Fiber optic cables are essential for today's digital communications. With the ability to support superior transmission speeds over longer distances compared to copper cabling, fiber optic cables have become the de facto media for data center links and high-speed connections between spaces, buildings, cities, and regions. But how exactly do fiber optic cables transmit data, and how much can they transmit? Let's take a closer look.
How Do Fiber Optic Cables Work?
Fiber optic cables contain thin glass strands, each encased in a protective coating. These strands are bundled together, surrounded by strength members, and enclosed within an outer jacket. A fiber optic cable can contain one strand or thousands of strands, depending on the required application and number of connections. A single fiber strand is typically 125 microns in diameter, roughly twice the width of a human hair. Within each fiber strand lies a smaller, pure glass core that transmits light pulses at specific wavelengths. These light pulses are encoded with data and launched into the fiber core by transmitters at one end of the fiber cable. These transmitters convert digital data represented by binary code (sequences of 1s and 0s) into corresponding light pulses. The light pulses propagate along the core to receivers at the other ends that decode the light pulses to reconstruct the binary code and return it to digital data.
Light signals also travel in different modes (paths) depending on the fiber optic cable type. Singlemode fiber optic cables have a small 9-micron core that allows light to travel in a single path over long distances using high-power lasers with tight tolerances. On the other hand, multimode fiber optic cables have a larger 50-micron or 62.5-micron core that transmits light pulses in multiple paths using cost-effective vertical cavity surface emitting lasers (VCSELs).
It's important to note that multiple light paths can travel at slightly different speeds in a multimode fiber optic cable, which is referred to as modal dispersion. This causes light pulses to spread out over time, limiting the distance of multimode fiber links. However, since VCSEL transmitters are significantly less expensive than high-power singlemode lasers, multimode fiber optic cable is preferred for shorter-distance applications, such as links between active equipment (switches and servers) in a data center. Understanding the difference between singlemode and multimode fiber is essential so you know how to choose the right fiber optic cables for your specific application and environment.
What Type of Data Does Fiber Optic Cable Transmit?
Since fiber optic cable is strictly a physical media, it can essentially transmit any data type, including text, numeric, tabular, audio, video, images, control information, etc. Data is formatted, authenticated, and routed via communication protocols that determine how the data is structured and transmitted. Hundreds of communication protocols are available for transmitting data, all of which depend on software and hardware within active equipment rather than the fiber cabling itself. Unlike copper cabling that uses metallic conductors, fiber optic cables cannot transmit power such as power over Ethernet (PoE).
The most common communication protocol for transmitting data over fiber optic cable is Ethernet. Widely used in local area networks (LANs), metropolitan area networks (MANs), and wide area networks (WANs) that comprise the Internet, Ethernet transmits various data types using frames. Each Ethernet frame includes unique data source, destination, and size information. Ethernet uses a technology called Carrier Sense, Multiple Access with Collision Detection (CSMA/CD) to transmit these frames, which lets devices know when the network is clear to send and prevents transmitting data simultaneously with other devices to avoid collisions. Ethernet also uses Transmission Control Protocol/Internet Protocol (TCP/IP) to transmit information between networks. TCP/IP encapsulates Ethernet frames in IP packets that contain IP address information to identify networks and devices on the internet. Other communication protocols can also use Ethernet by encapsulating their information into Ethernet frames.
Another common protocol for data transmission over fiber optic cable is InfiniBand, which enables higher bandwidth and lower latency in high-performance computing (HPC) environments like artificial intelligence (AI) environments. Fibre Channel is yet another data transfer protocol that efficiently transmits large amounts of data over fiber optic cables in storage area networks (SANs). It is often encapsulated into Ethernet frames as Fibre Channel over Ethernet (FCoE).
Various other protocols enable network management, security, and control. For example, hypertext transfer protocol (HTTP) and HTTP secure (HTTPs) are used to transmit information between web servers and browsers, and simple network management protocol (SNMP) is used to transmit device management and status information. There are also a variety of control protocols that transmit data between devices and systems to control, monitor, and automate industrial processes. There are even protocols used to transmit data between various automobile systems, such as between a car’s sensor and braking system.
How Much Data Can Fiber Optic Cables Send?
The amount of data fiber optic cables can send depends on the type of fiber, the application, and the active equipment. The terms bandwidth and data rate are often used interchangeably to describe the capability of a fiber optic cable. However, bandwidth is a property of the cable itself, while data rate measures how much data can be transmitted in a given amount of time.
Multimode fiber optic cable bandwidth is expressed as effective modal bandwidth (EMB), which is measured as Megahertz (MHz) per kilometer (km) for a given wavelength. This essentially means that a fiber optic cable with a bandwidth of 500 MHz-km can transmit 500 MHz of data up to one kilometer. Higher frequencies can essentially carry more data over the same distance or the same amount of data over farther distances. The following table shows how the bandwidth capability of multimode fiber optic cables has evolved.
| Multimode Fiber Type | EMB at 850nm |
| OM1 | 200 MHz-km |
| OM2 | 500 MHz-km |
| OM3 | 2000 MHz-km |
| OM4 | 4700 MHz-km |
| OM5 | 4700 MHz-km |
Singlemode fiber optic cable has no limit on modal bandwidth since it only has one mode. However, since bandwidth is limited by the capabilities of the active equipment, singlemode fiber optic systems technically have a bandwidth in the hundreds of GHz range. Transmitting light signals in one mode also allows singlemode fiber optic cable to use multiple wavelengths more effectively. Multimode fiber typically transmits at 850 nm and 1300 nm wavelengths, with the ability to use 880 nm, 910 nm, and 940 nm on OM5 multimode. Singlemode fiber can use several wavelengths ranging from 1270 to 1610 nm.
Data rate, measured in megabits per second (Mb/s) or gigabits per second (Gb/s), is considered the real measurement of how much data a fiber optic cable can transmit. Rather than a property of the fiber itself, data rate depends on the active equipment and its application and signaling rate per lane. Currently, the maximum signaling rate per lane for fiber optic cable is 100 Gb/s. However, higher overall data rates can be achieved using parallel optics technology that transmits data over multiple fibers or wavelength division multiplexing (WDM) technology that transmits data over multiple wavelengths on the same fiber.
At a signal rate per lane of 100 Gb/s, an 8-fiber multimode fiber optic cable can support a data rate of 400 Gb/s, with 4 fibers transmitting at 100 Gb/s and 4 fibers receiving at 100 Gb/s. Using WDM technology, a duplex singlemode fiber optic cable can support 400 Gb/s, with 4 wavelengths transmitting at 100 Gb/s on one fiber and 4 wavelengths receiving at 100 Gb/s on the other. While current industry standards enable up to 800 Gb/s data rates over fiber optic cabling, technology advancements will continue to increase data rates to 1.6 Terabits per second and beyond.
Because singlemode optical fiber cable offers much higher bandwidth than multimode, it can support current data rates over significantly farther distances. For instance, multimode fiber optic cables can support 10 Gb/s to distances of about 550 meters and 400 Gb/s to distances of about 100 meters, while singlemode can support these speeds to 40 kilometers or more.
The good news is that CablesPlus is a premier supplier of all types of multimode and singlemode fiber optic cables that support the data rate and distance you need for your applications—from short multimode data center links to long-distance singlemode fiber links and everything in between. Contact us today for all your fiber optic cable needs.
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