Optical communications

Student: Blidaru Catalina Elena

Introduction to Optical Communication

What is optical Fiber?• An optical fiber is a hair thin cylindrical fiber of glass or any transparent dielectric medium.• The fiber which are used for optical communication are wave guides made of transparent

dielectrics. • Its function is to guide visible and infrared light over long distances.

Source: http://www.slideshare.net/rahulohlan14/optical-fiber-communiction-systemhttp://electronics.howstuffworks.com/fiber-optic7.htm

Electromagnetic waves

Maxwell’s four equations describe the electric and magnetic fields arising from varying distributions of electric charges and currents, and how those fields change in time.  The equations were the mathematical distillation of decades of experimental observations of the electric and magnetic effects of charges and currents.  Maxwell’s own contribution is just the last term of the last equation.

Here are the equations:

1. Gauss’ Law for electric fields: (The integral of the outgoing electric field over an area enclosing a volume equals the total charge inside, in appropriate units.)

2. The corresponding formula for magnetic fields (No magnetic charge exists: no “monopoles”.)

3. Faraday’s Law of Magnetic Induction:

4. Ampere’s Law plus Maxwell’s displacement current

Source: http://galileoandeinstein.physics.virginia.edu/more_stuff/Maxwell_Eq.htmlhttp://electronics.howstuffworks.com/fiber-optic7.htm

Structure of optical fiber

Structure of optical fiber

• Core – central tube of very thin size made up of optically transparent dielectric medium and carries the light form transmitter to receiver. The core diameter can vary from about 5um to 100 um.

• Cladding – outer optical material surrounding the core having reflecting index lower than core. It helps to keep the light within the core throughout the phenomena of total internal reflection.

• Buffer Coating – plastic coating that protects

the fiber made of silicon rubber. The typical diameter of fiber after coating is 250-300 um.

Source: http://www.slideshare.net/rahulohlan14/optical-fiber-communiction-systemhttp://www.thefoa.org/

Working principle

Total Internal Reflection

• When a ray of light travels from a denser to a rarer medium such that the angle of incidence is greater than the critical angle, the ray reflects back into the same medium this phenomena is called total internal reflection.

• In the optical fiber the rays undergo repeated total number of reflections until it emerges out of the other end of the fiber, even if the fiber is bent.

Several applications of fiber optic

Configuration of a Fiber Optic Sensor System

Source: http://www.slideshare.net/rahulohlan14/optical-fiber-communiction-systemhttp://www.thefoa.org/

Total internal Reflection

Source and transmitters

• A basic fiber optic communications system consists of three basic elements:– Fiber media– Light sources– Light detector

Source: http://www.slideshare.net/rahulohlan14/optical-fiber-communiction-systemhttp://www.commspecial.com/fiberguide.htm

There are three types of fiber optic cable commonly used

Single Mode

Step-index Multimode fiber

Plastic optic fiber

Fiber media

Optical fibers are the actual media that guides the light

Optical fiber transmits light. But, what prevents the light from escaping from the fiber?

How Does fiber optic transmit light

The loss of fiber optic

• Material obsorption• Material Scattering• Waveguide scattering• Fiber bending • Fiber coupling loss

Source: http://www.slideshare.net/rahulohlan14/optical-fiber-communiction-systemhttp://www.commspecial.com/fiberguide.htm

A Light Sources

LED (Light emitting diode) ILD (injection laser diode)

Detectors•Detector is the receiving end of a fiber optic link.

There are two kinds of Detectors1. PIN (Positive Intrinsic Negative)2. APD (Avalanche photo diodes)

PIN

APD

Idea of Modulation

• When sending information by an optical fiber, the information must be encoded or transformed somehow into information that capable of being transmitted through a fiber. The signal needs to be modulated. There are two types of modulation Analog and digital.

Source: http://www.slideshare.net/rahulohlan14/optical-fiber-communiction-systemhttp://www.thefoa.org/

The advantages of fiber optic over wire cable

• Thinner• Higher carrying capacity• Less signal degradation• Light signal • Low power• Flexible• Non-flammable• Lightweight

Disadvantage of fiber optic over copper wire cable

• Optical fiber is more expensive per meter than copper• Optical fiber can not be join together as easily as copper

cable. It requires training and expensive splicing and measurement equipment.

Source: http://www.slideshare.net/rahulohlan14/optical-fiber-communiction-systemhttp://www.thefoa.org/

Project

Solar Board

References

• http://electronics.howstuffworks.com/fiber-optic7.htm• http://www.commspecial.com/fiberguide.htm• http://www.thefoa.org/• http://www.fiber-optics.info/fiber-history.htm