1. ECC3601:
OPTICAL COMMUNICATION
Lecture 3: Introduction to Fiber Optic and Light
Propagation
Makhfudzah bt. Mokhtar, PhD.
Department of Computer and Communication Systems
Faculty of Engineering
University Putra Malaysia

2. LEARNING OUTCOMES
At the end of this lecture, students should be able to:
-Describe ‘optical waveguide’
-Explain basic characteristics of fiber optic.

3. What is Optical Waveguide?
An optical
waveguide is a physical structure that
guides electromagnetic waves
in the optical
spectrum.
Common types of optical waveguides include optical fiber and
rectangular waveguides.
Optical waveguides are used as components in integrated optical
circuits or as the transmission medium in local and long haul optical
communication systems.
Optical waveguides can be classified according to their geometry
(planar, strip, or fiber waveguides), mode structure (singlemode, multi-mode), refractive index distribution (step or gradient
index) and material (glass, polymer, semiconductor).
Optical waveguide
From Wikipedia, the free encyclopedia

4. Optical waveguide: geometry
Conceptual diagram of light propagating from an optical fiber waveguide to a
rectangular optical waveguide
Optical waveguide
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr201002sf2.html

5. Optical waveguide: geometry
Light can be guided by planar or rectangular wave guides, or by optical fibers.
Optical waveguide
http://electron6.phys.utk.edu/optics421/modules/m8/Optical%20Wave%20Guides.htm

6. Optical fiber: structure
Chapter 24: Fiber Optics
Copyright © Delmar Thomson Learning

7. Optical fiber: structure
Fiber Optic Core:
The inner light-carrying layer with a high index of refraction.
Cladding:
The middle layer, which serves to confine the light to the core. It has
a lower refraction index than the core.
Jacket:
The outer layer, which serves as a "shock absorber" to protect the
core and cladding from damage. The coating usually comprises one
or more coats of a plastic material to protect the fiber from the
physical environment. Sometimes metallic sheaths are added to the
coating for further physical protection.
Optical waveguide
http://electron6.phys.utk.edu/optics421/modules/m8/Optical%20Wave%20Guides.htm

8. How does light propagate along
the fiber?
See video ‘Fiber optic cables-how they work’

9. Light refraction
Optical Image: Physics behind the Scenes
http://www.osa-univer.org.ua/prj_gallery06.phtml

10. Light refraction and reflection
* Refraction is the
change in direction of a wave due to a
change in its medium.
* Total internal reflection is a phenomenon that happens when a
propagating wave strikes a medium boundary at an angle larger than
a particular critical angle with respect to the normal to the surface.
Optical waveguide
From Wikipedia, the free encyclopedia

11. Light refraction and reflection
Optical Communication: Slide
Prof. Dr. Mohd. Adzir Mahdi

12. Optical fiber: modes
Based on modes, fiber can be divided into :
i) SINGLE MODE FIBER (SMF) and ii) MULTI MODE FIBER (MMF)
* Single mode fiber is an optical
fiber that carries only
a single ray of light (mode).
* Multi mode fiber is an
optical fiber that carries multiple
light rays or modes concurrently, each at a slightly
different reflection angle within the optical fiber core.
Multimode fiber transmission is used for relatively short distances because the
modes tend to disperse over longer lengths (this is called modal dispersion) . For
longer distances, single mode fiber (sometimes called monomode) fiber is used.
Multimode fiber has a larger core than single mode.
Single mode fiber | multi mode fiber
Wikipedia | http://searchnetworking.techtarget.com/definition/multimode-fiber

13. Optical fiber: modes
How dispersion exist in multi-mode fiber
Multimode step-index fibers trap light with many different entrance angles.
•Each mode in a step-index multimode fiber is associated with a different
entrance angle.
•Each mode therefore travels along a different path through the fiber. Different
propagating modes have different velocities.
•As an optical pulse travels down a multimode fiber, the pulse begins to
spread. Pulses that enter well separated from each other will eventually
overlap each other.
This limits the distance over which the fiber can transport data. Multimode stepindex fibers are not well suited for data transport and communications.
Optical waveguide
http://electron6.phys.utk.edu/optics421/modules/m8/Optical%20Wave%20Guides.htm

14. Optical fiber: modes
Light emerging from a multi-mode fiber
Light emerging from a single-mode fiber
Optical waveguide
http://electron6.phys.utk.edu/optics421/modules/m8/Optical%20Wave%20Guides.htm

15. Optical fiber: gradient
• Both types of fiber described earlier are known as step-index fibers
because the index of refraction changes radically between the core and
the cladding
• Graded-index fiber is a compromise multimode fiber, but the index of
refraction gradually decreases away from the center of the core
• Graded-index fiber has less dispersion than a multimode step-index fiber
Step-index fiber
Graded-index fiber
Chapter 24: Fiber Optics
Copyright © Delmar Thomson Learning

16. Preparation for Quiz 1
-Revise Lecture 2 slide