PHTN1220 Cabling, Connectors, Splices See Hecht, Chapters 8, 13.

Basic Reasons for Cabling Protection of fiber –Typical fiber can only withstand about 2 lb (1 kg of tension) before breaking. –Fiber also needs protection from crushing and from water absorption. Ease of handling –Bare fiber is hair-thin.

FIGURE 8-1 Cross sections of four grades of cable, from light-duty indoor to deep-sea submarine cable (not to scale). Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

Types of Cable Many different types A few main categories –Indoor cables for patch cords, etc. for use in air ducts (plenums), above false ceilings, etc. –Outdoor cables strung between poles in ducts underwater

FIGURE 8-2 Breakout cable. (Courtesy of Corning Cable Systems) Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

Composite and All-Dielectric Cables All-dielectric cables contain no conductive material –Less likely to be struck by lightning –Avoid grounding problems, useful in explosive environments, etc. Some cables have copper as well as fiber. –Can carry power for amplifiers or repeaters. –Can carry electrical as well as optical signals.

FIGURE 8-3 Composite cable contains both copper wires and fibers. (Courtesy of Corning Cable Systems) Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

Aerial Cables For stringing between poles Need strength members (steel, fiberglass, Kevlar) to prevent stressing the fiber Sometimes lashed to a messenger wire.

FIGURE 8-4 Aerial cable installations. Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

Submarine Cable Usually needs copper for provision of power to repeaters/amplifiers. Armor needed near shore to avoid anchor damage. Cable must be solid (no air pockets) to withstand pressure. Cable must be completely waterproof.

FIGURE 8-5 Fiber-optic submarine cable. (Courtesy of TyCom Ltd.) Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

Cable Structure Fiber must be protected from all stresses. Three main concepts in fiber protection –Tight Buffer –Loose Tube –Ribbon

Loose tube Buffered fiber loose in a tube containing air or in a gel. One tube may contain several fibers. Mainly used outdoors. Protects fiber from all stress including thermal stress. Not good for long vertical runs.

FIGURE 8-6 Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

Tight buffer Buffered fiber enclosed in a protective sheath. Easier than loose tube to handle and connectorize. Better for vertical runs, as in riser cables. Mainly used indoors.

FIGURE 8-6 Tightly buffered and loose tube structures for cables. Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

Ribbon Similar to tight buffer but with multiple fibers.

FIGURE 8-7 Fibers in a ribbon cable. Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

High fiber counts possible Courtesy Pirelli Cables Fiber ribbons Dielectric central member Filled buffer tube Water-blocking material Outer strength members 876 fibers FIGURE 8-8 Stacking ribbons inside loose tubes can give very high fiber counts. (Courtesy of Pirelli Cable)

Strength Members Relieve stress on fiber. May include a central core and/or layers surrounding the fiber(s). Common materials are steel, fiberglass, aramid yarn (Kevlar).

FIGURE 8-9 Modular cable containing 216 fibers, with 12 in each of 18 loose tubes. (Courtesy of Corning Cable Systems) Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

Joining Fiber Connectors –Temporary –Removable Splices –Permanent –Can be broken but splice must then be redone Connectors typically have greater losses than splices.

Attenuation in Connectors and Splices Typically greater for connectors than splices –Connectors on the order of 0.5 dB –Splices about 0.1 dB or less Caused by several factors: –core overlap –alignment of axes –different numerical apertures –spacing between fibers –reflection at fiber ends

Overlap of Fiber Cores If cores are not perfectly aligned at a connector or splice, some light will be lost. Loss = total area / overlapping area Example: overlapped area = 90% Loss = Loss in dB = 10 log = 0.46 dB This is approximate: assumes light is evenly distributed throughout core.

Overlap of fiber cores d Cladding Core This light couples into cladding where it will leak out Offset The light enters core and is transmitted FIGURE 13-1 Offset fibers can cause loss.

Mismatched Cores When light goes from larger to smaller core diameter, some light is lost –For single-mode fiber, use mode field diameter instead of core diameter Light can be lost between two sections of the same fiber type if the diameters vary –Diameter is not exact but has specified tolerance.

Loss with Different Core Diameters Proportion of power remaining after mismatch is given by this equation

Example: different cores See Hecht p. 302 Let d 1 = 8.9  m, d 2 = 7.9  m Proportion of power lost in the mismatch is

Example Continued The proportion of power remaining is P out /P in = 1– = That is, the “gain” of the splice is The loss in decibels is found as described earlier (see p. 100)

Other Fiber Mismatches From MM to SM fiber (much smaller core). –Loss about 17 dB From larger to smaller MM fiber. –Loss about 1.9 dB from 62.5 to 50  m core Fibers with asymmetrical or elliptical cores. Note: no light is lost when going from smaller to larger core.

FIGURE 13-2 Losses arise when cores are elliptical or off center. Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

Misaligned Fibers Loss due to some light not achieving total internal reflection For a given amount of misalignment, loss is greater with smaller N.A. Example: for a fiber with N.A. of 0.15, misalignment of 3  causes a loss of 1 dB.

FIGURE 13-3 Misaligned fiber axes cause losses. Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

Mismatched N.A. Loss occurs when going from larger to smaller N.A. Some light from first fiber will not propagate in the second. No loss going the other way.

Loss from NA mismatch Acceptance angle of Input fiber Light confined in first fiber Leaks out of second fiber With smaller NA Is larger than acceptance Angle of output fiber FIGURE 13-4 Mating fibers with different NAs can cause losses.

Loss due to NA Mismatch Note missing minus sign in Hecht (p. 304).

Example of NA Mismatch Light goes from a fiber with NA = 0.3 to one with NA = 0.2. Calculate the loss due to the mismatch.

Spacing Between Fibers Not applicable to splices. Connectors often include a small air gap between fiber ends to avoid scratching the fiber. Some light will spread out too far to reach the second fiber. Loss increases with NA.

FIGURE 13-5 End-separation loss. Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

Calculation of Spacing Loss Note minus sign added to make loss positive. Note that if an index-matching gel is used to separate the fibers, instead of air, the loss goes to zero.

FIGURE 13-6 Loss caused by fiber spacing for three types of fiber, neglecting reflection loss. Note sign should be positive for loss. As written, this is gain. Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

End Reflection Loss Occurs at all interfaces where refraction indexes change. Not applicable to splices. If a connector has an air gap there will be two of these reflections. This adds a loss of approximately 0.32 dB.

Equation for Reflection Loss

Other Losses Improperly cleaved fibers. Scratches. Dust.

Reflections in Connectors Can affect laser sources. Angled connectors can be used to prevent this. Caution! Mating angled and straight connectors will cause damage! Very bad news when the angled connector is on an expensive laser source! Check first!

FIGURE 13-7 A simplified generic fiber connector with coupling receptacle or adapter. Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

Connector Parts and Functions Ferrule aligns fibers. Polished fiber end aligned with end of ferrule. Body has locking mechanism to hold connector in place. Strain relief –Often cable held in place by epoxy or other glue.

Sleeves/Adaptors Join two connectors. Can mate connectors of different types. Can be cable- or bulkhead-mounted.

FIGURE 13-8 Connector panel. (Courtesy of Corning Cable Systems, Hickory, N.C.) Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

Standard Connectors Many types Screw on, bayonet or push on Single or multiple cables Standard or small form factor

FIGURE 13-9 SC connector, expanded and assembled. (Courtesy of AMP Inc.) A common push-on connector. Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

FIGURE ST connector, expanded and assembled. (Courtesy of Corning Cable Systems, Hickory, N.C.). Bayonet type. Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

FC/PC Connectors Screw-on connectors.

Drawing of FC/PC Connector

FIGURE Fixed shroud duplex (FSD) connector for FDDI network. (Courtesy of Corning Cable Systems, Hickory, N.C.) Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

FIGURE MT ferrule holds a dozen fibers in parallel grooves. Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

FIGURE Male MPO connector assembly (Courtesy of US Conec.) Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

FIGURE Small form-factor connectors. (a) MT-RJ connector. (Courtesy of Corning Cable Systems) Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

(b) Duplex LC Connector Outside resembles RJ- 45 phone jack Simplex or duplex 1.25 mm ferrule Photo from Lucent FIGURE 13-14

Fiber Splicing Two basic types –Fusion splicers weld fibers together using an electric arc. –Mechanical splicers butt fibers together, usually with an index-matching gel to avoid air gaps.

FIGURE Key components of a fiber splicer. Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

Fusion Splicer

Provides means to align fiber (microscope or camera/video display) Small arc pre-fuses fiber Some models can align fiber automatically for lowest loss. Fusing arc welds fibers. Some models can test fiber loss.

Fiber Splicing Enclosure

FIGURE Capillary splice joins two fibers. Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

Mechanical Splices

FIGURE Mass-splicing of 12-fiber ribbon in V-grooved plate. Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

Splice Housings Splices are weak They may be protected with plastic coating or jacket but they need additional protection Splice enclosure usually has room for several splices, protects them from stress and from the elements. Housing allows cable breakouts, suitable bend radius, etc.

FIGURE Splices arrayed inside housing. Jeff Hecht Understanding Fiber Optics, 4e Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.