How to select fiber optic cables?

To select or purchase a proper fiber optic cable, 3 issues need to be considered in advance: how many fibers are demanded to work? What type of optic fiber is effective for your project? What kind of environment will the fiber optic cable be applied to? The 3 factors are the key to the selection of fiber optic cables, so below will give some useful ideas from the 3 factors for right selection of optical cables.

Amount of optic fibers

In the simplest fiber optic cables, 2 fibers are enough, one is for transmission and another is for receiving. So at least 2 fibers are needed for any optical cable to accomplish transmission. In the cabling deployment, the amount of optic fibers must cover the amount of fibers for working, fibers for replacements and fibers for excess, which combined to ensure the good operation and life of optic fibers.

Types of optic fiber

There are single mode fiber and multiple mode fiber to be selected. For single mode fiber, it is quite suitable for long distance transmission due to without internodal dispersion. While multiple mode fiber is usually used in short distance transmission like in-building cabling. 

Generally, multimode fiber optic cable is available for transmission within 2km, single mode fiber optic cable is proper for transmission beyond 2km.

Application environment

For outdoor directly buried cabling, It is appropriate to use armored fiber optic cable.

For overhead cabling, it is better to use fiber optical cables with two or more strength ribs included in the outer protecting layer.

In the condition of cabling in buildings, used fiber optic cables have to be flame-retardant, non-poisonous and smokeless. 

In the vertical cabling of the building, distribution optical cables are suitable; While for horizontal cabling, breakout optical cables are applicable.

Multimode and Single mode

One of the first things to determine when choosing fiber optic cables is the "mode" of fiber that you need. The mode of a fiber cable describes how light beams travel on the inside of the fiber cables themselves. It's important because the two modes aren't compatible with each other — you can't substitute one for the other.
There's really not much variety with single mode patch cords, but there is for multimode. There are varieties described as OM1, OM2, and OM3. Basically, these varieties have different capabilities around speed, bandwidth, and distance, and the right type to use will depend mostly upon the hardware that is being used with them, and any other fiber that the patch cords will be connecting to. Take a look at the table below for some more detail around the OM varieties.

Jackets

Pre-term fiber can be used in a variety of installation environments, and as a result, may require different jacket materials. The standard jacket type is called OFNR, which stands for "Optical Fiber Non-conductive Riser". This is a long-winded way of saying, there's no metal in it, so it won't conduct stray electrical current, and it can be installed in a riser application (going from one floor up to the next, for instance). Patch cords are also available with OFNP, or plenum jackets, which are suitable for use in plenum environments such as drop-ceilings or raised floors. Many data centers and server rooms have requirements for plenum-rated cables, and the local fire codes will always have the final say in what jacket type is required. The final option for jacket type is LSZH, which stands for "Low Smoke Zero Halogen", which is a jacket made from special compounds which give off very little smoke and no toxic halogenic compounds when burned. Again, check with the local fire code authority to be sure of the requirements of the installation before making the jacket selection.

Simplex vs. Duplex

Simplex vs. duplex is just the difference between one fiber or two; between one connector at each end of a cable, or two connectors at each end. That's all there is to it. Duplex patch cords are the most common type, because the way that most fiber electronics work is that they need two fibers to communicate. One is used to transmit data signals, and the other receives them. However, in some instances, only one fiber is required, so simplex patch cords may be necessary for certain applications. If you're not sure, you can always be on the safe side by ordering duplex patch cords, and only using one of the two fibers.

Connectors

Remember what we said in the beginning about copper category cables? No matter what level of twisted pair you were dealing with (Cat 5, 5e, etc), you always knew you'd be dealing with an 8-position modular RJ-45 plug on the end of the cable. Well, with fiber patch cords, you've got a few options available when it comes to connectors. Let's take a look at the common connector types:LC— This is a small, squarish connector that is held in place by a push/pull mechanism. This is currently the most popular type of connector.

• SC— This connector is square, like an LC, but is approximately twice the size. It also holds into place using a push/pull mating mechanism.

• ST— This is a round connector that uses a bayonet-style mechanism that has to be twisted into place. It is about the same size as the SC connector. It was once the most popular connector type, but is losing ground rapidly.

• MTRJ— The MTRJ connector closely resembles an RJ-style modular plug, even getting part of its name from the resemblance.

These are the most common selections that you'll find when choosing amongst patch cords. If you're able to determine which of these characteristics you need, it's highly likely you will make the right choice when shopping for fiber optic patch cables.

Cable Jacket
All indoor fiber cabling must meet local fire codes. In the US, fire rating and jacket identification is defined by Article 77 of the National Electric Code (NEC). If your cable will run through risers or plenum spaces, make sure the cable jacket is rated accordingly.

In addition to fire rating, other cable jacket properties such as flexibility and strength under tensile load should be considered. For more information on jacket materials and fire ratings, see Fiber Optic Cable Jackets.

Application Starting Points

Selection Parameters for Fiber Optic Cables

Consideration of the following parameters while a selection of fiber optics connectors is advised by industrial experts.

• PC: PC stands for physical contact. There are two types in this polishing style, namely, flat physical contact and the rounded type. This polishing can offer a slight air gap or close fit contact. The reflection loss in this type of polishing is lesser than (-40 dB).  

• UPC: UPC stands for ultra-physical contact. This polishing style gives lesser than (-50 dB) reflection loss.

• APC: APC stands for angled physical contact. In this style of polishing, the contact surface is angled at 8 degrees which reduces back reflection to the value lower than (-60 dB). Therefore, APC gives the optimum efficient contact interface to the fiber optic connectors.

• Anaerobic Adhesive Termination: In this type of termination, the connector ferrule has a quick setting adhesive. This type is suitable for indoor fiber optic applications as the adhesives may not sustain water, high temperature, or rough handling. This type of termination can be adopted for the on-off type of connections.

• Epoxy-Polish Termination: In this type of termination, the ferrule is glued with epoxy and then the end is polished with a special film. The connectors with this termination type are suitable for applications where low loss is expected.

• Crimp Termination: Instead of glue or epoxy, this type of termination uses a crimp to attach the ferrule and fiber. The connectors with this termination type are suited for quick and firm termination but losses may be more in this case.

• Pre-Polished Termination: The pre-polished termination features factory installation. It involves in-built short stub fiber inserted and glued into the ferrule, therefore, the operator only has to insert the termination fiber like splicing. This is a quick and easy way of termination, however, these connectors are expensive. If cleaved during installation, these connectors can give nearly zero losses.

• Connector Contact Polishing Style: The connector contact polishing style determines the type of contact enabled between the connector and cable. The polishing style impacts the back reflection, which is a measure of light reflected from the contact end of the connector. The higher the back reflection, the higher is the reflection losses in the fiber-optic network. There are three main styles of connector polishing available as listed below.

• Termination Types: Since fiber optic connectors terminate the fiber optic cables, they are available in various termination types. One must consider termination types during the selection of connectors as it determines the connective force between the ferrule and the cable.

• Type of Fiber/Fiber Mode: The fiber optics connectors are associated with standard types of fiber optic cables and modes of transmission. The connector must complement the type of fiber cable being connected. The mode of transmission impacts the speed of transmission, input and output attributes, etc. Therefore, the connectors should be selected under fiber optic networking standards like 10GBase-LX4, 10GBase-LR, 10GBase-ER, 10GBase-LRM, 10GBase-SW, 10GBase-LW, 10GBase-EW, etc. These fiber optic cable network standards define the speed, mode, and distance of transmission. The fiber optic connector must complement the type of fiber optic transmission standard adopted by the user.

• Fiber Count: Different types of fiber optic connectors are suitable for a specific number of fiber-count in the optical fiber cable. For simplex cables that feature only one optical strand, FC, SC, ST, LU, etc type of connectors are suitable. For duplex cables with two optical strands, MU, MJRT, etc types of connectors are preferred. Further, for multi-fiber cables, which may have from 4 to 24 number of optical strands advanced connectors like MT connectors are suitable.

• Ferrule Material and Dimensions: The ferrules are long cylindrical bored slots on the end of connectors. The fiber optics cable is inserted through the ferrule itself. Therefore, ferrule has a slightly larger diameter than the cable outer diameter. Generally, 1.25 mm and 2.5 mm ferrule diameters are used in the industry. Depending on the application, the material of ferrule may also impact the operation. Ferrules are made of metals, ceramic or plastic materials. The operator must test the durability and functionality of the ferrule for specific application during selection.

• Coupling/ Attachment Mechanism: The connectors are designed for various types of coupling mechanisms. The coupling mechanism is basically a mechanical linkage to attach the connector with the cable. There are three common coupling mechanisms available in fiber optic connector designs, namely, push-pull latch coupling, screw coupling, and bayonet coupling. A push-pull latch offers a quick connection but reliability is limited in it. If integrated with an alignment pin, it can be highly reliable. The screw coupling mechanism offers easy but time-consuming installation and moderate durability if not tightened harshly. The bayonet is a twist and snaps type of coupling mechanism. This mechanism is quick, easy, and reliable, therefore, connectors with this type of coupling mechanism can be used for a permanent or on-off type of fiber-connector linkage.

• Connector Body: The connector body is the outer structure or housing that supports the ferrule and coupling mechanism. Its quality directly impacts the life-cycle of the connector. Thus, based on your application, metallic or plastic made connector body can be chosen.  

• Losses: The fiber optic connectors are subjected to signal losses to some extent. The losses can potentially impact the output of a fiber optic transmission network, therefore connectors with minimum loss estimation must be selected. There are two types of losses that must be considered while selecting the fiber optic connectors, namely, insertion loss and return/reflection loss.

  • Insertion Loss: The insertion loss takes place at the connecting point of the cable and connector. This can happen due to several reasons like end gaps, coaxial attachment, core mismatch, axial run-out, etc.

  • Return/Reflection Loss: Return loss occurs due to back reflection. Generally, the signals reflect back and return to the source, and it is known as return loss. Whereas, if the signal reflects back over the connector material it is known as back reflection. Both conditions can cause delays in data packet delivery and sometimes, permanent loss of signal.

• Mode of Transmission: The fiber optic transmission is often performed in one of the two modes of transmission, single-mode and multi-mode. Based on the applications, the mode of transmission is selected, eventually a suitable cable us selected. The highlighted features of single-mode and multi-mode fibers that make these cables suitable for specific applications are listed below.

  • Single-mode fiber optic cables: The beneficial features of single-mode fiber optic cables are as described below. The single-mode fiber optic cables enable optical signal transmission via a single path. Therefore, from transmitting source to receiver, the light waves of different frequencies transmit on the same path. This type of cable offers a minimum of attenuation. Therefore, loss of signal is not a concern in this mode of transmission. The source of light in these cables is a laser, therefore, the light intensity does not diminish. Single-mode fiber optic cables are suitable for long-distance transmission.

  • Multi-mode fiber optic cables: The beneficial features of multi-mode optical fiber are as follows. Multi-mode fiber optic cables are suitable for short-distance transmissions. These cables are affordable, therefore make a cost-effective choice for fiber-optic networks. The LED bulbs are sources of light in multimode optical fiber, therefore, it remains a sustainable fiber optic solution.

• Core Diameter: There is a varying range of core diameters available in the fiber optic cables. The core diameter and core material define the refraction phenomenon that means they define the mode of transmission. Therefore, the core diameter is an essential selection criterion for fiber optic cables. The single-mode cables are available in core diameter sizes 8µm to 10µm and multi-mode cables are available in 50µm to 62.5µm.

• Distance of Transmission: The distance of transmission is one of the important considerations while choosing between two types of fiber optic cables. The single-mode optical fiber cables are suitable for nearly 40km distance of transmission. Whereas, the multi-mode optical fiber cables are suitable for 550 meters to 2km of transmission distance.

• Bandwidth: For high-end fiber optic applications, extremely high bandwidth may be required. Single-mode fibers offer theoretically unlimited bandwidth. In case of limited bandwidth requirements, multi-mode fiber cables can be chosen which offer 28000MHz*km.  

• Speed of Transmission: While selecting fiber optic cable, it is important to match up the speed of transmission. Single-mode fiber often offers 10Gbps to 40Gbps transmission speed whereas multi-mode fiber offers 100Mbps to 10Gbps speed of transmission.

• Attenuation: There is a reduction in the power of a light signal during transmission, which is known as attenuation. Attenuation leads to loss of data. Therefore a fiber optic cable with the least possible attenuation. In single-mode fibers, the attenuation range is 0.4 dB/km to 1dB/km. However, multi-mode fiber cable may give higher attenuation beyond 2km distance. Therefore, transmission distance to attenuation comparison must be done during the selection of fiber optic cables. 

• Cable Construction: The optical fiber cable construction or the construction defines its functional reliability and sustainability for several applications. The utility of fiber optic cable for indoor, outdoor, commercial, domestic, industrial applications can be decided based on the construction itself. Therefore, the fiber cable construction becomes an important selection criterion. Lower is the loss value, higher is the performance efficiency of the connector.

Along with the above-mentioned selection factors, the operator has to consider color codes of the connectors which are stated under TIA 568 standards. Consideration of color codes makes the selection of fiber optic connectors convenient for indoor, commercial, and industrial applications.

Conclusion

In actual life, cabling environments are complicated and changeable. Knowing well about fiber optical cables is good for us to find the best solution, and strictly following the cabling standards as required.