Lecture 10

Optical Fiber Technology

April 28, 2004



The Lessons for Today:

Two Enabling Technologies:

  • Lasers: coherent sources of light
  • Glass fibers with low optical attenuation
  • The Advent of the Laser - The Requisite Communication Resource

    Human-made vs. Natural Sources of Electromagnetic Radiation (coherent  vs. incoherent light sources)
    The classical picture of light emission: Radiating lines of force from an oscillating charge (Review Lecture 6)

    The quantum mechanical picture of light emission: Absorption and Emission of Radiation by an Atom (applet)

    Coherent radiation: a continuous source  (sharp spectral lines)

    Incoherent radiation: a discontinuous or interrupted source  (broad spectral lines)
     

    Lasers: sources of fairly coherent radiation

    Given the "quantum nature" of atomic emission, how do we get a fairly continuous source?
    Answer: We induce a cooporative emission process. The Laser: Demonstration (applet)
    The key idea is that "population inversion" leads to "stimulated emission of radiation."
    The WWSR Laser Tutorial gives a very nice picture of how the whole thing works.
    Other interesting, but more advanced demonstrations of laser operation from Physics Education Research Group at Kansas State University (KSU).
    The Laser Adventure   by Rami Arieli

    On-Line Interactive Programs

    Ruby Laser (No longer available online)

    Helium Neon Laser (No longer available online)

    Diode Laser (No longer available online)

    The Development of an Appropriate Pipe - Light Propagation in a Glass Fiber

    Why does a hollow pipe light guide work?    Problem - beam divergence (the smaller the beam the faster it diverges) and loss at reflecting walls (diagram).  See schematic of a famous BTL version of an operational light pipe (circa 1960).

     Light rays at an interface: (diagram)
    Reflection - Law of Specular Reflection
     
    Refraction - Law of Snell

    Total internal reflection
    More on total internal reflection:
    A wonderful Total Internal Reflection  (TIR) applet.

    Two figures from  the Schott tutorial The Properties of Light Applied to Fibre Optics: (figure 1 and figure 2)

    Fiber characteristics:
    Types of optical fibres and their manufacture: from Schott tutorial (figure)

    Geometry of typical single-mode and multimode optical fibers - after Paul E. Green. Jr. (figure)

    Standard AT&T 144-fiber cable.  Typical cable used for intercity transmission. - after S.E. Miller & I.P. Kaminow. (figure)

    Radial index profiles of typical single-mode and multimode optical fibers. - after Suzanne R. Nagel. (figure)

    Attenuation:
    Data on Attenuation
    Dispersion: (velocity dependence on frequency/wavelength)
    Data on Dispersion

    How can the hugh capacity of optical fibers be used effectively?

    Review modulation schemes: FDMA (WDMA) and TDMA

    Two figures from  Web ProForum tutorials on DWDM: (figure 1 and figure 2)

    Two switching ideas: (figure 1 and figure 2)

    Optical Networks I:

    Fiber-to-curb (FTTC)

    Hybrid Fiber/Coaxial Cable (HFCC)

    Schematic Multiloop Network (OC-193)

    Optical Communication History:

    Alexander Graham Bell in 1880 reported the transmission of speech over 200 meter by modulating sunlight with a reflecting diaphragm ("photophone")

    To avoid the degradation of optical signals in the atmosphere, Kao and Hockman in England (and simultaneously Wirt in France) in 1966 suggested the use of dielectric wave guides or optical fibers.

    Historical reduction of optical loss - after Suzanne R. Nagel.

    Increase in bit rate-distance product during the years 1850-2000.  The emergence of a new technology is marked by a filled circle - after Govind P. Agrawal. 

    Progress in lightwave communication technology over the period 1974-1992.  Different curves show the increase in the bit rate-distance product for five generations of fiber-optic communication systems - after Govind P. Agrawal.

    A Short History of Fiber Optics by Jim Hayes

    A Fiber-Optic Chronology by Jeff Hecht

    General References:

    A Brief History of Optics

    Glass Links

    A general Glass History: from Iowa State University

    Fiber Optics Basics: by Terry Macy at Ohio University

    Fiber Optics Basics: a tutorial which emphasizes cable configurations - from LASCOMM

    Fibre Optic Technologies: from Mercury Communications Ltd

    Two Web ProForum tutorials on DWDM

    Dense wavelength division multiplexing (DWDM) tutorial

    Dense wavelength division multiplexing (DWDM) testing tutorials


     

    This page was prepared and is maintained by R. Victor Jones
    Comments to: jones@deas.harvard.edu.

    Last updated September 5, 2006