The fiber has become a major means, installation and maintenance of fibers that are long-distance wired signal transmission. The theoretical knowledge involved in the fiber, the components and layout points are a lot, and we have made some cards here.
Three kinds of light
Not all light can be used for signal communication in the fiber. The light of three wavelengths is mainly used in the light: 850 nm, 1300 nm, 1550 nm.
Where is it?
The optical wavelength of the single mode fiber is 1310 nm or 1550 nm, and the optical wavelength used in the multimode fiber is 850 nm.
Single mode and multi-mode difference
• The central glass core of the multimode fiber is coarse (50 or 62.5 μm), which can be transmitted in multiple modes. However, its die dispersion is large, which limits the frequency of transmitting digital signals, so the distance of multimode fiber transmission is relatively close, usually only a few kilometers.
• Single mode fiber center glass core is very fine (the core diameter is typically 9 or 10 μm), which can only pass one mode. Therefore, its die dispersion is small and is suitable for remote communication.
Line skin color
A simpler distinction method is that the multimode fiber outer skin is orange, and the single mode fiber outer skin is yellow.
Dispersion and loss
In a single mode fiber, 1310 nm light has a minimum dispersion, and 1550 Nm light has a minimum loss.
Therefore, what is the specific loss?
1310 nm: 0.35 ~ 0.5 dB / km
1550 nm: 0.2 ~ 0.3 dB / km
850 nm: 2.3 ~ 3.4 dB / km
The enemy of the optical signal is too much
Light loss is one of the reasons why the fiber signal is attenuated. In addition, scattering, absorption, etc. can also cause an optical fiber signal attenuation.
Reasons for light loss
• Natural loss of light
• Insertion loss inserted into optical components in optical transmission lines
• Optical head loss during fiber
• The impedance in the cable does not match the light generates reflection, which is called echo loss.
• Bending, squeezing, impurities, and unevenness of fibers can cause loss
• Fixed continues, commonly known as dead joints, generally used fiber optic welders for optical cable direct head.
• Active joint, commonly known as the live joint, is connected to the optical fiber jumper, device connection, etc. with a connected connector.
Fixed joint tips
Installing the fixed joint should use a secondary discharge method. Preheat the discharge of the fiber end surface, shaped to the end surface, remove dust and debris, and make the optical fiber end face pressure uniform by preheating.
Light also has noise
In addition to attenuation, there is noise in addition to attenuation, and noise in addition to attenuation. Attenuation means having a lot of signals, noise means more useless signals.
Causes of noise
• Random change of light intensity
• Time jitter caused
• Point noise and thermal noise of the receiver
• Optical fiber mode noise
• Pulse exhibition caused by dispersion
• Mode noise of LD
• The frequency of LD is 啁啾
What? Is there a dispersion?
Dispersion is also an important factor affecting light signal transmission.
Dispersion: The frequency width caused by the optical pulse along the optical fiber into a distance. It is the main factor that limits the rate of transmission.
Dispersion caused by dispersion
• Mode dispersion: only occurs in multi-mode fibers, because light of different modes are transmitted along different paths.
• Material Dispersion: Different wavelengths of optical travel speed.
• Wavele guide color: The cause is that the light energy is transmitted at a slightly different speed when the light energy is transmitted in the core and cladding. In a single mode fiber, it is important to change the dispersion of the fiber by changing the internal structure of the fiber.
Effect of fiber optic materials on propagation
• Glass fiber: The core and cladding are glass, small loss, long transmission distance, high cost;
• Collapse silicon fiber: core is glass, cladding is plastic, characteristic is similar to glass fiber, low cost;
• Plastic fiber: The core and cladding are plastic, large loss, the transmission distance is very short, the price is very low. Multi-use for home appliances, audio, and short-range image transfer.
The optical module is a component that realizes optical signal and electrical signal conversion, and common GBIC, SFP, SFP +, XFP, SFF, CFP, and the like.
The size of the GBIC optical module is too large, accounting for too many spaces, causing more interfaces that cannot be provided on the panel of the switches. Therefore, in recent years, the GBIC optical module has gradually replaced by SFP optical modules.
The optical interface is a physical interface used to connect the fiber optic cable. The principle is that the light from the optical transmissory medium into the light-eccentric medium thereby has a total reflection. There are usually several types such as SC, ST, FC.
FC type fiber joint / jumper
Commonly known as round heads, the external reinforcing mode is a metal sleeve, the fastening method is a screw buckle, typically in the ODF side. FC connector General Telecommunication network is adopted, there is a screw to the adapter, the advantage is to be secure, anti-dust, the disadvantage is that the installation time is slightly longer.
ST type fiber joint / jumper
Usually used in multimode connections, the ST head is fixed for half a week, and the disadvantage is to be easily broken, and more use in the deployment of the wireless network.
SC fiber joint / jumper
Commonly known as the square, generous, transmission equipment side light interface generally with SC connector, SC connecting head direct swap, very convenient, disadvantage is easy to fall.
LC fiber joint / jumper
Common interfaces, the specific interfaces of the square, the small party, and the SFP module, which is much smaller than the above interface, and the equivalent area of the switch can accommodate more ports, and the equipment of the radio technology uses this connector.
• FC type fiber optic connector is used up to the wiring frame
• The SC type fiber optic connector is used up to the router switch
• ST type fiber optic connector, usually in 10BASE-F, is often used in fiber distribution frames
• LC fiber optic connector is often used in routers
Finally, look at the installation steps of the fiber
• The length is good, open the cable, remove the cable sheath.
• Clean, remove oil filler cream in the cable.
• Bundle fiber.
• Check the number of fiber cores, perform fiber-on, and check whether the fiber color standard is incorrect.
• Strengthen the core.
• Various auxiliary line pairs, including business line pairs, control line pairs, shielding ground lines.
• Connecting of fibers.
• Fiber joint protection.
• Fiber fracture tray treatment.
• Complete the connection of the cable sheath.
• Protection of the cable connector.
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