Fiber Optics Frequently Asked Questions

Fiber Optics Frequently Asked Questions

  1. What is optical fiber?
    Optical fiber is a glass or plastic filament that guides a light wave along its path.
  2. What is multimode fiber?
    Multimode fiber is optical fiber that allows light to travel down multiple paths, also referred to as modes. It features a core diameter of 50 to 62.5 microns. Multimode fiber can be used to transmit AV signals in short to intermediate-distance applications, such as within a building.
  3. What is singlemode fiber?

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    Singlemode fiber is optical fiber that allows light to travel down a single path known as the fundamental mode. It features a core diameter of 8 to 9 microns. Singlemode fiber can be used to transmit AV signals over extreme distances up to many miles or kilometers.

  4. How is an AV signal transmitted down a fiber?
    A fiber optic transmitter converts the AV signal into an optical signal, using a VCSEL or laser diode as a light source. A glass fiber guides the optical AV signal along its path. A photodetector in a fiber optic receiver at the far end of the fiber converts the optical AV signal back into an electrical AV signal.
  5. What is a light-emitting diode?
    A light-emitting diode — LED is a semiconductor device that emits light when an electrical current passes through it. An LED that emits visible light is used in a variety of applications, including signage, area lighting, numerical displays, and indicator lights on electrical equipment. In fiber optics, an LED is used as a light source for low-speed signals such as, TOSLINK or 100BASE-SX Ethernet, due to its low cost. An LED is not recommended for transmitting high speed video signals over fiber.
  6. What is a laser diode?
    A laser diode is a semiconductor device that emits a narrow beam of coherent light, such as the beam of light from a laser pointer. In AV fiber optic transmitters, laser diodes are used as the light source for transmitting video, audio, and control signals.
  7. What is a VCSEL?
    VCSEL stands for Vertical Cavity Surface Emitting Laser. A VCSEL is a special type of laser diode that has lower manufacturing costs than other types of laser diodes. It can be mass-produced with high yield rates and has a smaller PCB footprint, making it ideal for use in fiber optic transmitters to send high resolution video, audio, and control signals.
  8. What is a photodetector?
    A photodetector is a semiconductor device that converts an optical signal into an electrical signal. A photodetector is used in a fiber optic receiver to convert optical AV signals.
  9. What wavelengths are used with multimode fiber?
    Multimode fiber is capable of transmitting a wavelength at or around 850 nm, 1300 nm, or 1550 nm. The most common wavelengths are 850 nm and 1300 nm due to the availability of low cost semiconductor light sources and photodetectors.
  10. What wavelengths are used with singlemode fiber?
    The most common wavelengths are 1310 nm and 1550 nm. At 1310 nm, chromatic dispersion is near zero, and at 1550 nm, attenuation is near its minimum. In OS1 singlemode fiber, wavelengths around 1390 nm should be avoided due to high attenuation caused by absorption. OS2 singlemode fiber is capable of transmitting any wavelength above its cutoff wavelength, which is typically around 1250 nm.
  11. What is the cutoff wavelength for singlemode fiber?
    The cutoff wavelength for singlemode fiber is the minimum wavelength that supports one mode of propagation. Above the cutoff wavelength, singlemode fiber propagates only one mode. Below the cutoff wavelength, singlemode fiber propagates more than one mode, similar to multimode fiber.
  12. How is an electrical AV signal converted into an optical AV signal?
    An electrical AV signal is converted into an optical AV signal using an optical transmitter or an electrical-to-optical converter. An optical transmitter uses a laser diode as the light source, varying the intensity of the laser light in accordance with the electrical signal. For an analog signal, the intensity of the light source varies with the voltage or current of the electrical signal. For digital signals, the light intensity is high or low, which represents logical ones or zeros.
  13. How is an optical AV signal converted back into an electrical AV signal?
    An optical signal is converted into an electrical signal using an optical receiver or an optical-to-electrical converter. The optical receiver uses a photodetector to receive the optical signal and convert it into an electrical signal.
  14. What are the problems with the direct conversion of analog video signals into optical signals?
    The direct conversion of an analog electrical signal to an optical signal and back has non-linear effects that distort analog video signals. It is difficult to compensate for these distortions. Fiber also has attenuation that causes optical power to dim over longer distances. When the dimmed optical signal is converted back into an electrical signal, the voltage levels are too low. Amplifiers can compensate for low voltage, but also increase signal noise, thereby reducing the signal-to-noise ratio. Fiber optic AV equipment that uses analog techniques suffers from increased noise and distortion, which produces a low quality video signal.
  15. How does Extron handle analog video signals in its fiber optic products?
    Extron fiber optic products convert analog signals to digital signals for an all-digital transmission of video, audio, and control signals. Converting the analog video signal to a digital signal for optical transmission ensures the highest quality video.

Fiber Optic Applications

  1. How far can I transmit an AV signal on an optical fiber?
    Optical AV signals can be transmitted for several kilometers or miles on singlemode fiber, and hundreds of meters or thousands of feet on multimode fiber. Newer, laser-optimized multimode fiber may extend transmission distances up to 2 km. Typically, multimode fiber is used within buildings, between floors or on the same floor, while singlemode fiber is designed for long haul transmission between buildings on a campus or between facilities.
  2. What AV applications require fiber technology?
    Fiber optical technology is ideal when transmitting video, audio, and control signals over long distances, in secure or hazardous environments, or anywhere where it is important to future-proof an AV system. Long distance transmission makes fiber optic products ideal for installation in stadiums, college campuses, medical facilities, corporate campuses, performing arts centers, concert halls, and office buildings. Low signal emissions make fiber optic products preferred for secure environments such as military or government applications. Fiber optics is the ideal technology for multi-gigabit digital video standards, ensuring that an AV system is upgradable to future standards.
  3. What are the advantages of fiber AV systems in large venues and long haul transmissions?
    Optical fiber is low-loss compared to electrical wire, and can transmit a signal over very long distances without the need of a repeater. Comparatively, optical transmission is lower in cost than electrical transmission for long distances.
  4. What are the advantages of fiber optic AV systems in government applications?
    Copper wires emit electrical signals that can be picked up with special listening equipment. To avoid these emissions, secure areas in government buildings and at military installations are electrically isolated from other parts of the facility to prevent any stray electrical emissions. Because optical fiber is immune to electrical interference and has zero electrical emissions, it is preferred over copper wire to carry sensitive information. To intercept an optical signal traveling down a fiber, the connection must be interrupted, which is easily detectable. Since optical fiber is made of glass, it can also be used to transmit information between secure facilities that are electrically isolated.
  5. What are the advantages of fiber optic AV systems in medical applications?
    Medical systems need to isolate electrical equipment from the patient for safety, usually have space constraints for cable runs, and must limit the effect of electrical interference on other sensitive medical equipment. Additionally, high-voltage video displays must be isolated from medical imaging machines. Often, the displays are mounted on booms so that they can be adjusted for optimal viewing by the surgeon and other medical staff. This type of mounting system requires that the cabling medium be small but also strong. Since fiber optic cables are made of glass, they isolate displays from medical imaging devices, are small enough to fit inside of mounting booms, and emit no electrical signals that could affect other equipment.
  6. What are the advantages of fiber optic AV systems in hazardous environments?
    There are often explosive or flammable vapors or gases in hazardous environments. If a copper wire carrying an electrical signal breaks, there is usually a spark, which can ignite vapors in this type of environment. Since fiber optic cables carry light, they do not spark if broken. For this reason, fiber optic cable is often used in hazardous environments.
  7. What are the advantages of fiber optic AV systems in electrically noisy environments?
    Heavy equipment, such as industrial machinery, air conditioners, and motors emit strong electrical signals that can interfere with AV signals carried in nearby copper wires. Made of glass, fiber optic cables do not pick up stray electrical signals, and are immune to electrical interference.
  8. How can fiber optic technology future-proof an AV system?
    The transition to digital video standards and higher resolutions has revealed the many limitations of copper cabling. High resolution digital video signals run at multi-gigabit data rates, pushing copper cabling to its limits. Installing fiber optic cables in today’s systems provides a path for future video signals. Fiber optic cable is an ideal cabling solution for the multi-gigabit data rates and long distances required in future AV systems.
  9. How does the size and weight of fiber cable compare to coaxial cable?
    Optical fiber is much smaller and lighter than electrical cables, and has a capacity that is thousands of times greater than coaxial cable. A 1,000 meter (3,280 foot) length of a 24-fiber distribution cable weighs 46 pounds and is 8.7 mm (0.33 inches) in diameter, compared to a 24-cable bundle of RG-6 that weighs 3,600 pounds and has nearly five times the diameter at 38 mm (1.5 inches). In practice, however, it would be impossible to transmit high resolution digital video over 1,000 meters of RG-6, while the fiber optic cable has more than enough capacity to carry multiple HD video signals over thousands of meters with pixel-for-pixel performance.
  10. When should singlemode fiber be used in an AV system?
    Singlemode fiber is optimal for long haul transmissions of up to 30 km (18.75 miles). It is ideal for transmitting signals between buildings on a university or corporate campus. It can also be used for long haul transmission between separate facilities.
  11. When should multimode fiber be used in an AV system?
    Multimode fiber is used to transmit signals for hundreds of meters or thousands of feet. It is ideal for transmitting signals between floors of a building, or from an equipment room to a wide variety of presentation rooms and spaces.
  12. What type of multimode fiber should be used for new installations?
    OM4 or better multimode fiber is recommended for all new installations. The resolution and color depth of video signals continue to climb. OM4 or better fiber optic cable provides a level of future proofing as video resolution and data rates continue to rise.
  13. What type of multimode fiber should be used when adding to an existing installation?
    Mixing multimode fiber with different core sizes in a single fiber run is usually not recommended. If existing fiber runs are being extended through fusing or connecting fibers together, the same fiber core size is normally used. However, if the installed fiber does not have the capacity to handle signals due to the upgrade, it may be necessary to install OM4 or better cable.
  14. Why is singlemode fiber less costly than multimode fiber?
    Singlemode fiber has a step index core, while multimode fiber has a graded index core with very tight performance requirements. Therefore, singlemode fiber is less costly to manufacture.
  15. Why not always use singlemode fiber?
    Laser light sources and photodetectors used for singlemode applications are significantly more expensive than those used for multimode. This difference translates into higher equipment costs for singlemode systems.

Design Considerations

  1. Can singlemode and multimode fiber be intermixed?
    Developing a system that uses both singlemode and multimode fiber is possible if using a switching system that supports both fiber types, such as the Extron FOX Matrix Series. Singlemode fiber must be connected to a singlemode port, and multimode fiber must be connected to a multimode port. Directly connecting singlemode and multimode fiber is not recommended as the difference in core sizes introduces losses into the system.
  2. What are the types of fiber optic connectors?
    Common types of fiber optic connectors include the ST, SC, FC/PC, FC/APC, and LC. The LC connector is very popular due to its high performance, small size, and ease of use. Multi-fiber connectors are also gaining popularity. The MTP/MPO are the preferred connector type for 40 Gbps and 100 Gbps data transmission standards.
  3. What if I am installing equipment that uses a different connector than the existing fiber infrastructure?
    The ST and SC connectors have often been standardized for legacy fiber installations. However, the LC connector is preferred for modern installations due to its compact size, self-locking feature, and alignment capability. The recommended solution is to terminate each end of the cable with the appropriate connector type. Alternatively, an adapter can be used with a patch cable to convert from one connector type to another.
  4. What is an optical loss budget?
    An optical loss budget is the maximum amount of optical loss or attenuation allowable in a fiber optic link. It is calculated as the difference between the output power of the transmitter and the sensitivity of the receiver. For more information about optical loss budget, please refer to the Extron Fiber Optic Design Guide, Second Edition.
  5. How is an optical loss budget used in AV system design?
    The total amount of loss in the fiber optic link is calculated by adding up attenuation caused by glass fiber, connectors, splices, and other optical components. This number is subtracted from the loss budget to determine the loss margin. A loss margin of at least 3 dB is recommended to account for future cabling repairs and aging of optical components. For more information about optical loss budget, please refer to the Extron Fiber Optic Design Guide, Second Edition.
  6. What types of fiber optic cables are available for AV applications?
    Fiber optic cables are available in many different construction types depending on the application. As with other types of indoor cable, fiber optic indoor cables are available as riser or plenum-rated. Outdoor cables are available as aerial cables or direct burial. Armored cables are also available to provide extra protection from rodents or tampering.
  7. What is dark fiber and how is it used for AV systems?
    Dark fiber is pre-installed fiber optic cable that was installed for future use but is not currently being used. Structured cabling is often installed with extra fiber optic cables for future expansion. If available, dark fiber can be used to install new AV equipment without the added cost of installing new fiber. When signals are being transmitted between floors of a building or between buildings on a campus, the availability of dark fiber simplifies the installation.

Extron Products

  1. What types of fiber optic products does Extron offer?
    Extron offers fiber optic matrix switchers, switchers, distribution amplifiers, signal processors, extenders, cables, and accessories. Extron products enable long-haul transmission of HDMI, DVI, 3G-SDI, high resolution RGB or HD component, and standard definition video, as well as audio, RS-232 control, and USB signals over fiber optic cable at extreme distances up to 30 km (18.75 miles).
  2. What types of fiber do Extron fiber optic products support?
    Extron fiber optic products include models for both multimode fiber at 850 nm wavelength and singlemode fiber at 1310 nm wavelength.
  3. What are the advantages of Extron all-digital technology?
    Extron all-digital technology delivers pixel-for-pixel transmission of video signals to ensure optimal image quality at high resolutions.
  4. What is the advantage of LC-type connectors on Extron products?
    The LC-type connector used on Extron products is very popular in fiber optics due to its high performance, small size, reliable connectivity, and precise core alignment.
  5. What types of fiber optic cabling products does Extron offer?
    Extron offers fiber optic bulk cables and factory-terminated fiber optic cable assemblies in both OM4 laser-optimized multimode and singlemode varieties. All Extron fiber optic cables are bend-insensitive to simplify installation and reduce bend-induced losses. Extron cables also include an ONFP-rated jacket for installation in plenum or riser spaces.
  6. What is the advantage of Extron bend-insensitive fiber optic cabling?
    Extron multimode and singlemode fiber optic cables are bend-insensitive to simplify installation and reduce bend-induced losses. Fiber optic bend losses are negligible down to a 7.5 mm fiber bend radius.
  7. What is the advantage of Extron OM4 laser-optimized fiber optic cabling?
    Extron multimode fiber optic cables meet or exceed OM4 performance ratings, making it the highest performance fiber optic cable available. It has the information-carrying capacity to handle the highest resolution video resolutions in use today, and is designed to handle even higher resolution video signals of the future.
  8. Does Extron offer fiber optic termination products?
    Extron offers a pre-polished, no-epoxy fiber optic termination system for quick, reliable termination of multimode and singlemode fiber optic cables. The Extron Fiber Optic Termination Kit includes all of the tools and equipment needed to strip, prepare, cleave, and terminate a fiber optic cable using Extron Quick LC Fiber Optic Connectors. A visual fault locator — VFL is included in the kit to provide a visual indication of a properly terminated fiber optic connector.
  9. What type of fiber optic test equipment does Extron offer?
    Extron offers a Fiber Optic Test Set with all of the tools needed to measure optical power and loss in multimode and singlemode fiber optic AV equipment and cabling. The light source includes both a multimode LED output that operates at 850 nm and 1300 nm, and a singlemode laser output that operates at 1310 nm and 1550 nm. The power meter, compatible with both multimode and singlemode fiber and featuring an easy-to-read LCD display, is used for measuring insertion loss in dB and optical power in dBm or watts.
  10. What training does Extron offer for using fiber optic technologies in AV systems?
    Extron offers advanced fiber optic training as part of the School of Emerging Technologies. The School of Emerging Technologies provides in-depth instruction designed to allow system designers and integrators to master additional AV technologies within a short time span. The training concentrates on new as well as evolving technologies, helping to refine digital AV system design by teaching concepts and techniques for different technologies. The student-instructor ratio is kept low to ensure that each class member receives individual attention. The School of Emerging Technologies provides instructor-led training and demonstration along with hands-on experiences in real-world scenarios to reinforce understanding of the technologies.


  1. What skills are needed to install optical fiber for AV systems?
    The skills needed to install fiber optic cabling are similar to the skills required for installing copper cabling. Fiber optic cables are constructed with strength members to allow pulling for long cable runs. Field termination kits are available that make fiber termination as easy as terminating coaxial cable. Also, as with electrical installations, installers need to be trained prior to working with fiber cables.
  2. How far can I bend optical fibers during installation?
    Manufacturers specify the minimum bend radius for optical fiber. It is extremely important not to bend the fiber beyond the manufacturer’s recommendation. If the specifications are unknown, the rule of thumb is that the minimum bend radius is 20 times the cable diameter for standard fiber optic cable. Many newer cables are using a special fiber construction called bend-insensitive fiber, which has an extremely tight bend radius.
  3. What happens if I bend a fiber too far?
    Bending fiber beyond the minimum bend radius causes loss in the fiber optic signal, and could potentially damage the fiber.
  4. What considerations exist when joining fibers using a connector?
    Special care must be taken when connecting and disconnecting optical cables to avoid damaging the fiber or the connector on the device. Dust caps should be used when a fiber cable is disconnected to protect the end from damage. The fiber and connector should be cleaned prior to mating. Also, there should be no optical signal in the cable or out of the connector when disconnecting, connecting, or during cleaning.
  5. When do I clean the fiber optic connectors?
    Both the fiber and connector ends should be cleaned immediately before mating. Ensure that no optical signal is present in the fiber during cleaning.
  6. Why do I need to clean fiber optic connectors?
    Even in clean environments, a single dust particle could completely block an optical signal. The size of a dust particle is about the same size or larger than the core of a singlemode optical fiber.
  7. What do I use to clean fiber optic connectors?
    Special solvents, cleaners, lint-free wipes, and swabs are available. The swabs are for cleaning inside of the connector on an instrument. Always follow the manufacturer’s cleaning recommendation.
  8. Can fiber optic light cause harm?
    Although the light used for fiber optic transmission is in the infrared range and is not visible to the human eye, it can still cause damage. Laser light is a concentrated beam that can cause injury or blindness. Avoid looking into a fiber if it is unknown whether there is an active light source.
  9. How do you repair a broken fiber?
    Common methods for repairing broken fibers include fusion splicing, mechanical splicing, or connector splicing. The most appropriate method depends on the optical loss budget, the application type, what equipment is available, and the skills of the repair technician. In most cases, a fusion or mechanical splice is used for repairs. A connector splice is generally used when another component or device must be installed in line with the fiber.
  10. What is a mechanical splice?
    A mechanical splice is a device that holds two fiber ends in a precisely aligned position to enable light to pass from one fiber to another. Index matching gel is used to hold the cores together.
  11. What is a fusion splice?
    A fusion splice involves a splicing machine to align the fibers and fuse or weld them together using an electric arc. This produces a very low-loss connection that is superior to a mechanical splice. However, the equipment required for fusion splicing is more costly.
  12. How do you identify the type of dark fiber installed if it is poorly documented?
    The color of the fiber jacket may identify the type of fiber. Multimode jacketing is orange or aqua, while singlemode is yellow. Cable markings may also help identify the manufacturer and type of cable. Manufacturer data sheets can provide performance specifications, and an optical loss test set or OTDR helps to determine losses in the fiber link. However, field testing to determine performance specifications is not an option.
  13. What cable markings are used for plenum-rated fiber optic cable?
    Plenum-rated fiber optic cable should be marked as OFNP, which stands for Optical Fiber Non-conductive Plenum. If the fiber optic cable includes a metallic armor, it is marked as OFCP for Optical Fiber Conductive Plenum.
  14. What cable markings are used for riser-rated fiber optic cable?
    Riser-rated fiber optic cable should be marked as OFNR, which stands for Optical Fiber Nonconductive Riser. If the fiber optic cable includes a metallic armor, it is marked as OFCR for Optical Fiber Conductive Riser.

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