1. Chapter 1:
Introduction to Optics and
optoelectronics

2. Light has many properties that make it very
attractive for information processing
1. Immunity to electromagnetic interference
– Can be transmitted without distortion due to electrical
storms etc
2. Non-interference of crossing light signals
– Optical signals can cross each other without distortion
3. Promise of high parallelism
– 2D information can be sent and received.

3. 4. High speed/high bandwidth
– Potential bandwidths for optical communication systems
exceed 1013 bits per second.
(1250 GigaByte/second)
5. Signal (beam) steering
– Free space connections allow versatile architecture for
information processing
6. Special function devices
– Interference/diffraction of light can be used for special
applications
7. Ease of coupling with electronics
– The best of electronics & photonics can be exploited by
optoelectronic devices

5. Radiation/Light Sources

6. Classification of radiation source by
Flux Output
1. A point source
• An LED or a small filament clear bulb with small emission
area
2. An area source
• An electroluminescence panel or frosted light bulb with
an emission area that is large
3. A collimated source
• A searchlight with flux lines that are parallel
4. A coherent source
• A laser which is either a point source or a collimated
source with one important difference: the wave in
coherence source are all in phase

8. Radiation spectrum
1. A continuous spectrum source
• Has a wavelength of emission that ranges from
ultraviolet to infrared.
2. A line spectrum source
• Has a distinct narrow bands of radiation throughout the
ultraviolet to infrared range.
3. A single wavelength source
• Radiates only in a narrow band of wavelength
4. A monochromatic source
• Radiates at a single wavelength/a very narrow band of
wavelength.

11. The nature of light

12. Light wave in a homogenous
medium
Ex
z
Direction of Propagation
By
z
x
y
k
An electromagnetic wave is a travelling wave which has time
varying electric and magnetic fields which are perpendicular to each
other and the direction of propagation,z.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)

13. k
Wave fronts
r
E
k
Wave fronts
(constant phase surfaces)
z


Wave fronts
P
O
P
A perfect spherical waveA perfect plane wave A divergent beam
(a) (b) (c)
Examples of possible EM waves
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)

14. z
Ex
= Eo
sin(wt–kz)
Ex
z
Propagation
E
B
k
E and B have constant phase
in this xy plane; a wavefront
E
A plane EM wave travelling along z, has the same Ex (or By) at any point in a
given xy plane. All electric field vectors in a given xy plane are therefore in phase.
The xy planes are of infinite extent in the x and y directions.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)

15. Light as plane electromagnet (EM) wave
• We can treat light as an EM wave with time varying
electric and magnetic fields
Ex and By perpendicular to each other propagating in z
direction.
Ex (z, t) = Eo cos (w t – kz + o)
Ex =electric field at position z at time t,
k = 2/λ is the propagation constant, λ is the
wavelength
and w is the angular frequency,
Eo is the amplitude of the wave and o is a phase
constant.
Ex (z, t) = Re[ Eo exp (jo) exp j(wt – kz)]

16. Electromagnet (EM) wave
• We indicate the direction of propagation with a vector
k, called the wave vector.
– whose magnitude, k = 2/λ
• When EM wave is propagating along some arbitrary
direction, k, then electric field at a point r is
Ex (r, t) = Eo cos (wt – k ∙ r + o)
– Dot product (k ∙ r) is along the direction of propagation
similar to kz.
– In general, k has components kx , ky & kz along x, y and z
directions: (k ∙ r) = kx x + ky y + kz z

17. y
z
k
Direction of propagation
r
O
q
E(r,t)r
A travelling plane EM wave along a direction k.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)

18. Maxwell’s Equation
2 2 2 2
2 2 2 2
0x x x x
o o r
E E E E
x y z t
  
   
   
   
2
2
0xE
x



2
2
0xE
y



Given wave equation:
Ex (z, t) = Eo cos (w t – kz + o)
2
2
2
cos( )x
o o
E
k E t kz
z
w 

   

2
2
2
cos( )x
o o
E
E t kz
t
w w 

   

2 2
cos( ) cos( ) 0o o o o r o ok E t kz E t kzw     w w       
2 2
( ) cos( ) 0o o r o ok E t kz   w w    

19. Phase velocity
• During a time interval t, this constant phase
moves a distance z.
– The phase velocity of this wave is therefore
z/t.
• Phase velocity,
f is the frequency (w = 2f )

w
f
kdt
dz
v 

20. Phase Velocity
2 2
( ) cos( ) 0o o r o ok E t kz   w w    
2
2
1
o o rk
w
  

 
1/2
o o rv   

 

w
f
kdt
dz
v 

21. Group Velocity
• There are no perfect monochromatic wave in practice
– All the radiation source emit a group of waves differing slightly
in wavelength, which travel along the z-direction
• When two perfectly harmonic waves of frequency w–w
&w+w and wave vectors k–k &k+k interfere, they
generate wave packet.
• Wave packet contains an oscillating field at the mean
frequency w that is amplitude modulated by a slowly
varying field of frequency w.
• The maximum amplitude moves with a wavevector k
and the group velocity is given Vg = dw/dk

22. Group velocity
         
       
, cos cos
, 2 cos cos
,v
x o o
x o
g
E x t E t k k z E t k k z
E x t E t k z t kz
dz d
dt k dk
w w  w w 
w  w
w w

             
    
 

23. w
w
w + w
w – w
kEmax
Emax
Wave packet
Two slightly different wavelength waves travelling in the same
direction result in a wave packet that has an amplitude variation
which travels at the group velocity.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)

24. What is refractive index, (n) ?

25. Interaction between dielectric medium and EM
wave
• When an EM wave is traveling in a dielectric medium,
– the oscillating Electric Field (E-field) polarizes the molecules
of the medium at the frequency of the wave.
• The field and the induced molecular dipoles become
coupled
– The net effect: The polarization mechanism delays the
propagation of the EM wave.
– The stronger the interaction, the slower the propagation of
the wave
– r: relative permittivity (measures the ease with which the
medium becomes polarized).

26. Phase velocity in dielectric medium
• For EM wave traveling in a non-magnetic dielectric
medium of r , the phase velocity,
• If the frequency  is in the optical frequency range,
– r will be due to electronic polarization as ionic polarization
will be too slow to respond to the field.
• At the infrared frequencies or below,
– r also includes a significant contribution from ionic
polarization and phase velocity is slower
oor 

1


27. Definition of Refractive Index
• For an EM wave traveling in free space (r= 1)
velocity
(1)
• The ratio of the speed of light in free space to its
speed in a medium is called refractive index n of
the medium,
n= c/v =  r (2)
18
103
1 
 mscv
oo

28. Example: phase velocity
• Considering a light wave traveling in a pure silica
glass medium. If the wavelength of light is 1m
and refractive index at this wavelength is 1.450,
what is the phase velocity ?
The phase velocity is given by
v= c/n = 3108ms–1/1.45
=2.069108ms–1

29. Refractive Index in Materials
• In free space, k is the wave vector (k=2 /)
and  is the wavelength
• In medium, kmedium=nk and medium = /n.
– Light propagates more slowly in a denser medium
that has a higher refractive index
– The frequency f remains the same
– The refractive index of a medium is not necessarily
the same in all directions

30. Refractive Index in non-Crystal Materials
• In non-crystalline materials (glass & liquids),
the material structure is the same in all
directions
– Refractive index, n, is isotropic and independent
on the direction

31. Refractive Index in Crystal Materials
• In crystals, the atomic arrangements and inter-
atomic bonding are different along different
directions
• In general, they have anisotropic properties
except cubic crystals.
– r is different along different crystal directions
– n seen by a propagating EM wave in a crystal will
depend on the value of r along the direction of the
oscillating E-field

32. Cubic crystal
hexagonal crystal

33. Refractive index and phase velocity
• For example: a wave traveling along the z-direction
in a particular crystal with its E-field oscillating along
the x-direction
– Given the relative permittivity along this x-direction is rx
then ,
– The wave will propagate with a phase velocity that is c/nx
• The variation of n with direction of propagation and
the direction of the E-field depends on the particular
crystal structure
rxxn 