In-Depth Look at the Fiber Optic Connector

In all fiber optic system, it is necessary to join two fibers together with low signal attenuation while maintaining low reflection levels depending upon the type of system used. Fiber optic connectors are used as the mechanical and optic means for cross connecting fibers and linking to fiber optic transmission equipment. With a wide range of fiber optic connectors with different merits and demerits available on the market, many factors, like performance and cost, should be taken into consideration when choosing a fiber optic connector. Every small decision will post a significant influence on deployments speeds and costs of the fiber optic patch cables. To specifically understand the fiber optic connector, this post will give an overall look of it.

Fiber Optic Connector

An optical fiber connector terminates the end of an optical fiber, and enables quicker connection and disconnection than splicing. The connectors mechanically couple and align the cores of fibers so light can pass. Better connectors loss very little light due to reflection or misalignment of the fibers. In all, about 100 fiber connectors have been introduced to the market. The table below shows some optical connectors.

Commonly Used Types of Fiber Optic Connectors

With so many fiber optic connectors used in fiber optic networks, there are only a few types widely applied. In this part, we will introduce five types of optical connectors

FC Connector

The FC connector was the first optical fiber connector to use a ceramic ferrule, but unlike the plastic bodied SC and LC, it utilizes a round screw-type fitment made from nickel-plated or stainless. The connector end face relies on an alignment key for correct insertion and is then tightened into the adapter/jack using a threaded collet. Although the FC adds complexity both in manufacturing and installation, it is still the connector of choice for precise measuring equipment such as OTDRs. What’s more, the FC connector does make it particularly effective in high vibration environments, ensuring that the spring-loaded ferrule is firmly mated.

ST Connector

Originally developed by AT & T shortly after the arrival of FC, ST or straight tip connector was one of the first connector type widely implemented in fiber optic networking applications. ST connector can be easily mistaken for FC connector at a glance, but the ST uses a bayonet fitment rather than a screw thread. Deployed predominately in multimode datacoms, it is available in network environments such as campuses, corporate networks and in military applications where the quick connecting bayonet had its advantages at the time. Nevertheless, it cannot be terminated with an angled polish, which limits use in single-mode fiber and FTTH applications. It is typically installed into infrastructures that were built at the turn of the century, but nowadays it has almost been swapped out for more cost-effective SC and LC connectors.

SC Connector

The SC or subscriber connector was developed by the laboratories at Nippon Telegraph and Telephone (NTT) in the mid-eighties, which was one of the first connectors to hit the market following the advent of ceramic ferrules. SC connector is a non-optical disconnect connector with a 2.5 mm pre-radiused zirconia or stainless alloy ferrule. It uses a push-on/push-off mating mechanism which is generally easier to use than the twist-style ST connector when in tight spaces. Due to its excellent performance, SC connector has dominated fiber optics for over a decade and now it remains the second most common connector for polarization maintaining applications.

LC Connector

Considered to be the replacement of the SC connector, LC or lucent connector is the most popular small form factor (SFF) connector. Like SC, it is also a push-pull connector, but LC utilizes a latch as opposed to the SC locking tab. Having half the footprint of the SC connector, about 1.25 mm ferrule, gives it huge popularity in datacoms and other high-density patch applications. With more and more density increasingly needed in data centers, the popularity of LC connector will continue growing. The following picture shows the different appearance of FC, ST, SC and LC connector, so you can easily distinguish them.

MPO/MTP Connector

MPO and MTP are compatible ribbon fiber connectors based on MT ferrule which allow quick and reliable connections for up to 24 fibers, so they are larger than the connectors we have mentioned above. MPO and MTP connectors feature male and female connector design. Male connectors have two guide pins and female connectors do not (see in the following image). Both connector types need an adapter to mate a pair of male and female connectors. Since MPO and MTP connectors are trying to align so many fibers at once, their coupling losses are typically bigger than single fiber connectors. This type of connector is extensively used with a fan-out assembly at the opposing end (such as LC, SC, FC etc.) in high-density patching environments, like data centers.

Summary

Knowing the differences among different connector types is necessary to get a deep understanding of the fiber optic connector. Taking time to select the right optical connector for the job can deliver big benefits when it comes to speed and cost. So before making connector choice, please think twice.