Semiconductor lasers for advanced communication_2003.ppt

Semiconductor lasers for advanced communication

1. by
Prof. D.S.Patil
Nano-simulation and fabrication laboratory
Department of Electronics
North Maharashtra University,
Jalgaon
Light sources for advanced
communication system (Current and
Future Trends)

2. Communication : Way of conveying one’s message, idea to the
society.
Communication is main driving force for technological
development: Telegraph, Telephone, Satellite, fiber optic,
Laser…………..
Phone
Mobile/Pager Satellite
Internet
Introduction
Use of Communication

3. Importance of Communication

4. Importance of Communication
WORLD INTERNET USAGE AND POPULATION STATISTICS
JUNE 30, 2014 -Mid-Year Update
World Regions
Internet Users
Dec. 31, 2000
Internet Users
Latest Data
Penetratio
n
(%
Population
)
Growth
2000-2014
Africa 4,514,400 297,885,898 26.5 % 6,498.6 %
Asia 114,304,0001,386,188,112 34.7 % 1,112.7 %
Europe 105,096,093 582,441,059 70.5 % 454.2 %
Middle East 3,284,800 111,809,510 48.3 % 3,303.8 %
North America 108,096,800 310,322,257 87.7 % 187.1 %
Latin America / Caribbean 18,068,919 320,312,562 52.3 % 1,672.7 %
Oceania / Australia 7,620,480 26,789,942 72.9 % 251.6 %
WORLD TOTAL 360,985,4923,035,749,340 42.3 % 741.0 %

5. Energy Consumption on Internet communication:
Internet and data centers consumes about 4% of total
electricity (8.7x10
11
kWhr/year including computers)
By 2018, the energy utilized by IP traffic will exceed 10% of
the total electrical power generation in developed countries.
Need to improve Data rate:
For high speed communication
Need to improve Bandwidth :
Increasing users attracts the attention in increasing bandwidth
Key Challenges in Internet Communication
WiFi
Wi-Fi. is current internet communication technology, that allows
an electronic device to exchange data or connect to the internet

6. What is Li Fi?
LI-FI is transmission of data through illumination ,ie sending data
through a LED light bulb that varies in intensity faster than human
eye can follow
It is possible to encode data in the light by varying the rate at which
the LEDs flicker ON and OFF to give different strings of 1’s and 0’s

7. History
The technology truly began during the 1990's in countries like
Germany, Korea, and Japan where they discovered LED's could be
retrofitted to send information.
On 12th July 2011. HARALD HASSused a table lamp with an LED
bulb to transmit a video of blooming flowers that was then
projected onto a screen behind him. During the event he
periodically blocked the light from lamp to prove that the lamp was
indeed the source of incoming data.
At TEDGlobal, Haas demonstrated a data rate of transmission of
around 10Mbps --comparable to a fairly good UK broadband
connection. Two months later he achieved 123Mbps
Back in 2011 German scientists succeeded in creating an
800Mbps capable wireless network by using nothing more than
normal red, blue, green and yellow

8. Why Li Fi?

9. How LI-FI Works ?
Operational principle is very simple, the ON state of LED represents
transmission of digital 1, if its OFF there is transmission of a 0. The
LEDs can be switched on and off very quickly, which gives nice
opportunities for transmitting data. Hence all that us required is
some LEDS and a controller that code data into those LEDs.
Architecture of Li Fi

10. Merits of LI-FI
Fast Data Transfer
High Security
Low Cost
Harmlessness
De-Merits of LI-FI
light can't pass through objects
Connectivity while moving
Interferences from external light sources like sun light,
normal bulbs, and opaque materials in the path of transmission
will cause interruption in the communication.

11. The increase of the capacity-distance product can be explained by the
four major innovations.
Bit-rate distance product (BL)
for different generations of
optical communication
systems.
Progress in Optical Communication

12. I
st
Generation:The development of low-loss fibers and
semiconductor lasers (GaAs) in the 1970‘s.
A Gallium Arsenide (GaAs) laser operates at a wavelength of
800nm. The optical communication systems allowed a bit rate of
45Mbit/s and repeater spacing of 10km.
Example of a laser diode.
Evolution of optical communication systems

13. II
nd
Generation:The repeater spacing could be increased by
operating the lightwave system at 1.3μm. The attenuation of the
optical fiber drops from 2-3dB/km at 0.8μm down to 0.4dB/km
at 1.3μm. Silica fibers have a local minima at 1.3μm.
The transition from 0.8μm to
1.3μm leads to the 2
nd
Generation
of lightwave systems. The bit rate-
distance product can be further
increased by using single mode
fibers instead of multi-mode
fibers.
Single mode fibers have a
distinctly lower dispersion than
multi mode fibers.
Lasers are needed which emit
light at 1.3 μm.

14. III
rd
Generation:Silica fibers have an absolute minima at
1.55μm. The attenuation of a fiber is reduced to 0.2dB/km.
Dispersion at a wavelength of 1.55μm complicates the
realization of lightwave systems. The dispersion could be
overcome by a dispersion-shifted fibers and by the use of
lasers, which operate only at single longitudinal modes. A bit
rate of 4Gbit/s over a distance of 100km was transmitted in the
mid 1980‘s.
Traditional long distance single channel fiber transmission system.
The major disadvantage of this generation optical communication
system is the fact that the signals are regenerated by electrical
means. The optical signal is transferred to an electrical signal, the
signal is regenerated and amplified before the signal is again
transferred to an optical fiber.

15. IV
th
Generation:The development of the optical amplifier lead to
this new Generation of optical communication systems.
Schematic sketch of an erbium-doped fiber amplifier (EDFA).

16. Much Higher Bandwidth ( Gbps) -Thousands of channels can
be multiplexed together over one strand of fiber
Immunity to Noise -Immune to electromagnetic interference
(EMI).
Safety -Doesn’t transmit electrical signals, making it safe in
environments like a gas pipeline.
High Security -Impossible to “tap into.”
Less Loss -Repeaters can be spaced 75 miles apart (fibers can
be made to have only 0.2 dB/km of attenuation)
Reliability-More resilient than copper in extreme
environmental conditions.
Size-Lighter and more compact than copper.
Flexibility-Unlike impure, brittle glass, fiber is physically very
flexible.
Advantages of Optic Fiber

17. The process of communicating using fiber-optics involves
the following basic steps:
Creating the optical signal using a transmitter,
Relaying the signal along the fiber, ensuring that the signal
does not become too distorted or weak
Receiving the optical signal and converting it into an
electrical signal.
Information
source
Electrical
transmit
Optical
source
Optical
fibre cable
Optical
detector
Electrical
receive Destination
Optic Fiber Communication

18. Requirement
of Optical
Source
Output
wavelength
must coincide
with the loss
minima of the
fibre
Output power
must be high,
using lowest
possible
current and
less heat
High output
directionality,
narrow
spectral width.
Reliability
Low distortion
Requirements of Source

19. LED LASER
Scattered incoherent light Narrow beam of coherent light
Spontaneous Emission Stimulated Emission
Modulation to several hundred
MHz
Modulation to several tens of GHz
High coupling loss Low coupling loss
Not suitable for single mode
fibers.
Suitable for single mode fibers.
LessBandwidth Higher Bandwidth
Light sources for Optic Fiber

20. The first semiconductor laser were reported by R.N. Hall et al.
from general Electric research laboratory and Marshal I. Nathan
et al. from IBM, Thomas J. Watson Research Center based on
GaAs pn junction in 1962.
Proposal of Heterostructure Semiconductor
Laser in 1970
(H. Kroemer, Z. Alferov: Nobel Prize 2000)
Continuous-wave (CW) lasing at room temperature was achieved
in an AlGaAs/GaAs double-heterostructure laser in 1970
First uncooled telecom lasers in 2000
Z. Alferov
H. Kroemer
History of semiconductor Lasers

21. LASER:-Light Amplification by Stimulated Emission of
Radiation.
Laser diodes are devices emitting coherent light produced in
the stimulated emission process
Lasers lasing wavelength ranges from the visible to the
infrared wavelength depending on the material of the active
layer.
Laser diodes composed of III-V compound semiconductor and
as some II-VI compound are used in visible wavelength.
Semiconductor LASER diode

23. ELECTRONS
PHOTON
INJECTION
CURRENT
QUANTUM WELL
CONDUCTING BAND
VALENCE BAND
INTERBAND TRANSITION
HOLES
POPULATION INVERSION
PHOTON ENERGY
An electron–hole pair produces single photon INJECTION
CURRENT
Photon Emission in Quantum Well Lasers

24. Semiconductor laser commonly used in fiber optic
communication because:
Long life
High reliability
Ruggedness
Compactness
Light weight
High efficiency of electro-optric conversion
Low applied voltage
Spectral purity compared to non laser source
Direct modulation capability up to tens of gigahertz

25. Simulation is
The process of creating a model of an existing or proposed system
to identify and understand those factors which control the system
and/or to predict (forecast) the future behavior of the system.
Almost any system which can be quantitatively described using
equations and/or rules can be simulated.
Nanoscale devices not seen by the eyes, so to study them
simulation can be used
Simulation can be used topredict the future behavior of a nano
scale system/nanodevice, and determine what you can do to
influence that future behavior.
That is,simulationcan beused to predict the way in which the
nanoscale system/nanodevice will evolve and respond to its
surroundings, so that you can identify any necessary changes that
will help make the system perform the way that you want it to.
Research Areas

26. Working with Simulation
Develop the model for
nanostructure.
Define Material
and Physical
Parameters
Search appropriate
computational
technique.
Implement the
Model (through
computer
simulation)
Predict output
charecteristics
Optimize the
results
Why Simulation?
Reduces fabrication cost, efforts.
Gives results that are experimentally not measurable.
To analyze the behavior and performance of complex
nanostructures.

27. James Clerk Maxwell (1831–1879)
Theoretical Physicist andMathematician
Maxwelldemonstratesthatelectricand
magneticfieldstravelthroughspacein
theformofwaves.
Maxwell'sequationsrepresentoneofthemostelegant
andconcisewaystostatethefundamentalsofelectricity
andmagnetism.
Fromthemonecandevelopmostoftheworking
relationshipsintheelectromagneticfield.
Maxwell’s Equations

28. Schrodinger Equation
Erwin Rudolf Josef Alexander
Schrödinger (1887-1961)
Physicist and theoretical biologist
In 1933, Nobel prize in physics
Itisawaveequationintermsofthewavefunctionwhich
predictsanalyticallyandpreciselytheprobabilityof
eventsoroutcome.
Equation states how the quantum state of a physical
system changes.

29. Carrier confinement
Optical confinement
Defect free semiconductor structures
Wishes of Laser
Diode
•as small as possible
•as fast as possible
•low costs, small power
consumption
•cheap
Essential Requirements for lasing

30. Bandgaps of the most important elemental and binary cubic semiconductors versus their
lattice constant at 300 K. The right-hand scale gives the light wavelengthcorresponding to
the band gap energy
BandgapEngineering

31. High Radiative Efficiency:-
Small Volume
High Carrier Concentration
Low Thresholds Current:
Small volume
Carrier density for population Inversion
HowtheQuantumStructuresaremade?
Using Heterojunctions.
Heterojunction utilization at the side where quantum
confinement is need to be done.
Why Quantum structures?

32. Heterostructure with size restricting the movements of the
charge carriers and forcing them into a quantum confinement.
According to the confinement direction of electrons in materials
can be divided as follows.
Quantum Heterostructures

33. 2.36
2.4
2.44
2.48
2.52
2.75 3 3.25 3.53.75 4
Distance (micron)
Refractive Index Refractive Index Profile of Quantum Well Laser
Small thickness of active region desired in terms of carrier confinement, but
not desirable in terms of light confinement
Optimization Necessary !

34. The Heterojunction:-region is actually lightly doped with p-type
material and has the highest index of refraction.
This produces a light pipe effect that helps to confine the laser light to
the active junction region. In the homojunction, however, this index
difference is low and much light is lost.
nGaAlAs
Metal
contact (+)
Metal
contact (-)
GaAs sandwiched between
the higher band gap AlGaAs.
GaAs is the active region
where lasing takes place
nGaAlAs
pGaAlAs
p GaAs1m
GaAssandwiched
between the higher band
gap AlGaAs
nGaAlAs
PGaAlAs
p GaAs
N GaAs
N-n-p-PN-p-P

35. 35
Double
Heterostructure:GFpFn
EEE  )(1)(
VVVC EfhfEf 
or, alternatively,
BasicLasercondition:
nm
hf
V> 0
P p N
E
V
E
C
E
FpE
Fn
E
el
E
hole
Single Quantum well laser

36. p
+
n
+
P p n
+
P p N
Homostructure Single Heterostructure (SHS)Double Heterostructure (DHS)
n
optical field
Optical confinement is higher for a DHS
Electrical confinement is higher for a DHS
lower I
th
Refractive index and mode profile

37. Visible Range Optical Communication
Infrared: The light absorption in water increases towards the red and
infrared part of the spectrum
Blue Light: Minimal light absorption in water is usually achieved for blue
light around 400-450 nm
Underwater communication

38. Semiconducting Materials Used for Light Sources
Material
Crystal
Structure
Lattice
Constant
a (Å) c (Å)
Band
Gap
(RT)
Eg(eV)
Exciton
Binding
Energy
E
b
(~meV)
Dielectric
Constant
(0) (∞)
ZnS Wurtzite 3.823 6.261 3.8 D 39 9.6 5.7
ZnSe
Zinc
Blende
5.668 - 2.70 D 20 9.1 6.3
GaN Wurtzite 3.189 5.185 3.39 D 21 8.9 5.35
InN Wurtzite 3.545 5.703 1.89 D - 9.3 9.3
SiC Wurtzite 3.081 15.117 2.86 ID - 9.66-
GaAs
Zinc
Blende
5.653 - 1.42 D 4.5 13.210.9
InP
Zinc
Blende
5.869 - 1.34 D 5.1 12.59.61
ZnO Wurtzite 3.246 5.207 3.37 D 60 8.753.75

39. Simple heterostructure of ZnO/Mg
xZn
1-xO.
Field intensity along junction plan for
ZnO/Mg
xZn1
-xO heterostructure Confinement factor as a function of Mg mole
fraction in barrier and active layer thickness

40. Excellent for visible devices because of their large energy
bandgaps
their highly efficient light emission
Ability for bandgapengineering through the use of alloying and
heterojunction
The AlN/GaN QW has a tunable intersubband
transition wavelength from 1.3 to 1.6 µm. Tuning is
accomplished by changing the well width (Lw).
III nitride materials for Telecommunication

41. This GaN/AlGaN waveguide coupler (left)
realized approximately 50% power splitting
(right). The 1.55-µm input optical signal was
launched at Port 1.
An optical waveguide designed for optical
communications shown in waveguide cross
section (left), simulated single-mode structure
(right, top), and radiation pattern versus exit
angle (right, bottom) uses GaN/AlxGa1-xN
heterostructures grown on sapphire substrates.

42. ProbabilityDensity for Varying
Well Width
Probability Density for Varying
Al Mole Fraction

43. Relative Wave function with
variation of distance
Probability Density dependence
on distance X

44. 0
0.1
0.2
0.3
0.4
0.5
3 4.5 6 7.5 9
Well Width (nanometer)
Energy (eV)
x = 0.15
x = 0.25
x = 0.35 Variation of energy with well width

45. FWHM of probability density obtained using theoretical analysis and
our equation as a function of Aluminum mole fraction (x))));
)005.1(
*0025.0(05.1(*205.055.1*69.4*305.7(
2
23
x
x
xxxWy



46. FWHM of probability density obtained using theoretical analysis and
our equation as a function of well width)));
)005.1(
*0025.0(05.1(*205.055.1*69.4*305.7(
2
23
x
x
xxxWy



47. Multiple Quantum Well Structure

48. Peak Optical gain at 375 nanometer wavelength
for ZnO/MgZnO quantum Well

49. Multiple Quantum Well Structure
Superlattice nanostructure

50. Energy as a function of barrier height and
the iteration entail for the accuracy
The wave function intensity in 3-well
superlattice structure

51. Near field intensity spread as a function of
wavelength
Near field intensity spread as a function of
Al mole
Variation of Optical confinement factor with Al
concentration, temperature and wavelength
FWHM as a function of Al concentration,
temperature and wavelength

52. Variation in Eigen energy with wire width.
Probability density in quantum wire nanostructure
Surface image of probability density
Nanowire structure.

53. Wave function intensity for varying
Al composition
FWHM of wave function intensity as
a function of Aluminum composition
FWHM of wave function intensity as
a function of wire width

54. Quantum Dot Embedded Nanostructure

55. 3-D confinement in dot at 375 nanometer
wavelength

56. ZnAc, Ethanol +
Lactic acid
Transparent
homogenous solution
obtained
Dip/Spin Coat substrate
Preheating
X times
Transparent ZnO /
MgZnO films
Final Annealing
MgAc
Stage 1
Stage 2
Stage 3
Processing steps for deposition of ZnO and MgZnO films

57. Dip coater and spin coater system
developed in our Laboratory