
Input and output polarizations of light through (a) a half-wavelength
plate and (b) through a quarter-wavelength plate.
© 1999 S.O. Kasap,Optoelectronics(Prent ice Hall)
x
E1
E2
Wedges can slide
Optic axis
d
D
Plate
Optic axis
Soleil-Babinet Compensator
© 1999 S.O. Kasap,Optoelectronics(Prentice Hall)
e-ray
Optic axis
A
B
o-ray Optic axis
A
E1
e-ray
E1
E1
E2
E2
E2  B
Optic axis
Optic axis
o-ray
The Wollaston prism is a beam polarization splitter. E 1 is orthogonal to the plane of
the paper and also to the optic axis of the first prism. E2 is in the plane of the paper
and orthogonal to E1.
© 1999 S.O. Kasap,Optoelectronics(Prentice Hall)
E

Levo
E
z
Dextro
E
E
z
z
Quartz
L
Optic axis
An optically active material such as quartz rotates the plane of polarization
of the incident wave: The optical field E rotated to E. If we reflect the
wave back into the material, E rotates back to E.
© 1999 S.O. Kasap,Optoelectronics(Prent ice Hall)
y
y
EL
E
Input


x
y
 E
x

ER
x
x
y
Output
y

EL
y


x
x
ER
Slow
Fast
Vertically polarized wave at the input can be thought of as two right and left
handed circularly polarized waves that are symmetrical, i.e. at any instant  = .
If these travel at different velocities through a medium then at the output they are
no longer symmetric with respect to y,    ., and the result is a vector E at an
angle  to y.
© 1999 S.O. Kasap,Optoelectronics(Prent ice Hall)
y
y
n2 = no
z
n 1
x
KDP, LiNbO3
(a)
n 2
z
n1 = no
y
x
Ea
Ea
n 2
4 5
x
z
x
n 1
KDP
LiNbO 3
(b )
(c)
(a) Cross section of the optical indicatrix with no applied field, n1 = n2 = no (b) The
applied external field modifies the optical indicatrix. In a KDP crystal, it rotates the
principal axes by 45  to x and y and n1 and n2 change to n1 and n2 . (c) Applied
field along y in LiNbO 2 modifies the indicatrix and changes n1 and n2 change to n1
and n2 .
© 1999 S.O. Kasap,Optoelectronics(Prent ice Hall)
Ey
V
y

d
Input
light
Ea
x
Ey

z Output
light
Ex
z
Ex
Tranverse Pockels cell phase modulator. A linearly polarized input light into an
electro-optic crystal emerges as a circularly polarized light. Ea is the applied field
parallel to y.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
QW P
Transmission intensity
V
y
P
Io
A
Detector
Input
light

Crys t al
Q
x
z
0
V 
V
Left: A tranverse Pockels cell intensity modulator. The polarizer P and analyzer A have
their transmission axis at right angles and P polarizes at an angle 45 to y-axis. Right:
Transmission intensity vs. ap plied voltage characteristics. If a quarter-wave plate (QWP)
is inserted after P, the characteristic is shifted to the dashed curve.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
(a)
Ea
z
z
(b)
no
ne
x
Ez
E
no
y

Input
light
Ea
y
Output
light
Ex
x
(a) An applied electric field, via the Kerr effect, induces birefringences in an
otherwise optically istropic material. (b) A Kerr cell phase modulator.
© 1999 S.O. Kasap,Optoelectronics(Prentice Hall)
V(t)
Coplana r str ip e le ctrodes
Thin buffer l ayer
d
P olarized
i nput
l ight
L
Li NbO3
Ea
EO Subs trat e
x
y
Wa veguide
z
Li NbO3
Cross-section
Integrated tranverse Pockels cell phase modulator in which a waveguide is diffused
into an electro-optic (EO) substrate. Coplanar strip electrodes apply a transverse
field E a through the waveguide. The substrate is an x-cut LiNbO3 and typically there
is a thin dielectric buffer layer ( e.g. ~200 nm thick SiO 2) between the surface
electrodes and the substrate to separate the electrodes away from the waveguide.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
V(t)
Electrode
C
In
B
B
A
A
Out
D
Waveguide
LiNbO3
EO Subst rate
An integrated Mach-Zender optical intensity modulator. The input light is
split into two coherent waves A and B, which are phase shifted by the
applied voltage, and then the two are combined again at the output.
© 1999 S.O. Kasap,Optoelectronics(Prentice Hall)
x
z
Top view
B
Cross-section
Input
PA (0)
Coupled waveguides
nA
A
E
d
EA
nB
B
A
ns
PA (z)
EB
PB (Lo )
PA (Lo )
Lo
x
(a)
(b)
PB (z)
z
(a) Cross section of two closely spaced waveguides A and B (separated by d)
embedded in a substrate. The evanescent field from A extends into B and vice versa.
Note: nA and nB > ns (= substrate index).
(b) Top view of the two guides A and B that are coupled along the z-direction. Light
is fed into A at z = 0, and it is gradually transferred to B along z. At z = Lo, all the
light been transferred to B . Beyond this point, light begins to be transferred back to
A in the same way.
© 1999 S.O. Kasap,Optoelectronics(Prentice Hall)
PB (Lo)/PA (0)
Transmission power ratio from guide A to
guide B over the transmission length Lo as a
function of mismatch  
100%
0
 3)/Lo
V
© 1999 S.O. Kasap,Optoelectronics(Prent ice Hall)
Waveguides
In
Cross-section
A
V(t)
B
d
Lo
Electrode
Fibers
V(t)
LiNbO3
A
Ea
B
LiNbO3
Coupled waveguides
An integrated directional coupler. Applied field E a alters the refractive indices of the
two guides and changes the strength of coupling.
© 1999 S.O. Kasap,Optoelectronics(Prent ice Hall)
Acoustic absorber
Induced diffraction
grating
Incident
light
Acoustic
wave
fronts

Diffracted light

Through light
Piezoelectric
crystal
Modulating RF voltage
Interdigitally electroded
transducer
Traveling acoustic waves create a harmonic variation in the refractive index
and thereby create a diffraction grating that diffracts the incident beam through
an angle 2 .
© 1999 S.O. Kasap,Optoelectronics(Prent ice Hall)
Incident opt ical beam
A
B
nmin
nmax
nmin
nmax
Acoustic
wave
Diffract ed opt ical beam
A'
x
x
B'


O

Q
P
si n
si n
Acoustic
wave front s
O'
vacoustic
nmin nma x
Simplified
n
nmin
nma x
n
Actual
Consider two coherent optical waves A and B being "reflected" (strictly,
scattered) from two adjacent acoustic wavefronts to become A' and B'. These
reflected waves can only constitute the diffracted beam if they are in phase. The
angle  is exaggerated (typically this is a few degrees).
© 1999 S.O. Kasap,Optoelectronics(Prentice Hall)
y
Faraday medium
Polarizer
Light
 E
E

E
B
 E
Reflector
Reflected light
Source
The sense of rotation of the optical fieldE depends only on the direction of the
magnetic field for a given medium (given Verdet constant). If light is reflected
back into the Faraday medium, the field rotates a further in the same sense to
come out as E with a 2  rotation with respect toE.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
P
Eo
t
P+
Eo
Eo
P-
Eo
E
P
sin t
P+
t
-cos2t
P(a)
DC
(b)
t
(c)
(a) Induced polarization vs. optical field for a nonlinear medium. (b) Sinusoidal optical
field oscillations between E o result in polarization oscillations between P + and P -. (c)
The polarization oscillation can be represented by sinusoidal oscillations at angular
frequencies  (fundamental), 2  (second harmonic) and a small DC component.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
Second harmonics
S1
S2
k2
v2
S3
Fundamental
v1
k1
Crystal
As the fundamental wave propagates, it periodically generates
second harmonic waves (S1, S2, S3, ...) and if these are in phase then
the amplitude of the second harmonic light builds up.
© 1999 S.O. Kasap,Optoelectronics(Prentice Hall)
KDP
Laser
Nd:YAG
Opt ic axis

 = 1064 nm
IM
 = 1064 nm
 = 532 nm
Filter
 = 532 nm
A simplified schematic illustration of optical frequ ency doubling using a KDP
(potassium dihydrogen phosph ate) crystal. IM is the index matched direction at an
angle  (about 35) to the optic axis along which ne(2 ) = no (). The focusing of
the laser beam onto the KDP crystal and the collimation of the light emerging
from the crystal are not shown.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
x
z
Ey
Ex
Wire-grid polarizer
Ey
y
The wire grid-acts as a polarizer
© 1999 S.O. Kasap,Optoelectronics(Prent ice Hall)
y
I

Oscillat ing molecular dipole y
p(t)
E
z
z
E
(a)
(b)
Oscillating dipole along y
x
(a) A snap shot of the field pattern around an oscillating dipole moment in the ydirection. Maximum electromagnetic radiation is perpendicular to the dipole
axis and there is no radiation along the dipole axis. (b) Scattering of
electromagnetic waves from induced molecular dipole oscillations is anisotropic.
© 1999 S.O. Kasap,Optoelectronics(Prentice Hall)
Absorber
o-ray
38.5
e-ray
Calcite
Optic axis
Air-gap
The Glan-Foucault prism provides linearly polarized light
© 2001 S.O. Kasap, Optoelectronics and Photonics: Principles and Practices
(Prentice Hall)
L-polarized
R-handed quartz
L-handed quartz
R-polarized
The Fresnel prism for separating unpolarized light into two divergent
beams with opposite circular polarizations ( R = right, L = left; divergence
is exaggerated)
© 1999 S.O. Kasap,Optoelectronics(Prentice Hall)
Rs = 50 
W
L
Light out
z
A
D
EO Cryst al
Rs
A
Vs
A
Z
L
C EO
Light in
B
B
B
(a)
Rp
(b)
(a) A step voltage is suddenly applied to an EO modulator. (b) An
inductance L with an equivalent parallel resistance Rp is placed across the
EO crystal modulator to match the capacitance CEO.
© 1999 S.O. Kasap,Optoelectronics(Prentice Hall)
Diffracted optical beam, k 
Incident op tical beam, k, 
k
2
Acoustic wave, K

2
K
k
Wavevectors for the incident and diffracted optical waves and the acoustic wave.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)