Fiber optics have enabled telecommunications companies to improve data network performance and speed significantly. Fiber optic cables form the foundation of these networks, and to optimize performance, you need to ensure the right kinds are in place. Two main categories of cables are single-mode and multi-mode.
Fiber optics involves sending light signals down fiber strands made of plastic or glass. Fiber optics use pulses of light to send messages in ones and zeros, as in all digital communication. The existence of a pulse represents a one, while the lack of a pulse represents a zero. A fiber optic system uses a laser located in the hardware to turn the light off and on.
The light moves down the optical core, a glass tube in the middle of the fiber, by reflecting off the core's sides. This core is encompassed by an optical material known as cladding, which is also made of glass and keeps the light rays within the core by reflecting them toward the middle of the fiber.
The fiber also has a plastic coating, known as a buffer coating, which keeps out moisture and contaminants. The cable itself and the outer jacket provide further protection.
Besides powering the source that generates the laser, no power is required to transport the data through the cable. The signal weakens over time but can travel a significant distance before it needs to be regenerated. The core, especially its size, is a major factor in the signal's quality and how far it can travel. Smaller cores enable the optical signal to move farther because they keep the laser on a straighter path. Single-mode fiber optic cables have significantly smaller cores than multi-mode cables.
Wavelengths are another crucial factor. These wavelengths are different colors of light that each take a different path down the fiber optic cable cores. None of them interfere with the other wavelengths' routes. The wavelengths that travel down the fiber depend on the light source used, and different types of fiber are better for various wavelengths. Single-mode and multi-mode fiber transmit signals at differing wavelengths.
What is single-mode fiber, and how does single-mode fiber work? Single-mode fiber optic cable features a small core that only allows one mode to be transmitted. This means the number of reflections decreases as the signal moves within the core, which lowers attenuation. This feature enables the signal to transmit at greater distances and faster speeds. Single-mode fiber is often used in applications that require longer distances and higher bandwidths.
Single-mode fiber uses a laser as the light source. The size of the core is 8 or 9 microns (μm), and the standard wavelengths are between 1,310 nanometers (nm) and 1,550 nm for single-mode cables. The color of the outer jacket is typically yellow, but various colors may be used.
OS1 and OS2 are the two classifications of single-mode fibers as defined by the standard ISO/IEC 11801-1:2017 from the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC). The primary difference between OS1 and OS2 is the way the cables are constructed. OS1 cables have a tight-buffered build, and OS2 features a blown cord or loose tube construction.
OS1-type fibers have a protective coating consisting of a layer of plastic and a layer of waterproof acrylate. This coating is color-coded to enable easy identification. The buffer allows the cables to be smaller, lighter, more flexible and more resistant to damage than OS2 cables. OS1 cables are also somewhat easier to install than OS2 cables. OS1 cords are typically used for local area networks (LANs), medium-distance local telecommunications loops and point-to-point connections.
OS2 cable fibers are bare except for the colored outer coating. Besides this protective covering, the fiber sits in a large, abrasion-resistant tube filled with a gel that protects the equipment from moisture. Installing OS2 cables is slightly more involved than implementing OS1 cables. OS2-type cables are used outdoors, such as for long-distance telecommunications lines.
One of the main differences between single-mode and multi-mode fiber cables is that multi-mode cables have a larger core that enables several modes of light to travel through the cord at once. This means the number of reflections increases as the rays progress, which enables more information to move through the cable at one time. The signal's quality decreases over longer distances due to the high attenuation and dispersion rates.
Multi-mode fiber is most commonly used for short distances and applications with less intensive bandwidth needs. A common use is short-distance audio/video and data transmission within LANs. Radio frequency broadband signals, like those used by cable companies, can't be transmitted using multi-mode fiber.
Multi-mode fiber uses a light-emitting diode (LED) as its light source. The core size for multi-mode cables is between 50 μm and 62.5 μm, and the wavelengths are between 850 nm and 1,300 nm.
The light traveling through a multi-mode fiber optic cable may behave in two different ways, depending on the design of the cable.
In step-index multi-mode fiber, some light rays — or modes — zig-zag and reflect off of the cladding, while others travel in more of a straight line. This occurs because of the cable's larger core. Because of this inconsistency, some modes reach the receiver before others, and the pulse begins to lose its original shape.
It's necessary to leave space between each pulse to prevent them from overlapping, which reduces the amount of transmitted data. This type of cable is best used for sending information over shorter distances.
The core design of this multi-mode fiber causes the modes in the middle to travel at a slower pace than the ones along the outside near the cladding. The core design causes the light to move helically instead of zig-zagging off of the cladding, which reduces the distance it has to travel.
Because of the shortened travel distance and the increased speed, the light near the edges reaches the receiver at around the same time the light in the center does, reducing the dispersion of the digital pulse. LANs are the best use for this kind of fiber.
ISO/IEC 11801 also defines five classifications of multi-mode fibers:
Distance is the primary consideration when choosing between single-mode and multi-mode fiber optic cable. Other factors, like cost and future upgrades, play a role as well.
When you need to transmit data over longer distances, you should use single-mode fiber optic cable. Although single-mode cable is more expensive than multi-mode fiber optic cable, multi-mode cable doesn't have the capabilities required to work over longer distances.
If you're working over a short distance, you can choose multi-mode fiber optic cable, as it's less expensive and generally works as well as single-mode cables over short intervals.
When it comes to choosing the specific cable classification, you'll need to look at your requirements and the specifications of each type, including the bandwidth, data rate and distances required. The application you're using the cable for can also help you choose the right classification:
Comparing single-mode and multi-mode fiber is just one part of choosing the right fiber optic cable. Some of the other factors you'll need to consider include:
You'll also need to consider various other factors when choosing the right fiber optic cable for a project. Working with professionals — like the experts at Multilink — can help you select the ideal cable for the job.
Fiber optics has enabled telecommunications companies to offer increased speeds and bandwidth to their customers. Companies need reliable fiber optic cable to provide customers with the best service possible and remain competitive.
At Multilink, we provide several types of high-quality fiber optic cable. To ensure quality, we follow a stringent quality management system, use bend-sensitive fiber and test all our products before we put them on the market.
The main types of cable we offer are:
At Multilink, we have more than 35 years of experience supplying quality products and solutions to the telecommunications industry, and we're ready to provide you with the fiber optic cable you need. Contact us or browse our website to learn more.Back to Multilog