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Fiber Optic Cable Buying Guide
Fast data transmission, thinner, lighter cables and long signal range are just a few of the benefits that make fiber optic cable a solid choice for corporate data networking and telecommunications.
This buying guide will help you:
- Understand what fiber optic cable is and recognize key features
- Learn the important questions to ask before selecting fiber optic cable
- Find the right type of fiber optic cable for your network
- Compare the different types of optical fiber cable available
How to Choose Fiber Optic Cable
Fiber optic cable selection can be complex due to the variety of cable types, performance characteristics and more precise installation requirements. Start by determining requirements for the following:
- Network Speed
- Cable Jacket
Once you have narrowed down your choices, you should also consider cost and future-proofing. Additional requirements will be driven by the needs of your specific application. If you need assistance in determining requirements or selecting pre-terminated or custom fiber cable, please contact us.
Network Speed and Distance
Multimode fiber (MMF) used to be the automatic choice for datacenters and corporate networks because it was less expensive than singlemode fiber (SMF). Nowadays, the cost difference is not so significant. For example, the price of a 3 meter LC-to-LC duplex SMF cable is about one US dollar more than the equivalent MMF cable.
Instead of focusing on singlemode vs. multimode, focus on the connection distance and network speed dictated by the overall network design. If you need to move a large amount of data over a relatively short distance (for example, less than 300 meters), OM3 MMF might be the best choice. If data transmission speed or distance are key requirements, consider SMF. Note that MMF range depends on the OM rating of the cable.
Refer to Table 2: Fiber Optic Cable Speeds and Lengths for guidance.
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.
Fiber optic cable terminations are typically dictated by the ports on your network equipment. For example, if your 10G Ethernet switch has multi-fiber MTP ports, you'll need cables with the required number of fibers.
If you are selecting cable for a 40GbE or 100GbE application, consider Active Optical Cables (AOCs). They combine an optical fiber cable and transceivers, eliminating the connector entirely.
Application Starting Points
|Key Requirement||Fiber Solution||Product Options|
|10G Server Rack||OM3 or OM4 cable||
|40G Switch to Switch||MTP, AOC||
|40G Switch to 10G Servers||MTP-to-LC fan-out cables
|High Port Density||Connectors with Push/Pull Tabs||Push/Pull Tabs|
|200/400G Switch to Switch||OM4 with CS connector||OM4/CS|
Fiber Optic Cable Basics
What is Fiber Optic Cable?
Fiber optic cable (also referred to as optical fiber cable) transmits data as pulses of light through flexible, optically pure fibers of glass or plastic. It has become a popular choice for Ethernet networking and telecommunications applications thanks to its fast data transmission speeds over long distances.
Core - At the center of a fiber optic cable is a thin glass tube called a core that transports light pulses generated by a laser or light emitting diode (LED). Singlemode cores are typically 8.3 or 9µm, while multimode cores are available in 50 and 62.5µm diameters.
Cladding - A thin layer of glass that protects and surrounds the fiber core, reflecting light back into the core causing light waves to travel the length of the fiber.
Primary Coating - This layer of thicker plastic is also known as the primary buffer. It is designed to absorb shocks, prevent excessive bending and reinforce the fiber core.
Strength Member or Strengthening Fibers - From gel-filled sleeves to strands of Kevlar, the strength member is engineered to protect the fiber core from excessive pull forces and crushing, particularly during installation.
Outer Jacket - The outer jacket, or cable jacket, provides a final layer of protection for the core conductor and further strengthens the cable. The jacket is color coded to identify the type of optical fiber in the cable: yellow for single mode, orange for multimode, and so on. Cable jackets also have fire ratings, such as OFNR, OFNP or LSZH.
How Fiber Optic Cable Works
Light pulses travel down the core of the fiber optic cable by reflecting off of the sides. With the exception of the light source, no power is required to transmit a signal. Light pulses will travel for many miles before they weaken and need to be regenerated.
Core size is important in determining how far a signal will travel. In general, the smaller the core, the farther the light will go before it needs regenerated. Single Mode Fiber (SMF) has a small core, which keeps the path of light narrow and allows it to travel up to 100km. Multimode Fiber (MMF) has a bigger core capable of carrying more data but it is susceptible to signal quality problems over longer distances, making it more suited to premises cabling and short haul networks.
How far can a fiber optic cable carry a signal?
Signal transmission distance is dependent on the type of cable, the wavelength and the network itself. Typical ranges are about 984 ft. for 10 Gbps multimode cable and up to 25 miles for singlemode cable. If a longer span is required, optical amplifiers or repeaters can be used to regenerate and error correct the optical signal.
Can the light generated by a singlemode laser damage your eyes?
Yes, the laser light from the end of a singlemode cable or the transmit port on a switch can seriously damage your eyes. Always keep protective covers over the ends of fiber cables and ports.
Advantages of Fiber Optic Cable vs. Copper Cable
Data Transmission - Photons traveling at the speed of light reach speeds over a hundred times faster than electrons traveling over a copper conductor. In comparing the data transmission speed of fiber and copper, fiber wins easily. Copper currently maxes out at 40 Gbps, whereas OM5 fiber reaches speeds of 100 Gbps.
Distance - Over long distances, copper and fiber cables both experience signal loss, but this attenuation is much greater with copper. Over 100 meters, it is estimated that fiber loses only 3% of its signal strength, whereas copper loses 94% over the same distance.
Electromagnetic Interference (EMI) - Copper wires produce a field of electromagnetic interference, which can cause signaling errors in other cables. Fiber optic cables do not conduct electricity and are not susceptible to EMI.
Electrical Isolation - Because fiber optic cables do not carry electricity, there is no need to ground the transmitter and receiver. Nor is there any danger of electrical shock, arcing, heat or fire.
Lighter, Thinner Cable - Fiber cables are about a quarter the diameter and a tenth the weight of copper cables, making them easier to install and promoting better air flow in rack enclosures.
What's the difference between fiber optic and Ethernet cable?
Ethernet cable has become synonymous with copper category cable but Ethernet is actually the networking protocol that allows devices to communicate over copper or fiber cable. Depending on requirements, network designers may choose to use either fiber or copper cable, and may use both in different parts of the network. Fiber is typically used to connect two high-speed devices (e.g. switch to switch) in data centers and campus networks where bandwidth and distance may be critical factors. In some cases, a network designer may be able to save money by using copper cable with similar performance in place of fiber optic cable. For example, less expensive 10G-certified Cat6a cables can be used in place of duplex fiber cables, which also require costly transceivers.
In residential applications, most telecommunications carriers have adopted some form of Fiber to the X (FTTX), a general term that encompasses configurations such as Fiber to the Premises (FTTP) and Fiber to the Home (FTTH). The last cable run will be defined by the equipment installed by the carrier in the home or business. If the output port is copper, then a standard copper Ethernet patch cable can be used. If the output port is fiber, then a fiber Ethernet cable is needed between the switch or router and the computer. The computer would need a fiber port or a media converter to transition from fiber to copper in order to complete the connection.
Fiber Optic Cable Types
Singlemode vs. Multimode
Fiber optic cable is available in two "modes": multimode or singlemode. Mode refers to pulses of light: multiple pulses or a single pulse.
Multimode fiber (MMF) is available in two core sizes: 50µm and 62.5µm. The relatively wide core allows it to carry multiple streams of data simultaneously at wavelengths of 850nm or 1300nm. Multimode fiber uses a light emitting diode (LED) or Vertical Cavity Surface Emitting Laser (VCSEL) as its light source and is typically used to carry a high volume of data over relatively short distances due to high dispersion and attenuation rates.
Singlemode fiber (SMF) has a much smaller core size of 8.3µm or 9µm and a single light path that can travel long distances. It uses a laser diode which operates in the 1310 and 1550nm range. Singlemode is typically used for longer spans, such as campus data networks, cable TV transmission and telecommunications networks.
Why is multimode fiber optic cable is designated 50/125 or 62.5/125?
These designations refer to the diameter of the core and cladding. For example, a 50/125 cable has a 50 micron core and a 125 micron cladding.
Simplex vs. Duplex
Simplex cable uses a single strand of fiber with a transmitter (TX) on one end and a receiver (RX) on the other. The cable is not reversible and supports only one-way transmission. It is typically used in monitoring applications where a sensor sends time-sensitive data back to a centralized system.
Full duplex cable uses two fibers to simultaneously transmit and receive data, essentially two simplex cables that work together to handle bidirectional data transfer. The twin connectors on either end are capable of transmitting and receiving simultaneously. Half duplex cables are also capable of two-way communication but not at the same time. Duplex cables are typically used to connect network devices in a high-speed network, such as switches, servers and storage systems.
Miscellaneous Fiber Cable Types
Duplex Zipcord Fiber
Zipcord is a type of electrical cable with two or more connectors that can be separated by pulling them apart.
Duplex zipcord fiber consists of two fibers surrounded by strength members and an outer jacket. The example on the right is a duplex multimode zipcord cable with twin LC connectors on either end.
Mode Conditioning Cables
A Mode Conditioning patch cord (MCP) is a duplex cable with multimode to multimode on the receive (Rx) side and singlemode to multimode on the transmit (Tx) side.
By allowing a singlemode signal to be converted and transmitted over multimode fiber, Mode Conditioning cables avoid the expense of an expensive network upgrade to replace legacy Gigabit LX transceivers.
Can I mix singlemode and multimode fiber and equipment on the same network?
No. Singlemode fiber (SMF) and multimode fiber (MMF) have different core sizes so mixing cable types causes differential mode delay (DMD), resulting in errors at the receiver. Mode Conditioning patch cables avoid DMD by launching the singlemode signal at an offset to the center of the MMF core. This "mode conditioning" creates a signal that is similar to typical multimode launch.
Active Optical Cables (AOCs)
Active Optical Cables (AOCs) are fiber optic cables with transceivers permanently bonded to each end, eliminating the need for connectors. AOCs are typically used in top-of-rack applications where link distances are short. The thin cables help to maintain air flow when port density is high.
Multi-Strand Fiber Cables
Multi-strand fiber is similar to duplex fiber. It has multiple strands of fiber carrying data in one direction and a similar number of strands supporting data transfer in the opposite direction. Multi-strand fiber is designed to support data rates above 25G and uses an MPO/MTP connector.
Cables typically have 12 or 24 fiber strands (referred to as 12F or 24F) in a single jacket. Multi-strand fiber can also be made as a breakout cable with an MPO/MTP connector on one end and multiple duplex LC connectors on the other end.
A loopback cable, also known as loopback tester or loopback adapter, is used to test signal transmission and diagnose problems. It plugs into an Ethernet or serial port and routes the transmit line to the receive line so that outgoing signals can be redirected back into the source for testing.
OM and OS Designations
The designations "OM" and "OS" stand for Optical Multimode and Optical Singlemode respectively. They were first defined in the ISO/IEC 11801 standard covering premises cabling and classify optical cable according to wavelength and bandwidth.
The chart below compares the different fiber types.
Table 1: Fiber Optic Cable Types
|Fiber Type||Core Diameter (µm)||Jacket Color||Wavelength||Overfilled Bandwidth (@850nm)||Effective Bandwidth (@850nm)|
|Singlemode||OS1/OS2||8.3 or 9||Yellow||1310nm
In multimode fiber, light takes different paths (modes) as it travels down the cable. The paths that are closer to the center of the core are shorter so, all things being equal, light that takes these paths will take less time to travel the length of the cable. Multimode fiber compensates for this by slowing down the shorter paths and allowing longer paths to move faster so all modes arrive at the receiver at the same time. Of course, this is an ideal situation. In reality, modes arrive at slightly different times causing the light pulses to spread out and making it harder for the receiver to interpret the signal.
Overfilled vs. Effective Bandwidth
Older multimode cables use Light Emitting Diodes (LEDs) as their light source. These LED sources "overfilled" the fiber by using all available paths. Overfilled Launch (OFL) Bandwidth is a measure of the data transmission capacity of cable with an LED source, and is used with legacy fiber cable running at speeds of less than 1 Gbs.
Faster networks require a more focused light source and it came in the form of Vertical Cavity Surface Emitting Laser (VCSEL), pronounced "vixel", a semiconductor that omits a laser beam perpendicular to its surface. Not only was the beam narrower and resulted in lower signal dispersion, VCSELs were also cheaper to manufacture and more power efficient. VCSEL light sources did have one problem though. The light they produced was not uniform across the whole cable core. In essence, the core was "underfilled", with some modes carrying a stronger light pulse than others. It also meant that Effective Modal Bandwidth (EMB) rather than OFL had to be used to measure the performance of multimode fiber.
Comparing Multimode and Singlemode Speeds and Distances
Table 2: Fiber Optic Cable Speeds and Lengths
|Fiber Type||Fast Ethernet 10/100||Gigabit GbE 10||Gigabit 10GbE||40 Gigabit 40GbE||100 Gigabit 100GbE||400 Gigabit 400GbE||40 Gigabit SWDM4||100 Gigabit SWDM4|
What Is SWDM?
Shortwave Wavelength Division Multiplexing (SWDM) transmits data over a cable using different wavelengths in the 850 to 953 nm range. SWDM4 transceivers use four light sources operating at different wavelengths to produce a multiplexed signal which is transmitted over two-fiber duplex MMF cable. Increasing bandwidth by using wavelength instead of additional fibers reduces cost and allows 40G and 100G data transmission rates over existing two-fiber cable.
SWDM4 works with legacy 10G OM3 and OM4 duplex MMF, as well as the newer OM5 wideband multimode fiber (WBMMF). OM5 is specifically designed to support SWDM4 wavelengths in the 850-953 nm range.
Fiber Optic Cable Termination
Unlike copper category cable that uses the ubiquitous RJ45 connector regardless of cable type, glass and plastic fiber optic cable can be terminated using a variety of connector types. Connector choice is determined by the equipment and the requirements of the application, including the anticipated number of mating cycles and the amount of vibration.
Singlemode fiber requires a clean, precisely aligned transceiver that injects light into its small core with sub-micron accuracy. By contrast, multimode fiber is a little more forgiving.
Ferrule Connector (FC)
The FC was the first optical fiber connector to use a ceramic ferrule. These connectors precisely position and lock the fiber core relative to the transmitter and receiver. FC connectors have been largely replaced by the cheaper and easier to install SC and LC connectors but are still preferred in high vibration environments due to their screw-on collet.
Straight Tip (ST)
ST was at one time the most common fiber optic connector for both singlemode and multimode fiber. It features a bayonet-style twist lock connector and is inexpensive and easy to install. It is still used in industrial and military applications but elsewhere, it has been largely replaced by smaller form factors.
Subscriber Connector (SC)
SC connectors have a reliable snap-in locking mechanism that latches with a simple push-pull motion. They are an inexpensive, durable option rated for 1,000 mating cycles. This connector is used in simplex and duplex (shown) configurations. SC connectors have been mostly replaced by LC connectors in corporate networks.
Mechanical Transfer Registered Jack (MT-RJ)
This Small Form Factor (SFF) connector is used with multimode fiber. It is easy to terminate and install, and its smaller size allows twice the port density of ST or SC connectors. It is similar in design and operation to a RJ45 connector, making it ideal for Fiber–to-the-Desktop (FTTD) applications.
Lucent Connector (LC)
The LC connector was designed to address complaints that ST and SC connectors were too bulky and easily dislodged. LC connectors have a footprint approximately 50% smaller than the SC connector. Thanks to this small size and secure latching feature, it is widely used in data centers and telecom switching centers where packing density is critical.
Multiple-Fiber Push-On/Pull-Off (MTP/MPO)
The MTP/MPO connector has a horizontal, multi-fiber interface designed specifically for use with high-bandwidth QSFP-DD transceivers. The connectors are about the same width as SC connectors but can be vertically stacked in patch panels and switches. They are ideal for high bandwidth applications such as cloud services and core data centers.
The new CS connector is 40% smaller than a standard LC duplex connector, making it ideal for very high-density 200G and 400G networks utilizing the QSFP-DD and OSFP transceiver interfaces. The connector features a push/pull tab and a spring-loaded zirconia ferrule.
Fiber Optic Cable Jackets
Most indoor fiber optic cables use a low-cost, fire resistant polyvinylchloride (PVC) jacket. Some installations (e.g. confined spaces, but not risers or plenum) may opt for the more expensive Low Smoke Zero Halogen (LSZH) jacket, which is made of thermoplastic or thermoset compounds and offers superior flame retardant and produces little smoke or toxic fumes when burned.
Polyethylene (PE) is preferred for outdoor applications due to its resistant to moisture and sunlight (UV rays), abrasion resistance and flexibility over a wide range of temperatures.
Colored jackets and connectors are used to identify the mode and OM rating of indoor and military cables, making it easy to identify at a glance the capabilities of a cable and ensuring that installers use the correct cable type for each connection. Outdoor cable jackets are typically black so they can resist damage from the sun, precluding the use of any color coding.
Color code standards and conventions specified in TIA-598D are shown in the table below. Jackets are also printed with additional information about the cable. For example, the jacket of an OM4 multimode cable with core dimensions of 50/125 and a bandwidth of 850 nm laser-optimized might be labeled “OM4 850 LO 50 /125".
|Mode||Cable Type||Jacket Color||Connector Color|
|OM5||Lime Green||Light Blue|
The National Fire Protection Association's National Electrical Code (NEC) defines levels of fire resistance for fiber optic cables. Indoor fiber installations are typically classified as plenum, riser or general purpose. Cables installed in plenum spaces and risers must meet standards for flame spread and smoke production outlined in NEC Article 770 and the UL 1651 Standard for Optical Fiber Cable.
UL 1651 defines the following optical-fiber cable types:
- Optical Fiber Nonconductive Plenum (OFNP)
- Optical Fiber Conductive Plenum (OFCP)
- Optical Fiber Nonconductive Riser (OFNR)
- Optical Fiber Conductive Riser (OFCR)
- Optical Fiber Nonconductive General Purpose (OFNG)
- Optical Fiber Conductive General Purpose (OFCG)
|Application||Nonconductive||Conductive||USA Test||Acceptable Substitute|
All areas that are not plenum or riser on the same space or floor
|OFNG||OFCG||UL 1581 (OFNG)||Riser or Plenum Rated cable|
A vertical space, typically inside walls and between floors
|OFNR||OFCR||UL 1666 (OFNR)||Plenum Rated cable|
Space above and below floors typically occupied by heating and air conditioning ductwork
|OFNP||OFCP||UL 910 (OFNP)||No substitute|
What's the difference between conductive and non-conductive fiber optic cable?
Non-conductive cables contain nothing that could carry electrical current. Conductive cables include metallic strength members, sheathing or other metal components that could potentially carry an electric current, even though that is not the intended purpose.
Note: Fire regulations vary from country to country. In the US, Article 770 of the National Electrical Code governs installation and testing of premises fiber cabling. In Europe, this falls to the IEC/CEI although individual countries may have their own standards organizations, such as the British Standards Institute (BSI) in the UK.
Fiber Optic Cable Performance
Optical Return Loss
When a pulse of light reaches the end of the fiber core, some percentage of light is reflected back towards the source. This Optical Return Loss (ORL), expressed in decibels (dB), only affects fiber with a laser light source and can reduce data transmission speeds. Singlemode fiber, and multimode fiber with a VCSEL light source, are sensitive to ORL. Older multimode fiber with an LED light source is not subject to ORL.
Are Optical Return Loss and Back Reflection the same thing?
ORL and Back Reflection are often used interchangeably but they are actually different. ORL is the total power lost from all system components, including the fiber itself. Reflected power is only one component of ORL.
Optical Return Loss can be minimized by ensuring that ferrules are clean and connectors are properly mated. It can also be reduced by choosing fiber optic cable with end-faces that are shaped to optimize the physical interface. Original fiber connectors had ferrules with a simple flat face, leaving a relatively large area that could be damaged with repeated mating. Physical Contact (PC) connectors are polished to a slightly rounded surface to reduce the size of the end face. The end face of Ultra Physical Contact (UPC) connectors have an even greater radius so the fibers touch at the apex of the curve near the fiber core.
The ferrules of an Angled Physical Contact (APC) connector are cleaved at an angle between 5 and 15 degrees. The angle directs the reflected light out of the core resulting in a lower ORL value.
Insertion Loss refers to the amount of light lost between two fixed points in the fiber and is measured in decibels (dB). Insertion Loss can occur when fiber is terminated with a connector or spliced, and is often the result of fiber core misalignment, dirty ferrules or poor quality connectors. The combined insertion loss of all system components should be within the limits specified in the link-loss budget agreed with the installer.
Fiber Cable Installation FAQs
What is the minimum bend radius for fiber optic cable?
For a cable that is not under pulling tension, the minimum radius should not be less than 10 times the cable diameter. For example, a multimode cable with an outside diameter of 3.0 mm has a minimum bend radius of 30 mm. The bend radius for a cable under tensile load may be greater. Refer to the cable's spec sheet for details.
What is the maximum tensile rating (pulling force) for fiber optic cable?
During installation, a fiber optic cable may be stressed when it is pulled through ductwork and around bends. Even pulling a cable from the payoff reel can potentially cause damage. After installation, cables can also be subjected to sustained pulling forces, for example, at cable drops or when run through risers.
The maximum tensile rating of a fiber optic cable is the highest pulling force that the cable can be subject to before the cable's fibers or optical properties are damaged. The cable manufacturer will typically provide two values: maximum tensile rating during installation and maximum tensile rating while in operation.
Fiber optic cable should ideally be pulled by hand in a smooth, steady motion. It should never be jerked, pushed or subjected to excessive twisting.