The using of fiber optic connectors has traditionally been the biggest concern in fiber optic systems. While connectors were once unwieldy and difficult to use, connector manufacturers have standardized and simplified connectors greatly. This increases the user use convenient connectors during the use of optical fiber systems; It is also emphasizing taken proper care of and deal with the fiber optic connectors. To learn more about the fiber optic connectors, you should read this tutorial.
What is Fiber Optic Connector?
Fiber Optic Connector, or optical fiber connector, is removable activities between optical fiber and optical fiber connection device. It is to put the fiber of two surface precision docking, so that the optical output of optical energy to maximize the fiber optic coupler in receiving optical fiber, and optical link due to the intervention and to minimize the effects on the system, this is the basic requirement of fiber optic connector. To a certain extent, fiber optic connector also affects the fiber optic transmission reliability and the performance of the system.
Key Features of Fiber Optic Connectors
The key features of fiber connector include optical properties, interchangeability, repeatability, tensile strength, temperature, insertion times, etc.
- 1. Optical Properties: The optical performance requirements of fiber optic connectors, mainly are the two basic parameters of Insertion Loss and Return Loss.
- Insertion Loss is a connection loss of the link effective optical power loss because of the insertion of the connector. Insertion Loss is smaller the better, general requirements should not be more than 0.5 dB.
- Return Loss (or Reflection Loss) refers to the suppression of link connector optical power of reflection, its typical value should not be less than 25 dB. In actual application of the connector, the pin surface after the special polishing process can make the return loss larger, generally not less than 45dB.
- 2. Interchangeability and Repeatability: Fiber optic connectors are universal passive devices, the fiber connector of the same type, can be used in any combination and can be used repeatedly, thereby additional imported losses are generally in the range of less than 0.2dB.
- 3. Tensile Strength: To the done fiber optic connectors, the general requirements of the tensile strength shall be not less than 90N.
- 4. Temperature: Generally, fiber optical connector must be used at a temperature of -40C to +70C.
- 5. Insertion Times: Currently fiber optic connectors can generally be pluged more than l000 times.
Structure of Fiber Optic Connectores
Optical fiber to fiber optic interconnection can be made by a joint, a permanent connection, or a connector, and is different from the plug in it can be to disconnect and reconnect. Fiber optic connector types are as various as the applications for which they were developed. Different connector types have different characteristics, different advantages and disadvantages, and different performance parameters. But all connectors have the same four basic components.
Ferrule: The fiber is installed in a long, thin cylinder, the ferrule, which act as a fiber alignment mechanism. The ferrule is bored through the center at a diameter that is slightly larger than the diameter of the fiber cladding. The end of the fiber is located at the end of the ferrule. Ferrules are typically made of metal or ceramic, but they may also be constructed of plastic.
Connector Body: Also known as the connector housing, the body holds the ferrule. It is usually constructed of metal or plastic and includes one or more assembled pieces which hold the fiber in place. The details of these connector body assemblies vary among connectors, but the welding and/or crimping is commonly used to attach strength members and cable jackets to the connector body. The ferrule extends past the connector body to slip into the couping device.
Cable: The cable is attached to the connector body. It acts as the point of entry for the fiber. Often, a strain relief boot is added over the junction between the cable and the connector body, providing extra stength to the junction.
Coupling Device: Most fiber optic connectors do not use the male-female configuration common to electronic connectors. Instead, a coupling device such as an alignment sleeve is used to mate the connectors. Similar devices may be installed in fiber optic transmitters and receivers to allow these devices to be mated via a connector. These devices are also known as feed-through bulkhead adapters.
Types of Fiber Optic Connectors
According to the different classification methods, fiber optic connectors can be divided into different types. According to the different transmission media, fiber connectors can be divided into single-mode and multimode fiber optic connectors. According to the different structures, fiber connectors can be divided into various types like ST, SC, FC, LC, MT-RJ, MPO/MTP, MU, DIN, E2000, SMA, BICONIC, D4, etc. According to the pin end surface of the connector, they can be divided into PC, UPC and APC. According to the number of fiber cores, fiber connectors can be divided into single-core and multi-core fiber optic connectors. In all, about 100 fiber optic connectors have been introduced to the marketplace, but only a few represent the majority of the market. Here is a rundown of the connectors that have been the leaders of the industry.
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ST Connector: ST is probably still the most popular connector for multimode networks, widely used in the optical distribution frame (ODF), like most buildings and campuses. It has a bayonet mount and a long cylindrical 2.5 mm ceramic (usually) or polymer ferrule to hold the fiber. Most ferrules are ceramic, but some are metal or plastic. ST connectors are constructed with a metal housing and are nickel-plated, can be inserted into and removed from a fiber-optic cable both quickly and easily. They have ceramic ferrules and are rated for 500 mating cycles. From a design perspective, it is recommended to use a loss margin of 0.5 dB or the vendor recommendation for ST connectors.
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SC Connector: This is a kind optical fiber connector developed by Japan's NTT. SC is a snap-in connector with a 2.5 mm ferrule that is widely used for it's excellent performance. Its shell is rectangular, adopted by the pin type and the structure of the coupling sleeve size. The end face of the pin is used more PC or APC model grinding method, fastening way is to use the plug pin bolt type, do not need to rotate. SC connector latches with a simple push-pull motion. SC connectors provide for accurate alignment via their ceramic ferrules. Typical matched SC connectors are rated for 1000 mating cycles. SC connector features with low price, involve loss small ripple, high compressive strength and high density installation.
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FC Connector: FC connector was originally developed by NTT, Japan. FC is short for FERRULE CONNECTOR. It also uses a 2.5 mm ferrule, its external strengthening way is to use metal sleeve, fastening way as the turnbuckle. FC connectors offer extremely precise positioning of the fiber-optic cable with respect to the transmitter's optical source emitter and the receiver's optical detector. FC connectors feature a position locatable notch and a threaded receptacle. FC connectors are constructed with a metal housing and are nickel-plated. They have ceramic ferrules and are rated for 500 mating cycles. This kind of connector is simple in structure, convenient operation.
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LC Connector: LC type connector is a famous BELL developed by the institute of research, using convenient operation modular jack (RJ) latch mechanism is made. The pin and the size of the sleeve is adopted by the general SC, FC, half size is 1.25 mm. It can improve the density of optical fiber connector in the optical fiber distribution frame. Otherwise, it's a standard ceramic ferrule connector, easily terminated with any adhesive. LC connector features with good performance and is highly favored for single mode.
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MT-RJ Connector: MT-RJ is a duplex connector used with single-mode and multimode fiber optic cables. It uses pins for alignment and has male and female versions. MT-RJ connectors are constructed with a plastic housing and provide for accurate alignment via their metal guide pins and plastic ferrules. MT-RJ connectors are rated for 1000 mating cycles. The typical insertion loss for matched MT-RJ connectors is 0.25 dB for SMF and 0.35 dB for MMF.
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MPO/MTP Connector: The MPO Connector is the industry acronym for "Multi-fiber Push On", with push-on insertion release mechanism, provides consistent and repeatable interconnections and available with 4, 8, 12, or 24 fibers. MTP® is a trademark of US Conec for MPO connector. The MTP/MPO is a connector manufactured specifically for a multifiber ribbon cable. The MTP/MPO single-mode connectors have an angled ferrule allowing for minimal back reflection, whereas the multimode connector ferrule is commonly flat. The ribbon cable is flat and appropriately named due to its flat ribbon-like structure, which houses fibers side by side in a jacket.
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MU Connector: MU connector looks like a miniature SC with a 1.25 mm ferrule, with a simple push-pull design and compact miniature body. It is used for for compact multiple optical connectors and self-retentive mechanism for backplane applications. The connectors are composed of plastic housing. MU connectors are the optical connectors which miniaturized and were advanced the density application and performance.
The table below illustrates some types of above connectors and lists some specifications. Each connector type has strong points.
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| Connector Type | Coupling Type | Fiber Type | Insertion Loss | Polish | No. of Fibers | Typical Applications |
| ST | Twist on | SM, MM | 0.40 dB(SM) 0.50dB(MM) | PC, UPC | 1 | LANs |
| FC | Screw on | SM, MM | 0.5 - 1.0 dB | PC, UPC, APC | 1 | Datacom, Telecommunications |
| SC | Snap on | SM, MM | 0.2 - 0.45 dB | PC, UPC, APC | 1 | CATV, Test Equipment |
| LC | Snap on RJ45 style | SM, MM | 0.15 dB (SM) 0.10 dB (MM) | PC, UPC, APC | 1 | Gigabit Ethernet, Video Multimedia |
| MU | Push / Pull | SM, MM | 0.30 dB | PC, UPC, APC | 1 | Data Communications, Voice Networks, Telecommunications, DWDM |
| MT-RJ | Snap on RJ45 style | SM, MM | 0.30 dB | N/A | 2 | Gigabit Ethernet, Asynchronous Transmission Mode (ATM) |
| MPO / MTP | Push / Pull | SM, MM | 0.30 dB | N/A | 4, 8, 12, 16 | Active Device Transceiver, Interconnections for O/E Modules |
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DIN Connector: DIN is an abbreviation for Deutsches Institut für Normung or German Institute for Standardization, which is a German manufacturing industry standards group. DIN connector encompasses several types of cables that plug into an interface to connect devices. It is round, with pins arranged in a circular pattern. Typically, a full-sized DIN connector has three to 14 pins with a diameter of 13.2 millimeters. This type of connector was used widely for PC keyboards, MIDI instruments, and other specialized equipment.
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E2000 Connector: E2000 fiber optic connector has a push-pull coupling mechanism, with an automatic metal shutter in the connector as dust and laser beam protection. One-piece design for easy and quick termination, used for high safety and high power applications. E2000 connector available for Singlemode PC, APC and Multimode PC. The E2000 Connector is one of the few fiber optic connectors featuring a spring-loaded shutter which fully protects the ferrule from dust and scratches. The shutter closes automatically when the connector is disengaged, locking out impurities which could later lead to network failure, and locking in potentially harmful laser beams.
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Obsolete Connectors
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SMA Connector: Amphenol developed the SMA from the "Subminiature A" hence SMA, microwave connector. The model 905 had a machined ferrule exactly 1/8 inch in diameter that mated in a machined adapter. When the adapters were not precise enough for better fibers, a necked-down ferrule that mated with a Delrin adapter for better insertion loss performance. These connectors are still in use on some military and industrial systems.
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BICONIC Connector: This is the Biconic, the yellow body indicating a SM version (MMs were usually black). Developed by a team led by Jack Cook at Bell Labs in Murray Hill, NJ, the Biconic was molded from a glass-filled plastic that was almost as hard as ceramic. It started with the fiber being molded into the ferrule. This lasted until the company could get a 125 micron/5mil pin insert into the plastic mold, at which point the fiber was glued into the ferule with epoxy. When singlemode versions first appeared, the ferrules were ground to center the fiber core in the ferrule to reduce loss. Since it was not keyed and could rotate in the mating adapters, it had an airgap between the ferrules when mated, meaning loss was never less than 0.3 dB due to fresnel reflection. Usually MM Biconics had losses of 0.5-1 dB and SM 0.7 dB or higher.
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D4 Connector: D4 connector was probably the first connector to use ceramic or hybrid ceramic/stainless steel ferrules. It's keyed and spring loaded, the ferrule has a 2.0mm diameter ferrule. D4 connectors have a high-performance threading mounting system and a keyed body for repeatability and intermateability.
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Color Codes
Since the earliest days of fiber optics, orange, black or gray are multimode and yellow is singlemode. However, the advent of metallic connectors like the FC and ST made color coding difficult, so colored boots were often used. The TIA 568 color code for connector bodies and/or boots is Beige for multimode fiber, Blue for singlemode fiber, and Green for APC (angled) connectors.
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