Lasers fiber optics
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Lasers & Fiber Optics. Engr. Hyder Bux Mangrio Engr. Fayaz Hassan Mangrio. Introduction. L&FO labs Lab #01: Introduction to Fiber optics Communication System Lab #02: Optical Sources Lab #03: Optical Detectors Lab #04: Optical fiber attenuation losses Lab #05: Analog voice transmission

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Lasers & Fiber Optics

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Lasers fiber optics

Lasers & Fiber Optics

Engr. Hyder Bux Mangrio

Engr. Fayaz Hassan Mangrio


Introduction

Introduction

L&FOlabs

  • Lab #01: Introduction to Fiber optics Communication System

  • Lab #02: Optical Sources

  • Lab #03: Optical Detectors

  • Lab #04: Optical fiber attenuation losses

  • Lab #05: Analog voice transmission

  • Lab #06: Understanding basic function of S122A splicer

  • Lab #07: Perform Fusion/Mechanical Splicing


Introduction1

Introduction

  • Lab #08: Understanding the basic function of OTDR

  • Lab #09: Perform fiber measurement on OTDR

  • Lab #10: Fiber attenuation measurement using Cut-Back method

  • Lab #11: Optical Field Spectrum Analyzer

  • Lab #12: Overview of Power meter & Light Source


Information

Information

  • Email:

    [email protected]

  • Webpage: https://sites.google.com/a/faculty.muet.edu.pk/hydermangrio/

  • Optical Communication Laboratory

  • Consultation Timings:

    Monday(8am to 3pm) & Friday (8am to 1pm)


Laboratory

Laboratory

  • There will be at least 13 labs covering in 13 weeks course. Each lab will be approximately 2 hours long. The lab report / Handout is due to the lab assistant before next lab.


What is lightwave technology

What is lightwave technology?

  • Lightwave technology uses light as the primary medium to carry information.

  • The light often is guided through optical fibers (fiberoptic technology).

  • Most applications use invisible (infrared) light.

(HP)


Why lightwave technology

Why lightwave technology?

  • Most cost-effective way to move huge amounts of information (voice, data) quickly and reliably.

  • Light is insensitive to electrical interference.

  • Fiber optic cables have less weight and consume less space than equivalent electrical links.

(HP)


Use of lightwave technology

Use Of Lightwave Technology

  • Majority applications:

    • Telephone networks

    • Data communication systems

    • Cable TV distribution

  • Niche applications:

    • Optical sensors

    • Medical equipment


Lw transmission bands

LW Transmission Bands

193

229

353

461

THz

Frequency

Near Infrared

UV

Wavelength

(vacuum)

1.0

0.6

1.8

1.6

1.4

1.2

0.8

0.4

0.2

µm

HeNe Lasers

633 nm

Longhaul Telecom

Regional Telecom

Local Area Networks

1550 nm

CD Players

780 nm

1310 nm

850 nm


Introduction to fiber optics

Introduction to Fiber Optics

  • Fiber optics is a medium for carrying information from one point to another in the form of light. Unlike the copper form of transmission, fiber optics is not electrical in nature.

  • A basic fiber optic system consists of a transmitting device that converts an electrical signal into a light signal, an optical fiber cable that carries the light, and a receiver that accepts the light signal and converts it back into an electrical signal.


Introduction to fiber optics1

Introduction to fiber Optics


Optical sources

Optical Sources

  • Two main types of optical sources

    • Light emitting diode (LED)

      • Large wavelength content

      • Incoherent

      • Limited directionality

    • Laser diode (LD)

      • Small wavelength content

      • Highly coherent

      • Directional


Light emitting diodes led

Light Emitting Diodes (LED)

  • Spontaneous emission dominates

    • Random photon emission

  • Spatial implications of random emission

    • Broad far field emission pattern

    • Dome used to extract more of the light

  • Spectral implications of random emission

    • Broad spectrum


Laser diode

Laser Diode

  • Stimulated emission dominates

    • Narrower spectrum

    • More directional

  • Requires high optical power density in the gain region

    • Optical Feedback: Part of the optical power is reflected back into the cavity

    • End mirrors

  • Lasing requires net positive gain

    • Cavity gain

      • Depends on external pumping

      • Applying current to a semiconductor pn junction

    • Cavity loss

      • Material absorption

      • Scatter

      • End face reflectivity


Optical detectors

Optical Detectors

  • Inverse device with semiconductor lasers

    • Source: convert electric current to optical power

    • Detector: convert optical power to electrical current

  • Use pin structures similar to lasers

  • Electrical power is proportional to i2

    • Electrical power is proportional to optical power squared

    • Called square law device

  • Important characteristics

    • Modulation bandwidth (response speed)

    • Optical conversion efficiency

    • Noise

    • Area


How does fibre optic work

HOW DOES FIBRE OPTIC WORK ?

  • Carries Signals as Light Pulses

    • signals converted from electrical to light (and visa-versa) by special equipment

      • e.g. fibre-optic “transceiver” (transmitter / receiver)


Fibre construction

FIBRE CONSTRUCTION

8, 50, 62.5

Core Glass

125 Cladding Glass


Primary buffer

PRIMARY BUFFER

Primary Buffer 250

Cladding 125

Core (62.5)


Secondary buffer

SECONDARY BUFFER

Secondary Buffer 900

Primary Buffer 250

Cladding 125

Core (62.5)


Fibre material

FIBRE MATERIAL

  • Silica Glass

    • used for high-speed data applications

  • Plastics

    • used for low-speed data / voice applications

  • Composite Constructions

    • used for low-speed and specialized applications


Fibre transmission

FIBRE TRANSMISSION

  • Multi-Mode

    • graded-index

      • used for short / medium distance applications

    • step-index

      • early fibre type - no longer used

  • Single-Mode

    • a.k.a Mono-Mode

      • used for long-distance / very high-speed applications

      • e.g. cross-country and transatlantic communications


Light transmission

LIGHT TRANSMISSION

MultiMode

Step Index

MultiMode

Graded Index

SingleMode


Common fibre sizes

50 µm

62.5 µm

100 µm

8 µm

125 µm

125 µm

125 µm

140 µm

MultiMode Graded Index

SingleMode

COMMON FIBRE SIZES


Advantages disadvantages of fiber optics

Advantages/Disadvantages of Fiber Optics

  • Advantages

  • Enormous potential bandwidth

  • Small size and weight

  • Electrical Isolation

  • Signal security

  • Low transmission loss

  • Potential low cost


Advantages disadvantages of fiber optics1

Advantages/Disadvantages of Fiber Optics

  • Disadvantages

  • High cost for connector and interfacing

  • Requires specialized and sophisticated tools for maintenance and repairing

  • Higher initial cost in installation


Light source

Light-Source

  • What is light?

  • Properties of Light.

  • Refractive Index

  • Law of Refraction

  • Law of Reflection

  • Total Internal Reflection


Refractive index

Refractive Index

  • The guidance of the light beam which acts as a transmission channel for information (through the optical fiber) takes place because of the phenomenon of total internal reflection (TIR),

    which is dependent on the refractive index of the medium.

    The refractive index (n) of a medium can be written

    as:


Total internal reflection

Total Internal Reflection

  • A ray of light incident on a denser medium i.e. n1<n2

    According to Snell’s Law and the law of reflection we have

    n1 sin θ1 =n2 sin θ2 and θ1=θ3


Total internal reflection1

Total Internal Reflection

  • The angle of incidence, for which the angle of refraction is 90º, is known as the critical angle and is denoted by θc .Thus, when

    θ1=θc =sin-1(n2/n1)

    θ2=90. When the angle of incidence exceeds the

    angle of critical (i.e.,θ1>θc), there is no refracted ray

    and we have total internal reflection.


Total internal reflection2

Total Internal Reflection


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