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8/12/2019 Semiconductor Laser Basics
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Design & Implementation of
Semiconductor laser choasCommunication System
Supervised By
Dr.Zafar Ali Shah
Presented By
Saqib Bashir(120812)
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Table of Content
Laser fundamental
Lasing action
Fundamental Components Choas Theory
Semiconductor LASER
Modeling Research Interest
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4
Laser Fundamentals
The light emitted from a laser is monochromatic, that is, it is of one
color/wavelength. In contrast, ordinary white light is a combination of man
colors (or wavelengths) of light.
Lasers emit light that is highly directional, that is, laser light is emitted asa relatively narrow beam in a specific direction. Ordinary light, such as
from a light bulb, is emitted in many directions away from the source.
The light from a laser is said to be coherent, which means that the
wavelengths of the laser light are in phase in space and time. Ordinary
light can be a mixture of many wavelengths.
Laser light can deposit a lot of energy within a small area.
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5
Lasing Action
1. Energy is applied to a medium raising electrons to an unstableenergy level.
2. These atoms spontaneously decay to a relatively long-lived,lower energy, metastable state.
3. A population inversion is achieved when the majority of atomshave reached this metastable state.
4. Lasing action occurs when an electron spontaneously returns to
its ground state and produces a photon.5. If the energy from this photon is of the precise wavelength, it will
stimulate the production of another photon of the samewavelength and resulting in a cascading effect.
6. The highly reflective mirror and partially reflective mirror continue
the reaction by directing photons back through the mediumalong the long axis of the laser.
7. The partially reflective mirror allows the transmission of a smallamount of coherent radiation that we observe as the beam.
8. Laser radiation will continue as long as energy is applied to thelasing medium.
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6
Lasing action Diagram
Energy
Introduc
tion
Ground State
Excited State
Metastable State
SpontaneousEnergy Emission
Stimulated Emissio
of Radiation
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Fundamental Components
Active MediumThe active medium may be solid crystals such as ruby or
Nd:YAG, liquid dyes, gases like CO2 or Helium/Neon, orsemiconductors such as GaAs. Active mediums containatoms whose electrons may be excited to a metastableenergy level by an energy source.
Excitation Mechanism
Excitation mechanisms pump energy into the active mediumby one or more of three basic methods; optical, electrical orchemical.
High Reflectance MirrorA mirror which reflects essentially 100% of the laser light.
Partially Transmissive Mirror
A mirror which reflects less than 100% of the laser light andtransmits the remainder.
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Fundamental Laser
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LASER- Matlab Model
The parameter values used in the calculations are [2] z, = 3 ns, zp = 1 ps, No = 1
x ioz4 m-3, GN = 1 x lo-' ' m3 s-' , J b = 1.4 Jrk, and f, = 0.866f, (N 2.25 GHz).
m = 1.4 (J, = 0.56 Jfh
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LASER- Matlab Model
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Chaos
Complex and fast non linear behaviour
Exhibited by a relatively simple
deterministic system
Ruled by at least three non lineardifferential equation
Or two such equations and one
perturbation
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What is Chaos?
Broadband noise-like time evolution Nonlinear COUPLED system
At least three degrees of freedom
Highly sensitive to initial conditions.
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Types of Chaotic waveform
Pulsed
Continuous
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Types Of LASER
Solid state lasers
Gas lasers
Excimer lasers
Dye lasers
Semiconductor lasers
Microchip lasers
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Semiconductor Laser
Modern high-speed data transmission is
accomplishedwith fiber optic systems,
which generally consist of a laserlight
source, the fiber itself, and a detector. Themost commonlight source is the
semiconductor laser diode because
small size
Ruggedness
manufacturing cost
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Semiconductor Laser Model
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Operating points
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Laser Response Curves
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Laser threshold current
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10mA Model Response to 2ns,
1mA Pulse
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15mA Model Response to 2ns,
1mA Pulse
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Research interest
A cost-effective method of datatransmission is direct modulation of the
laser diode drive current combined with a
photo detector at the other end. Thisscheme is known as Intensity
Modulation/Direct Detection, or IM/DD.
One of the factors limiting the data rate is
the switching speed of the laser diode.Improving the characteristics of the
switching is thus an area of extreme
interest.
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