8/12/2019 Semiconductor Laser Basics

1/24

8/12/2019 Semiconductor Laser Basics

2/24

Design & Implementation of

Semiconductor laser choasCommunication System

Supervised By

Dr.Zafar Ali Shah

Presented By

Saqib Bashir(120812)

8/12/2019 Semiconductor Laser Basics

3/24

Table of Content

Laser fundamental

Lasing action

Fundamental Components Choas Theory

Semiconductor LASER

Modeling Research Interest

8/12/2019 Semiconductor Laser Basics

4/24

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.

8/12/2019 Semiconductor Laser Basics

5/24

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.

8/12/2019 Semiconductor Laser Basics

6/24

6

Lasing action Diagram

Energy

Introduc

tion

Ground State

Excited State

Metastable State

SpontaneousEnergy Emission

Stimulated Emissio

of Radiation

8/12/2019 Semiconductor Laser Basics

7/24

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.

8/12/2019 Semiconductor Laser Basics

8/248

Fundamental Laser

8/12/2019 Semiconductor Laser Basics

9/24

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

8/12/2019 Semiconductor Laser Basics

10/24

LASER- Matlab Model

8/12/2019 Semiconductor Laser Basics

11/24

8/12/2019 Semiconductor Laser Basics

12/24

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

8/12/2019 Semiconductor Laser Basics

13/24

What is Chaos?

Broadband noise-like time evolution Nonlinear COUPLED system

At least three degrees of freedom

Highly sensitive to initial conditions.

8/12/2019 Semiconductor Laser Basics

14/24

Types of Chaotic waveform

Pulsed

Continuous

8/12/2019 Semiconductor Laser Basics

15/24

Types Of LASER

Solid state lasers

Gas lasers

Excimer lasers

Dye lasers

Semiconductor lasers

Microchip lasers

8/12/2019 Semiconductor Laser Basics

16/24

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

8/12/2019 Semiconductor Laser Basics

17/24

Semiconductor Laser Model

8/12/2019 Semiconductor Laser Basics

18/24

Operating points

8/12/2019 Semiconductor Laser Basics

19/24

Laser Response Curves

8/12/2019 Semiconductor Laser Basics

20/24

Laser threshold current

8/12/2019 Semiconductor Laser Basics

21/24

10mA Model Response to 2ns,

1mA Pulse

8/12/2019 Semiconductor Laser Basics

22/24

15mA Model Response to 2ns,

1mA Pulse

8/12/2019 Semiconductor Laser Basics

23/24

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.

8/12/2019 Semiconductor Laser Basics

24/24