Fiber Optic Connector Falak Shah, th 6 Semester, Electronics and Communications Department, Institute of Technology, Nirma University. Abstract c) Buffer- A material applied over the coating that may be used to protect an optical fiberThis paper reviews the fiber connectors available for fromphysical damage, providing mechanicalconnecting fibers in a link end to end and their isolation or protection, or both.connection process. Beginning with the structure of d) Small form factor (SFF)-It refers to any ofthe connector, followed by commonly used connector several physically compact connectortypes and their applications, it journeys towards designs that have been developed for use inspecial connectors for harsh military environments fiber optic systems. They are about half thefinally explaining the mechanism for end to end fiber size of conventional connectors. e) Cladding- The dielectric materialconnection. surrounding the core of an optical fiber. f) Cleave- The process of separating an optical fiber by a controlled fracture of the glass for thepurpose of obtaining a fiber end that is1.Introduction flat, smooth, and perpendicular to the fiber axis.There are 110 design types of Fiber Optic connectors g) Coupling Loss- The optical power lossavailable as on today. Connectors are used for suffered when light is coupled from onemany different applications including optical device toanother. h) Ferrule- A mechanical fixture, generally atelecommunications, local area networks, and harsh rigid tube, used to confine the stripped endenvironments. When choosing a connector and of a fiberbundle or an optical fiber.coupling for a particular application, fiber type, i) Fiber Optic Connector- A fiber opticrequired optical performance, maintenance, and component normally assembled onto a cablesystem cost are taken into consideration. If an and attachedto a piece of apparatus for theexisting system is being modified, compatibility with purpose of providingexisting components is must. Specifically, a contact interconnecting/disconnecting of fiber opticcables.scheme, a connector style, terminations, and j) Hackle- A surface irregularity characterizedmaterials need to be chosen. This paper introduces by a rippled or stepped break in the fiber,the commonly used connectors followed by a usuallydue to improper cleaving.discussion of military application connectors and k) Connector Insertion Loss- Total Opticalfinally concludes explaining the mechanism for Power Loss caused by insertion of an opticalconnecting fibers end to end. component such as a connector, splice, or couple into a previously continuous path or The loss in the power of a signal that results2. Definitions from inserting a passive component into a previously continuous path. Examples a) Adhesive-A polymeric compound, usually ofsuch passive devices are connectors, inline an epoxy, used to secure the optical fiber in star couplers and splices a spliceassembly or connector. l) Mode- In terms of ray optics, a possible path b) Back reflection (Backscattering) - The followed by light raysdependent on index of return of a portion of scattered light to the refraction, wavelength of light and input end of afiber; the scattering of light in waveguide dimensions. the direction opposite to its original propagation.
m) Multi-mode Fiber- An optical fiber that will allow two or more bound modes to propagate in thecore at the wavelengths of interest. n) Pistoning- The axial movements of an optical fiber within a connector or connector ferrule. o) Single-Mode Fiber- An optical fiber in which only the lowest order bound mode can propagateat the wavelength of interest. p) Splice- An interconnection method for joining the ends of two optical fibers in a permanent orsemi permanent fashion. q) Strength Member- That part of a fiber optic Figure 2. Ferrule in connector cable composed of Kevlar aramid yarn, steel strands,or fiberglass filaments included for increasing the tensile strength of the cable, and in certain applications, to support the weight of the cable. 4. Summary of commonly used connectors3. Fiber connector Structure 4.1. SC ConnectorA fiber-optic connector joins fibers in a way that light SC stands for Subscriber Connector.passes from one fiber to the other. The main goal isminimizationof signal loss and reflections, while Manufactured By: NTT (Nippon Telegraph andproviding mechanical stability. Losses forvarious Telephone) of Japan.connector types are in the range of 0.25 dB to1.5dB.A fiber-optic connection consists of three Application: SC Connectors are frequently used forcomponents: twomale connector plugs, and a Network applications. SC connector is widely used incoupling (or in-line adapter). Theconnector plug singlemode systems. SC connectors have low costconsists of a ferrule, a strain relief boot, and housing and they are simple and durable.or body. The coupling device allows twoconnectors Ferrule Diameter:It has a 2.5mm diameter ferrule,to mate through a panel. It hasreceptacles on each made of ceramic or metal. A 124~127µm diameterend and a precision sleeve toalign two mated hole is drilled in the center of the ferrule. It is usuallyconnectors. bonded by epoxy or adhesive. They provide accurate alignment due to ceramic ferrules. Standard: IEC 61754-4 Coupling Type: It hasa square shaped design, with push-pull latching mechanism. Its molded housingprovides optimum protection. Losses & Other Details:The SC connector is also available in a Duplex configuration. SC connectors allowup to 1000 mating cycle. They have insertion loss of 0.25 dB and return loss >55 dB.They are available in single and multimode.Figure 1. Fiber Connector Structure
Figure 4. ST connectorFigure 3. SC connector 4.3. FC Connector4.2. ST connector FC stands for Ferrule connector or fiber channel.Stands for straight tip connectors. Application: It is designed for telecommunicationManufactured By: AT&T applications.It is being used in long haul and localApplication: ST connectorsare used in network connections. They are also useful in high-telecommunications fieldfor both long haul and local vibration environments.network applications. They are the most commonly Ferrule Diameter: FC connector also has a 2.5mmused connectors for multimode applications. ferrule made of ceramic (zirconia) or stainless alloy)Ferrule Diameter:It has a 2.5mm keyed long Standard: IEC 61 754-143cylindrical ferrule for the durability and repeatabilityrequirements in telecommunication links. Coupling Type:It is designed with a threaded coupling. Due to such coupling, connections areStandard: IEC 61 754-2 standard durable. It makes use of screw on mechanism inCoupling Type: Ithas a twist-lock bayonet couplers.coupling.Couplers are keyed and spring-loaded. They Losses &Other Details:It is available in simplexcome in push-in and twist types. Because they are mode only. It is rated for 500 mating cycles. Thespring-loaded, they must be seated properly. It must Insertion Loss for FC connectors is 0.25 dB. It isbe removed and reconnected if high insertion loss is available in single mode and multimode. It is nowobserved. It can be inserted and removed easily due gradually being replaced by SC and LC connectors.to its design. It can have metal or plastic housing.Losses & Other Details: They are available insimplex version only. Itallows 500 mating cycles.TheInsertion Loss for correctly matched ST connectors is0.25 dB.It is available in single mode as well asmultimode fibers.
4.5. MU Connector MU stands for miniature unit connector. Manufactured By:It was developed by NTT. Application: It is a popular connector type in Japan. Applications include high-speed data communications, voice networks and telecommunications. They even support dense wavelength division multiplexing (DWDM). They can also be used for multiple optical connections.Figure 5. FC connector Ferrule Diameter: 1.25 mm Standard: IEC 61754-64.4. LC connector Coupling Type:It has push/pull mechanism, butLC stands for Lucent Connector. benefit is that 2 channels can fit in the footprint of a single SC. It is with square shaped.Manufactured By:Lucent Losses & Other Details:It comes in simplex as wellApplication: The LC has good performance and is as duplex form. It is a small form factor SChighly favored for single mode. Due to its small size, connector. They have insertion loss of 0.25 dB andit is used forhigh-density connections. return loss >55 dB.Ferrule Diameter:LC connectors use a 1.25mmceramic ferrule –half the size of the 2.5mm ferruleused in above mentioned connectors.Standard: IEC 61754-20Coupling Type: simplex and duplex – push and latchLosses & Other Details: Externally LC connectorsresemble a standard RJ45 telephone jack. Internallythey resemble a miniature version of the SCconnector. Insertion loss is <0.2 dB and return loss>50 dB. The LC is a small form-factor (SFF) Fiberoptic connector. Figure 7. MU connector 4.6. SMA Connector SMA stands for Subminiature version A. Manufactured By:Amphenol Fiber Optic Products Application: Industrial lasers, military; telecom multimode. The SMA connector has exceptional mechanical durability. Figure 6. LC Ferrule Diameter: The SMA connector holds aconnector single fiber. The Ferrule is traditionally made of
steel, although ceramic versions are available. SMA905 and SMA 906 multimode connectors areavailable with stainless alloy or stainless steelferrules. The stainless alloy ferrule may be drilledfrom 125um to 1550um to accept various fiber sizes.Coupling Type:SMA connectors use a threaded plugand socket. SMA connectors have a threadedCoupling nut. Figure 8. MT-RJ connectorLosses & Other Details:Simplex only.Multimodeonly.SMAconnectors come in twovarieties: the SMA-905 has a straight ferrule,whereas the SMA-906 has a stepped ferrule designSMA 906 ferrule has a step, which requires a half 5. Connectors for harsh militarysleeve to be installed when mating a SMA 906 environmentconnector with SMA 905 mating sleeves. AT&T has developed a new type of connector that uses expanded-beam optics to maintain accurate alignment, even under severe shock and vibration.4.7. MT-RJ Connector The reliable optical card-edge connector (ROC) uses expanded beam optics to achieve optical alignment.MT-RJ stands for Mechanical Transfer Registered Each terminus consists of a cleaved fiber aligned on- axis with a sapphire ball lens. The gap between theJack or Media Termination - recommended jack. fiber end and the ball lens is filled with an index- matching gel. The LRM assembly was subjected toManufactured By:Tyco Inc. high frequency (sine sweep) vibration, random vibration, and mechanical shock test but negligibleApplication:MT-RJ connectors are used in building increase in optical loss was observed.The self-communication systems for duplex multimode sealing feature of the connector provides adequateconnections. protection for handling in military environments.An additional feature of the ROC connectoris its abilityFerrule Diameter: It has a miniature 2.45×4.4 mm to self-seal or shield the optical fiber endstwo-fiber ferrule with two guide pins parallel to the whenunmated, protecting the fibers and internalfibers on the outside. It is easier to terminate and mechanisms fromenvironmental contamination andinstall than ST or SC connectors.  abusive handling. Standard: IEC 61754-18Coupling type: It is derived from MT ferrule design.The guide pins align ferrules precisely when matingtwo MT-RJ connectors. MT-RJ connectors are Figure 9. ROC connector expanded beam methoddesigned with male-female polarity which meansmale MT-RJ connector has two guide pins andfemale MT-RJ connector has two holes instead. MT-RJ uses a form factor and latch similar to the RJ45 6. Connection mechanismconnectors. Two separate fibers are included in one The steps for Fiber optic Connection are as followsunified connector. The small size allows double thedensity than ST or SC connectors. 6.1.Setup and Tools
The tools that are needed for fiber optic Connection The steps involved in the stripping processinclude are a) Jacket preparation is the first step wherein a a) Safety Glasses for protection and safety. tight knot is to be tied at one end of the b) Cable to be assembled. jacket to prevent the internal parts from c) Jacket Stripper for stripping outer jacket. sliding out. The boot of the connector is d) Buffer Scissors for cutting Buffer member inserted into the cable, small side first. This e) Kevlar Scissors to cut through strength is followed by the crimp sleeve. member. b) The strip Dimension/marking of the Jacket f) Alcohol pads for wiping the fiber clean stripping tool is set as per the jacket before insertion to connectors. diameter. The jacket is bitten firmly without g) Syringe and epoxy for injecting epoxy and twisting or pulling the stripping tool. Then adhesion. after the removal of tool, the jacket is h) Hand Crimp Tool for crimping sleeve onto twisted slowly and it comes off quite easily. the jacket holding assembly together. c) The Kevlar and inside it the PVC coated i) Polishing disk for polishing the end face of glass fiber are then exposed. The Kevlar is the fiber cut using the Kevlar scissors leaving about j) The required connector. 3/8 inches of strength member. k) Scribing tool to scribe the glass from the d) The buffer stripping tool is used to strip connector itself away the protective buffer coating from the l) Three types of lapping film for deburring, wire thus leaving the glass uncovered. For rough and fine polishing. this, the fiber has to be kept slightly taut to m) Glass plate for smooth surface when fix the fiber tightly in the jacket and prevent polishing slipping. Then the buffer is cut out bit by bit n) Small trash bin in straight motion such that the fiber doesn’t bend while stripping. Taking large bites or6.2. Fiber Stripping bending can crack the glass as the bufferKnowledge about internal Fiber structure needs to be tube is strongly attached to it.known for this section. It consists of e) After clearing all debris left over from the stripping process in the trash bin, the fiber a) Outer jacket is cleaned of any minute surface debris b) Strength member-Usually aramid Yarn or using good quality alcohol (91% to 99% Kevlar alcohol). Wiping it with alcohol pads in c) Buffer member-PVC coating straight motion removes all the leftover d) Fiber-core and cladding debris thus ending the stripping process. 6.3. Adhesive preparation It is made up of two steps a) Mixing the epoxy-It has 2 portions that need to be mixed properly (dark and light). They must be properly mixed together to ensure hardening after some time. Setting time is around 30 minutes so only to be mixed when all tools ready to use.Figure10. Fiber coating layers
b) After removing the needle plunger, the lightly for about 20 seconds.As the stub of epoxy is poured into the syringe and at three glass is rubbed off, the sound gets quieter; quarters filled condition, plunger is fitted an indication to stop brushing. back and needle pushed removing any air c) The 3 micron yellow colored lapping film is bubbles present. used for the pre-polishing stage. Here, the connector is first fixed into the polishing disk and placed on the double layer of6.4.Connectorization process yellow lapping film placed on glass. It is rubbed slowly in figure of eight motion till a) This epoxy is then injected into the smoothening is felt and the piece of glass is connector till a small dark spot is visible at completely gone. the connector face. After removing the d) There is also a 0.3 microns white lapping needle halfway through the body. More film for final smoothing polish. Two layers epoxy is filled in till a similar spot is visible of this film are placed on the smooth and at the back end of the connector. cleaned glass plate for cushioning effect so b) The fiber is then inserted through the back that the round curve at fiber end is obtained. end of the connector while rotating the The gentle motion of figure eight is connector back and forth to allow fiber find repeated in this film too for three times. the hole in the ferrule. The connector is This concludes the polishing process unless brought down till some portion of it covers an stub is visible in which case, above three the Kevlar it just meets the jacket. steps need to be repeated. c) The crimp sleeve previously loaded into the fiber is brought forward to the junction of 6.6. Visual inspection jacket and connector. The large part of the crimp sleeve is crimped hard down onto the a) The fiber connector is finally observed for connector and smaller on the jacket using a any scratches on its face by using a hand crimp tool. microscope and if any scratches found, d) The boot also previously loaded is now motion on white lapping film is repeated brought up and attached over the back end once or twice till its completely clean. of the cable. A protective sleeve is attached over the ferrule to protect the fiber and connector while it is allowed to settle and fix 7. Acknowledgement for 18 hours. The other end of the cable too I acknowledge the motivation provider for writing of has to be left as it is to prevent slipping of this term paper, Dr. DhavalPujara, for his constant the fiber during this settling process. guidance and words of motivation. I also6.5. Polishing acknowledge Professor Dhaval Shah for guiding me regarding technical paper writing rules and a) After settling, the protective sleeve is regulations. removed. Three cuts are made on the glass protruding from the connector end with a 8. References scribing tool having a wedged of 60° and then this glass protrusion is twisted and Fleck Research, Global Connector Research Group, Inc. pulled away. A tiny portion still remains  NASA-NASA-STD 8739.5 with Change 2 that has to be deburred. Approved: 1998-02-09 Revalidation Date: 2008-07- b) The 12 micron pink colored lapping film is 25 used to debur the tiny stub of glass that is Practical LEOS Applications -M. Leonard Riaziat protruding . The connector is first Keiser, Gerd (August 2003). Optical brushed on this film while it is held in hand Communications Essentials. McGraw-Hill Networking Professional.
 Shimoji, Naoko; Yamakawa, Jun; Shiino,Masato. "Development of MT-RJ Connector" THE RELIABLE OPTICAL CARD-EDGECONNECTOR (ROC) Stephen L. Benning WrightLaboratory - Avionics Directorate Wright-PattersonAFB OH 45433-7301 A New Type of Fiber Optic Connector Designedfor Military Optical Backplanes R.J. Pimpinella,AT&T Bell Laboratories www.thefoa.org (Fiber optic association) International Standard IEC(Internationalelectrotechnical Commission)-61754 Fibre opticconnector interfaces