Choosing Fiber Optic Connectors for Your Application

Optical Loss – A Critical Consideration
Whether a fiber optic connector must interface with a simple transmitter or the latest ROADM multiplexer, the connector interface is of critical importance because of its unique loss characteristics. To illustrate this point, consider the difference between connectors for fiber optic cable vs. copper cable.
Power loss for both types of connectors are stated in decibels (dB). That’s about where the similarity ends, because copper connectors and fiber optic connectors have opposite loss characteristics.
Copper connectors produce negligible loss when compared to losses produced by the copper twisted-pair cable to which they are attached. With fiber, the exact opposite is true. In a typical fiber optic system, fiber optic connectors produce far more loss than that produced by the fiber optic cabling. That’s why careful connector selection, particularly in regard to a connector’s loss specifications, is so crucial.
Other considerations that affect connector loss involve how the connector is joined to the field fiber, and how meticulously fiber optic connectors are cleaned and inspected prior to coupling.
Narrowing the Field
There are nearly 100 styles of fiber optic connectors, so choosing the right one for a particular application might seem daunting. However, this connector guide simplifies the selection process by focusing on the most useful and popular connector styles currently available.
In many cases, the types of connectors that you must use are dictated to you, especially if you are upgrading a legacy system. In that case, you may have to use the same type of connectors that are already in place in order to accommodate existing equipment and cabling. Even so, it’s a good idea to know the loss characteristics and other attributes of the connectors that you are working with. For example, a connector’s “insertion loss” specification relates to optical loss that results from differences in concentricity, ferrule endface geometry or other irregularities. Knowing the connector’s insertion loss specification can be useful when testing.
In some cases, such as a new install, connectors may or may not be specified. If connectors are not specified, you will likely be presented with a loss budget for cabling and connectors that you must adhere to. In this case, you have to give some serious thought to selecting the best connectors for the job. You also have to take into account the connector termination method (e.g. fusion splicing, epoxy, or mechanical termination) because this can have a significant impact on optical loss and back reflection characteristics.
Choosing The Right Connector
The following are considerations for choosing fiber optic connectors for your application.
Talk Like a Pirate….ARRG!
ARRG stands for Alignment, Ruggedness, Repeatability and Geometry. When choosing connectors, this memory aid will help you recall desirable connector qualities. The following attributes apply to most connector styles.
Alignment – A quality connector will keep fiber properly aligned with the fiber to which it is mated. Proper alignment is especially critical for single mode fibers which have a very small fiber core through which signals are transmitted. Always buy quality connectors and mating sleeves from recognized manufacturers to ensure that connectors are manufactured to high tolerances and provide optimal alignment.
Ruggedness – Will connectors be installed in high-traffic areas? If so, a good choice are epoxy-style connectors, which have the fiber bonded to the ferrule. This resists optical disconnects caused by tugging, temperature changes and other external forces. As added protection, consider a spring-loaded “non-optical disconnect” connector, such as the SC connector or LC connector, which are specifically designed to prevent optical disconnects. For harsh outdoor environments, “hardened” connectors are available.
Repeatability – Will there be a number of occasions when your connector will be disconnected? If so, consider using a connector that is known for good “repeatability.” The term repeatability refers to the performance of any class of connectors that are known to provide consistent loss performance that varies by a relatively narrow margin. Such connectors are typically keyed, or contain a keyway feature that prevents ferrule endface rotation. Keyed connectors ensure that connectors that are uncoupled from one another maintain the same ferrule endface orientation when they are recoupled, resulting in connector losses that are predictable, consistent and “repeatable”.
Geometry – The shape of the connector ferrule endface has a major affect on interface loss. For example, UPC connectors have ferrules that have a domed endface surface to insure contact at the core of two mated fibers, which helps to reduce insertion loss. Other connectors have an angled ferrule endface (APC connectors) which helps to minimize back reflection by directing endface reflections away from the core of the fiber. Knowing how ferrule endface geometry affects loss is important when selecting connectors, especially if you plan to polish your own connectors. Polishing procedures vary for different endface geometries.
Now that you know the general qualities you are looking for, it’s time to choose a specific connector for your application. The following approach uses a simple 3-step process of elimination.
Step 1. Weed Out Connectors that Can’t Meet the Loss Budget – Loss budgets will usually have connectors and cabling losses broken out separately from the rest of the network. Except for very long fiber links, losses for fiber optic cabling are usually negligible, so you’ll want to focus most of your attention on choosing the right connectors. Begin by narrowing down your possible connector choices to those that can stay within the loss budget of your application. For each connector being considered, simply multiply the number of connectors required by the dB loss specified for that type of connector. Now add fiber-optic cable loss to that number. If you are still within loss budget, great. You can proceed to Step 2.***
***It is possible to be within the loss budget but still have connections that produce unacceptable levels of back reflection. An Optical Return Loss (ORL) Test Set can be used to measure the level of back reflection. Also, an OTDR is useful for identifying the location of high-ORL events such as defective splices and connectors so that corrective action can be taken.
Step 2. Consider Installation Time, Material Costs, and Skills Required – After narrowing your list down in Step 1, it’s time to consider the costs associated with each type of connector, including installation skills required. Will you have to put your best installers on the job?
Step 3. Your Own Preferences – After completing Steps 1 and 2, let’s say that you have narrowed your connector list down to two possibilities. Now you can use your own personal preference to make the final decision. Simply choose the connector with which you are most comfortable and proficient. This will increase your speed and productivity on the jobsite and help to ensure quality terminations.
Tip: When trying new connectors and termination procedures for the first time, do enough of them in the shop to become proficient. Experimenting in the field is never a good idea.
Most Popular Connector Styles
Name: SC Connector
• Mode: Singlemode and Multimode
• Applications: Wide variety of singlemode applications especially datacom and telecom including premises installation. Often found in older corporate networks. It was designed to replace the ST connector.
• Ferrule size: 2.5mm
• Ferrule construction (typical): Pre-radiused zirconia
• Connector body: Composite. Similar in appearance to LC connector, except the SC is larger. Color coded according to fiber type; blue or green for singlemode, beige or black for multimode.
• Styles available: Simplex and duplex
• Latching mechanism: Push-pull, snap-in design
• Optical loss:
    Insertion loss: SM 0.10 – 0.30 dB; MM 0.10 – 0.40 dB
    Repeatability: 0.20 dB
• Meaning of name: Subscriber Connector, Square Connector or Standard Connector
Advantages: An excellent performer. Non-optical disconnect design (an advantage over the ST connector which the SC is replacing). Minimum back reflection when ultra-polished. Push-pull design helps prevent endface damage during connection. Square shape allows connectors to be packed closely together. Can fit into smaller spaces where the ST or FC cannot. The SC’s push-pull design allows quick patching of cables into rack or wall mounts.
• Disadvantages: Smaller LC connectors are replacing SC connectors in high density applications where space is at a premium.

What are the advantages of factory vs. field terminated assemblies?

When looking at terminating fiber optic connectors for a job there are several factors that are taken into account to help decide which way is best. There are field polish connectors in which some form of epoxy (glue) is used to hold the fiber in place. With this one, you have to polish it in the field as well which if you haven’t ever done it, can be very difficult. There are also factory polished style connectors that can be mechanical connectors, pigtails, splice on connectors or pre-terminated cable assemblies. The mechanical connectors have a piece of fiber already in them and you just have to align your field fiber up to the fiber inside the back of the connector. This can be difficult or take some time to master. A fiber pigtail consists of a piece of fiber optic cable that has a connector on one side and no connector on the other side. These can either be fusion spliced to another piece of fiber, or run through conduit and terminated at the other end. The alternate solution would be to have your cable assemblies built to the length that is needed with optical connectors already installed on them in a factory setting. Let’s look at some different qualities to see how this will be beneficial.

Polish Quality
All connectors whether installed in the field or in a factory have to be polished in order to work properly and get the end result of passing a signal over the fiber optic cable. So let’s look at the two different ways to polish. First, you can always hand polish a connector. In this process, you will use a polish puck, rubber durometer pad and a glass plate along with polish film to achieve a suitable connector endface. There are some technicians that have been doing this for a long time and could get close to a perfect polish on the ferrule endface. Not everyone can do a good hand polish. There are several factors that come into play and can cause various results on your finished optical connectors such as the amount of pressure applied while doing your figure 8 on the polish paper. When in a dusty area debris can get on the polish film, causing a connector to be ruined. See how little things in this process can affect the end of the connector and how long it takes to get a good connector? If a connector is bad due to being over polished, pitted or even shattered you will have to repeat the whole process.

On the other hand a factory polish is finished using a polish machine in a manufacturing facility. The amount of pressure is the same. Polish machines have holders that allow many connectors to be polished at once to save time. The procedures used have been honed over time to be the most efficient which helps to produce high quality polishes. In a factory all connectors are checked to a higher standard and are not allowed to be shipped until checked by quality control where they will be scoped and tested. This gives each and every factory connector a perfect outcome.

Plug & Play
When getting factory terminated fiber optic cable assemblies cut to length you are providing yourself with the simple concept of plug and play. This means all you have to do is run your link and then just plug the connectors into your rack, switch or connection point. This not only saves time on your cable installation but also will save you in labor and installation costs. Plug and play is not always a possibility due to restrictions in conduit size or the number of bends that are required to go through. We get that and that is why there are several ways that a connector can be put on a cable. All we are saying is, imagine if you get a house hold item such as a toaster; would you rather take the toaster out of the box, plug it into an outlet and have toast in a matter of minutes? On the opposite side; would you like to get a toaster that does not have a cord and you have to go find all the tools that are needed? Now you have to refresh yourself on how to strip a power cord so you can put a plug on one end. Then you have to open the toaster and get your other end prepped. Point being, we all like to just pull things out of the box, plug them in and away we go.

Pulling Eyes
What is easier than getting a cable that has all the connectors on it and a way to pull it in place? Essentially this is what you have with a pulling eye installed. All a pulling eye is, is a loop that is connected to the Kevlar of a cable assembly. Why the Kevlar? Kevlar, when you have multiple pieces stranded together is not only strong but almost impossible to break. It does not stretch when pulled on and it keeps the fiber cable from stretching. We have had instances when cable has not been pulled by the Kevlar, instead pulling on the jacket of the fiber. The jacket of the cable will stretch and eventually with too much pressure it will break. Also, when a jacket is pulled, when released you get what is called a growing effect of the fiber. Meaning it looks like kids through their growth spurts. The jacket after being released shrinks to try and get back to its original form. When this happens the fibers that are inside will come out the end making it look like your fiber is extending. Not only is this bad for the jacket that protects the fibers but it can also cause breaks in your cable that will not be realized until it is tested. So when pulling fiber cable, always make sure you are pulling correctly using the Kevlar. It’s better to just have a pulling eye installed and save yourself a huge headache.

Higher Overall Quality
When looking at fiber optic connectors there are several factors to consider. Looking above at all the advantages of a factory polish termination along with pulling eyes, you can see how it can save you money and time to go with the factory built cables. Now if you do have to install connectors in the field, the alternative would be to get connectors that are already factory polished such as the ones on a fiber pigtail used when fusion splicing. When doing a job, no one is purposely trying to have bad connectors. Factory polished connectors whether they are pigtails, mechanical connectors or pre-terminated fibers all have the high quality that you will need to show your customer that you take pride in the work you do and want to use the best possible connectors available. Nothing is better than a connector that is polished by a machine, and then put through a rigorous testing phase before they can be considered done and ready.

What Fiber Optic Connectors Are Used for Non Standard Fiber Sizes?

The question I seem to be asked over and over is “What fiber optic connectors are used when I have non-standard size multimode and singlemode fiber”? The frequency of this question led me to write this blog. It can be very frustrating when installers and technicians are faced with this situation, the proper fiber has been identified, but what good is it to me if I cannot install connectors. Fortunately, there are answers and I hope to relieve some of the angst that you may have.
Most telecommunications projects utilize standard equipment and fibers that are readily available, but what happens when this is not the case? The standard LC, SC, ST and FC style optical fiber connectors with ferrule holes at or around 126um will suffice 99% of the time but, nonstandard applications such as medical, automotive, high power and others utilize specialty fibers where the standards will not work.
Non-Standard (Specialty, Large Core) Fiber
As most of us know, standard singlemode optical cable is made with a 9um optical glass core and a 125um cladding (9/125) with multimode standards being 50/125 and the old North American standard of 62.5/125. Many non telecommunication optical applications utilize non-standard fibers. Following is a list of just a few of these fibers:
100/140 – This fiber is identifiable by its green jacket color and has a typical attenuation of about 4 dB/km.
200/230 – 200/230 will typically have a blue jacket and has a standard attenuation of 6dB/km. You may notice that as the fiber cores increase in size, so does the standard attenuation.
960/1000 – This fiber is actually manufactured using plastic instead of the glass we usually find in fiber. Commonly black jacketed, this fiber is popular for optical audio cables; its 300 dB/km attenuation relegates it to short distance transmissions.
Large core fibers are also available: 300/330, 400/440, 500/550/ 600/660, 800/880 and many others too numerous to mention.
Precision-Drilled Connectors
Specialty fibers will not accept the standard 126um fiber connectors, so the technician must search out alternative solutions. Let’s first address the components that make up a fiber connector:
The Fiber Connector:
Strain Relief Boot
The strain relief boot allows the fiber exiting the connector to maintain its bend radius. A connector without a boot would kink the fiber causing attenuation (loss) or possibly a break in the fiber itself. It is important that the boot not be glued into place, gluing the boot will hinder the spring inside the connector, so the boot should be slip fit onto the connector body.
Connector Body
The body of the connector holds the ferrule in place and allows the connector to be crimped to the fiber and body via the use of a crimp sleeve. Connectors that only crimp to the fiber and not the body (like an ST) will allow the ferrule to piston when force is applied to the fiber, this is why LC, SC and FC connectors are dual crimp and have the advantage of non-optical disconnection.
The Ferrule
The most important component of any connector is the Ferrule. In the past, ferrules were made from stainless steel but due to performance issues most of today’s ferrules are made from ceramic (Zirconia). The ferrule’s primary function is to hold the fiber precisely to allow for the transmission of optical signal. Most standard ferrules have a hole size of 126um.
When specialty/uncommon (large core) fibers are used, many times ferrules with the larger hole sizes are not available. When larger size holes are needed, the ferrule must be drilled to accommodate these sizes.
When drilling a ceramic connector ferrule, issues occur that effect the hole tolerance and concentricity. During the drilling process, the ceramic material will chip and flake making the ferrule unusable. Because of these issues, the only ferrule type that can be consistently drilled is stainless alloy.
When drilling stainless alloy ferrules, sizes range typically from 250um to as large as 1550um, these sizes step in 10um increments (example 310um, 320um, 330um etc). When manufacturing these drilled ferrules, specifications for hole tolerance, concentricity, length and diameter are all measured and have pass/fail criteria. Some companies offer two options for their drilled ferrules, standard and premium. A standard drilled optical connector has a hole tolerance specification of -10µm/+50µm and a concentricity value of +/- 50µm. Premium drilled connectors will have tighter tolerances; so if higher performance (low attenuation) is required the premium product is the answer. Premium drilled optical ferrules have a hole tolerance specification of -4 µm/+10 µm and a concentricity value of +/- 25 µm. The premium ferrule will allow for better light transmission, which makes this the most popular of all drilled connectors.
Understand that the ferrule cannot be drilled while inserted inside of the connector body. All ferrules are drilled before the connecter is manufactured. Once the ferrule is drilled and passes all specifications then it is installed into the finished connector. Many times (like in medical devices) the ferrule is the only thing that is installed onto the fiber, leaving the body and strain relief boot out.
It is important to also note that the older SMA905 and SMA906 connectors can be drilled and are commonly used in military, medical, aerospace and research facilities where higher power lasers and heat dissipation are required. The SMA connector uses a larger 3mm ferrule, compared to the typical 2.5mm for SC, FC and ST and the 1.25mm ferrules used for LC connectors.
Installation of the optical connector
Once you have identified the correct connector style (ST, FC, SC, LC) and hole drill size the next question is “How to install these connectors?” When considering standard fiber optic connectors (dozens of manufacturers) it really boils down to only three options on how to install the connector on the optical fiber. These options are:
Hand/Machine Polishing
All fiber optic connectors are manufactured using this epoxy/polish procedure. The move in the fiber industry over the last decade has been to shy away from this process. Labor, consumables, skill level and overall quality is deeming this process obsolete for field connector terminations. The thought process is to let the industry manufacturing professionals handle the task.
Mechanical Connectors
A mechanical connector is manufactured and machine polished by the connector manufacturer with a small piece of fiber inserted into the connector, this fiber is precision cleaved inside the back of the ferrule and the end is then machine polished. The field installer simply cleaves his fiber and inserts it into the back of the mechanical connector and clamps it into place. Using mechanical connectors drastically reduces labor, and the required skill level of the technician. These connectors are more expensive than epoxy style connectors but the savings in labor costs tend to outweigh the expense.
Mechanical Splice
Fusion Spliced Connector
Most people believe that fusion splicers are used to lengthen and repair fiber optic cables. While this is true, the most common use of a fusion splicer is to attach premade pigtails or the newer Splice on Connectors (SOC). Although the perception is that the investment in the fusion splicer makes this process expensive, the reality is that fusion splicing a connector is the least expensive, lowest labor, highest quality way to install a factory manufactured connector.
Now that we have identified the field installation processes for fiber connectors how do we apply this to large core/specialty/Non Standard drilled connectors? Reality is that there are really only two options you have. Fusion splicers cannot splice these specialty fibers and there are no mechanical connectors made today that can be used with these larger core fibers. This leaves us with field installing these connectors using the epoxy/hand polishing procedure or purchasing the cable with the connectors installed by a fiber optic manufacturer. The obvious choice is having your cables manufactured by a company that is a reputable fiber assembly house. These pre-terminated cables will be professionally manufactured and tested; your job is to simply install the cable.
Remember that when using specialty/large core fibers there are solutions to your connectorization needs and most of the time the answer is a precision drilled fiber optic connector.

Fiber Optic Connectors and Termination Videos


Fiber Optic connectors are definitely distinctive compared to the traditional copper cable connectors. Instead of the metal-to-metal contact, fiber optic connectors need to align microscopic glass fibers in order for the communication data to carry efficiently.
Each connector contains three key components: Ferrule, Connector Body and Coupling Mechanism.
The ferrule is the thin structure that holds the glass fiber in place and they are generally made of ceramic, metal or plastic. The connector body is what holds the ferrule in place and allows it to attach to the members within the cable fiber. A coupling mechanism which essentially holds the connector while it is linked to another device. It may contain a clip or bayonet nut depending on the connector type.
Now, let’s look at some popular connectors and what they are used for within networking applications:
SC Connector-(also known as the square connector) this type of connector contains a push-pull motion, snap-in connector with a spring loaded 2.5 mm ceramic ferrule to hold a single fiber. This connector is also the second most popular connector due to its method of maintaining applications. It can be used with either single-mode or multimode fiber optic cabling.
LC Connector- this connector uses a 1.255 mm ferrule (half the size of the SC) and contains the standard ceramic ferrule. This connector is also a push-pull connector (similar to the SC) and utilizes a latch locking tab and can easily be terminated.
Applications: Ideal for applications within dense rack/patch panels
ST Connector- (also known as a straight tip connector) this connector contains rounds ceramic ferrule, with bayonet mount locking features,enclosing a twist lock and a 2.5 mm keyed ferrule. This type of connector can be used with either single-mode or multimode fiber optic cabling.
Applications: Networking environments such as school campuses, corporate offices, military, etc.

What are the interfaces and structures of fiber adapters?

Fiber optic adapters, also known as flanges or fiber optic connectors, are primarily used to connect two fiber optic connectors in a fiber cabling system, and are often assembled on various adapter panels and chassis.

When deploying a network, it is often necessary to connect two cables with the same connector or different connectors. Which product should you choose for fast cable connection and ensure stable performance? At this point, you need to use a fiber optic adapter with low insertion loss, durability, and repeatability. This article will mainly introduce the type of fiber adapter interface, structure, and the difference between fiber optic couplers and fiber adapter advantages and solutions.

Fiber Optic Adapter Definition

Fiber optic adapters, also known as flanges or fiber optic connectors, are primarily used to connect two fiber optic connectors in a fiber cabling system, and are often assembled on various adapter panels and chassis. Important fiber optic connection components are widely used in television networks, local area networks, video transmission, optical fiber communication systems, and FTTH fiber optic homes. Conventional fiber optic adapters are available in flanged and non-flanged versions, where the fiber optic adapter without a flange can be directly attached to a panel or tray, and the fiber optic adapter with a flange needs to be screwed.

Fiber Optic Adapter Interface Type

According to the diversity of fiber optic connectors, there are many types of interfaces for fiber optic adapters, as shown in the figure below. According to the same connector at both ends of the fiber adapter, its interface can be divided into six types: LC-LC, SC-SC, ST-ST, FC-FC, MPO-MPO, and E2000-E2000. According to the different connectors at both ends of the fiber adapter, its interface can be divided into six types: LC-SC, LC-ST, LC-FC, SC-FT, SC-FC, and FC-ST. These two ends have different connections. The adapter for the device is often referred to as a hybrid adapter. In addition, the use of fiber adapters for SC and FC interfaces is relatively more widely used in all interface types.

Fiber Optic Adapter Structure

As shown in the figure below, a common LC-LC duplex fiber adapter is used as an example. It is made of corrosion-resistant plastic, has good corrosion resistance and internal shading, and is made of stainless steel clips, full flanges, dust plugs. As well as high-precision ceramic bushings and other components, it can ensure that two connectors can be accurately connected while minimizing losses. It should be noted that the main function of the flange of the fiber optic adapter is to fix the adapter on the adapter panel. Therefore, a variety of fine and fixed flanges are particularly used for shooting.

Difference between fiber adapter and fiber coupler

As shown in the figure below, the design of the fiber adapter is very compact. It is a bridge between two cables that connect the same interface or two cables with different interfaces. The main reason for the fiber adapter and the fiber coupler is the connector type at both ends. Normally, if the two cables to be connected have the same type of connectors, they are called fiber couplers. If the two cables to be connected have different connectors, they are called fiber adapters. For example, a fiber optic adapter is used to connect the ST-ST connector. At this time, the connector at both ends of the fiber optic adapter is the same, so it can be called a fiber optic coupler. Otherwise, it is called a fiber adapter. However, fiber adapters have the same type of interface, but also have different types of interfaces. There are a total of twelve options.

Fiber Optic Adapter Benefits

Can provide a large number of high degree of matching and conversion adapters, including special male and female conversion optical adapter, with low insertion loss, good interchangeability, good repeatability, high temperature, acid and alkali resistant and stable performance. The following are more advantages of fiber optic adapters.

1.High protective dust plug
Each fiber adapter is equipped with a corresponding high protective dust cover, which can be kept clean, 100% to avoid contamination of the adapter and the cable by dust, and greatly reduce the failure rate.
2. Connect the cable + convenient and simple
It is possible to connect two identical connectors or different connectors. When two optical cables need to be connected, only two optical cables must be aligned with the ceramic sleeve and inserted separately.
3 high-precision ceramic casing
The fiber optic adapter uses a ceramic sleeve imported from abroad and adopts a high-density production process to achieve high-precision fast connection of the fiber end face, which is definitely your ideal choice.
4. Compact design and easy operation
Optical fiber adapters are lighter in weight, compact in design, easy to operate, and user-friendly to help you easily connect and remove cables.

Optical fiber adapter plays an increasingly important role in optical fiber connection. It is an inconspicuous and critical connection component. It has strong practicability and high cost performance. It is widely used, especially for television networks, local area networks, video transmission, and optical fiber. For applications such as communication systems and FTTH fiber-to-the-home applications, fiber optic adapters are a good choice and solution! If you have any fiber optic adapter requirements, please contact us