Fiber Optic Connectors & Adapters

The most common connectors used in the fiber optic telecommunications industry consists of the LC, SC, ST, FC, MTRJ, and MU. The purpose of these connectors is to provide a reliable mechanical connection to couple and align the fiber cores so that the laser light can pass through to a network or device. Most optical fiber connectors are spring-loaded allowing the two endfaces to press together firmly resulting in a direct glass or plastic contact, depending on the type of fiber. It’s important to avoid air gaps or contamination. SC connectors are a popular connector used with multimode fiber. Includes a 2.5 mm ferrule, and a square shaped connector with a push-pull latching mechanism allowing it to be used in tighter spaces ST connectors are used with multimode fiber, and have a 2.5mm shaft and bayonet locking ring for twist-connect and disconnect of a 125 micron multi-mode fibre. It is similar in appearance to a BNC connector. The connector is keyed which prevents rotation of the ceramic ferrule. LC connectors are used in single and multimode applications. The LC connector is often found on small form-factor pluggable transceivers. FC connectors are the most widely used fiber optic connector in the telecommunications industry. Includes a floating ferrule and threaded body to provide good mechanical isolation in high-vibration environments. MT-RJ Connectors (Mechanical Transfer Registered Jack) uses a form factor and latch similar to the RJ-45 connectors. Two separate fibers are included in one unified connector. The smaller size allows twice the port density on a face plate than ST or SC connectors do. Fiber Optic Adapters are a mechanical device used to align and join two or more fibers with different connection types.

SC connectors

SC connectors use a round 2.5mm ferrule to hold a single fiber. They use a push-on/pull-off mating mechanism which is generally easier to use than the twist-style ST connector when in tight spaces. The push-pull design also reduces the chance of fiber endface damage when connection is made. Two SC connectors are usually held together with a plastic clip (this is referred to as a duplex connection). Developed in Japan by NTT (the Japanese telecommunications company), the SC connector is believed to be an abbreviation for Subscriber Connector, or possibly Standard Connector.

ST Connectors

  • Rugged metal bayonet coupling ring
  • Keyed for repeatable performance
  • Precision ceramic ferrule and metal ferrules.
  • Low insertion loss: <0.5 dB Max, < 0.3 dB Typical
  • Connector mating using bulkhead feed-through adapters

The ST connector was one of the first connector types widely implemented in fiber optic networking applications. Originally developed by AT&T, it stands for Straight Tip connector. ST connections use a 2.5mm ferrule with a round plastic or metal body. The connector stays in place with a “twist-on/twist-off” bayonet-style mechanism. The single index tab must be properly aligned with a slot on the mating receptacle before insertion; then the bayonet interlock can be engaged, by pushing and twisting, locking at the end of travel which maintains spring-loaded engagement force on the core optical junction. Although extremely popular for many years, the ST connector is slowly being supplanted by smaller, denser connections in many installations.

LC Simplex/Duplex

  • Single mode 6/125, 9/125 and Multimode 50/125, 62.5/125
  • Pull-proof design
  • RJ-45 style latching mechanism
  • PC and APC end face geometries available
  • LC Duplex includes 2 connector bodies + duplex clip * Low insertion loss: -0.20 dB (Typical)
  • Low return loss (Single mode): min. -45 dB

One popular Small Form Factor (SFF) connector is the LC type. This interface was developed by Lucent Technologies (hence, Lucent Connector) and is replacing SC connectors in corporate networking environments due to their smaller size, uses approximately 50% less space in a panel. It uses a retaining tab mechanism, similar to a phone or RJ45 connector, and the connector body resembles the squarish shape of SC connector. LC connectors are normally held together in a duplex configuration with a plastic clip. The ferrule of an LC connector is 1.25mm.

FC Connectors

  • Threaded metal coupling ring – excellent stability
  • Available in PC and APC end face geometries
  • Pull proof design
  • Designed to the NTT-FC standards
  • Precision keyed ceramic ferrule; metal ferrules available
  • Low insertion loss: <0.5 dB max, < 0.34 dB typical
  • Connector mating using bulkhead feed-through adapters
  • Low cost

The Fixed Connection (FC) connector has a threaded body which was designed for use in high-vibration environments and needs to be mated more carefully than the push-pull types due to the need to align the key, and due to the risk of scratching the fiber endface while inserting the ferrule into the jack.

MT-RJ Connectors

  • Small 2 fiber design (conforms to SFF)
  • Multimode applications 50/125 um, 62.5/125 um
  • Single mode applications 6/125, 9/125 um
  • Reduces required space by 50% throughout the network
  • RJ-45 latching mechanism, small 2 fiber design
  • PC and APC end face geometries
  • Low insertion loss: -0.35 dB Typical Multi-Mode, -0.25 dB Typical Single mode
  • Low return loss (Single mode): > -35 dB

The MTRJ connector closely resembles an RJ-style modular plug, even getting part of its name from the resemblance. MTRJ connectors are always duplex in that they hold two fibers. MTRJ This is another popular SFF connector. Based on a specification by NTT, it was developed by AMP/Tyco and Corning, and stands for Mechanical Transfer-Registered Jack. The body and ferrule are normally made from plastic or plastic composite, and lock into place with a tab (just like a modular RJ-style plug). It is easier to terminate and install than ST or SC connectors.

Fiber Optic Adapters

SC-Simplex-Adapters Housing material: Plastic (UL 94V-0) Sleeve: Phosphor-Bronze; Ceramic Spring plate: Stainless steel Dust caps. SC-Duplex-Adapters Housing material: Plastic (UL 94V-0) Sleeve: Phosphor-Bronze; Ceramic Spring plate: Stainless steel Dust caps. ST-Simplex-Metal LC-Duplex-Adapters Housing material: Plastic (UL 94V-0) Sleeve: Ceramic, Phosphor-bronze Spring plate: Stainless steel Dust caps. Adapters Housing material: Zinc diecast Plating: Nickel Sleeve: Phosphor-Bronze; Ceramic Dust caps. FC-Simplex-Metal Adapters Housing material: Metal Plating: Nickel Dust caps Sleeve: Phosphor-Bronze; Ceramic.

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