Fiber optic cables are strands of extremely thin glass or plastic that are used to transmit data at high speeds. They are often used in long-distance telephone and internet connections. Fiber optic cables are much faster and more reliable than traditional copper cables. There are two main types of fiber optic cables: single mode and multimode.
Single Mode Fibers
A single-mode fiber is an optical fiber designed to carry only a single ray or mode of light. These fibers have a very small core, typically just a few microns in diameter, which allows only a single mode of light to propagate. This makes single-mode fibers ideal for long-distance communications, as they can carry signals over great distances with very little loss.
Single-mode fibers are also used in applications requiring high precision, such as fiber optic gyroscopes and interferometers. In these devices, the small core of the single-mode fiber ensures that the light remains highly focused, which is essential for accurate measurements.
While single-mode fibers are very efficient at carrying light over long distances, they are also more challenging to work with than other types of optical fibers. This is because the small core of the fiber makes it difficult to splice and connect. As a result, single-mode fibers are typically used in applications where the fiber will not need to be frequently spliced or connected, such as in long-haul telecommunications networks.
There are two types of single-mode fiber optic cables: OS1 and OS2. OS1 is designed for long-haul, high-bandwidth applications such as data centers and enterprise networks. OS2 is designed for shorter distances and lower bandwidths.
OS1 fiber is made from pure silica glass and has a core diameter of eight to ten microns. It has a very low attenuation rate, making it ideal for long-distance applications. OS1 fiber is also very resistant to temperature changes and can operate in a wide range of temperatures (-40 to +85 degrees Celsius).
OS2 fiber is made from silica-based glass and has a core diameter of nine to ten microns. It has a lower attenuation rate than OS1 fiber but is not as resistant to temperature changes. OS2 fiber can operate in a range of -20 to +70 degrees Celsius.
Multimode Fibers
Multimode fibers are optical fibers designed to support multiple light modes. They are typically used in short-distance applications such as gigabit Ethernet and fiber-to-the-home (FTTH) connections.
Multimode fibers have a larger core diameter than single-mode fibers, which allows them to pass multiple propagation paths for light. This results in a higher bandwidth than single-mode fibers but also a higher attenuation rate. Multiple modes results in a major distance limiting disadvantaging factor called modal dispersion. The primary advantage of choosing multimode fiber is that very low-cost Vertical Cavity Surface Emitting Laser (VCSEL) multimode optical transceivers may be used. Most VCSEL sources transmit at 850nm.
Multimode fibers are typically used in applications where transmission distance is not as critical, such as intra-datacenter connectivity. They are also often used in fiber-to-the-home (FTTH) applications, as they are less expensive to manufacture than single-mode fibers.
Dating back to the 1970s multimode fibers had a 62.5 micron core inside a 125 micron cladding (62.5/125 now referred to as OM1). As higher speeds were required, 50/125 micron multimode fibers were developed, the first is referred to as OM2. Higher and higher bandwidth multimode fibers have since been developed including: OM3, OM4 and OM5.
Final Thoughts
There are two types of fiber optic cables: single mode and multimode. Single-mode cables are very low loss and support transmission of a single mode of light. Multimode cables, with their large core size allow multiple modes of light. Single-mode cables are typically used for long-distance communication, while multimode cables are used for shorter distances.
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