Fiber Optics: An Introduction

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Fiber Optics An Introduction

• Carey Williamson

University of Calgary
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Introduction

• Optical fiber makes possible the transmission of
  digital data at several gigabits per second
  (Gbps) over long distances with very low error
  rates

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Optical Fiber

• Manufactured from refined glass
• Very few impurities
• Very thin (e.g., 8-12 microns for core)
• Core is surrounded by cladding

Cladding
Core
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Fiber-based Transmission

• Bits are represented as pulses of light
• Transmitted using lasers
• Light pulses, once transmitted into the core,
  continue to travel down the fiber, according to
  the physical principle of total internal
  reflection
• Very little signal attenuation (loss)

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Fiber Optic Transmission

• Transmission performed using laser
• Usually a fixed wavelength
• Some are tunable to different wavelengths
• Receiver uses photo-electric diode to detect
  incoming signals
• Usually a fixed wavelength
• Some are tunable to different wavelengths
• Optical-electrical conversions required

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Fiber Optic Transmission

• Can transmit using several different wavelengths
  on the same fiber (monomode
  versus multimode fiber)
• Called Wavelength Division Multiplexing (WDM)
• Same principle as Frequency Division Multiplexing
  (FDM)

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Fiber Optics Facts

• Optical fiber works best with wavelengths of
  light around either 0.85, 1.3, or 1.5 microns
• Each band has a theoretical bandwidth of
  approximately 25 TeraHz
• Current laser technology can achieve several Gbps

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Fiber Optic Transmission

• Various physical layer phenomena serve to
  constrain the current achievable bandwidth on
  optical fiber
• Dispersion modal, chromatic, material
• Absorption
• Attenuation
• Repeaters or amplifiers are needed to facilitate
  long range transmission

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Summary

• Optical fiber offers immense bandwidth
• B-ISDN/ATM assumes fiber optic based transmission
  at the physical layer
• International standard for fiber-based
  transmission SONET
  (Synchronous Optical Network)