Single Mode Fiber and Multimode Fiber

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• fiber optic cables are specified using the mode, composition (glass/plastic), and core/cladding size
  • E.g.,
    • 8.3 micron core/125 micron cladding single mode glass
    • 62.5 micron core/125 micron cladding multimode plastic

Single Mode Fiber

• Single Mode Fiber (SMF)
  • has a small core (8-10 microns)
  • long wavelength
    • 1,310 nm or 1550 nm
  • uses a laser to generate a near infrared light signal
    • generated by a high-power, highly coherent laser diode
  • support data rates up to 100 Gbps
  • supports runs of many kilometers
  • 2 grades of SMF:
    • OS1 for indoor use
    • OS2 for outdoor use

Multimode Fiber

• Multimode Fiber (MMF)
  • larger core (62.5 or 50 microns)
  • shorter wavelength light transmitted in multiple waves of varying length
    • 850 nm or 1,300 nm
  • uses less expensive and less coherent LEDs or vertical cavity surface emitting lasers (VCSELs)
    • consequently is less expensive to deploy than SMF
  • does not support as high signaling speeds or long distances as single mode
    • more suitable for LANs than WANs
  • graded by optimal mode (OM) categories
    • defined in ISO/IEC 11801 standard
    • OM1/OM2
      • OM1 is a 62.5 micron cable
      • OM2 is a 50 micron cable
      • rated for up to 1 Gbps
      • use LED transmitters
    • OM3/OM4
      • both 50 micron cables
      • manufactured differently
      • designed for use with 850 nm vertical-cavity surface-emitting lasers (VCSEL)
        • referred to as laser optimized MMF (LOMMF)
        • not as powerful as a laser used for SMF
        • supports higher modulation than LED-based optics