Practical Industrial Data Networks: Design, Installation ...masek/Fiber_Optics_2.pdf · Practical Industrial Data Networks: Design, Installation and Troubleshooting 6.6.2.1 Fusion

Practical Industrial Data Networks: Design, Installation and

Troubleshooting

Chapter 6

Fiber Optics Overview

(II)

Feb. 17th 2011

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Chapter 6: Fiber optics overviewPractical Industrial Data Networks: Design, Installation and Troubleshooting

Objectives

• List of main features of fiber optics cables

• Fix problems with:

• Splicing and connection

• Laser and LED transmitters

• Driver incompatibility

• Incorrect bending radius in installation

• Shock and other installation issues

• Interface to cable connectors

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How to connect fibers?

• How to connect electrical wires?

– Weld

– Twist

• How to connect electrical cables to equipments?

– BNC connector and other types of coaxial connectors

– Plug and socket connectors

– USB connectors

– Etc.

• How to connect fibers?

• How to connect fibers to optical devices?

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6.6 Connecting fibers

• Connecting fibers together and to optical devices, such as light sources and photo detectors

• Can be done using splices or connectors

• A splice is a permanent connection used to join two fibers

• A connector is used where the connection needs to be connected and disconnected repeatedly

• A device used to connect three or more fibers or devices is called a coupler

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6.6.1 Connection losses (I)

• Attenuation – the fraction of the optical power lost in the connection process, the sum of losses caused by:

– Lateral misalignment of the fiber cores

– Misalignment of the fiber axes (most important in connecting multimode fibers)

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Lateral Misalignment

Angular Misalignment

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6.6.1 Connection losses (II)

– Differences in core diameters

– Core diameter mismatch occurs when the core diameter of the transmitting fiber (t) is larger than the core diameter of the fiber at the receiving end (r)

– Core diameter of Multimode fiber is 50 µm or 62.5 µm

– Single mode fiber is around 9 µm in diameter

– Diameter mismatch loss are approximated by:

Lossdia = 10 • log10 (diar/diat)2

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6.6.1 Connection losses (III)

– Numerical aperture differences of the fibers

– Define the NA of any type of fiber to be:

– n1 and n2 are refractive indices of core and cladding, respectively

– NA mismatch loss occurs when the numerical aperture of the transmitting fiber (t) is larger than that of the receiving fiber (r)

– The calculated loss for numerical aperture mismatch is approximated by:

LossNA = 10 • log10(NAr/NAt)

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6.6.1 Connection losses (IV)

– Fresnel reflection from the ends of fibers

– End separation loss

– Caused by the difference of refractive indices of two fibers

– And the spacing of the fiber ends

– Air gap will appear between two fibers

– Refractive index for air is 1, for fiber core is 1.46

– The light will be reflected back into the fiber due to a step in the refractive index on the glass-air-glass interface

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6.6.1 Connection losses (V)

– The minimum loss on the glass/air interface is about 0.35 dB

– The reflected light can damage the light source

– The use of index-matching gel in the gap can reduce Fresnel reflection loss

– End finish and cleanliness of fibers

– Physical contact finish minimizes the back reflection due to the tiny refractive index discontinuity

– Angled finish let the reflection to exit the core and dissipate in cladding

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6.6.2 Splicing fibers

• Splices are "permanent" connections between two fibers

• Splicing is only needed if the cable runs are too long for one straight pull

• Or need to mix a number of different types of cables

• Use splices to restore the broken outdoor cables

• Two types of splicing fibers

– Fusion splicing

– Mechanical splicing

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6.6.2.1 Fusion splicing (I)

– Fibers are welded together by an electric arc

– Cannot do this in an explosive atmosphere

– Factory splicing machines often use a small hydrogen flame

– Precisely pre-align the fibers

– Produce consistently lower loss splices

– Requiring expensive equipment: good fusion splicing equipments cost $15,000 to $40,000

– The splices only cost a few dollars each

– Today's single mode fusion instruments are

automated

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Fusion splicing instrument

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– Fusion splicing requires stripping a longer length of bare fiber than termination

– The Miller, perhaps the most rugged, has the disadvantage of being “right-handed”

– The No-Nik is careful with the fiber but requires careful cleaning

– The Micro-Strip allows setting strip length for consistent strips

6.6.2.1 Fusion splicing (II)

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From Left: the Miller Stripper, No-Nik and Micro-Strip

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6.6.2.1 Fusion splicing (III)

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– Quality of the splice depends on the quality of the cleave

– Most splicing machines come with a recommended cleaver

– Put the bare fiber onto the V-groove

– Cover the left cap to hold the fiber

– Close the right cap and press it to clamp and tense the fiber

– Push the blade which is under the fiber to cleave it

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6.6.2.1 Fusion splicing (IV)

– The process of splicing preparation is the same for all splice types: strip, clean & cleave

– Repeat the process for two fibers

– Place two fibers into the guides in the fusion splicing machine and clamp them in place

– Set the splicing parameters or choose factory recommended settings

– The machine will control the splicing process itself

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6.6.2.1 Fusion splicing (V)

– The ends of the fibers are on moveable stages which are used to align the fibers and set the end gap automatically

– Optical Core Alignment (also called “Profile Alignment”): two fibers are illuminated from two directions, 90 degrees apart, software recognizes the core of the fibers and aligns them automatically using movable stages, also estimates splice loss after the fusion splicing is complete

– Local Injection and Detection

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6.6.2.1 Fusion splicing (VI)

– The splicer will show the fibers being spliced on the video screen

– Fiber ends will be inspected, and the bad one should be rejected

– Fibers will be moved into the right position through the automated splicing

– Pre-fuse cycle will remove any dirt on the fiber ends and preheat the fibers for splicing

– The fibers will be fused by an automatic arc cycle that heats them in an electric arc and feeds the fibers together at a controlled rate

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6.6.2.1 Fusion splicing (VII)– Splicing machines generally have a

heating device for heat shrinking a protective sleeve over the finished splice

– The sleeve is made of plastic with a metal rod inside

– It can protect fiber from moisture or other environmental hazards

– One fiber should pass through the sleeve before splicing

– Sleeves have a standard length

– Put the sleeve into the heat device and close the transparent cover

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6.6.2.2 Mechanical splicing (I)

– Fibers are held together in an alignment structure

– Using an adhesive (index matching gel or glue) or mechanical pressure

– Rely on aligning the outer diameters of the fiber cladding

– Little glass tubes, V-grooves, sleeves, 3-rods and various proprietary clamping structures

– Low price for the tools to make mechanical splices

– Have a high consumable cost per splice

– Work well with both single mode and multimode fiber

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6.6.2.2 Mechanical splicing (II)

– After preparation, the fibers are inserted into the splicing element. The assembly tool is then used to close the cap, forcing the clamping and locating surfaces against the fibers and aligning the fibers precisely and permanently in place.

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3M Fibrlok™ II Universal Optical Fiber Splice 2529

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6.6.2.3 Choose the splicing

– Based on cost and location

– Fusion is expensive equipment and cheap splices

– Mechanical is cheap equipment and expensive splices

– If make a lot of splices (thousands in an big telecommunication or CATV network), use fusion splices

– If needs just a few splices, use mechanical splices

– Fusion splices give very low back reflections and are preferred for single mode high speed digital or CATV networks

– Mechanical splices are preferred for multimode fibers

– If it is an underwater or aerial application, the greater reliability of the fusion splice is preferred

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6.6.3 Connector

• Make flexible interconnections between optical devices

• Repeatedly align the fibers

• Have significantly greater losses than splices

• Main loss is the axial misalignment of the fibers

• Connector loss is in the range from 0.2 to over 3 db

• Butt joint with the fiber ends

• The fiber is mounted in a ferrule made of metal or ceramic

• The central hole of ferrule matches the fiber cladding diameter

• Fiber is glued into the ferrule, the end is cut and polished to be flush with the face of the ferrule

• Types of connectors: SC, ST, etc.

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6.6.3.1 SC connector (I)– Subscriber Connector (SC), a general purpose push/pull style Connector

developed by NTT, Japan

– SC is a snap-in connector that is widely used in single mode systems for it's excellent performance

– Built with a cylindrical ceramic ferrule

– Square cross-section for high packing density

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SC connector SC connector SC adapter

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6.6.3.1 SC connector (II)– Push–pull latching mechanism

– SC connectors offer low cost, simplicity, and durability

– SC connectors provide for accurate alignment

– Specified loss of less than 0.6 db (typically 0.3 db)

– Typical return loss of 45 dB

– It is also available in a duplex configuration

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6.6.3.2 ST connector (I)– Straight Tip connector

– An older standard used for data communications

– ST is the most popular connector for multimode networks, like most buildings and campuses

– Has a round cross-section

– It has a bayonet mount and a long cylindrical ferrule to hold the fiber

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ST connector ST connector and adapters

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6.6.3.2 ST connector (II)

– Most ferrules are ceramic, but some are metal or plastic

– Relies on the internal spring to hold the ferrules together

– Have to make sure connectors are seated properly

– If it has high connection loss, reconnect them

– Tensile strength is less than 1 kg force

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ST connectorAdaptor of ST connector

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6.6.3.3 FC connector (I)

– The ferrule connector (FC) is a sort of fiber-optic connector with a threaded body

– The FC connector is designed for use in high-vibration environments

– It is commonly used with both single-mode optical fiber and polarization-maintaining optical fiber

– The FC Connector is the most popular connector used today

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6.6.3.3 FC connector (II)

– The fiber end is embedded in a 2.5 mm ferrule made of ceramic or stainless steel

– The tip is typically polished to produce a rounded surface, called "physical contact" (PC) polish

– Different designed: FC/PC (FC/SPC, FC/UPC), FC/APC (Angled Physical Contact)

– The angle of FC/APC ferrule is 8 degree

– The Insertion Loss for matched FC connectors is 0.25 dB

– The FC screws on firmly, but make sure the “Key” has been aligned in the slot properly before tightening

– How to distinguish FC/PC and FC/APC?

– The color of boot: blue or black for FC/PC, green for FC/APC

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6.6.3.4 Other types of connectors (I)

– Small Form Factor (SFF) connectors for high density connection

– LC is a new connector that uses a 1.25 mm ceramic ferrule, half the size of the ST

– The ferrule connector is easily terminated with any adhesive

– Good performance, highly favored for single mode

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6.6.3.4 Other types of connectors (II)

– MT-RJ is a duplex connector with both fibers in a single polymer ferrule

– It uses pins for alignment and has male and female versions

– Multimode only, field terminated only by pre-polished/splice method

– The MT-RJ connector has become the most common SFF connector

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6.6.3.4 Other types of connectors (III)– Opti-Jack is a neat, rugged duplex connector cleverly designed as

two ST-type ferrules in a package with the size of a RJ-45, has male and female (plug and jack) versions

– E2000/LX-5 is like a LC but with a shutter over the end of the fiber

– MU looks a miniature SC with a 1.25 mm ferrule, popular in Japan

– MT is a 12 fiber connector for ribbon cable, main use is for pre-terminated cable assemblies

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Opti-Jack E2000/LX-5 MU connector MT connector

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6.6.3.5 Structure of connectors (I)

– The fiber ferrule: is built around a long cylinder with 2.5mm outer diameter, 124--127µm inner diameter

– The connector sub-assembly body: the ferrule is assembled in it, has mechanisms to hold the cable and fiber in place

– The connector housing : assembles with sub-assembly body and provides the mechanism for snapping into a mating sleeve (adapter) and hold the connector in place

– The fiber cable: are crimped onto the connector sub-assembly body with strength member (Kevlar) by a crimp eyelet

– The stress relief boot: covers the joint between connector body and fiber cable, protects fiber cable from mechanical damage

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6.6.3.5 Structure of connectors (II)

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SC Connector Structure

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6.6.3.6 Ferrules (I)

– The ferrule is the most important and costly part of a fiber connector

– Materials of ferrules include ceramic, plastic or stainless steel

– Holds the end of the fiber and precisely aligns it to the socket

– The fiber is inserted into the ferrule and cemented with an epoxy or adhesive

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6.6.3.6 Ferrules (II)

– Connectors may also use crimped ferrules that do not require cement

– Give fiber long-term mechanical strength and prevent the contamination from environment

– If the length, hole centering, inside and outside diameters are not exact, a poor connection will result

– 2.5mm ferrule for standard fiber optic connectors: SC, ST, FC, Opti-Jack connector, etc.

– 1.25 mm ferrule for small form factor fiber optic connectors: LC, MU, etc.

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6.6.4 Connector handling (I)

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• Most fiber optic connectors are designed for indoor use

• Connectors for outdoor use require to be hermetically sealed to protect the optical faces from contamination

• Do NOT touch the end of the connector ferrules

Assemble a ST fiber optic connector

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6.6.4 Connector handling (II)

• Clean connectors with lint-free wipes and isopropyl alcohol

• Compressed air sprays are available for cleaning connectors and adapters without needing to physically touch the mating surfaces

• Indoor fiber connectors are 500 to 1000 mating cycles

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fiber connector/adapter cleaning kit Compressed air

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6.6.5 Assemble a fiber connector (I)

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Thorlabs Fiber Optic Assembly Parts

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6.6.5 Assemble a fiber connector (II)

– Step 1: Clean Fiber Optic Connectors, use the isopropyl alcohol to completely cover the connectors to remove contaminations

– Step 2: Add Strain Relief Boots and Crimp Sleeves

– Step 3: Prepare Furcation Tubing

– Step 4: Inserting the Optical Fiber into the

Furcation Tubing

– Step 5: Trim and Strip Fiber to Length

– Step 6: Clean Optical Fiber

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6.6.5 Assemble a fiber connector (III)

– Step 7: Add Epoxy to the Connector

– Step 8: Insert Fiber into Connector

– Step 9: Fully Seat Connector

– Step 10: Secure Crimp Sleeve

– Step 11: Epoxy Curing

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6.6.5 Assemble a fiber connector (IV)

• Fiber Polishing

– Step 1: Scoring the Fiber

– Step 2: Cleaving the Scored Fiber

– Step 3: Assemble the Polishing Disc and Connector

– Step 4: 5 μm Polish, 3 μm Polish, 1 μm Polish, 0.3 μm Polish

– Step 5: Final Inspection

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6.6.6 Optical couplers

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• Optical couplers or splitters and combiners are used to connect three or more fibers or other optical devices

• Split the input power to a number of outputs

• Coupler configuration depends on the number of ports and whether each of these are unidirectional

1:2 optical coupler Optical coupler

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6.7 Splicing trays/organizers and termination cabinets

• Different types of storage units that are used for housing optical fiber splices and end of cable terminations

• Splicing trays

• Splicing enclosures

• Termination in patch panels and distribution frames

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6.7.1 Splicing trays (I)

• Splices are generally located in units

• Referred to as ’splicing centers’, ‘splicing trays’ or ‘splicing organizers’

• Provide a convenient location to store and to protect the cable and the splices

• Provide cable strain relief to the splices themselves

• Located at intermediate points along a route where cables are required to be joined

• Locates at the termination and patch panel points at the end of the cable runs

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6.7.1 Splicing trays (II)

• Sheath of the input cable is stripped away and brought into the splicing center

• The fibers are looped completely around the tray and into a splice holder

• The fibers are spliced onto the outgoing cable if it is an intermediate point

• Or on to pigtails if it is a termination point

• Looped completely around the tray and then fed out of the tray

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6.7.1 Splicing trays (III)

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A typical splicing tray

A example of a splicing tray

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6.7.1 Splicing trays (IV)

• Cables are physically attached to the splice tray to provide strain relief

• Fibers are looped completely around the tray to provide slack and tension relief

• Each splice joint is encased in a splice protector (plastic tube) or in heat shrink before it is clipped into the holder

• Allows different fibers to be cross-connected and to be looped back for testing purposes

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6.7.2 Splicing enclosures (I)

• The splicing trays are not designed to be left in the open environment and must be placed in some type of enclosure

• Direct buried cylinders

– Two cables are joined to continue a cable run

– Placing the splice trays in a tightly sealed cylindrical enclosure

– Enclosure is made from heavy duty plastic or aluminum

– Container is completely sealed from moisture ingress and contains desiccant packs to remove any moisture that may get in

– Cables normally enter the enclosure at one end only to allow the enclosure to be lifted from the ground for easier splicing access

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6.7.2 Splicing enclosures (II)

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Direct buried cylinders

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6.7.2 Splicing enclosures (III)

• Termination cabinets

– a lot of cables

– splicing trays are stored in a larger wall mounted cabinet

– approximately 500 mm × 500 mm ×100 mm

– For outdoor use, the cabinets must be sealed against bad weather conditions

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6.7.2 Splicing enclosures (IV)

• Patch panels and distribution frames

– Installed in the back of patch panels and distribution frame

– For connection of patch cords to the main incoming cable

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6.7.3 Termination in patch panels and distribution frames (I)

• Three main methods of connecting an incoming cable into a patch panel or distribution frame

• Firstly:

– Fibers of incoming cable have a large minimum bending radius

– Splice each fiber to a fiber patch cord with a smaller bending radius

– Reduces undue stress on the incoming cable

– Introduce small losses into the link

– Replaces the more fragile glass of the incoming cable with more flexible and stronger glass of the patch cords

– Termination cabinet for splicing trays

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6.7.3 Termination in patch panels and distribution frames (II)

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• Secondly:

– Place the fibers from the incoming cable into a breakout unit

– Breakout unit separates the fibers and allows a plastic tube to be fitted over the incoming fibers to provide protection and strength as they are fed to the front of the patch panel

– There are no splices keep losses to a minimum

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6.7.3 Termination in patch panels and distribution frames (III)

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• Third method:

– Tight buffered fibers in incoming cable are flexible and strong

– Can be taken directly to the front of the patch panel

– Referred to as direct termination

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Chapter 6: Fiber optics overviewPractical Industrial Data Networks: Design, Installation and Troubleshooting 54

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Practical Industrial Data Networks: Design, Installation ...masek/Fiber_Optics_2.pdf · Practical Industrial Data Networks: Design, Installation and Troubleshooting 6.6.2.1 Fusion