Many friends have been asking related questions about optical fiber when they are wiring. So today we will have a detailed understanding of optical fiber through this article.
1. multi-mode optical fiber
When the geometric size of the optical fiber (mainly the core diameter d1) is much larger than the wavelength of the light wave (about 1µm), there will be dozens or even hundreds of propagation modes in the optical fiber. Different propagation modes have different propagation speeds and phases, resulting in time delays and light pulse broadening after long-distance transmission. This phenomenon is called modal dispersion of optical fiber (also called inter-modal dispersion).
mode dispersion will narrow the bandwidth of multimode optical fiber and reduce its transmission capacity. Therefore, multimode optical fiber is only suitable for smaller capacity optical fiber communication . The refractive index distribution of
multimode optical fiber is mostly parabolic distribution, that is, gradient refractive index distribution. The diameter of its core is about 50µm.
2. single-mode optical fiber
When the geometric size of the optical fiber (mainly the core diameter) can be similar to the wavelength of light, such as the core diameter d1 in the range of 5 to 10µm, the optical fiber only allows one mode (the fundamental mode HE11) to propagate in it, and the remaining higher-order modes are all cut off. Such an optical fiber is called a single-mode optical fiber.
Because it has only one mode of propagation and avoids the problem of mode dispersion, single-mode optical fiber has an extremely wide bandwidth and is especially suitable for large-capacity optical fiber communications. Therefore, to achieve single-mode transmission, the parameters of the optical fiber must meet certain conditions. According to the formula calculation, for the optical fiber with NA=0.12 to achieve single-mode transmission above λ=1.3µm, the radius of the fiber core should be ≤4.2µm, that is, its core diameter d1≤8.4µm.
Since the core diameter of single-mode optical fiber is very small, it imposes more stringent requirements on its manufacturing process.
3. What are the advantages of using optical fiber?
1) The passband of optical fiber is very wide and can theoretically reach 30T.
2) The support length without relay can reach tens to hundreds of kilometers, and the copper wire is only a few hundred meters.
3) is not affected by electromagnetic fields and electromagnetic radiation .
4) Light weight and small size.
5) Optical fiber communication is not electrified and is safe to use in flammable, explosive and other places.
6) The operating environment temperature range is wide.
7) Long service life.
4. How to choose an optical cable?
In addition to the number of fiber cores and fiber types, the selection of optical cables must also select the structure and outer sheath of the optical cable according to the usage environment of the optical cable.
1. When directly burying optical cables for outdoor use, loose-threaded armored optical cables should be used. When used overhead, a loose tube optical cable with a black PE outer sheath with two or more reinforcing ribs can be used.
2. When selecting optical cables for use in buildings, tight-buffer optical cables should be selected and attention should be paid to their flame retardant, toxic and smoke characteristics. Generally, the flame-retardant but smoke-free type (Plenum) or the flammable and non-toxic type (LSZH) can be used in pipelines or forced ventilation areas. The flame-retardant, non-toxic and smoke-free type (Riser) should be used in exposed environments.
3. When laying vertical or horizontal cables in the building, you can use tight-buffered optical cables, distribution optical cables or branch optical cables that are common in the building.
4. Select single-mode and multi-mode optical cable according to network application and optical cable application parameters. Usually indoor and short-distance applications are mainly multi-mode optical cables, and outdoor and long-distance applications are mainly single-mode optical cables.
5. In the connection of optical fiber, how to choose the different applications of fixed connection and movable connection?
The movable connection of optical fiber is realized through optical fiber connector . An active connection point in an optical link is an explicit segmentation interface. When it comes to the choice between movable connections and fixed connections, the advantages of fixed connections are reflected in lower cost and smaller optical loss, but poor flexibility, while the opposite is true for movable connections. When designing the network, it is necessary to flexibly choose the use of active and fixed connections based on the entire link situation to ensure both flexibility and stability, so as to give full play to their respective advantages. The movable connection interface is an important interface for testing, maintenance, and changes. The movable connection is relatively easier to find the fault point in the link than the fixed connection, making it easier to replace faulty components, thereby improving system maintainability and reducing maintenance costs.
6. Optical fiber is getting closer to user terminals. What is the meaning of "fiber to the desktop" and what factors need to be paid attention to in system design?
In the application of horizontal subsystems, the relationship between "fiber to the desktop" and copper cables is complementary and indispensable. Optical fiber has its own unique advantages, such as long transmission distance, stable transmission, not affected by electromagnetic interference , high bandwidth support, and no electromagnetic leakage. These characteristics make optical fiber play an irreplaceable role in some specific environments:
1. When the transmission distance of the information point is greater than 100m, if you choose to use copper cable. It is necessary to add repeater or add network equipment and weak current room, thereby increasing costs and potential faults. This problem can be easily solved using optical fiber.
2. There are a large number of electromagnetic interference sources in specific working environments (such as factories, hospitals, air conditioning rooms, power equipment rooms, etc.). Optical fibers can operate stably in these environments without being affected by electromagnetic interference.
3. There is no electromagnetic leakage in optical fiber. It is very difficult to detect the signal transmitted in the optical fiber. It is a good choice in places with high confidentiality requirements (such as military, R&D, auditing, government and other industries).
4. In environments with high bandwidth requirements, reaching more than 1G, optical fiber is a good choice. The application of
optical fiber is gradually extending from the backbone or computer room to desktop and residential users, which means that more and more users who do not understand the characteristics of optical fiber are beginning to come into contact with optical fiber systems. Therefore, when designing an optical fiber link system and selecting products, you should fully consider the current and future application requirements of the system, use compatible systems and products, facilitate maintenance and management to the greatest extent possible, and adapt to ever-changing actual on-site conditions and user installation needs.
5, can fiber optic connectors be directly terminated on 250µm optical fiber?
cannot. Loose tube optical cable contains bare optical fiber with an outer diameter of 250 µm, which is very small and fragile. It cannot fix the optical fiber, is not enough to support the weight of the optical fiber connector, and is very unsafe. To terminate the connector directly on the optical cable, at least a 900 µm tight tube layer must be used to wrap the 250 µm optical fiber outside, so as to provide protection for the optical fiber and support for the connector. Can
6 and FC connectors be directly connected to SC connectors?
can. These are just different connection methods for two different types of connectors.
If you need to connect them, you must choose a hybrid transfer adapter. Use an FC/SC adapter to connect the FC connectors and SC connectors at both ends respectively. This method requires that the connectors should all be flat ground. If you must connect oblique angle (APC) connectors, you must use the second method to prevent damage.
The second method is to use a hybrid jumper and two connection adapters. Hybrid patch cords use different fiber optic connector types on both ends, and these connectors will be connected to where you need to connect, so that you can use the universal adapter in the patch panel to connect to the system, but it will bring an increase in the attenuation budget of the system.
7. The fixed connection of optical fiber includes mechanical optical fiber splicing and thermal fusion splicing. So what are the selection principles of mechanical optical fiber splicing and thermal fusion splicing?
Mechanical optical fiber splicing, commonly known as optical fiber cold splicing, refers to an optical fiber splicing method that does not require a thermal fusion splicer and uses simple splicing tools and mechanical connection technology to achieve permanent connection of single-core or multi-core optical fibers. In general, when splicing optical fibers with small core numbers and scattered locations, mechanical splicing should be used instead of thermal splicing.
Mechanical optical fiber splicing technology was often used in early engineering practices such as line emergency repairs and small-scale applications in special occasions. In recent years, with the large-scale deployment of fiber-to-the-desktop and fiber-to-the-home (FTTH), people have realized the significance of mechanical fiber splicing as an important fiber splicing method.
For fiber-to-the-desktop and fiber-to-the-home applications that feature a large number of users and dispersed locations, when the user scale reaches a certain level, the construction complexity, construction personnel, and fusion splicers cannot meet the time requirements of users to activate services.Due to its simple operation, short personnel training period, and small equipment investment, mechanical fiber splicing provides the most cost-effective fiber splicing solution for large-scale fiber deployment. For example, in high places in corridors and small spaces, where lighting is insufficient and on-site power supply is inconvenient, mechanical optical fiber splicing provides design, construction and maintenance personnel with a convenient, practical, fast and high-performance optical fiber splicing method.
8. In the fiber-to-the-home system, what are the differences between the requirements for the optical cable connector box and the optical cable connector box used in the outdoor lines of telecom operators?
First of all, in the fiber-to-the-home system, it is necessary to reserve the location of the optical splitter installation and termination, accommodating and protecting the jumpers in and out of the optical splitter in the connector box according to actual needs. Because the actual situation is that the optical splitter may be located in optical cable joint boxes, optical cable transfer boxes, distribution boxes, ODF and other facilities, and terminate and distribute optical cables therein.
Secondly, for residential areas, optical cable connector boxes are more often installed underground, so the requirements for the underground performance of optical cable connector boxes are higher.
In addition, in fiber-to-the-home projects, it may be necessary to consider the entry and exit of a large number of small-core optical cables. The core diameter of
multimode fiber is 50~62.5μm and the outer diameter of cladding is 125μm. The core diameter of single-mode fiber is 8.3μm and the outer diameter of cladding is 125μm. The working wavelengths of optical fibers include short wavelength 0.85μm, long wavelength 1.31μm and 1.55μm. Optical fiber loss generally decreases as the wavelength is lengthened. The loss of 0.85μm is 2.5dB/km, the loss of 1.31μm is 0.35dB/km, and the loss of 1.55μm is 0.20dB/km. This is the lowest loss of optical fiber. The loss of wavelengths above 1.65μm tends to increase. Due to the absorption effect of OHˉ, there are loss peaks in the ranges of 0.90~1.30μm and 1.34~1.52μm, and these two ranges are not fully utilized. Since the 1980s, single-mode optical fiber has tended to be used more often, and the long wavelength 1.31μm has been used first.
multi-mode fiber
multi-mode fiber (Multi Mode Fiber): The central glass core is thicker (50 or 62.5 μm) and can transmit multiple modes of light. However, its inter-modal dispersion is large, which limits the frequency of digital signal transmission, and will become more serious as the distance increases. For example: a 600MB/KM optical fiber only has a bandwidth of 300MB at 2KM. Therefore, the transmission distance of multimode optical fiber is relatively short, generally only a few kilometers.
Single Mode Fiber
Single Mode Fiber: The central glass core is very thin (the core diameter is generally 9 or 10 μm) and can only transmit one mode of light. Therefore, its inter-modal dispersion is very small and is suitable for long-distance communications, but there are still material dispersions and waveguide dispersions. Therefore, single-mode optical fiber has higher requirements for the spectral width and stability of the light source, that is, the spectral width must be narrow and the stability must be good. Later, it was discovered that at the wavelength of 1.31 μm, the material dispersion and waveguide dispersion of single-mode fiber are one positive and one negative, and they are exactly equal in size. This means that at a wavelength of 1.31μm, the total dispersion of single-mode fiber is zero. Judging from the loss characteristics of optical fiber, 1.31μm is exactly a low-loss window for optical fiber. In this way, the 1.31μm wavelength region has become an ideal working window for optical fiber communication, and is also the main working band of , the current practical optical fiber communication system. The main parameters of 1.31μm conventional single-mode fiber are determined by International Telecommunications Union ITU-T in the G652 recommendation, so this fiber is also called G652 fiber .
7. What is the difference between multi-mode optical fiber transceiver and single-mode optical fiber transceiver ?
Price: multi-mode is cheap, single-mode is expensive
Distance: multi-mode is less than 2KM, single-mode It can transmit about 100KM
Wavelength: multi-mode 850/1310NM, single-mode 1310/1550NM
Others are similar
Remarks
Multimode transceiver corresponds to multimode optical fiber. Single mode and single mode correspond to each other and cannot be mixed.
Multi-mode transceivers are currently on the market at low prices. Basically, those around 200 yuan are very good. Enterprise-level transceivers of more than 300 yuan are enough, and the bandwidth is 100Mbps. Compared with the
single-mode transceiver, there are fewer supplies on the market and the price is more expensive. It basically costs about 1,000 yuan each. The bandwidth is 1000Mbps, which is much higher than the multi-mode.
