Overview of Fiber Optic Loopback

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. In this article, the author will especially emphasize the using of loopback in fiber optic communication. Hope it can provide some help for your application!

Types of Fiber Optic Loopback

So, what is exactly the fiber optic loopback? 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.


You may find that loopback also has different types of optical connectors and fibers. Categorized by connectors, fiber optic loopback has SC, LC, MTRJ, E2000 types, etc. LC fiber optic loopback complies with the RJ-45 style interface. Having a low insertion loss, low back reflection and high precision alignment, LC fiber optic loopback is widely used all over the world. Another frequently used type is SC fiber optic loopback. Its connector is compliant to IEC, TIA/EIA, NTT and JIS specifications. Now it is the most popular loopback with low cost but high performance. In addition, to separate by fiber types, single-mode loopback (9/125) and multimode loopback (50/125, 62.5/125)  are deployed for the application.

Fiber Optic Loopback Testing

Typically, a loopback test is a test in which a signal is sent from a communication device and looped back to the device as a way to determine whether it is functioning well or as a way to troubleshoot a defective node in the network. As for fiber optic loopback testing, optical loopbacks are used to verify the operational reliability of the device. Using fiber optic loopback cable or fiber optic loopback module for data transmission, the signal emitted by the device is looped from the transmit (Tx) end of an active component back to the receive (Rx) end of the same component.


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.


In a word, fiber optic loopback is basically a patch cord used for fiber optic loopback testing. 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.

Related Article: Which Fiber Loopback Should I Use for My Transceiver?

Related Article:  What Is Loopback Cable And How to Use It?

MTP/MPO Fiber Patch Cord Overview

A MTP/MPO fiber patch cord is a fiber optic cable capped at either end with MTP/MPO connectors, which can be connected to an optical switch, cable television (CATV) or other telecommunication equipment rapidly and conveniently. It is ideally suited for a high density environment that demands space saving and innovative cable management solutions. Since the MTP/MPO fiber patch cord is composed of MTP/MPO connectors and a fiber optic cable, this article will firstly introduce the MTP/MPO connectors and then discuss common kinds of MTP/MPO fiber cables.

MTP/MPO Connectors

Though MTP and MPO are literally different from each other, they often be used interchangeably. According to CommScope (a famous multinational telecommunications company), the MPO connector is a multi-fiber connector that is defined by IEC-61754-7, and the MTP is a registered trade mark of US Conec (a leader in providing passive components for high density optical interconnects), which identifies a specific brand of the MPO style connector. In other words, the MTP product complies with the MPO standard. Therefore, the MTP connector is a MPO connector.

As a kind of multi-fiber connector, the MTP/MPO connector is most commonly used for 12 or 24 fibers (as shown in the following figure) in a single connector pushing up to and beyond 100Gbps data transmission. Thus it satisfied the huge demand for more bandwidth and more space efficiency of data centers and ever-expanding server clusters. The best part is that this kind of connector takes roughly the same space as a single simplex SC connector. MTP/MPO connectors are paving the way for increased data transmission speeds and rack density.

MTP(MPO) connector for 12 and 24 fibers

Popular MTP/MPO Fiber Cables

The most commonly used MTP/MPO fiber cables are MTP/MPO trunk cables and MTP/MPO harness cables.

MTP/MPO trunk cables are designed for high density application which offers excellent benefits in terms on-site installation time and space saving. Trunk cables serve as a permanent link connecting the MTP/MPO modules to each other. Theoretically, trunk cables are available with 12, 24, 48 and 72 fibers. Their ends are terminated with the customer’s choice of 12-fiber or 24-fiber MTP/MPO connectors (as shown in the following figure).
MTP(MPO) Trunk Cable

MTP/MPO harness cables are designed for high density applications requiring high performance and speedy installation. Harness cables provide a transition from multi-fiber cables to individual fibers or duplex connectors. The MTP/MPO harness cables are terminated with MTP/MPO connectors on one end and standard LC/FC/SC/ST/MTRJ connectors (generally MTP to LC) on the other end (as shown in the following figure). Therefore, they can meet a variety of fiber cabling requirements.
MTP(MPO) Harness Cable

Designed for the reliable and quick operations in data centers, the MTP/MPO fiber patch cord is an important part of the multi-fiber connection system. The obvious benefits of this kind of fiber patch cord are less space requirements and improved scalability. Furthermore, it also provides significant space and cost savings.

The Relationship between the Cut Off wavelength and Optical Fiber

What is cut off wavelength? When many people see the item they may ask such question. Well, cut off wavelength can be defined as the wavelength below a singlemode fiber wavelength and they usually acts as multimode fiber, meaning it will allow propagation of more than one mode at a time. In another word, cut off wavelength above singlemode operation but it is ensured in a singlemode fiber.

Fiber cut off wavelength depends on the method of fixing the fiber. We all know that fiber optic cable can be putted into loose tubes or tightly coated with elastomeric or PVC or Nylon, to make tight buffered fiber or the matrix to be fiber optic ribbon. Cut off wavelength reduces the numbers of bends in fiber, so the cut off wavelength plays an important role in singlemode fiber at the defining the wavelength region of singlemode fiber. It reminds me that I have met a product from Corning, it mainly told us the cut off wavelength is the quite important for the fiber in defining the region of singlemode operation and then Corning said, bends and stress makes the cut off wavelength to a lower value.

Cut-off wavelength is the wavelength above which an optical fiber will allow singlemode transmission. Cut off wavelength can also be defined as the wavelength below which multimode transmission starts. It just means that above a certain wavelength, multiple modes stopped and singlemode optical fiber (Related product: singlemode simplex fiber) is designed to a mode for transmission. Cut off wavelength is also a unique parameter of single mode fiber. There are two points we should know that normal cable and installation condition all reduce the cut off wavelength. The cable wavelength is more important than fiber cut off wavelength.

fiber mode

As for the multimode fiber, why we do not talk about it? Well, because the cut off wavelength is the wavelength below which multimode transmission. (Related product: multimode fiber patch cable). The fiber mode transmission acts as the figure. Thus, we also can see that cut off is also the feature of singlemode fiber, it is an unique characteristic for singlemode fiber. Thus it is clear that cut-off wavelength determines the fate of single mode transmission. ITU-T recommend that the cut off wavelength less than 1260nm or 1260nm for singlemode fibers. It means that the wavelength that below 1260nm is an acceptable single mode. We know that the 1310nm and 1550nm wavelength are used widely and with the introduction of DWDM and shifted fiber, 1260nm wavelength is not more acceptable than 1310nm. It means that singlemode fiber will allow a wavelength mode over 1261nm. Cut off wavelength is important for singlemode fiber, because it is the standards of condition and singlemode fiber to allow single mode transmission. Warm tips: Fiberstore is a famous fiber optic patch cords supplier. If you want to get related singlemode and multimode fiber cable, you can get them from here easily.

Very Effective Method of Fiber Optic Cables Selection

After the distribution network plan is developed, the next step we have to do is the selection of the right fiber optic cable. Remember the bulk of the Fiber Optic Cable installed today is for either telephone or office applications. Industrial sites bring some challenges that are not address by many of the common fiber optic cable installation design. Just due to the local telephone company would rather a particular type of fiber optic cable does not mean it is the right one for a facility.

The common rule of thumb for selection optical cable in industrial setting is to use 62.5/125 μm or 50/125 μm Multi-mode fiber cable. The cable should be rated for both indoor and outdoor use and must have an FT-4 flame rating if it is used for indoors. Aluminum interlock armor is preferred over steel tape for all but long, buried runs. Fiber counts should be a minimum of 12, with 24 fibers as the standard for main backbones. More specific selection details depend on the area where the cable will be installed.

Indoor Office Installation

Fiber selection for office applications is relatively simple. The fiber must be flame-rated for either FT-4 general use or FT-6 for plenum. Typically, tight-buffered cable with Kevlar strength members and a light jacket is used. There is little reason to use loose tube as it is more difficult to install and usually does not meet the flame rating standards. As well, fiber optic cables in these environments do not require armor as the chance of crush or pull damage is relatively low. Because jacketed fiber optic cable is more rugged than most coaxial and twisted-pair cables, plan to armor fiber only in the places where coaxial cables would be Armored Fiber Cable.

8 Fibers 62.5 125μm Multimode Armor Single

Indoor Industrial Installations

If fiber optic cable is being installed in plant-floor conditions. It is possible to be installed in existing cable trays and be subjects to more stresses than office cable systems. Thus, some form of armor is recommended, usually aluminum interlocked (TEC style) armor. This armor must be electrically bonded to ground at all distribution cabinets.

Inter-building Installation

Industrial sites often need a combination of indoor and outdoor fiber routing. Telecommunication industry guidelines recommended switching between indoor and outdoor fiber cable types at each transition, a solution than is not practical for most industrial sites. On a typical site, this would require numerous patch boxes or splices and is not worked for both cost and attenuation(signal loss) reasons. Instead, FT-4 flame-rated, tight-buffered cable should be used so that the cable can transmit both indoor and outdoor environment.

Long-Run Outdoor Installations

Outdoor fiber cable generally falls into three categories, direct burial, underground conduit, and aerial. These cables are manufactured specifically for outdoor applications and are recommended for any long outdoor cable runs, especially in region subject to cold weather. Most are loose tube designs with high tensile strength, to withstand environmental conditions, and gel filling, to prevent water migration. The jacket materials are specially selected to be abrasion and ultraviolet resistant. If a facility is planning to install long outdoor runs it will need to work closely with the manufacturer ti determine the right cable for its application.

Indoor and Outdoor fiber optic cable delivers outstanding audio, video, telephony and data signal performance for educational, corporate and government campus applications. With a low bending radius and lightweight feature, this cable is suitable for both indoor and outdoor installations. Typical indoor and outdoor cables are loose tube and tight buffer designs, and we also supply ribbon cables, drop cables, distribution cables and breakout cables. These are available in a variety of configurations and jacket types to cover riser and plenum requirements for indoor cables and the ability to be run in duct, direct buried, or aerial/lashed in the outside plant. In addition, Fiberstore is doing with 30% of the price and it is a quite happy thing.

How to Choose Suitable Fiber Optic Cable

Nowadays as we know, Fiber Optic Cable can eliminates the problem of twisted pair, such as the near-end crosstalk (next), electromagnetic interference (EMI), and security vulnerabilities to support high-speed data communications. It is difficult to make the right decision when it comes to data network cabling, because it can make a huge difference in your network that can reliably support current and future needs. We have many factors to consider and now I will introduce different optic cables and then you can find the suitable ways through it.

Single-Mode Fiber Cable and Multimode Fiber Cable

Single-Mode fiber cables include a tiny core that 5 to 10 microns, its function is eliminating distortion and producing higher transmission speeds. Single-Mode fiber optical fiber need laser technology to send and receive data. Single-Mode has the ability of carrying a signal for miles and it can apply to long haul or extreme bandwidth and it’s transmission rate can reach to 50 times more distance than Multimode but at the same time its cost more.

Multimode fiber optic cables, as its name, it allows the signal to travel in multiple modes, It is available with fiber core diameters of 62.5 and a slightly smaller 50 microns. The distances of Multimode fiber cables are that long cable runs in multiple paths may lead to signal distortion, it results in not clear and not completely data transmission. Multimode fiber cables can be used in applications covering short distances, the best function is data center connections. Multimode fiber cables is the economical choice in these applications, there are different kinds of performance levels within Multimode fiber cables, such as OM3 fiber optic cable for distances within 300m, OM4 fiber optic cable supports Gigabit Ethernet distances within 550m and 10G applications.

OM3 Multimode Simplex Tight Buffer Round Riser Indoor Fiber Optic Cable

Indoor Fiber Optic cable Or Outdoor Fiber Optic cable

Indoor Fiber Optic cable are just that we called “tight-buffered” cables. the Indoor fiber cable has the features that flexible, and tough, containing multiple Tight Buffered or Unit Cord fibers. Available Indoor fiber cables have these types:

1. Simplex and Zip Cord: simplex fiber optic cables are one fiber and tight-buffered and it used for Indoor. Zip cord just only the two web of these joints, it is mostly used for patch cord and backplane applications but the Zip cord also can be used for desktop connections. There fiber optic cables who have one fiber are usually used Indoor.

2. Distribution cables: these fiber optic cables include several tight-buffered fibers bundled under the same jacket, the size is small and use for short. The fibers are double buffered and can be directly terminated, but because their fibers are not individually reinforced, these cables need to be broken out with a “breakout box” or terminated inside a patch panel or junction box. The distribution cable is smaller and used in dry and short conduit runs, plenum and riser applications, is the most popular cable for indoor use.

3. Breakout cables: These fiber optic cables are made of several simplex cables bundled together inside a common jacket for convenience in pulling and ruggedness. This is a strong and hard design, large but more expensive than the distribution fiber cables. It suits to conduit runs, riser and plenum applications, it is ideal fiber cables for industrial applications where ruggedness is important or in a location where only one or two pieces of equipment (such as local hubs) need to be connected.

The major difference between indoor and outdoor cables is water blocking. Any conduit is someday likely to get moisture in it.

Outdoor fiber cables are designed to protect the fibers from years of exposure to moisture.

Outdoor fiber optic cable need more protection from water ingress, vermin, and other conditions encountered underground and Outdoor fiber cable also need to increase strength for greater pulling distance. Buyer should know that cables will face with the potential hazards such as it will be exposed to chemicals or extreme temperatures.

1. Loose Tube cables: these fiber cables are inside small plastic tube, it provides a small, high fiber count cable. This type of cables is ideal for outside plant trunking applications, because it can fill with gel or water absorbent powder to prevent harm to the fibers from water. Since the fibers only have a thin buffer coating, they must deal with it carefully to protect it from damage. Is also can be used in conduits, strung overhead or buried into the ground.

2. Ribbon Cable: these fiber optic cables provides the highest packing density, because all the fibers are laid out in rows , and usually 12 fibers and put them on top of each other. Some fiber optic cable designs use a “slotted core” with up to 6 of these 144 fiber ribbon assemblies for 864 fibers in one cable! Since it’s outside plant cable, it’s gel-filled for water blocking.

3. Armored Cable: this Armored fibre cable installed by direct burial in areas where rodents are a problem usually have metal armored between two jackets to prevent rodent penetration. This means the fiber optic cable is conductive so it need to be grounded properly. You’d better choose armored fiber cable when use fiber optic cables directly buried outdoor.

Armored Fibre Cable

4. Aerial Cable: these cable can be lashed to a another cable or messenger or it had metal or aramid strength members to make them self supporting. Aerial cables are for outside installation on poles.

Fiberstore is a reliable fiber optic cable shop, it provides different kinds of fiber optic cables you want, including all above what I mentioned in the article, and at the same time Fiberstore is doing with 30% discount of the price on fiber optic cables, then if you want to buy fibre optic cable(fiber optic cable), welcome to enter into our online store.