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Fiber-Optic Communications

Fiber-Optic Communications. James N. Downing. Chapter 4. Fiber and Cable Fabrication. 4.1 Optical Fiber Fabrication. Fused Silica Glass Medium of choice for fiber communications

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Fiber-Optic Communications

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  1. Fiber-Optic Communications James N. Downing

  2. Chapter 4 Fiber and Cable Fabrication

  3. 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.

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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.

  10. 4.2 Fiber Cable • Fiber Cabling Considerations • Provide protection for ease of handling • Must withstand extremes of environment, installation forces, and stresses

  11. 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

  12. 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

  13. 4.2 Fiber Cable • Types of Cables • By applications • Light duty • Heavy duty • Plenum: between walls • Riser: between floors • Indoor • Outdoor

  14. 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

  15. 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

  16. 4.3 Connectors • Types of Connectors • Major Categories • Standard • Small • Sub Categories • Ferrule • Connection method • Number of fibers

  17. 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

  18. 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

  19. 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

  20. 4.4 Connector Losses • Insertion Loss • The attenuation of any connector or component inserted inline • Used for power budget calculations

  21. 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

  22. 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

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