Fiber optic connector guide
At least 100 optical fiber connector types have been created and introduced to the market by several manufacturers since 1980 and they all basically do the same work: mating two fibers ends without making it permanent, lining up tiny glass fibers so light pulses can travel through them.
Structure
Fiber optic connectors are essentially integrated with the same mechanisms:
The ferrule: This is the most important component of fiber optic connectors because it holds the glass fiber. It is made of ceramic, high-quality plastic or metal. According to the way their ferrules are polished, fiber optic connectors can be classificated as:
- PC (Physical Contact): PC connectors are polished with slight curvature, which reduces the air gaps between fibers. They need to have at least 40dB of Optical Return Loss (ORL) or higher, says a report made by Berkeley Nucleonics Corporation.
- UPC (Ultra Physical Contact): UPC connectors also have a convex end-face, but have a finer surface finish. Their ORL is 50 dB or higher, which makes them reliable for transmitting TV and data signals.
- APC (Angled Physical Contact): APC connectors have an 8° angle cut in their ferrules, which makes connections between optical fibers even tighter. Industry standards indicate that APC connectors need to have 60 dB or higher ORL.
Connector body: Is the structure that holds the ferrule, the coupling mechanism and the boot. It is made of plastic or metal.
Coupling mechanism: It mates the connector with the device it has to be attached to. A report from Meridian Technologies says the coupling mechanism can be push-pull or bayonet.
Color code
According to the TIA 568 color code, connectors with beige bodies or boots work with multimode fiber, blue ones with single mode fiber and Green is for APC connectors, says the Connector Identifier Guide from the Fiber Optics Association.
For an optical fiber connector to be considered the best it needs to have low insertion loss, low cost and be easy to terminate.
FC (Ferrule Connector)
Designed by Nippon Telephone and Telegraph (NTT), the FC is a 2.5mm zirconia ceramic ferrule, which stays in place with a screw-on nut mechanism. It is available for both single and multimode fiber, but it's widely used in single mode applications and in high-speed optical fiber communication networks. It is also used in high-vibration environments due to its threaded body. Its insertion loss is of 0.3 dB.
ST (Straight Tip)
The ST was created and licensed by AT&T and is still one of the most popular connectors used in commercial wiring, for indoor applications or long line systems. It holds the fiber with a ceramic, plastic or metal 2.5mm ferrule that stays in place with a “twist-on/twist-off” bayonet mount, which has made common for technicians to also call them “Set and Twist”, “Stab and Twist” or “Single Twist” connector. It has an insertion loss of about 0.5 dB.
The SC was created by the Japanese telecommunication company NTT, but it wasn’t widely used at the beginning because it was highly expensive at the time. Its 2.5mm ferrule uses a pull-on/pull-off joining system, that holds single mode fibers with precision and has given it the name of “Set and Click” and “Stab and Click” connector. This connector is used for telecoms and analog CATV. It has a typical connection loss of 0.25 dB.
SC, ST and FC connectors share the same ferrule size, which makes it possible for them to be joined with each other using hybrid mating adapters.
LC (Lucent Connector)
The LC, also known as Little Connector, was created by Lucent Technologies and is widely used in single mode applications because it can be simply terminated with any adhesive and has a good performance. It has a 1.25mm zirconia ferrule that uses a retaining tab mechanism and has a typical insertion loss of 0.10 dB. LC connector small size reduces space needed for patch panels in 50% in contrast with SC or ST connectors.
MTRJ (Mechanical Transfer-Registered Jack)
MTRJ is duplex connector, meaning it holds two fibers at the same time. Its body and ferrule are made of plastic and it has male and female versions that stay in place with pins. MTRJ only works with multimode optical fiber.
RJ45 (Registered Jack 45) - (Ethernet Connector )
RJ45 is a standard type of connector that features 8 pins. It is normally used for data transmission in Ethernet networks, or to connect a patch panel to a network switch. It is also used in LAN and ADSL broadband Internet connections.
Is not a fiber connector, but in a world with standarized UTP connections, is important for the list and worth mentioning.
MPO (Multi-fiber Push-on)
Is a multi-fiber connector that brings together from 12 to 24 fibers in a single rectangular ferrule and is used for building 40Gb to 100Gb optical parallel connections. It comes in UPC and APC versions. A male MPO connector has two pins on its ferrule tip, while females has two holes. Its typical insertion lost is 0.25dB.
Choosing between connectors
No stores or technicians seem to agree when asked “What are the most popular optical fiber connectors?” There isn’t any verified information for such a frequently asked question. Therefore, we decided to investigate it searching over every optical fiber equipment store that would let us check which ones were their most popular products. Using Beyondtech’s information and the data we collected, we found that
- SC connector is the most popular connector in 34% of the visited online stores.
- LC connector in 32%
- ST connector in 28%
- FC connector in 6%.
Source: The Most Used Fiber Optic Connectors / Beyondtech White Papers
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