What is Fiber-Optic Communication?
Single-mode and multimode fiber-optic communication are ways to transmit information by sending pulses of light through one or more strands of glass. Either requires fiber-optic cable, transmitting and receiving devices and various connectors. Following a few best practices will ensure all components are compatible with one another to optimize system performance.

Types of Fiber

There are two types of fiber cabling options: single-mode and multimode. The fiber you choose will depend on your budget, bandwidth requirements, fiber capacity, application and more. 

Multimode fiber includes multiple strands of glass. It has a large core, 62.5 or 50 microns, which allows multiple light modes to be propagated. Its fiber capacity accommodates high bandwidth and high speeds. Multimode fiber’s max distance is dependent on the application and equipment being used. At best, multimode fiber is able to reach up to 2 km. Because of the large core size, multimode fiber is susceptible to modal dispersion, or light bouncing around inside the cable.

Single-mode fiber includes a single strand of glass with one mode of transmission. It has a narrow core size of 9/125 microns, which virtually eliminates modal dispersion. When it comes to fiber capacity, single-mode fiber offers a higher transmission rate than multimode fiber. Single-mode fiber’s max distance is also dependent on the application and the equipment being used. In the best situations, single-mode fiber can run distances of 130 km or greater.

Another type of fiber cable is known as single strand fiber, or SSF, which allows for two independent wavelengths on the same piece of cable, often 1310 nm and 1550 nm. Single strand fiber offers double the fiber capacity compared to multimode fiber, but it is typically more expensive.

When considering fiber capacity, keep in mind that the number of connectors and splices in your cabling can result in signal loss. Usually, the signal loss factor is a loss of dB per slice.

Fiber Transmitters, Receivers and Transceivers

While single strand fiber allows for two independent wavelengths on the same cable, your transmitters and receivers must be matched correctly for communication to work. For example, one unit must be a 1310/1550 device (transmitting at the 1310 wavelength, receiving at 1550) and the other must be a 1550/1310 device (transmitting at 1550, receiving at 1310).

Transceivers for your fiber installation come in multiple varieties, including small-form-factor pluggable (SFP) and 10-Gigabit small-form-factor pluggable (XFP and SFP+). Standard SFPs support speeds up to 1 Gbps while XFP and SFP+ support 10 Gbps. SFP transceivers are typically more expensive, but they offer more flexibility because of their smaller size and ability to be hot swapped. When choosing a transceiver, keep in mind that the devices must support the same speeds. For example, you can’t connect an SFP+ transceiver, which supports 10 Gbps, into a device that only supports 1 Gbps.

Types of Connectors

Single-mode and multimode fiber transceivers use a range of connectors. ST connectors are round. SC connectors are square. A third type, called LC is smaller than SC or ST and is less easily disconnected. SFP transceivers use LC connectors.  

Calculating Power Budget

Power budget refers to the amount of light available to transmit signals through single-mode or multimode fiber over a given distance. To calculate the power budget of your system, you can use the formula Transmit Power ‐ Receive Sensitivity = Power Budget using values provided by your device vendor. Be aware, however, that distance, connections and splits can affect power budget. To know your power budget for certain, you should use a power meter.

Need help selecting the components for your fiber installation? Try our fiber optic patch cable selector tool. Or contact the experts at Black Box to find the equipment that best suits your application.
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