Fiber Optic Connectors

Fiber Connection / Polish Styles

The connection of fiber optic cables is done by the ferrules. They are the most important components of fiber optic connectors and could be made of different materials, such as plastics, stainless steel and ceramics, but most of the ferrules used in optical connectors are made of ceramic material. The actual fiber is positioned inside the ferrule. The ferrule itself is a high-precision part with very precise dimensions. Only a very small tolerance between the fiber itself and the channel inside the ferrule is allowed.
The diameter of the optical fiber itself is too small to be polished directly and the ferrules are used to protect the fibers. Due to the differences of the materials (fiber, ferrule) a proper polishing setup is critical for optimum results.
The different polish styles of the fiber optic connector ferrules cause different back reflection and result in different return loss. A straight angled polish style causes reflected light to travel backwards into the fiber, there as the APC with an angled contact surface leads the small portions of reflected light into the cladding.
The higher the return loss the better is the performance. The polish styles of the fiber optical ferrules are:

- PC: Physical Contact, singlemode and multimode, 40dB return loss or higher
- UPC: Ultra Physical Contact, singlemode and multimode, 50dB return loss or higher
- APC: Angled Physical Contact, only singlemode, 60dB return loss or higher

The insertion loss should be less than 0.3 dB.

PC physical contact APC angled physical contact

Connectors with APC, angled contact surfaces must have a perfect guidance to avoid any rotation of the ferrules.

Connector Types

ST"Straight Tip" or "Single Termination"singlemode and multimode, uses a plug and socket which is locked in place with a half-twist bayonet lock, developed by AT&T, leading connectors in the late 80s and early 90s, insertion loss 0,3dB to 0,5dB2,5mm ferrule
SC"Subscriber Connector" or "Square Connector"singlemode and multimode, uses a push-pull socket, mainly used since 2002, with optional duplex clip, developed by NTT Japan, optical loss 0,2dB to 0,4dB2,5mm ferrule
LC"Lucent Connector"singlemode and multimode, PC, UPC or APC, uses a push-pull socket, standard connector for IT applications by EN-50173, with optional duplex clip, developed by Lucent (USA), insertion loss 0,1dB to 0,3dB1,25mm ferrule
E2000  mainly used in Germany, singlemode and multimode, PC, UPC or APC, uses a push-pull socket and an automatic light and dust cap on both sides of the connection, insertion loss 0,1dB to 0,2dB1,25mm ferrule
MT-RJ"Mechanical Transfer Registered Jack"singlemode and multimode, new small form factor connector, IEC 61754-18, connects two fibers and integrates them into a single design, commonly used for networking applications, half the size of a SC connector, insertion loss 0,1dB to 0,15dBone ferrule with two fibers 750 micrometer apart
MU'Mini-SC'singlemode and multimode, developed by NTT Japan, mainly used in Asia, optical loss 0,1dB to 0,2dB1,25mm ferrule
FC"Mechanical Transfer Registered Jack"singlemode and multimode, PC and APC, bayonet lock, very seldom used, insertion loss 0,15dB to 0,2dB2,5mm ferrule

More and more multifiber connectors are used, especially in high densitiy applications. The MPO (Multi-Fiber Push-On) connector is a 12 fiber connector with a very small footprint, developed especially for data centers with high numbers of interconnected fibers. The MPO family includes adapters, connector fanouts and cable assemblies.
MPO pre-assembled cables have a very small diameter of 5,4 mm for up to 48 fibres and 6,4 mm for up to 96 fibres. This is possible because of the design with micro bundles protecting tubes around the installed MPO-connectors. The central strength element and the aramid yarns are pre-conditioned for the use with MPO multi fiber connectors. It results in an also mechanically very strong cable.
The MPO-MPO cables normally have standard non-pinned (female) connectors. They match to pinned (male) connectors in MPO cassettes.

cassette with two MPO fanouts
(here: EFB Elektronik, Germany, Type: DCBK81913.24)
MPO connector with 12 individual fiber connections

MPO"Multi-Fiber Push-On"singlemode and multimode (OM3, OM4), 4, 8 or 12 fiber connector on tight buffered ribbon cordage, push-on/pull-off release latch, PC or APC polishing style, insertion loss 0,15dB to 0,6dB2,5mm x 6,4mm combined ferrule for 12 connections

Color Coding for Connectors

- Orange/Brown: Multimode Connectors 50 / 62,5
- Blue: Singlemode Connectors PC and UPC (physical contact connector and ultra polished connector)
- Green: Singlemode Connectors APC (angled polished connector)

E2000 Connector

The E2000 connector has several advantages. It is available for singlemode and multimode, with the polish styles PC, UPC and APC and it uses a push-pull socket with an advanced dust cap that opens automatically as soon as the connector is pushed into the socket. The cap also serves as a light protection for strong laser light emitted out of the fiber connectors.

E2000 Duplex connectordimensions

   E2000 color coding
- Singlemode PCBlue
- Singlemode APCGreen
- Multimode PCBlack-Orange

Plastic Optical Fiber

Plastic optic fibers are fiber optic cables with a plastic core carrying the information in the form of light. Plastic optic cables work only on very short limited lengths. Toslink is the most usual plastic optic fiber.
These cables have a plastic core with a diameter of 960Ám, 100 times the diameter of the singlemode glass core and about 20 times the diameter of the multimode glass core.