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In an optical fiber, single-encoded beam transmits by total internal reflection through it. Fiber optics are flexible materials to guide optical rays. It can carry hundreds of Gbps over tens of kilometres affecting to very less attenuation. Optical fiber connectors are used to terminate the end of an optical fiber. A fiber optic connector enables quicker connection and disconnection than splicing, which refers to holding two or more fiber optics precisely aligned by making a junction to pass the optical rays through it. Connectors mechanically couple and align the cores of the fiber so light can pass. If the connector is much better, then there will be a very small loss of light due to reflection or misalignment. The connector can be supplied as a pre-assembled one-piece connector or as connector kits.
1.1 Design of fiber optic connectors
The basic connector unit is a connector assembly. It consists of a connector plug and an adapter. Connector plugs may be male connectors with protruding ferrule that hold the fibers and aligns two fibers for mating. To mate the two connectors that fits the mechanism of connectors, mating adapters are being used. Bayonet, screw-on or snap-in are the coupling types which are the connector mechanisms.
Figure 1.1.1: connectors Figure 1.1.2: adapters
2 Fiber Optic Connector Types
2.1 SC connectors
SC stands for Subscriber Connector or Square Connector or for Standard Connector. These connectors are available in single mode and multi mode. It uses the push-pull or snap-in coupling method. It is built around a ferrule which its diameter is 2.5mm and cylindrical in shape. The ferrule is made out of ceramic or metal which is a stainless alloy. High precision hole is drilled inside the ferrule where the hole diameter is 124~127 µm. Stripped bare fiber is inserted through it and bonded by epoxy or adhesive. The ferrule is assembled in the sub-assembly body. The end of the ferrule protrudes out of the sub assembly body to mate with another SC connector inside an adapter (aka coupler). A connector housing is then assembled with the sub-assembly body to provide the mechanism for snapping into an adapter and hold the connector in place. Fiber cable and strength member are crimped on to the connector sub-assembly body. This is done by using a crimp eyelet. This helps to reduce the stress which can affect on the fiber itself by providing the strength for mechanical handing of the connector. Mechanical damages can be occurred in the fiber cable and it can cause loss of optical rays through the cable. As a solution stress relief boot covers the joint between connector body and fiber cable.
Figure 2.1.1: SC connector structure
2.1.1 Applications of SC connectors
Widely used in single mode systems for its excellent performance.
Use in Datacom and Telecom.
For Gigabit Interface Converters.
Can use for multimode and single mode applications
Conforms to a standard
Can be duplex
Possibility of high density
Fast push-pull action
Not very robust
Figure 2.1.2: SC optical fiber connectors
2.2 ST connectors
ST connectors are probably the most popular connectors for multimode networks. But it is also available for single mode purposes.ST stands for Straight Tip. They are keyed for repeatable performances. Twist-on mechanism is used in ST connectors. It has bayonet coupling ring and a long cylindrical ceramic or polymer ferrule which its diameter is 2.5mm same as SC connectors. Ferrule is there to hold the fiber. ST connectors are spring loaded. Therefore the user has to mate the connectors properly using an adapter without letting it to give a high loss.
Figure 2.2.1: ST connector
Figure 2.2.2: ST connector Figure 2.2.3: ST Adapter
2.2.1 Applications of ST connectors
Highly use for multimode fiber optic LAN applications.
Use for repeatable performance.
Good for easy field installation
There can be some incompatibility
Poor disconnect protection results in smashed ends.
Angled Physical Contact (APC) is not possible.
ST-ST mating adapter
Figure 2.2.4: ST connector
2.3. FC connectors
FC refers to Ferrule Connector or Fiber Channel. It is one of the most popular single mode connectors. But it is also available in multimode. It consists of a floating ferrule that provides good mechanical isolation. The ferrule diameter is 2.5mm. Some older ferrules were made out of ceramic covered with stainless steel. Threaded metal coupling ring is used in FC connectors. FC and SC connectors are invented by Nippon Telegraph and Telephone (NTT) Company in Japan. Either it is commonly used in earlier days, now it's been mostly replaced by SC and LC connectors.
fc connector http://www.fiberoptics4sale.com/Merchant2/fofs_img/clip_image008_0000.jpg
Figure 2.3.1: parts of a FC connector Figure 2.3.2: FC connectors mating
Specially use for telecommunication applications. (Datacom,Telecom)
For measurement equipments.
For single-mode lasers
Provides non-optical disconnect performance
PC and APC end face geometries are available.
Rotate ferrule to tune loss.
Consist of all performance levels.
Compatibility problems between brands of the product
2.4. LC Connectors
LC refers to Lucent Connector, Little Connector or Local connector. It uses the snap-in coupling mechanism. It is push and pull type. Simplex and Duplex LC connectors are available. It's a small form factor connector which its ferrule diameter is 1.25mm and that is half of the size of the ferrules of SC, ST and FC connectors. These connectors are specially uses for single mode applications.
Figure 2.4.1: Duplex LC connector
Figure 2.4.2: simplex adapter Figure 2.4.3: Duplex adapter
Widely used in fiber optic patch cord
Use for High density connections
Use for SFP and XFP transceivers
Low return loss
All types conform to a standard
Provides pull-proof stability in system rack mounts
Fiddly and not Robust
Figure 2.4.4: Simplex LC connector
2.5 MT-RJ Optical Connectors
Mechanical Transfer Registered Jack or Media Termination- Recommended Jack has RJ-45 style structure. MTRJ connector is with duplex fiber channel inside one single connector. 0.75mm space is there in between the two channels. These connectors in are duplex and multimode only. It does not have a ferrule with the diameter of 1.25mm. Instead, it has a two fiber ferrule design which has derived from MT connectors. There are two guide pins parallel to the fibers on the outside. These pins align the ferrules precisely when mating two MT-RJ connectors. Overall size is more close to the size of an RJ45 connector. These connectors are designed with male polarity which has two guide pins and with female polarity which consist of two holes instead.
Figure 2.5.1: MT-RJ connector Figure 2.5.2: MTRJ Adapter
Use in intrabuilding communication systems.
For duplex multimode connections
Small form factor connector
Reduces required space by 50% throughout the network
Low insertion and return loss
Available both PC and APC end face geometries
Hard to clean
Very poor single mode performance
Male/female compatibility issues
2.6. E2000 Connector
It is also called LX.5 connector or LSH. It uses snap-in mechanism. It is available in single mode and multimode. It looks so similar to a SC connector externally. It has a 1.25 ferrule and these connectors are easy to install with a push-pull latching mechanism. A spring loaded shutter protects the ferrule fully from dust and scratches. Shutter closes automatically when the connecter gets disengaged. Therefore impurities which can lead to network failure and potentially harmful laser beams will be suppressed. These connectors are popular in Europe.
Figure 2.6.1: E2000 Connector Figure 2.6.2: E2000 Adapter
Use for Telecom
For DWDM systems
Possibility to use in high density applications
Fast push pull action
Safety shutter may transparent to infrared light and it can damage.
2.7 MU Connector
Miniature Unit connectors look like mini SC connectors. It is more popular in Japan. Snap-in is used as the coupling type for these connectors. Simplex and Duplex connectors are also available. 1.25mm ferrule is used in MU connectors, which is the smallest single ferrule. These connectors and adapters were developed by NTT. Push-pull mechanism incorporates with these connectors.
Figure 2.7.1: Simplex and duplex MU connectors
Figure 2.7.2: MU adapter-simplex Figure 2.7.3: MU adapter-duplex
For High speed data communications
For voice networks
Use in dense wavelength division multiplexing (DWDM)
Use in multiple optical connections
As a self retentive mechanism in backplane applications
2.7.2 Advantages & disadvantages
It is a small form factor connector and also it is advantageous because it is well engineered.
MU connectors are fiddly and not robust. So it becomes an advantage of while using these connectors.
2.8 FDDI Connectors
These types of connectors have two ferrules of 2.5mm diameter for each. These connectors have a fixed shroud over the ferrules. This sheltered the ferrules from damage. FDDI is a duplex connector which mates to their specific networks. The whole network is connected by a combination of FDDI connectors and ST or SC connectors. FDDI connectors are used to connect to the equipment from a wall outlet and the rest of the network is connected by one of other two types of connectors. Since the ferrule diameter is equal in all 3 types of connectors mentioned above, it's possible to mate those using adapters. FDDI connectors are produced only for multimode purposes and designed by ANSI.
http://www.fiberoptics4sale.com/Merchant2/fofs_img/clip_image023.png fddi connector kitFigure 2.8.1: Assembled FDDI connector Figure 2.8.2: FDDI connector
To connect to equipment from a wall outlet, to build up a network.
Couple directly with active device receptor.
Hard to assemble
Awkward strain relief
2.9 ESCON Connector
Enterprise Systems Connection or ESCON connectors are designed by IBM for mainframe computers. Although it is more similar to FDDI connectors, instead of a fixed shroud these connectors consist of a retractable, spring-loaded shroud. It has a robust strain relief design and a ceramic ferrule which its diameter is 2.5mm. Snap in coupling method is used for these connectors.
Figure 2.9.1: ESCON connector
Use for IBM mainframe computers and peripherals.
2.10 SMA Connectors
SMA refers to Sub Miniature A. There are two types of SMA connectors. They are SMA 905 and SMA 906. These have become obsolete connectors in the present. SMA 905 connectors have a ferrule with typically a 3.14mm diameter. The diameter of SMA 906 ferrule is stepped into two diameters, which are typically 0.118inches and then 0.089inches. These connectors are designed only for multimode purposes and simplex only. SMA connectors make use of threaded connections. Both types of SMA connectors are available with stainless alloy or stainless steel ferrules. The stainless alloy ferrule may be drilled from 125µm to 1550µm. This helps to access various fiber sizes.
Figure 2.10.1: SMA connectors
For military systems
For industrial purposes.
Insensitive to vibration
High insertion loss
No anti-rotation feature
Two incompatible styles
2.11 MTP and MPO Connectors
MPO stands for Multiple-Fiber Push-on/ Pull-off. These are compatible ribbon fiber connectors which allow quick and reliable connections up to 12 fibers. They can replace in installations where many fiber connections may required.MTP and MPO connectors terminate ribbon fibers or ribbonized single fibers. Ferrule of each of these connectors have a diameter of 2.5*6.4mm and it includes two 0.7mm diameter holes. These holes are running parallel to the fibers on the outer side of the ferrule. There are precision metal guide pins which are there to align the fibers with tight tolerance. Holes inside the ferrule hold these guide pins. MTP and MPO are commercial names where these connectors are based on MT connectors. These connectors use the multiplex push-pull coupling method as the mating mechanism. These connectors are used for both single mode and multimode purposes.
Figure 2.11.1: MTP-MPO connectors Figure 2.11.2: MTP-MPO adapters
Use for indoor cabling.
Use for device interconnections
Allow quick and reliable connections
Coupling loss is typically bigger than single fiber connectors.
Features of Optical Connectors
Low insertion loss and back reflection loss
Free-floating ceramic ferrule
UL-rated plastic housing and boot
Boots in a variety of colours
High precision alignment
References: Beyond Optics (online)