FiberOptic Communications James N Downing Chapter 4 Fiber

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 – Uses a silica soot that reacts with Si. Cl 4 and produces Ge. O 2. The Ge. O 2 and P 2 O 5 increase the refractive index. – The preform is a single, glass rod of about 1 m by 2 cm with the refractive index of the finished fiber.

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 1000 d. B/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 20 d. B/km

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) • Si. Cl 4 and Si. O 2 are heated to 18000 C, leaving a soot on the inside of the tube • Attenuation: 3 d. B/km at 85 nm

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: 4 d. B/km at 850 nm

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 2 d. B/km

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 2 d. B/km

4. 1 Optical Fiber Fabrication • Fiber Drawing and Coating – The fiber can be “drawn” by heating the preform to 20000 C and pulling the melting glass away from the preform at speed of about 1 m/sec. – The fiber is coated by dipping, spraying, or electrostatic methods.

4. 2 Fiber Cable • Fiber Cabling Considerations – Provide protection for ease of handling – Must withstand extremes of environment, installation forces, and stresses

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

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

4. 2 Fiber Cable • Types of Cables – By applications • • • Light duty Heavy duty Plenum: between walls Riser: between floors Indoor Outdoor

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

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

4. 3 Connectors • Types of Connectors – Major Categories • Standard • Small – Sub Categories • Ferrule • Connection method • Number of fibers

4. 3 Connectors • Standard Connectors: 2. 5 mm 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

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 Vgroove for alignment purposes

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

4. 4 Connector Losses • Insertion Loss – The attenuation of any connector or component inserted inline – Used for power budget calculations

4. 5 Splices • Mechanical – Can be installed in the field with minimum tools – Losses: 0. 3 db • Fusion – Junction must be heated – Special tools – Losses: 0. 1 d. B

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