connectorization

ConnectorisationConnectorisation

To make a continuous links for long distance networks

Cable can not be made as per network length

Cable length standardisation (2 to 6 Km)

For Branching and Looping of cable

For Network Transfer (one carrier to another)

For Signal Splitting and Multiplexing in Optical Networking

For Routing and distribution of cables

For Signal launch, detect and regeneration

Cable Jointing and Termination forms the Cable Jointing and Termination forms the backbone of Networking without which backbone of Networking without which

network is not possiblenetwork is not possible

Cable Jointing - Importance

Cable Jointing - Problems

Every joint in the network induce signal loss which limit

signal transmission distance.

Network reliability more dependent on joints rather then

cable and transmission equipment.

Additional cost for jointing components - Planning,

purchase, storage, installation and maintenance (including

spares and tools).

Training and skilled manpower maintenance.

Cable (Fiber) Jointing - Methods Splicing - Mechanical Splice & Fusion splice

Splicing is used to connect two fibers in a permanent joint.

Both capable of splice losses in the range of 0.15 to 0.1 dB .

It is most preferred way in making a cable to cable link in

trunk routes and cable termination to a exchange boxes.

Connector Termination

Used to connect two fibers in a temporary flexible joint

which can be jumped /interchanged with other cables in the

network

Capable of insertion losses in the range of 0.5 to 0.1 dB.

It is most preferred way in Distribution and networking of

cables in exchanges and user side

Mechanical Splicing

Ends of two fibers are stripped, cleaned, carefully butted

together and aligned using a mechanical assembly having

precision V groove.

Gel is used at the point of contact to reduce light reflection and keep the splice loss at a minimum.

Ends of the fiber are held together by friction or compression

Splice assembly features a locking mechanism so that the fibers remained aligned.

Fiber can be removed anytime and same mechanical splice can be used again for same or other fiber jointing.

Similar concept is used for loss / continuity testing of fiber by OTDR / Power meter where number of fibers needs splicing.

Fusion Splicing

Ends of two fibers are stripped, cleaned, carefully brought together and fused together after melting using an electric arc.

Gel is not required at the point of contact as arc produces continuous fiber without a break

Require special expensive splicing equipment but can be performed very quickly, so cost becomes reasonable for quantity.

Fusion splices being fragile, a heat shrink sleeve with metal rod is placed over it to protect them.

This is the method by which smaller lengths (2 – 6 Km) of cable are joined together to make long route varying from few to hundreds of Km.

Fiber can’t be removed without cutting and same splice sleeve can not be used again for fiber jointing.

How is Splicing done??

Connectorisation

Optical connectors are the means by which fiber optic cable is usually connected to peripheral equipment and to other fibers.

Similar to their electrical counterparts in function and outward appearance but are actually high precision devices.

Connectors are used to couple two optical fibers (cables) together or to connect fibers to transmitters or receivers. Connectors are designed to be de-mountable.

FO connector centers the small fiber so that its light gathering core lies directly over and in line with the light source (or other fiber) to tolerances of microns.

FO cables are connectorised at both the ends with various types of FO connectors. These cable assemblies are called patch cords. If they are cut in two pieces, they become pigtails (with only one connector end).

Cable Constructionso Mainly less costly indoor cables are used, which does not have high strength requirement.

o Basic 250 fiber will be tight buffered to 900 or 600 with Nylon/ PVC and then sheathed with PVC/ LSOH. Aramid Yarns are put in between them to provide tensile strength.

o Based on fiber count, three variations are popularoSimplex – Single Fiber cord.

oDuplex – Two fiber cord. Three variations are used.o(1) Flat – Thin oval outer jacket over two parallel simplex cords.o(2) Zip – Outer sheath of two simplex cords joined by a thin web (or zip) during production. Most popular construction in duplex. o(3) Round –Two tight buffered fibers are placed along side and sheathed with Aramid yarn around them.

o Multi-fiber Cord Cable – oTwo or more Simplex cord are stranded over CSM or around each other and jacketed with PVC / LSOH.

Cable Constructions

Cable Constructions

Types of Fibers–SM (9/125/250micron) – Standard MM (50/125micron) – StandardMM (62.5/125 micron) – Standard MM (100/140 micron) – Standard but not used much

Diameter of Cords Simplex cord can have different diameters. 900 (0.9mm) Tight buffered fiber –1.6mm - Buffer diameter will be 600 micron1.8mm - Buffer diameter will be 600 micron.2mm - 2.5mm -3.0mm – Most popular size.

Duplex cord can also have different diameters as above.

Types of FO Connectors - Standard

(1) FC (Ferrule Convex) - •Keyed ferrule with a screw-on threaded barrel fastening system. •All metal connector gives durable, reliable & low loss connection. •Industry standard particularly in SM telecom applications.

(2) SC (Subscriber Connector) -•Latched type connection makes it impossible for the connector to pull out without releasing the latch by pressing.•Popular both for SM and MM fibers.•Body is generally made of plastic.

(3) ST (Straight Tip) - •Developed by AT&T, now mostly used in MM applications.•Twist lock bayonet coupling mechanism ensures quick, highly repeatable, low loss over all connection •Anti-rotation tab makes the fiber to always return to the same rotational position assuring constant, uniform performance.

Types of FO Connectors - Standard

Types of FO Connectors - SFF

(1) LC - •RJ45 style housing allows easy disengagement in dense spaces. •All plastic connector designed and patented by Lucent.•Ferrule size, half of standard make double fiber density in shelves. •Popular both for SM and MM fibers.

(2) MT-RJ -•RJ45 style housing allows easy disengagement in dense spaces •Designed and patented by AMP and used mostly for MM fibers.•Very small duplex connector where body & ferrule both made of plastic and one ferrule accommodate two fibers (MT style ferrule). •Thermoset and thermoplastic options in ferrule

(3) MU - •Designed and patented by NTT, Japan, it really is a shrunken SC. •Popular both for SM and MM fibers.•Plastic Body with Latched type connection like SC Connectors.•Very popular for high density, low profile interconnect applications and backpanel connector applications.

Types of FO Connectors - Others

SIMPLEX (1) SMA

(2) E-2000

(3) D4

(4) BICONIC

(5) DIN 47256 (LSA)

DUPLEX (1) FDDI

(2) ESCON (3) VOLITON

(4) OPTI-JACK

(5) SC-DC

FO Connectors - SFF v/s Standard

SC-DC, LC, MT-RJ , Current Duplex SC, Volition, and Opti-J ack.

Connector Ferrule

Ferrule is the heart of the connector.

It is basically a hollow rod with a through hole of around 125micron diameter at the center for inserting the fiber.

Metal, glass, plastic and ceramic ferrules have been used, but ceramics seems to be the best choice currently.

Ceramic is the most environmentally stable material, closely matching the expansion coefficient of glass fibers. It is easy to bond to fiber with epoxy glues, and its hardness is perfect for a quick polish of the fiber.

New type of plastic, Liquid Crystal Polymer (LCP), offers promise for molded ferrules at lower costs. Performance and durability yet to be proven.

Adapters & Sleeves

Adaptors are used to connect two or more cable assemblies to each other through connector mating.

Mostly made of plastic or metal. Outer shapes vary and could be rectangular, circular, square or any other flanged type.

Adaptors use one split sleeve per connection for aligning the ferrules of the two connectors together. Split sleeves have been made from metal, plastic and ceramic also. Ceramic sleeves gives less insertion loss as compared to others. For SM applications, Ceramic sleeves are preferred.

Based on the connectors to be mated on both side adaptors can be of different types like FC-FC, SC-SC, ST-ST, FC-SC, SC-ST.

Generally simplex or duplex type adapters are used for simplex and duplex cable assembly respectively, but sometimes adaptor with more than two ports like Quadruple, 8 port are also used.

Connector Termination Process

(1) Cutting Cable - Longer length cable is unwinded from reel, checked physically and cut into smaller length depending upon the requirement.

(2) Stripping the Cable - Outer jacket of cable is removed at a specified length using hand-tool.

(3) Cutting Aramid Yarn - Aramid yarn strength member are cut at specified length by scissors.

(4) Buffer Stripping – Tight Buffered fiber is fed into the automatic stripping machine, set to strip specified length. Machine strips off the buffer to leave bare fiber.

(5) Fiber Termination - Epoxy glue is first prepared by mixing with hardener and then feed into the ferrule hole by syringes and needles. Then fiber is feed into the connector ferrule by hand till some bare fiber protrudes out of ferrule.


(6) Crimping - Crimping of the Kevlar around the fiber is done to provide retention strength to the connector.

(7) Curing - Connector having fiber is put into heat curing oven for a specified time to cure the epoxy and make it fix the fiber inside the connector.

(8) Cleaving - Protruded fiber above ferrule is cut by special diamond cutting tool.

(9) Polishing- Most critical step and done in 3-4 steps. A batch of terminated connectors are placed in the polishing machine. Machine carries out polishing of ferrule end face in 3-4 steps by changing the polishing papers and rubber pads in between the process.

(10) Visual Inspection and Re-polish - Surface of the ferrule end face is checked through a microscope for smoothness. If not smooth then, polishing process is performed again.

Insertion Loss

Insertion Loss (IL) denotes the amount of optical power lost at the interface of two connectors.

It is a function of the polishing equipment & the technique used for the polishing. A machine that produces poor end-face geometry will almost always generate unacceptable levels of loss.

Current industry standard and TEC specifications for SM is 0.3dB, but commonly expected level is 0.2dB. Current industry standard for MM is 0.5dB,

Poor insertion loss readings are generally a result of fiber misalignment, separation between connections and/or the quality of the finish on the end of the connector.

It is the most important parameter for determining the performance of the connector and cable assembly.

Back Reflection / Return Loss

Back Reflection (BR) is light reflected back through the fiber toward the source. Light reflection occurs at the contact point of two connectors when they are mated.

Quality of the polish on the connector end-face determines if it will pass/fail the Back Reflection test.

Return loss (RL) has the same meaning but in opposite context. Return loss should be high for better performance. BR is specified such as -55dB whereas RL is specified such as 55dB.

A high level of Back Reflection will cause transmission problems for systems that depend on the speed and clarity of a fiber system, since the desired high data rates can encounter bit errors if the signal is distorted. A distorted signal will transmit a poor image or sound.To minimize interference low levels of Back Reflection must me maintained.

TEC Specifications for RL is 45dB (or BR -45dB). Current industry standard is -55dB for normal PC polishing.

Factors Affecting IL & BR

PC, SPC, UPC / MPC and APC

These are terms that describe connector end-faces and also relate to the Back Reflection designation:

PC - Physical Contact, a description of the contacting spherical end-face. It generally means a Back Reflection value of -35db. SPC - Super PC, designates a PC connector with a BR value of -45db. UPC - Ultra PC (also called MPC means Maximum PC), designates a PC connector with a BR value of -55db. APC - Angled PC, indicating the application of an angle (usually 8°) which deflects Back Reflection to <-65db.

What is Angled PC??

Geometrical Parameters

Apex Offset Apex defines the highest point on the spherical surface at the end-face of the polished connector. Apex Offset is the distance between the center of the fiber and this actual high point.

Although Apex Offset describes a physical condition of the polished fiber, rather than a performance parameter, it is considered an acceptance criterion in itself.

Excessive Apex Offset leads to a high IL and high BR.

TEC specification is 50mm maximum.


Radius of Curvature•It is the radius generated on a connector’s end face. It is the measurement of a connector's end-face spherical condition.

•It must be such that when mated with another connector most of the compression that occurs is applied to the material that surrounds the fiber (also referred to as ferrule absorption).

•A proper radius, in conjunction with fiber under-cut allows for correct fiber-to-connector compression.

•TEC specification for radius of curvature is 10-25mm.


Fiber Undercut/Protrusion When fiber is recessed inside ferrule, it is known as Undercut. When it protrudes above the ferrule it is called Protrusion.

Undercut affects both BR & IL. When connectors are mated, ferrule material surrounding the fiber compresses, which allows fibers with an acceptable undercut to make contact. Fibers that do not make intimate contact have air gap which increases BR & IL .

Limited fiber undercut is preferred to fiber protrusion. Generally, undercut is much more common than protrusion as a result of the polishing process. If excessive protrusion is present, fiber chipping and/or cracking may take place during the connector mating.

TEC specifications is 100nm.

Current standard is 50nm.

Factors Affecting Connector Performance

Connector Selection

Cable/Fiber Selection

Epoxy type

Fiber Stripping & Cleaving

Polishing Process Polisher and the polishing technique used are the most important factors. Machine needs to attack the connector evenly from all sides to assure proper end-face geometry. Polishing technique used will contribute to the finished result and will control the clarity of the polish and control Fiber Undercut.

Cleanliness

Reference cables / Adapters

Cable Assemblies - SC to SC

Cable Assemblies - LC to LC

Cable Assemblies - Various Types

connectorization

Documents