Basic Knowledge of Fiber Connector

Remateable connections are made possible by Fiber Connectors. Fiber Connectors are therefore generally used where flexibility is needed at termination points when an optical signal is routed. Examples would include connections from receivers to equipment pigtails, or normal termination, or when re-configuring systems. Remateable connections make it easy to meet changing customer requirements by simplifying system reconfigurations.


Optical fiber connectors are used to join optical fibers where a connect/disconnect capability is required. Due to the polishing and tuning procedures that may be incorporated into optical connector manufacturing, connectors are often assembled onto optical fiber in a supplier’s manufacturing facility. However, the assembly and polishing operations involved can be performed in the field, for example, to terminate long runs at a patch panel.

Optical fiber connectors are used in telephone exchanges, for customer premises wiring, and in outside plant applications to connect equipment and cables, or to cross-connect cables.

Most optical fiber connectors are spring-loaded, so the fiber faces are pressed together when the connectors are mated. The resulting glass-to-glass or plastic-to-plastic contact eliminates signal losses that would be caused by an air gap between the joined fibers.

Performance of optical fiber connectors can be quantified by insertion loss and return loss. Measurements of these parameters are now defined in IEC standard 61753-1. The standard gives five grades for insertion loss from A (best) to D (worst), and M for multimode. The other parameter is return loss, with grades from 1 (best) to 5 (worst).

A variety of optical fiber connectors are available, but SC and LC connectors are the most common types of connectors on the market. Typical connectors are rated for 500–1,000 mating cycles.The main differences among types of connectors are dimensions and methods of mechanical coupling. Generally, organizations will standardize on one kind of connector, depending on what equipment they commonly use.

In many data center applications, small (e.g., LC) and multi-fiber (e.g., MTP/MPO) connectors have replaced larger, older styles (e.g., SC), allowing more fiber ports per unit of rack space and higher data rate application such as 100 Gigabit Ethernet.

Features of good connector design:

  • Low insertion loss
  • High return loss (low amounts of reflection at the interface)
  • Ease of installation
  • Low cost
  • Reliability
  • Low environmental sensitivity
  • Ease of use

Outside plant applications may require connectors be located underground, or on outdoor walls or utility poles. In such settings, protective enclosures are often used, and fall into two broad categories: hermetic (sealed) and free-breathing. Hermetic cases prevent entry of moisture and air but, lacking ventilation, can become hot if exposed to sunlight or other sources of heat. Free-breathing enclosures, on the other hand, allow ventilation, but can also admit moisture, insects and airborne contaminants. Selection of the correct housing depends on the cable and connector type, the location, and environmental factors. Careful assembly is required to ensure good protection against the elements.

Depending on user requirements, housings for outside plant applications may be tested by the manufacturer under various environmental simulations, which could include physical shock and vibration, water spray, water immersion, dust, etc. to ensure the integrity of optical fiber connections and housing seals.

what’s the difference of Fiber Connectors?

Given the variety of splice options available to fiber network planners today identifying the best connector for FTTH can be overwhelming. Consequently often not much thought is given to connector selection with choice driven by cost, availability or what’s been used before. However each connector has its own unique design and therefore, pros and cons. Over time or depending on project size this can have a dramatic impact on deployment speeds and costs.

So what are the differences and what do they mean to your implementation? This table of common connectors gives an overview of strengths and weaknesses, with more detail in the accompanying descriptions:

1.Standard Connector (SC)

Simple, rugged and low cost, SC connectors use a ceramic ferrule to deliver accurate alignment of the SMF. The SC connector comes with a locking tab that enables push on / pull off operation.

At the time of writing the most popular choice for such equipment like Fiber Multiplexers, GPON and EPON ONU’s, Fiber Media Converters and more.

Figure 3: SC connector

2.Ferrule Core Connector (FC)

Although the FC connector was widely used in fiber optic networks until of late, its use is dwindling fast. This connector uses a threaded container and a position locatable notch to achieve exact locating of the SMF in relation to the receiver and the optical source. Once the connector is installed, its position is maintained with total precision.

FC connector is pretty common choice for example in Video over Fiber Transmission Equipment.

Figure 4: FC connector

3.Lucent Connector (LC)

The Lucent Connector, sometimes referred to as the Little Connector, is a small form factor FOC that uses a 1.25 mm ferrule. There are 3 different types of LC connectors:

  • Single Mode LC APC
  • Single Mode LC UPC
  • Multi-Mode LC UPC

If you had used any SFP module, you have sure seen this connector.

Figure 5: LC connector

LC connector is always present on SFP’s, and if some equipment uses SFP as transmitter, like for example our USB over fiber transmitters, then you can recognize it easily.

4. ST Connector

The ST connector’s keyed bayonet design is similar to that of a BNC (Bayonet Nut Connector or Bayonet Neill-Concelman) connector. The connector is used widely for MMF and SMF FOC and is extremely easy to use. The ST connector is manufactured in two versions – the ST and the ST-II. Both types are keyed and spring loaded, and use a “push-in and twist” mechanism.

Figure 6: ST connector

In some cases, if Multimode type cable is required, some of our customers order RCA audio over fiber converter, with ST connectors:

5. MTP/MPO connector

The MT ferrule connector is another of NTT’s inventions and has been around since the 1980s, although the technology has only recently become popular under branded versions of the Multiple Fiber Push-On/Pull-Off connector, such as MTP and MPO. It is larger than the other connectors but for good reason – it can support up to 24 fibers in a single ferrule.

Multi-fiber connectors are not currently designed for field-fit applications so must be lab terminated. In high density patch environments such as datacenters they are used extensively, both at single mode and multi-mode wavelengths. On a ‘per-fiber’ basis the costs are relatively inexpensive. However as might be expected, the attenuation loss can be higher than a single ceramic ferrule connector. That being said, it is possible to order ‘low loss’ MTP/MPO connectors which have comparable insertion loss performances. These are more costly however.

Network planners should also consider that whilst still using a uniter/adaptor much like other connectors, the MTP/MPO must also be mated to an opposing male or female connector. This may require more than one connector specification or type within inventory, adding to cost and complexity.

Because the sequence of the fibers cannot physically be changed after termination, the connector is often supplied with a fan-out assembly at the opposing end (such as LC, SC FC etc.). This allows the operator to change channels simply by re-patching the fanned-out side of the cable. The consequence of this is that the small form high density design of the MTP/MPO will only benefit one side of the assembly.

Fiber-Mart can supply many kinds fiber connectors. If you have any questions or requirement of fiber connectors,welcome to contact us:

Introduction of Loopback Cable

What is Loopback Cable?

When testing the transmission equipment, fiber optic loopback device is often used as the testing tool. It is known as the routing of electronic signals, digital data streams, or flows of items back to their source without intentional processing or modification. Fiber optic loopback is widely used for various applications. In terms of telecommunication, loopback is a hardware or software method to feed a received signal or data back to the sender. It is very useful for solving physical connection problems.This post will be a guide on how to choose a right loopback cablefor specific transceiver module.


Types of Fiber Optic Loopback

So, what is exactly the fiber optic loopback? Before deciding which loopback cable to use, we should firstly know the structure and classification of fiber loopback cable.By diagnosing the problems of optical equipment, fiber optic loopback provides an easy way to test the performance of the optical network devices. Generally, fiber optic loopback cable and fiber optic loopback module are both fiber optic loopbacks. Fiber optic loopback cable is the traditional fiber optic loopback with a visible cable. It is equipped with two fiber optic connectors on each end of the cable. When sticking the connectors together, the cable will shape like a loop. As for fiber optic loopback module, the biggest difference is that it has a enclosure to protect the inside cable. And the looped space is reduced for an easier usage and economic package.According to the optical connector type of the loopback, fiber loopback cables can be divided to LC, SC, FC, ST, MTP/MPO, E2000, etc. In testing fiber optic transceiver modules, the most commonly used are LC, SC and MTP/MPO loopback cables.


Figure 1: LC & SC Loopback Cable

The LC and SC loopbacks are made with simplex fiber cable and common connectors; it’s not difficult to understand their configurations. As for the MTP/MPO loopback, it is mainly used for testing parallel optics, such as 40G and 100G transceivers. Its configuration varies since the fiber count is not always the same in different applications.

8 Fibers MTP/MPO Loopback Cable Configuration

In a 8 fibers MTP/MPO loopback, eight fibers are aligned on two sides of the connector, leaving the central four channels empty. And the fibers adopt a straight configuration of 1-12, 2-11, 5-8, 6-7. The polarity channel alignment is illustrated in the following figure.


Figure 2: 8 Fibers Loopback Polarity Channel Alignment

12 Fibers MTP/MPO Loopback Cable Configuration

The only difference between the 12-fiber MTP loopback and the 8-fiber loopback is that the central four channels are not empty. Its alignment is 1-12, 2-11, 3-10, 4-9, 5-8, 6-7.


Figure 3: 12 Fibers Loopback Polarity Channel Alignment

24 Fibers MTP/MPO Loopback Cable Configuration

The 24 fibers MTP loopback also adopts type 1 polarity. Its alignment design is shown below.


Figure 4: 24 Fibers Loopback Polarity Channel Alignment

How to Use Loopback Cable?

The loopback cables are often used in conjunction with testing software to “loop” traffic right back into the port. If the data sent out into the loopback plug is identical to the data received from the loopback plug, you can assume that the basic communication functions of the port are working properly. So the common application of loopback cable is Loopback Test.


Loopback Test

Fiber loopback cable is often utilized to check whether the transceiver module is working perfectly as designed. As we all know, transceiver module has two ports, a transmitter port and a receiver port. The former one is to send out laser signals and the latter is to receive signals. When performing the loopback test, the fiber loopback cable can be directly plugged into the output and input port of transceiver module respectively (the ports at the ends of the connection must be compatible). Thus, during the testing process, the loopback cable directly routes the laser signal from the transmitter port back to the receiver port. Then we can compare the transmitted pattern with the received pattern to troubleshoot a defective node in the network. Fiber optic loopback testing is the easiest way to ensure that the transceiver works faultlessly. When selecting a suitable fiber loopback for the transceiver, we should consider the connector type, polish type, and cable type.


When it comes to practical application, fiber optic loopback test is often employed for checking fiber optic transceivers. Since transceiver has two ports for receiving and transmitting the light signal, it is necessary to test the ports to see whether they are still under operation. Thus, fiber optic loopback test is the most convenient way for transceiver maintenance. The testing process is by routing the laser signal from the transmitter port back to the receiver port. Then the transmitted pattern is compared with the received pattern to make sure they are identical and have no error.


All in all, loopback cables play an important role in troubleshooting in laboratories and manufacturing environments. They facilitate the testing of simple networking issues and are available at very low costs.Similar to other cables, it also has multiple classifications of fiber types, connector types for different needs. The deployment of fiber optic loopback components has greatly saved the trouble for device checking. There is no doubt that using fiber optic loopback is an effective method in fiber optic communication. There are many loopback cable manufactures on the market, providing single mode and multimode fiber optic loopback plugs available with FC, LC, MT-RJ, SC connectors. Fiber-Mart is one of the fiber loopback cable providers, all loopback cables are precision terminated and feature extremely low loss characteristics for transparent operation in the test environment.I believe you can find a suitable products for your devices in Fiber-Mart. please contact us: