Fiber-Optic Communications

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Fiber-Optic Communications

• James N. Downing

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Chapter 4

• Fiber and Cable Fabrication

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4.1 Optical Fiber Fabrication

• Fused Silica Glass
• Medium of choice for fiber communications
• Uses a silica soot that reacts with SiCl4 and
  produces GeO2. The GeO2 and P2O5 increase the
  refractive index.
• The preform is a single, glass rod of about 1m by
  2cm with the refractive index of the finished
  fiber.

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4.1 Optical Fiber Fabrication

• Deposition Preform Methods
• Rod-in-tube
• A tube with a higher index is inserted into a
  lower index tube and the two are melted to make
  the preform.
• Attenuation 500 to 1000dB/km.
• Double crucible method
• Core and clad fibers are heated and pulled
  through nested platinum crucibles that are
  narrowed to fiber size.
• Attenuation 5 to 20dB/km

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4.1 Optical Fiber Fabrication

• Deposition Preform Methods
• Inside Vapor Deposition (IVD)
• Deposits silica soot on inside wall of fused tube
  and then heated
• Modified Chemical Vapor Deposition (MCVD)
• SiCl4 and SiO2 are heated to 18000C, leaving a
  soot on the inside of the tube
• Attenuation 3dB/km at 85nm

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4.1 Optical Fiber Fabrication

• Deposition Preform Methods
• Plasma Chemical Vapor Deposition (PCVD)
• Similar to MCVD except heat source is ionized
  electric charge instead of gas burner
• More precise layering and refractive index
  profiling
• Attenuation 4dB/km at 850nm

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4.1 Optical Fiber Fabrication

• Deposition Preform Methods
• Outside Vapor Deposition (OVD)
• Flame hydrolysis causes soot to be deposited on
  the outside of the rod. The rod is then removed
  and the resulting tube is collapsed to make the
  preform.
• Attenuation 1 to 2dB/km

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4.1 Optical Fiber Fabrication

• Deposition Preform Methods
• Axial Vapor Deposition (AVD)
• Similar to OVD
• Rod is drawn through soot trail several times to
  make the differing layers
• Attenuation 1 to 2dB/km

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4.1 Optical Fiber Fabrication

• Fiber Drawing and Coating
• The fiber can be drawn by heating the preform
  to 20000C and pulling the melting glass away from
  the preform at speed of about 1m/sec.
• The fiber is coated by dipping, spraying, or
  electrostatic methods.

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4.2 Fiber Cable

• Fiber Cabling Considerations
• Provide protection for ease of handling
• Must withstand extremes of environment,
  installation forces, and stresses

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4.2 Fiber Cable

• Fiber Cable Construction
• Buffer jacket around the fiber
• Strength member provides mechanical support
• Outer jacket provides protection from abrasion
• Loose buffer to shield against environment issues
• Tight buffer directly on the fiber

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4.2 Fiber Cable

• Types of Cables
• By installation
• Simplex one-way communication
• Duplex two-way communication
• Multifiber many fiber pairs in bundle
• Ribbon fibers in a row

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4.2 Fiber Cable

• Types of Cables
• By applications
• Light duty
• Heavy duty
• Plenum between walls
• Riser between floors
• Indoor
• Outdoor

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4.3 Connectors

• Connector Considerations
• Tolerances are stringent
• Precision alignment
• Fiber and Cable Preparation
• Ends must be smooth and clean
• Cleaving good enough for splices
• Polishing for all connectors

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4.3 Connectors

• Connector Installation
• Depends on the connector and application
• Flat finish Used for multimode applications
• Domed PC finish Provides for good core contact
• APC finish Polished at 80 angle for matching
  purposes

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4.3 Connectors

• Types of Connectors
• Major Categories
• Standard
• Small
• Sub Categories
• Ferrule
• Connection method
• Number of fibers

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4.3 Connectors

• Standard Connectors 2.5mm ceramic ferrule
• FC Earliest design with threaded coupling and
  adjustable keying to minimize loss
• SC Rectangular snap-in-plug in which the housing
  is not directly attached to the cable
• ST Evolved from copper connectors and the most
  popular similar to FC but with quick connects
  and bayonet coupling and ½ turn keying

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4.3 Connectors

• Standard Connectors
• FDDI Two 2.5 mm ferrules stacked together
• ESCON IBM fiber optic based channel control
• SFF
• MT 12 single or multimode fibers
• LC doubles the count of standard connectors in
  same area. Used with RJ-45.
• VF-45 contains a fiber holder, hinged door, and
  V-groove for alignment purposes

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4.4 Connector Losses

• Intrinsic Loss
• Caused by mismatches in
• Numerical aperture
• Core diameter
• Core area
• Extrinsic Loss
• Caused by differences in connectors which cause
  misalignment

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4.4 Connector Losses

• Insertion Loss
• The attenuation of any connector or component
  inserted inline
• Used for power budget calculations

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4.5 Splices

• Mechanical
• Can be installed in the field with minimum tools
• Losses 0.3db
• Fusion
• Junction must be heated
• Special tools
• Losses 0.1dB

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4.5 Splices

• Applications
• Splice Tray Secures a long row of splices and
  prevents them from moving inside the closure
• Splice Panel Provides sealed protection for
  splice trays
• Splice closure Used in aerial and underground
  telephone cable runs