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Pop Quiz: May 2005

Test your knowledge of fiber optics.

TRUE OR FALSE
  • The larger the core diameter of the fiber, the greater the bandwidth.
  • Thomas Edison was the first person to discover the concept of “light piping.”
  • Fiber optic cabling has virtually replaced copper for most telephone and television signal transmission applications.
  • The transmission of light and the transmission of sound share many similar characteristics.
  • Compared to copper, fiber optic cable has virtually no bandwidth limitations.         

ANSWERS

1. FALSE. Large core fiber is also called “multimode” fiber. Its larger diameter causes more light to be reflected within the core, and these reflections create longer paths (or “modes”) for the light to travel through the fiber. This causes a smearing or spreading effect on the output rise-time of the light pulse, which limits the maximum speed of light changes that the fiber will allow. Because data is usually transmitted by pulses of light, this, in essence, limits the maximum data rate of the fiber.

2. FALSE. Edison's invention of the light bulb in 1880 and transmission of electricity through wires overshadowed William Wheeling's patented light piping method. The use of light as a transmission medium was abandoned for almost 70 years until the invention of the fiberscope in the 1950s.

3. TRUE. Telephone companies began replacing copper cabling in the late 1970s, and today use optical fiber throughout telephone systems as the backbone architecture and long-distance connection between city phone systems.

4. TRUE. In fact, about the only characteristic in which they radically differ is in transmission speeds — light travels about 186,000 miles per second, while sound only travels about one-fifth of a mile per second. The quality of both light and sound transmission are affected by attenuation, reflection, dispersion, and phase of the signal, among other things.

5. TRUE. Single-mode fiber offers bandwidth well into the GHz range. Experiments have been conducted with 3,000-mile-long samples where 100 GHz of data was successfully passed. Copper cabling is still limited to the MHz region.

Sources: Communications Specialties, www.fiber-optics.info

CLARIFICATION

The March issue's Bright Idea featuring Extron's IPL T PCS4 inaccurately stated that the device can be placed in standby mode. To clarify, the product's electrical current thresholds can be set to define full power, power off, and standby states for individual devices and groups of outlets.

 


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