Optical communications

Chapter 2.4Chapter 2.4

Pham Quang Thai

Pqthai.hcmut@gmail.com

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Content

• Geometrical optics

• Optical propagation in fiber

• Fiber fabrication

• Signal degradation in fiber• Signal degradation in fiber

• Types of fiber

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Multi-mode

• Contain many modes

• Large core radii

• Work with poor beam quality

light sources (LED)

• Easier to launch optical power

Multi-mode

• Contain many modes

• Large core radii

• Work with poor beam quality

light sources (LED)

• Easier to launch optical power

Single-mode

• Contain only one mode

• Small core radii

• Works with high quality light

source (Laser)

• Transverse intensity profile is

Single-mode

• Contain only one mode

• Small core radii

• Works with high quality light

source (Laser)

• Transverse intensity profile is • Easier to launch optical power

into the fiber

• Intermodal dispersion

• Short distance communications

• For high-power laser applications

• Easier to launch optical power

into the fiber

• Intermodal dispersion

• Short distance communications

• For high-power laser applications

• Transverse intensity profile is

independent on launch

conditions

• No intermodal dispersion

• Long distance communications

• For fiber lasers and amplifiers

• Transverse intensity profile is

independent on launch

conditions

• No intermodal dispersion

• Long distance communications

• For fiber lasers and amplifiers

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Multimode: Step index fiber

• Step index (SI) fibers

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Multimode: Graded index fiber

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Single mode fiber

• Single mode (SM) fiber

– The core can be SI or GI, but contains only one mode

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Examples for chapter 2.4

• Problems 2-19:

– Determine the normalized frequency (V) at 820

nm for a step index fiber having a 25-μm core

radius, n1=1.48 and n2=1.46 radius, n1=1.48 and n2=1.46

– How many modes propagate in this fiber at 820

nm?

– How many modes propagate in this fiber at 1.32

μm?

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Examples for chapter 2.4

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Examples for chapter 2.4

• Problem 2-27

– Calculate the number of modes at 820 nm and 1.3

μm in a graded-index fiber having a parabolic-

index profile (α=2), a 25-μm core radius, n1=1.48 index profile (α=2), a 25-μm core radius, n1=1.48

and n2=1.46.

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Think-pair share

• Commercial fiber specifications

• Some experiments with single mode and

multimode fibers

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