Fiber optic cable can be divided into several types. Usually we see single-mode and multimode fiber types available on the market. Multimode fibers are described by their core and cladding diameters. The diameter of the multi-mode fiber is either 50/125 µm or 62.5/125 µm. At present, there are four commonly used OM (multimode) fibers: OM1, OM2, OM3 and OM4. Each type of them has different characteristics. The article will compare these four kinds of fibers from history,the side of core size, bandwidth, data rate, distance, color and optical source in details.
The picture above shows the development of OM multimode fibers. The Lime Green OM5 fibers are newly released and sure to be the mainstream transmission media in the near future.
specification of OM1, OM2, OM3 and OM4
Multimode fiber is provided with the core diameter from 50 µm to 100 µm. Apart from OM1 with a core size of 62.5 µm, other three types are all using the 50 µm. The thick core size makes them able to carry different light waves along numerous paths without modal dispersion limitation. Nevertheless, in the long cable distance, multiple paths of light can cause signal distortion at the receiving end, resulting in an unclear and incomplete data transmission. And this is why all the types of multimode fiber can only be used for short distance.
Bandwidth is the bit-rate of available or consumed information capacity expressed typically in metric multiples of bits per second. The higher bandwidth is, the faster transmission speed can be. According to overfilled launch (OFL) and effective modal bandwidth (EMB) measurements, OM1 and OM2 fibers can only support OFL, but OM3 and OM4 are able to support both measurements. At the wavelengths of 850/1300 nm under OFL, the respective bandwidth of OM1, OM2, OM3, OM4 is 200/500 MHz*km, 500/500 MHz*km, 1500/500 MHz*km and 3500/500 MHz*km. And at the wavelength of 850 nm under EMB, the bandwidth of OM3 is 2000 MHz*km and OM4 even reaches 4700 MHz*km.
Data rate is a technical term that describes how quickly information can be exchanged between electronic devices. With a higher data rate, the transmission can be more effective. OM1 and OM2 support the Ethernet standards from 100BASE to 10GBASE with a minimum data rate of 100 Mbps and a maximum data rate of 10 Gbps. Compare with OM1 and OM2, OM3 fibers and OM4 fibers are enhanced to support much higher data rates of 40 Gbps and 100Gbps in 40G and 100G Ethernet.
Multimode fiber is typically used for short distance transmission. But the maximum reaches are varied in different multimode fiber types. Also, on account of different data rates, the transmitting distances are different. However, the common feature is that OM1 always supports the shortest distance yet OM4 supports the longest. For instance, based on the same data rate of 10 Gbps, the maximum reach of OM1 is 33 m, OM2 is 82 m, OM3 is 300 m and OM4 is 550 m. Thus, if a medium-sized transmission is required, OM3 and OM4 fibers are the best choices.
Color & Optical Source
The outer jacket can also be a method to distinguish OM1, OM2 from OM3, OM4. The common jacket color of OM1 and OM2 is orange, and OM3, OM4 are in aqua. In addition, OM1 and OM2 are using a light-emitting diodes (LEDs) optical source but OM3 and OM4 adopt the vertical-cavity surface-emitting laser (VCSELs) optical source.
color and optical source of OM1, OM2, OM3 and OM4
OM1 fibers and OM2 fibers are widely employed for short-haul networks, local area networks (LANs) and private networks. OM3 is applied to a larger private networks. Different from the previous multimode types, OM4 is more advanced to be used for high-speed networks in data centers, financial centers and corporate campuses.
It is very important to choose the right fiber type for your application. Future-proofing network design is crucial for network planning, but there is often a cost for that speed. With a higher performance, OM3 fibers and OM4 fibers are definitely more expensive than OM1 and OM2 fibers . So plan well and spend wisely.
1.What is singlemode and multimode fiber? What is the difference between them?
The concept of single-mode and multi-mode is to classify fibers according to the propagation mode—the concept of multi-mode fiber and single-mode fiber propagation mode. We know that light is an extremely high-frequency (3×1014Hz) electromagnetic wave. When it propagates in an optical fiber, it is found from theories of wave optics, electromagnetic fields, and Maxwell equations.
When the fiber core has a geometric dimension much larger than the wavelength of the light, the light will propagate in the fiber in dozens or even hundreds of propagation modes, such as TMmn mode, TEmn mode, HEmn mode, etc. (where m, n=0, 1, 2, 3, …).
Among them, the HE11 mode is called the basic mode, and the rest are all called high-order modes.
When the fiber’s geometric size (mainly the core diameter d1) is far greater than the wavelength of light (about 1μm), there will be dozens or even hundreds of propagation modes in the fiber. Different propagation modes have different propagation speeds and phases, resulting in delays and widening light pulses after long-distance transmission. This phenomenon is called the modal dispersion of the fiber (also called inter-modal dispersion).
Mode dispersion can narrow the bandwidth of multimode fiber and reduce its transmission capacity. Therefore, multimode fiber is only suitable for smaller-capacity fiber communication.
The refractive index distribution of a multimode fiber is mostly a parabolic distribution, ie, a graded index profile. Its core diameter is about 50μm.
When the fiber’s geometry (mainly the core diameter) can be similar to the wavelength of light, if the core diameter d1 is in the range of 5~10μm, the fiber only allows one mode (base mode HE11) to propagate in it, and all other high-order modes are all cut off. This kind of fiber is called single-mode fiber.
Since it only has one mode to propagate and avoids the problem of mode dispersion, single-mode fiber has a very wide bandwidth and is particularly suitable for large-capacity optical fiber communications. Therefore, in order to achieve single-mode transmission, the parameters of the fiber must satisfy certain conditions. Through formulae calculations, for a fiber with NA=0.12, single-mode transmission above λ=1.3 μm, the radius of the fiber core should be ≤ 4.2 μm, ie its core diameter d1 ≤ 8.4 μm.
Because the core diameter of a singlemode fiber is very small, more stringent requirements are imposed on its manufacturing process.
2.What are the advantages of using optical fiber?
1) The passband of the fiber is very wide and the theory can reach 30T.
2) The length of non-relay support is up to tens to hundreds of kilometers, and the copper wire is only a few hundred meters.
3) Not affected by electromagnetic fields and electromagnetic radiation.
4) Light weight and small size.
5) Optical fiber communication is not powered, and the use of safety can be used in flammable, volatile and other places.
6) The use of a wide range of ambient temperatures.
7) Long service life.
3.how to choose the optical cable?
In addition to selecting the number of optical fiber cores and optical fibers, the optical cable must be selected according to the use environment of the optical cable to select the structure of the optical cable and the outer sheath.
1) Optical cable for outdoor use When loosely buried, it is better to use loose-sheathed cable. When overhead, a loose PE cable with a black PE sheath with two or more ribs can be used.
2) Optical fiber cables used in buildings should use tight-fitting optical cables and pay attention to their fire-retardant, toxic and smoke characteristics. The type of flame-retardant but smoke (Plenum) or flammable and non-toxic type (LSZH) can be used in the pipeline or in forced ventilation. The type of flame-retardant, non-toxic and non-smoking (Riser) should be used in the exposed environment.
3) When vertical or horizontal cabling is installed in a building, it can be used when using tight-fit optical cable, distribution optical cable or branch optical cable that are common in the building.
4) Select single-mode and multi-mode optical cables based on network applications and optical cable application parameters. Usually, indoor and short-distance applications use multimode optical cables, while outdoor and long-distance applications use single-mode optical cables.
4.In the connection of optical fibers, how to choose different applications of fixed connection and active connection?
The active connection of the fiber is achieved through a fiber optic connector. An active connection point in the optical link is a clear split interface. In the choice of active connection and fixed connection, the advantages of fixed connection are reflected in lower cost, light loss, but less flexibility, and the active connection is the opposite. When designing the network, it is necessary to flexibly select the use of activities and fixed connections according to the entire link situation to ensure flexibility and stability, so as to give full play to their respective advantages. The active connection interface is an important test, maintenance, and change interface. The active connection is relatively easy to find the fault point in the link than the fixed connection, which increases the convenience of replacement of the faulty device, thereby improving system maintenance and reducing maintenance costs.
5.Fibers are getting closer to user terminals. What do you need to pay attention to when it comes to the meaning of “fiber to the desktop” and system design?
“Fiber-to-the-desktop” in the application of the horizontal subsystem, and the relationship between copper and copper cable is complementary and indispensable. Optical fiber has its unique advantages, such as long transmission distance, stable transmission, free from electromagnetic interference, high support bandwidth, and no electromagnetic leakage. These characteristics make the optical fiber play an irreplaceable role in some specific environments:
1) If the information point transmission distance is greater than 100m, if you choose to use copper cable. Replicators must be added or network equipment and weak rooms must be added to increase costs and hidden troubles. Using fiber can easily solve this problem.
2) There are a large number of sources of electromagnetic interference in specific work environments (such as factories, hospitals, air-conditioning rooms, power equipment rooms, etc.), and optical fibers can be operated stably without electromagnetic interference in these environments.
3) There is no electromagnetic leakage in the fiber. It is very difficult to detect the signal transmitted in the fiber. It is a good choice for places where the security level is relatively high (such as military, R&D, auditing, government, etc.).
4) The environment with high demand for bandwidth has reached more than 1G. Optical fiber is a good choice.
There are many differences between single-mode fiber and multi-mode fiber, and the selection method is not the same. Let’s talk about it today. For more details, please keep an eye on Singlemode fiber and multimode fiber different and selection method(2).
It is well known that optical fibers can be classified into single-mode fibers and multi-mode fibers depending on the modulus of the transmission point. The core of a singlemode fiber is relatively thin, and the transmission frequency bandwidth, capacity, and transmission distance are long, but because it requires a laser source, higher cost. Multimode fiber such as Multimode attenuator、Multimode copper cable、OM1/OM2 Multimode PVC jack、Multimode indoor cable、Multimode MPO Cassette etc.
As fiber deployment has become mainstream, Multimode fiber has attracted much attention, currently Russian and Finnish researchers collaborate on a proof-of-concept program to further expand the use of multimode fibers with larger core diameters; researchers use high-power lasers and anisotropic materials and expect to develop optical transmissions Maintain coherence of the fiber. Maintaining the coherence of light is a necessary condition for realizing quantum computers and sensor networks. It also helps multimode fibers to replace expensive singlemode fibers in more remote communications applications.
Optical fiber is the backbone of modern communications. Singlemode fiber dominates long distance applications because of its reliability; however,This fiber has an internal diameter of only 10 micrometers (us) and is very expensive. The lower cost multimode fiber has an inner diameter of 100us, which is currently used for short-distance communication. Generally, it supports distances of 1,000 meters and 1-Gbit/s transmission speed.
Fig. 1: Lateral distribution of light radiation intensity in the output beam (Data source: MIPT)
Fibers that can maintain coherence are more advantageous than semiconductor sensors because they require little power. The result comes from the inability of distributed sensor systems to function. In addition, these fibers can be used not only in high-power laser systems, but also as sensors because changes in polarization characteristics result from changes in the environment that they sense accurately.
Protecting optical fibers has advantages over semiconductor sensors because they require little power and can handle,The result of a distributed sensor system. Not only can they be used in high power laser systems, but the use as sensors comes from the observed fact that changes in their polarization properties make it possible to accurately sense the changes caused by environmental factors.
Figure 2: The figure shows the diameter of the outer protective layer along the length of the three tapered fibers (left side) and its core diameter (right side). illustration A cross-section of an anisotropic fiber structure is shown; the fiber is composed of a core, an oval inner protective layer and an outer protective layer. (Data Source: MIPT)
Fiber lasers use optical resonators to reflect light back and forth, thereby causing lasers. At present, this laser is only finished
Using the basic mode (upper left in Figure 1), the power is limited to the 10 nm fiber capacity. Increasing the transmission power of large lasers leads to uncontrolled variations in the refractive index of the fiber, causing parasitic nonlinear effects. The solution adopted by Russian and Finnish researchers was to change the core and the inner protective layer (Figure 2). Russian and Finnish researchers have used this technique to confirm the concept that less than 1% of the energy transmitted through high-power lasers is lost in the 100us fiber. Researchers have completely preserved the polarization properties of optical fibers by creating an internal protective layer for the anisotropic properties of large optical fibers (indicating that they propagate only in the length direction because the internal protective layer is oval).
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