Basic knowledge of optical fiber Part I Optical fiber theory and structure 1. Light and its characteristics: 1. Light is electromagnetic wave, and the wavelength range of visible light is 390~760nm (nanometer).
The part above 760nm is infrared light and the part below 390nm is ultraviolet light. Four kinds of optical fibers are used: 850 nm, 1300 nm, 13 10 nm and 1550 nm.
2. Refraction, reflection and total reflection of light. Because the propagation speed of light in different substances is different, when light is emitted from one substance to another, it will be refracted and reflected at the interface between the two substances.
Moreover, the angle of refracted light will change with the angle of incident light. When the angle of incident light reaches or exceeds a certain angle, the refracted light will disappear and all the incident light will be reflected back, which is the total reflection of light.
Different substances have different refraction angles for light with the same wavelength (that is, different substances have different refractive indexes), and the same substance has different refraction angles for light with different wavelengths. Optical fiber communication is based on the above principle.
2. Optical fiber structure and type: 1. Optical fiber structure: Bare optical fiber is generally divided into three layers: the middle high refractive index glass core (core diameter is generally 50 or 62.5μm), the middle low refractive index Shi Ying glass cladding (diameter is generally 125μm), and the outermost resin cladding is used for reinforcement. 2. Numerical aperture: Not all the light incident on the end face of the optical fiber can be transmitted by the optical fiber, but only the incident light within a certain angle range.
This angle is called the numerical aperture of the optical fiber. The larger numerical aperture of optical fiber is beneficial to the docking of optical fiber.
Optical fibers produced by different manufacturers have different numerical apertures (at & amp； T turn). 3. Types of optical fiber: A. According to the transmission mode of light in optical fiber, it can be divided into single-touch optical fiber and multimode optical fiber.
Multimode optical fiber: The central glass core is thick (50 or 62.5μm), which can transmit multiple modes of light. However, its large intermodal dispersion limits the frequency of transmitting digital signals, and it will become more serious with the increase of distance.
For example, a 600MB/KM optical fiber has only 300MB bandwidth at 2KM. Therefore, the transmission distance of multimode fiber is relatively short, generally only a few kilometers.
Single-mode fiber: The glass core in the center is thin (the core diameter is generally 9 or 10μm) and can only transmit one mode of light. Therefore, its intermodal dispersion is very small, which is suitable for long-distance communication, but its dispersion plays a major role. Therefore, single-mode fiber requires high spectral width and stability of light source, that is, narrow spectral width and good stability.
B according to the optimal transmission frequency window, it can be divided into conventional single-mode fiber and dispersion-shifted single-mode fiber. Conventional type: optical fiber manufacturers optimize the transmission frequency of optical fiber at a single wavelength, such as 1300nm.
Dispersion shift type: optical fiber manufacturers optimize the transmission frequency of optical fiber at two wavelengths, such as 1300nm and 1550nm. C. according to the refractive index distribution, it can be divided into abrupt fiber and graded fiber.
Abrupt type: The refractive index from the central core of the optical fiber to the glass cladding is abrupt. It has low cost and high dispersion between modules.
Suitable for short-distance low-speed communication, such as industrial control. However, due to the small dispersion between modes, single-mode fibers are all abrupt.
Graded fiber: the refractive index decreases gradually from the central core of the fiber to the glass cladding, which can make the high-mode light propagate in sinusoidal form, reduce the intermodal dispersion, increase the bandwidth of the fiber and increase the transmission distance, but the cost is higher. Nowadays, multimode fibers are mostly graded fibers. 4. Common optical fiber specifications: single mode: 8/ 125μ m, 9/ 125μ m, 1125μ m, multimode: 50/ 125μm, European standard: 62. Optical fiber manufacturing: At present, optical fiber manufacturing methods mainly include: in-tube CVD (chemical vapor deposition), in-rod CVD, PCVD (plasma chemical vapor deposition) and VAD (axial vapor deposition).
2. Optical fiber attenuation: The main factors causing optical fiber attenuation are intrinsic, bending, extrusion, impurities, unevenness and butt joint. Inherent: it is the inherent loss of optical fiber, including Rayleigh scattering and inherent absorption.
Bending: when the optical fiber is bent, some light in the optical fiber will be lost due to scattering, resulting in loss. Squeeze: Loss caused by slight bending of optical fiber when squeezed.
Impurity: Loss caused by absorption and scattering of light propagating in optical fiber by impurities in optical fiber. Non-uniformity: Loss caused by non-uniform refractive index of optical fiber materials.
Butt joint: Losses caused by fiber butt joint, such as: different axes (the coaxiality of single-mode fiber is required to be less than 0.8μm), the end face is not perpendicular to the axis, the end face is uneven, the butt joint diameter is not matched, and the welding quality is poor. Advantages of optical fiber: 1, the passband of optical fiber is very wide. Theoretically it can reach 3 billion MHz.
2. The road section without relay is long, tens to 100 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. For example, 900 pairs of twisted-pair 2 1 thousand telephone lines have a diameter of 3 inches and a weight of 8 tons/km.
Optical cable with ten times the traffic, with a diameter of 0.5 inch and a weight of 450P/KM. 5, optical fiber communication is not charged, safe to use, and can be used in flammable and explosive places.
6, the use of a wide range of environmental temperatures. 7, chemical corrosion, long service life.
Part ii optical cable 1. Manufacturing of optical cable: The manufacturing process of optical cable is generally divided into the following procedures: 1. Screening of optical fibers: Select optical fibers with excellent transmission characteristics and qualified tension. 2. Optical fiber dyeing: standard full chromatography should be used for identification, and it is required not to fade or migrate at high temperature.
3. Secondary extrusion: select plastics with high elastic modulus and low linear expansion coefficient, extrude them into pipes with certain size, add moisture-proof and waterproof gel into the optical fiber, and finally store them for several days (not less than two days). 4. Stranding of optical cable: A plurality of extruded optical fibers are stranded with the reinforcement unit.
5. Squeeze the outer sheath of the optical cable: add a sheath to the stranded optical cable. 2. Optical cable type: 1. According to the laying methods, there are: self-supporting aerial cable, pipeline optical cable, armored underground optical cable and submarine optical cable.
2. According to the structure of optical cables, there are bundled optical cables, stranded optical cables, tight optical cables, ribbon optical cables, nonmetallic optical cables and branched optical cables. 3. According to the use, there are: long-distance communication optical cable, short-distance outdoor optical cable, hybrid optical cable and building optical cable.
3. Optical cable construction: Over the years, we have gained a set of mature methods and experiences by doing optical cable construction. (1) optical cable.
2. Introduction of optical fiber interface
Optical fiber can be divided into single mode (conducting long wavelength laser) and multimode (conducting short wavelength laser) according to the different internal light waves. The connection distance of single-mode optical cable can reach 10 km, and the connection distance of multimode optical cable is much shorter, which is 300 meters or 500 meters (mainly depending on the laser, there are generally two kinds of light sources that generate short-wavelength laser, one is 62.5 meters and the other is 50 meters).
According to the difference of optical cable connector, optical fiber can be divided into SC interface and LC interface. SC interface is 1GB interface, (sc = * * artcard) LC interface is 2GB interface, (LC = lucent connector).
Judging single mode and multimode of optical port
1. passes through the marked center wavelength. The central wavelength of 850nm is multimode, and 13 10nm or 1550nm is single mode.
2. Activate the transmitter of the optical port and quickly check whether the transmitter emits red light. If there is, it is a multimode port, otherwise it is a single-mode port.
Optical fiber classification
Single-mode fiber and multimode fiber. The inner core fiber diameter of single-mode fiber is smaller than that of multimode fiber.
There are two kinds of central high refractive index glass core diameters of multimode fiber: 62.5μm and 50 μ m.
There are three kinds of central high refractive index glass core diameters of single-mode fiber: 8μm, 9μm and10 μ m.
Under the same conditions, the smaller the fiber diameter, the smaller the attenuation and the farther the transmission distance. The transmission power of multi-mode port is smaller than that of single-mode port, which is directly related to the model of GBIC or SFP, generally between -9.5dBm and -4dBm; Generally, the range of single-mode optical ports is about 0dBm, and some ultra-long-distance interfaces will be as high as +5dBm.
Received power range
The receiving power of multimode port is generally between -20dBm and 0dBm; Single mode is between -23 dBm and 0dBm.
The maximum acceptable power is called overload optical power, and the minimum acceptable power is called receiving sensitivity.
In engineering, it is required that the normal working received optical power is less than the overload optical power by 3-5dBm and greater than the receiving sensitivity by 3-5dBm. Generally speaking, the actual received power is between -5 and-15dBm for both single-mode and multimode interfaces, which is a reasonable working range. Generally support hot plug.
Gbic gigabit rate interface converter, the optical fiber interface used is mostly SC or ST type.
SFP small package GBIC, the optical fiber used is LC type. Single mode: SM, wavelength 13 10 Single mode long-distance LH wavelength 13 10, 1550.
Multimode: millimeter wavelength 850 1300
SX/ left indicates the connector model that can use the front "/"of multimode or single-mode fiber to indicate the pigtail.
"SC" joint is a standard square joint, which is made of engineering plastics and has the advantages of high temperature resistance and difficult oxidation. SC connectors are usually used for optical interfaces on the transmission equipment side.
The shape of "LC" joint is similar to that of SC joint, but smaller than that of SC joint. "FC" connector is a metal connector, which is generally used on the ODF side. Metal connectors are plugged and unplugged more often than plastic connectors. We can often see "FC/PC", "SC/PC" and so on on the label of pigtail connector. The FC circular SC square headband is threaded (most commonly used on distribution frames) and directly connected to the SFP module of the equipment.
ST- clip circle
Grinding and polishing of PC microspheres
The angle of APC is 8 degrees and polished with microspheres.
SC card type (most commonly used in router switches)
MT-RJ is square with two optical fibers at one end (useful on Huawei 8850)
3. Broadband installation of popular science knowledge, broadband is divided into several types.
1, ADSL: provides broadband data transmission, that is, electrical signal transmission, through copper twisted pair (that is, ordinary telephone line);
2. Cities at the speed of light: A. FTTB (PON+LAN \ PON+AD) with optical fiber access to buildings B. FTTH with optical fiber to the home (compared with traditional ADSL, the broadband speed is greatly improved).
3.FTTX+LAN: realize Gigabit optical fiber to the center switch of the community (building). The central switch and corridor switch are connected by 100 Mbps optical fiber or five kinds of network cables, and the corridor adopts integrated wiring (that is, users often use network cables to enter the home).
4. Optical fiber dedicated line: Optical fiber is used as information transmission medium to provide high-speed Internet access service with fixed IP address and symmetrical upstream and downstream network speeds.
4. What is the knowledge of optical fiber access network?
From the perspective of the whole telecommunication network, the whole network can be divided into two parts: public network and customer end network (CPN), in which CPN belongs to users, so the telecommunication network in the usual sense refers to public telecommunication network.
Public telecommunication network can be divided into three parts: long-distance network, relay network and optical fiber access network. The combination of long-distance network and trunk network is called core network.
Compared with the core network, the optical fiber access network is between the local exchange and the users, and mainly completes the task of enabling users to access the core network. The access network consists of a series of transmission devices between the service node interface (SNI) and the user network interface (UNI). In recent years, the new technological revolution represented by the Internet is profoundly changing the traditional telecom concept and architecture. With the gradual opening of the optical fiber access network market in various countries, the relaxation of telecommunications control policies, the increasing and expanding competition, the rapid emergence of new business needs, and the development of wired technology (including optical fiber technology) and wireless technology, optical fiber access network has begun to become the focus of attention.
Driven by the huge market potential, various optical fiber access network technologies came into being. Optical fiber communication has the advantages of large communication capacity, high quality, stable performance, anti-electromagnetic interference and strong confidentiality.
Optical fiber plays an important role in trunk communication, and in optical fiber access network, optical fiber access network will also become the focus of development. Optical fiber access network is a long-term solution to develop broadband access.
1. The basic structure of optical fiber access network (OAN) refers to the information transmission function of optical fiber access network with optical fiber as the main transmission medium. It is connected with service nodes through optical line terminals (OLT) and users through optical network units (ONU).
Optical fiber access network includes remote equipment-optical network unit and local equipment-optical line terminal, which are connected by transmission equipment. The main components of the system are OLT and remote ONU.
They complete the signaling protocol conversion from service node interface (SNI) to user network interface (UNI) in the whole access network. Access devices themselves have networking capabilities and can form various network topologies.
At the same time, the access equipment also has the functions of local maintenance and remote centralized monitoring, and forms a maintenance management network through transparent optical transmission, and is brought into the unified management of the network management center through corresponding network management protocols. The function of OLT is to provide the interface between access network and local exchange, and to communicate with users' optical network units through optical transmission.
It completely separates the switching function of the switch from the user optical fiber access network. Optical line terminals provide maintenance and monitoring for themselves and users. It can be placed directly in the exchange office of the local exchange or at the remote end.
The role of ONU is to provide user interface for access network. It can access a variety of user terminals and has photoelectric conversion function and corresponding maintenance and monitoring function.
The main function of ONU is to terminate optical fiber from OLT, process optical signals, and provide business interfaces for many small businesses, commercial users and residential users. The network end of ONU is an optical interface, and the user end is an electrical interface.
Therefore, ONU has optical/electrical and electrical/optical conversion functions. It also has the functions of voice digital-to-analog and analog-to-digital conversion.
ONU is usually placed near users, and its location has great flexibility. Optical fiber access network (OAN) can be divided into two types: active optical network (AON) and passive optical network (PON).
Second, active optical fiber access networks Active optical networks can be divided into AON based on SDH and AON based on PDH. Local equipment (CE) and remote equipment (RE) of active optical network are connected through active optical transmission equipment. Transmission technologies are SDH and PDH, which have been widely used in backbone networks, but mainly SDH technology. This paper mainly discusses SDH (Synchronous Optical Network) system.
The concept of SDH is an active optical network based on SDH, which was first proposed by Bell Communication Research Institute in the United States in 1985, and is called Synchronous Optical Network (SO). It consists of a set of hierarchical standard transmission structures, and is suitable for transmitting various adaptive payloads (that is, the part of the network node interface bitstream that can be used for telecommunications services) on physical media such as optical fiber, microwave and satellite.
This standard became the new standard of 1986 American digital system. CCITT, the predecessor of ITU-T, accepted the concept of SO in 1988, and reached an agreement with American Standards Institute (ANSI). After modification, it changed its name to synchronous digital hierarchy (SDH), making it a general technical system suitable for optical fiber, microwave and satellite transmission.
SDH network is a revolution to the original PDH (Quasi-synchronous digital hierarchy) network. PDH is asynchronous multiplexing. When any network node receives a low-speed branch signal, the optical fiber access network must go through the processes of multiplexing, code conversion, code speed adjustment, timing, scrambling and descrambling. Moreover, PDH only stipulates the electrical interface, but there is no unified regulation on the line system and optical interface, so it is impossible to establish the global information network.
With the introduction of SDH technology, the transmission system not only has the function of providing the physical process of signal propagation, but also has the function of signal processing and monitoring. SDH can support services of various circuit layers, such as asynchronous digital series with various rates, DQDB, FDDI, ATM, etc. , as well as various new services that may appear in the future, through the definitions of various containers C and virtual containers VC and the cascaded multi-frame structure.
A large number of backup channels in section overhead enhance the scalability of SDH network. Through software control, the original manual wiring change method in PDH is used to realize cross connection and add-drop multiplexing connection, which provides flexible uplink/downlink circuit capability, makes the network topology dynamically variable, enhances the flexibility and security of the network to adapt to business development, and can realize the circuit protection, height and optimal utilization of communication capability in a larger geometric range, thus laying a foundation for strengthening networking capability and re-establishing the network in just a few seconds.
In particular, SDH self-healing ring can recover quickly within tens of milliseconds after the circuit fails. These advantages of SDH make it the basic transmission network of broadband service digital network.
5. There are several obvious development stages of optical fiber connectors in network common sense.
There are two obvious development stages of optical fiber connectors: the first stage: in order to save space and develop to miniaturization, optical fiber connectors have developed from traditional FC, st, SC and SC to LC, MTRJ and E2000. The second stage: In order to save space and meet the requirements of multi-core use, optical fiber connectors have developed from LC, MTRJ and E2000 to MU and MTP/MPO, and now there is MTP.
In the second stage, the benefits of this development are obvious. Just look at the requirements of 40G and 100G for optical fiber network transmission specifications, that is, multi-core transmission, that is, 8 cores or 20 cores. In this way, MPO/MTP can meet the requirements of high-speed network applications in a small space.
However, it also brings great challenges, even impossible tasks, to engineers working in the field. Of course, there is a good substitute now, that is, the factory's pre-connected system products.
6. How to clean 6. LC optical fiber connector?
Tips for cleaning optical fiber connectors
1. Why not use cotton balls dipped in alcohol to clean the light connector? The cleaning requirements of optical fiber connectors are much higher than those of camera lenses. The fiber of cotton or lens paper is thick, which is easy to cause the wear of optical fiber joints. Cotton balls or lens paper are no longer used to clean optical fiber connectors abroad. For optical fiber testing instruments, it is forbidden to clean optical fiber connectors with cotton balls or lens paper.
2. Why use OAM fiber connector cleaner? OAM fiber interface cleaning agent is a high-tech product developed by OMA company in the United States, which is used to clean various fiber interfaces in optical fiber communication transmission networks. Its function can make the return loss of optical signal as small as hundreds of thousands or even one millionth. OAM fiber interface cleaner adopts alcohol-free special fiber, which has the following advantages:
(1) Safe and reliable: Compared with traditional cleaning methods such as alcohol, ether, cotton balls or lens paper, the unique design structure and material selection make each cleaning achieve ideal results. No adverse effects on the environment and operators. Can effectively prevent the fire caused by alcohol and ethanol.
(2) Easy to use: you don't need to carry many other traditional items at work, just wipe it gently, and the dust and grease at the optical fiber connection interface will be removed.
(3) Economical and practical: adopting new design structure and patented product materials greatly reduces the production cost. Commodity prices are only a fraction of similar imported products. Each cleaning belt can clean more than 500 optical fiber interfaces, and the cleaning belt in the cleaner can be replaced.
(4) Wide application: it can be used not only for optical experimental research units, but also for the construction and maintenance of indoor and outdoor optical fiber communication, as well as the quality assurance and matching of optical fiber equipment and components suppliers.
(5) Strong applicability: it can be used for various types of optical fiber interfaces such as SC, FC, LC, ST, D4 and DIN.
3. How to use 3.OAM fiber connector cleaner? ? Push open the pull button at the upper end of the optical fiber interface cleaner, put the contaminated optical fiber connector into one of the cleaning grooves, and gently wipe it. ? After the initial cleaning, in order to ensure the cleaning effect, the connector can be put into another cleaning tank for cleaning again. ? After cleaning, release the button and it will automatically close. Use it again and again like this.
4. Why use compressed gas dust collector? Compressed gas dust collector, also known as "air brush", is especially suitable for occasions where conventional dust removal methods are not effective, and can safely and quickly remove dust, fiber scraps, metal ions and other pollutants on the surfaces of precision electronic and optical instruments. This product is widely used for dust removal and maintenance of various optical fiber communication, printed circuit boards, electronic instruments, optical instruments, electronic computers, intelligent equipment, communication equipment, audio-visual equipment, medical equipment, advanced cameras and video cameras. This product has flexible dust removal, which is safe and harmless.
5. How to use the compressed gas dust collector? ? Hand-held compressed gas dust collector, the tank body is upright, 5- 10cm away from the object to be cleaned, pull open the safety plate on the upper part of the actuator, and frequently press the actuator for purging for a short time. For hard-to-reach parts, please use an extension tube. ? Do not shake or tilt the water tank when using. This will cause the compressed gas in the tank to flow out in the form of liquid, which may frostbite the skin or damage the glass products. ? Continuous use of compressed gas dust collector will lead to the decrease of purging force, but it will return to normal after a period of time.
? Please use the compressed gas dust collector in a ventilated environment. ? The compressed gas dust collector is a pressure vessel, which shall not be close to the fire source, pry, knock or prick. It shall be placed in an environment below 50℃ and out of the reach of children.
7. What are the common fiber interface types?
SC square plug-in
FC circular spiral nozzle
ST round t-head
Several common optical fiber connectors in network engineering are described in detail:
① FC-type optical fiber connector: the external strengthening method is metal sleeve, and the fastening method is turnbuckle. Usually used on ODF side (most commonly used in distribution frame)
(2) SC-type optical fiber connector: The connector connected with GBIC optical module is a rectangular shell, and the fastening method is plug-in plug-in type, without rotation. (most commonly used in router switches)
③ ST-type optical fiber connector: commonly used for fastening optical fiber distribution frame, round shell and turnbuckle. (For 10Base-F connection, the connector is usually ST type. Usually used in fiber distribution frames)
④ LC-type optical fiber connector: The connector connected with SFP module adopts modular jack (RJ) locking mechanism, which is convenient to operate. (commonly used by routers)
⑤ MT-RJ: Square optical fiber connector with integrated transceiver, with dual optical fiber transceivers at one end.