COMMS3_MIDTERM

• Bands of light

  • Infrared
  • Visible
  • Ultraviolet

  
• Infrared


  Band of light frequencies too high to be seen by the human eye, with wavelengths ranging between 770 nm and 106 nm. Optical fiber systems generally operate in this band.

  
• Visible


  Band of light frequencies to which the human eye will respond, with wavelengths ranging between 390 nm and 770 nm.

  
• Ultraviolet


  Band of light frequencies too low to be seen by the human eye, with wavelengths ranging between 10 nm and 390 nm.

  
• Wavelength units


  Microns (1 micron = 10^-6 meter), Nanometers (1 nm = 10^-9 meter), Angstroms (1 Angstrom = 10^-10 meter)

  
• Finding the Modes


  Number of paths (modes) = V/2, where V depends on frequency, refractive indexes, and core diameter

  
• Response Time


  Time between 10% and 90% points, time to convert electrical to light energy or vice versa (5 to 10 ns). Affects overall bandwidth, approximated by BW = 0.35 / tr

  
• Optical Fiber Link Budget Losses

  • Cable losses
  • Connector losses
  • Source-to-cable interface loss
  • Cable-to-light detector interface loss
  • Splicing loss
  • Cable bends

  
• Cable losses


  depend on cable length, material, and material purity. They are generally given in dB/km and can vary between a few tenths of a dB to several dB per kilometer.
• Connector losses


  Mechanical connectors are sometimes used to connect two sections of cable. If the mechanical connection is not perfect, light energy can escape, resulting in a reduction in optical power. Connector losses typically vary between a few tenths of a dB to as much as 2 dB for each connector.
• Source-to-cable interface loss


  used to house the light source and attach it to the cable is seldom perfect. Therefore, a small percentage of optical power is not coupled into the cable, representing a power loss to the system of several tenths of a dB.
• Cable-to-light detector interface loss


  used to house the light detector and attach it to the cable is also not perfect and, therefore, prevents a small percentage of the power leaving the cable from entering the light detector. This, of course, represents a loss to the system usually of a few tenths of a dB.
• Splicing loss


  If more than one continuous section of cable is required, cable sections can be fused together (spliced). Because the splices are not perfect, losses ranging from a couple tenths of a dB to several dB can be introduced to the signal
• Cable bends


  bent at too large an angle, the internal characteristics of the cable can change dramatically. If the changes are severe, total reflections for some of the light rays may no longer be achieved, resulting in refraction.