Difference between Multimode and Single mode Fiber

An optical fiber is a flexible, transparent fiber that is slightly thicker than a human hair and is constructed of extruded glass or plastic. Optical fibers are most commonly employed to convey light between two ends of a fiber and are widely utilized in fiber-optic communications, where they allow transmission over greater distances and at higher bandwidths than wire connections. A transparent cladding material often covers a transparent core with a reduced index of refraction. The property of total internal reflection keeps light in the core, which causes the fiber to operate as a waveguide.

In general, there are two types of optical fiber: multimode fibers (MMF), which enable many propagation channels or transverse modes, and single mode fibers (SMF), which support only one mode. The primary distinction between multimode and single-mode fiber is that the diameters of the core and cladding in multimode fiber are 50-85 μm and 125-400 μm, respectively. In contrast, the single-mode has core and cladding diameters of 8-12 μm and 125 μm, respectively.

In this article, you will learn the difference between Multimode and Single mode fiber. But before discussing the differences, you must know about Multimode and Single mode fiber with their example.

What is Multimode Fiber?

Multimode fibers were invented before single-mode fibers in the 1960s. It is a form of optical fiber that can carry numerous light beams or modes at the same time, each with a marginally different reflection angle inside the optical fiber core.

Multi-mode fiber is primarily utilized to transmit over relatively shorter distances because the modes are more prone to disperse over longer distances. It is referred to as modal dispersion. The single-mode fiber is another typical form of optical fiber that is utilized for longer distances, and Multi-mode optical fiber is another name for multi-mode fiber.

The core and cladding diameters of multimode fiber are larger than the operational wavelength of the light signal and larger than the single mode. It a contains a core diameter of 50 to 85 μm. For light propagation, a multimode fiber uses a geometrical optic model in which the light ray rebounds back and forth and reflects from the fiber's core cladding. Several rays are sent in the fiber, each of which takes a separate path. Their path eventually corresponds to the fiber mode, and the speed of these rays varies.

High-speed data transmission may not be possible with multimode fibers, and mixing and matching fibers is also not a good idea. Connecting a single-mode fiber to a multi-mode fiber can lead to a 20-dB loss or 99% of total power.

Characteristics of Multimode fiber

There are various characteristics of multimode fiber. Some main characteristics of multimode fiber are as follows:

1. It is easier to terminate.
2. It is the most utilized cable in local area networks today.
3. It has a large core diameter of 50 to 85 μm.
4. It is mostly utilized at shorter distances.
5. Senders and receivers are more economical using the multimode fiber.

What is Single Mode Fiber?

In 1984, single-mode fiber developed after the multimode fiber. It overcomes the limitations of multimode fiber, such as intermodal dispersion, boosts bit rates, and regenerator distance. The core diameter of a single-mode fiber is roughly 8-12 μm, which is a tiny multiple of the operational wavelength of the light signal. Its diameter range causes all of the light ray's energy to move in a single mode. As a result, it only involves a single ray of light.

Chromatic dispersion is a form of dispersion that was introduced by single-mode fiber. The energy of a light signal or pulse has a limited bandwidth. Moreover, the single-mode fiber can generate pulse smearing due to the formation of various propagation speeds of pulse frequency components. It is due to glass's physical qualities. The smearing of the pulse due to chromatic dispersion rises as the pulse spectrum widens, and it ultimately relies on the signal's wavelength.

When a silica-based optical fiber with a 1.3 μm band is utilized, there is no chromatic dispersion problem. However, it causes dispersion in the 1.55 μm band. Dispersion-shifted fiber and DFB (Distributed-Feedback) laser were developed to eliminate chromatic dispersion. The distributed-feedback laser reduces the spectrum of the transmitted pulse near its modulation bandwidth, reducing chromatic dispersion loss.

Characteristics of Single mode fiber

There are various characteristics of single mode fiber. Some main characteristics of single mode fiber are as follows:

1. It has a small core diameter, which comes range between 8-12 μm.
2. It is complex and costly to terminate.
3. It is commonly utilized over long distances.
4. Utilizing the single mode fiber is more expensive for both the sender and receiver.
5. It is commonly utilized cable in wide area networks today.

Key differences between Single Mode and Multimode Fiber

There are various key differences between single mode and multimode fiber. Some of the key differences between single mode and multimode fiber are as follows:

1. The core and cladding diameters of single-mode fiber are 8-10 micrometers and 125 micrometers, respectively. On the other hand, the multi-mode fiber has core and cladding dimensions of 50 to 85 microns and 125 to 400 microns, respectively.
2. The wavelength range of single-mode fiber is 1260 to 1640 nanometers. In comparison, the wavelength of the multimode signal produced by LED is 850 nm to 1300 nm.
3. As single-mode fiber may travel a wide distance of up to 20-40 km, the regenerator is installed between those distances. On the other hand, the multimode fiber covers limited lengths and requires a regenerator every 2 km.
4. Single-mode fiber is mainly utilized in WAN, MAN, and data center applications. In contrast, Multimode fiber is mainly utilized for applications such as LAN and SAN.
5. Single-mode fiber has improved transmission quality with only a little loss. In contrast, multimode fiber utilizes multiple rays for producing interference and attenuation.
6. Multimode fiber has a higher fiber cost than single-mode fiber. On the other hand, multimode fiber has lower installation and connector costs than single-mode fiber.
7. The bandwidth of single-mode optical fiber is almost 400 MHz/km. In comparison, multimode fiber has a lower bandwidth of 50 - 60 MHz/km.
8. Single-mode fibers may be classified as OS1 or OS2, with applications at wavelengths of 1310nm and 1550nm, respectively. In contrast, the most popular varieties of multimode fiber are OM1, OM2, OM3, OM4, and OM5.
9. The TIA-598C establishes the standard of coating for non-military uses in single mode fiber, such as it is coated with a yellow outer sheath. In contrast, the TIA-598C establishes the standard of coating for non-military applications in multimode fiber, such as whether it is coated with an orange or aqua outer sheath depending on the type.
10. Handling or manufacturing a single mode fiber is tough because light coupling becomes more difficult as distance increases. In contrast, multimode fiber is simple to produce and handle.

Head-to-head comparison between Single Mode and Multimode Fiber

Here, you will learn the head-to-head comparisons between single mode and multimode fiber. The main differences between single mode and multimode fiber are as follows:

Conclusion

Single mode fiber is a successor to multimode fiber that eliminates multimode fiber's disadvantages, such as short distance coverage, attenuation issues, high fiber cost, and unnecessary use of regenerators or repeaters. However, multimode fiber is a more cost-effective option for shorter distances due to lower installation and connector costs.