What is a Fiber Optic Adapter/ Coupler?

What is Fiber Optic Adapter?

Fiber optic adapters (also known as Fiber couplers, Fiber Adapter) are designed to connect two optical cables together. They have a single fiber connector (simplex), dual fiber connector (duplex) or sometimes four fiber connector (quad) versions. The optical fiber adapter can be inserted into different types of optical connectors at both ends of the optical fiber adapter to realize the conversion between different interfaces such as FC, SC, ST, LC, MTRJ, MPO and E2000, and is widely used in optical fiber distribution frames (ODFs) Instruments, providing superior, stable and reliable performance.

Features of Fiber Optic Adapter

The optical fibers are connected by an adapter through its internal open bushing to ensure the maximum connection between the optical connectors. In order to be fixed in a variety of panels, the industry also designed a variety of finely fixed flange.

Transformable optical adapters are available with fiber optic connectors of different interface types on both ends and provide a connection between APC faceplates. Duplex or multi-adapter adapts to increase installation density and save space.

Fiber Optic Adapter types

  • Lucent Connectors (LC)
  • Standard Connectors (SC)
  • ST Connectors
  • Ferrule Core (FC) Connectors
  • Multi-Position Optical (MPO) Connectors
  • MT-RJ Connectors

Fiber connectors differ based on what types of cables they connect. For example, single-mode fiber connectors and multimode fiber connectors each pair with the cable with the same mode compatibility. 

With many electronics that require fiber optic connections, several types of terminations exist. The most common fiber connectors are LC and SC. SC and LC connector types are so common that many systems have designs to accommodate them. What are the different types of fiber connectors? They are as follows:

1. Lucent Connectors (LC)

LC/UPC Multimode Duplex Fiber Adapter/ Coupler with Flange

LC connectors have some of the smallest ferrules, measuring 1 1/4 mm, which is approximately half the size of an ST connector. Their tiny size puts them into the small form factor category of terminations. These connectors work well for multimode transceivers and single-mode cables.

2. Standard Connectors (SC)

SC/ UPC Singlemode Simplex Fiber Adapter

SC connectors have a 2 1/2 mm ferrule that snaps cleanly into place. Using a push and pull motion secures the connector. These types of terminations have high levels of performance, which along with a price drop since their introduction, has contributed to their vast popularity in multiple applications. In fact, many formerly ST connectors applications now use SC connectors instead, since SC was invented to supplant ST in both telecommunications and data communications.

3. ST Connectors

ST connectors are among the oldest of fiber cable connector types. Until 2005, this proprietary AT&T brand of connector ranked as one of the most popular fiber terminations. While solutions that solve some issues ST connectors present have replaced these connectors, they still remain popular. Today, their cost is low due to their age, making them a choice for budget-mindful projects.

The design of ST connectors is a 2 1/2 mm ferrule that has a bayonet-style connection between the fibers through an adapter. These ferrules use a spring-load design that can make installation difficult unless the parts have precise seating, though a keyed slot assists with aligning the ferrules for connection.

4. Ferrule Core (FC) Connectors

FC/UPC Fiber adapter

FC connectors rank as some of the most popular for use with single-mode connections before the introduction of LC and SC connectors. These use a keyed, screw-in type ferrule. However, the process of screwing in the ferrule requires extra time and effort compared to snap-in SC connectors. 

The screw-in design prevents the connection from interruptions, even when someone pulls the cable or the system has applications in areas with a lot of movement. Video over fiber is one use for these types of connectors due to the constant flow of data through the cable and the security of the connector.

Like ST and SC connectors, FC terminations use a 2 1/2 mm ferrule. With a hybrid adapter, anyone can create a bridge between these connector types.

5. Multi-Position Optical (MPO) Connectors

MPO/APC Singlemode fiber adapter/coupler

MTP is the commercial brand of MPO connectors. MTP and MPO connectors are the same, except the MTP brand has a specific use for high-performance applications, whereas MPO works on more mechanical situations. These two connectors usually connect ribbon cables with multiple fibers.

These connectors have two to six rows of 12 or 16 fibers. MPO connectors with 12 fibers per row can have two to six rows, with two the most common number. Connectors that have 16 fibers per row do not have more than two rows. Connections between ferrules use pins and holes to mate the ends of the fiber with another cable or an electronic device. Most often, this type of connector has applications in either high-speed links that use multimode or for pre-terminated cable groupings.

6. MT-RJ Connectors

MT-RJ Fiber Optic Adapter

Today, MT-RJ connectors have disappeared from use. However, some systems may still require these connectors for repairs. MT-RJ only works for multimode cables with duplex fibers. Both fibers go into the ferrule that connects to its mated half with pins and holes, similar to MPO terminations. Some plug-and-jack variations on this type of connector also exist.

What Are the Advantages and Disadvantages of Fiber Connectors?

Fiber connectors have distinctive pros and cons for the different models. When considering the different types of connectors, weigh their applications and the positive and negative attributes of each to ensure proper selection and installation of the terminations.

Advantages and Disadvantages of LC Connectors

The small footprint of LC connectors makes them ideal for use in crowded spaces, such as for transceivers and networking. Other advantages of these terminations include the ability to use a clip to convert to a duplex from a simplex and the ease of adding a connector to the end of a cable. These connectors also have a design that makes pulling them out of place difficult.

The small size can pose a problem when removing them, especially in high-density sites. Most people have difficulty reaching the clip to disconnect these terminations due to the tiny size of the ferrule and the cramped space these connectors often appear in. Many people solve this issue by using an extractor for LC connectors.

Advantages and Disadvantages of SC Connectors

SC connectors have a square shape for the ferrule, which eases arranging them into a small space. Plus, its sturdy hold prevents connection problems, even if someone pulls the cable. This advantage solves an issue with ST connectors that can interrupt fiber optic signals if someone pulls on the cable. Since the SC has a standard 2 1/2 mm size, it can pair with an FC or ST connector with a hybrid adapter.

The disadvantage of using SC connectors is the size of their ferrules. These connectors require more space than small form factor designs, like the LC. Therefore, for the most compact spaces or crowded areas, LC connectors might provide a better solution.

Advantages and Disadvantages of ST Connectors

Since ST connectors are older, several multimode fiber cable systems use these types of terminations. While pushing and twisting each spring-loaded ferrule is simple, the process does require more time than other connectors. In some instances, the spring-loaded connector can disrupt the connection by pushing the fibers together when someone pulls the cable.

When working in small spaces, pushing in and twisting each connector also becomes difficult, especially in cases when the two halves do not have proper seating for a solid connection.

Advantages and Disadvantages of FC Connectors

FC connectors work in situations that may require assurance of a termination that will interrupt data flow. For applications such as industrial environments or on ships that may encounter rough conditions and cable movement, FC connectors work well.

Since these connectors screw into place, they also need more time for installation. In densely packed spaces, the round shape and screw-in connection require more space for installation and stacking compared to square-shaped SC connectors.

Advantages and Disadvantages of MTP and MPO Connectors

The ability to bundle multiple fibers onto a single connector is the biggest advantage of MPO connectors. When used in high-density situations, MPO connectors can save space compared to SC connectors or other alternatives. Another advantage of some MTP connectors is the ability to remove the exterior housing to easily change the type of connector or repolish the ends.

While MPO connectors offer many advantages over other terminations, especially in crowded racks, this feature also is a drawback. With so many fibers housed in a single connector, cleaning the connectors efficiently is difficult.

Advantages and Disadvantages of MT-RJ Connector

The main disadvantages of MT-RJ connectors are their rarity and their difficulty for field testing. Adding this type of termination to a fiber optic cable requires polishing and splicing, like the requirements for single-mode cables. Consequently, many technicians choose to use other multimode connectors for fiber optics that offer easier installation and testing.

Choosing the Right Types of Fiber Connectors

Knowing the type of cable and the proper connectors for use with the cable and application help the most. The equipment the connector plugs into will also play a role in choosing the type to use. Ask the following questions about a project to choose the right fiber connector types:

1. Is the Cable Single-Mode or Multimode?

Cables have two main formats, single-mode and multimode. These modes describe the interior design and the number of rays that light travels through the fiber in. Single-mode fiber cable uses a 9-micron core through the center that light travels along in one path, thereby reducing loss and increasing potential bandwidth to 100,000 gigahertz. Both CATV and telephony use single-mode fiber cables.

Multimode uses a much larger central core, measuring 50 microns, for accommodating many different rays of light. These cables often appear in use with local area networks and other networking applications. The type of connector used must work with the cable design. For instance, SC connectors come in both single-mode and multimode formats

To identify the type of cable, look at the jacket color. Single-mode cables have yellow or blue covers on the cables. Multimode fiber cables will be orange, bright green or aqua. Military applications also use plain green and slate for multimode cables. Since manufacturers differ in their color choices but remain consistent across the brand, always check with the cable maker first to verify the colors used.

Connectors also have colors to designate their type. Beige typically indicates multimode connectors. Blue is for ultra-physical contact (UPC) single-mode connections, and green goes with single-mode angled physical connector (APC) fiber connectors. When determining whether to use single-mode or multimode, another decision appears when choosing single-mode connectors — the type of physical contact.

2. What Is the Type of Physical Contact for Single-Mode Connectors?

The type of connection with single-mode cables is crucial. Today, single-mode connectors use physical contact (PC). Some PC connectors have convex ends, which increase the contact between the cores of the cables. This reduces loss and reflectance, earning the name of ultra-physical contact.

In some single-mode connectors, angling this physical connection to 8 degrees creates an angled physical connector, which reduces reflectance even more than convex PC connectors. This type of connection ensures better connectivity for use with CATV and similar applications.

3. What Connector Does a Device Require?

Lastly, consider what type of connector the electronics require. Look at the type of connection required and use that to inform a decision on the type of terminations needed for the fiber optic cables leading to the device.

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