twisted-pair cable twisted-pair wire

plastic outer coating

woven or braided metal

insulating material

copper wire

protective coating

glass cladding

optical fiber core

Optical FiberOptical Fiber

An optical fiber is a thin (2 to 125µm), flexible medium capable of guiding an optical ray.

Preferable because of,

• Large bandwidth, light weight, and small diameter

• Nonconductivity (no EMI & RFI)

• Longer distance signal transmission with lesser attenuation

• Security & greater repeater spacing

• Designed for future applications needs

Optical FiberOptical Fiber

The basic question is“how much information is to be sent and how far does it have

to go?”

Five basic categories of application have become important for

optical fiber:

• Long-haul trunks

• Metropolitan trunks

• Rural exchange trunks

• Subscriber loops

• Local area networks

Basic fiber optic communication systemBasic fiber optic communication system

Transmission WindowsTransmission Windows• Optical fiber transmissions uses wavelengths in the near

infrared portion of the spectrum

• Both Lasers and LEDs are used to transmit light through fibers

• Lasers are used for 1310 nm or 1550 nm single mode

transmissions

• LEDs are used for 850- or 1300 nm multimode applications

Fiber Optic Loss CalculationsFiber Optic Loss Calculations

Fiber Optic TypesFiber Optic Types

• Step-index multimode fiberStep-index multimode fiber– the reflective walls of the fiber move the light pulses to

the receiver• Graded-index multimode fiberGraded-index multimode fiber

– acts to refract the light toward the center of the fiber by variations in the density

• Single mode fiberSingle mode fiber– the light is guided down the center of an extremely

narrow core

Three basic types of optical fibers are used in communication systems

Optical Fiber Transmission CharacteristicsOptical Fiber Transmission Characteristics

Optical Fiber Transmission Modes

Optical Fiber Transmission CharacteristicsOptical Fiber Transmission Characteristics

Step-index multimode fiber has an index of refraction profile that “steps” from low to high to low as measured from cladding to core to cladding.

Relatively large core diameter and numerical aperture characterize this fiber.

The core/cladding diameter of a typical multimode fiber used for telecommunication is 62.5/125 μm (about the size of a human hair).

The term “multimode” refers to the fact that multiple modes or paths through the fiber are possible. Stepindex multimode fiber is used in applications that require high bandwidth (< 1 GHz) over relatively short distances (< 3 km) such as a local area network or a campus network backbone.

Step-index multimode fiber

Components - Optical Fiber CableComponents - Optical Fiber Cable

Components - Optical Fiber CableComponents - Optical Fiber Cable

Indoor Optical Fiber CableIndoor Optical Fiber Cable

Outdoor Optical Fiber CableOutdoor Optical Fiber Cable

Next Lecture TopicsNext Lecture Topics

Topics include,

•Dispersion in optical fiber

•Multiplexing

•Fiber Optic Sources

•Fiber Optic Detectors

•Fiber Optic System Design Considerations