Do you know what is single-mode fiber, multimode fiber? Although it is only one word, the difference is still quite big. Today, Shenzhen Tianbo will take you to understand their difference?
Multimode fiber
When the geometry of the fiber (mainly the core diameter d1) is much larger than the wavelength of the light wave (about 1 μm), there are dozens or even hundreds of propagation modes in the fiber. Different propagation modes have different propagation speeds and phases, resulting in delays and widening of light pulses after long-distance transmission. This phenomenon is called modal dispersion of optical fibers (also known as inter-mode dispersion).
Mode dispersion narrows the bandwidth of multimode fiber and reduces its transmission capacity, so multimode fiber is only suitable for smaller capacity fiber communication.
The refractive index distribution of the multimode fiber is mostly a parabolic distribution, that is, a graded refractive index distribution. Its core diameter is about 50μm.
Single mode fiber
When the geometry of the fiber (mainly the core diameter) can be close to the wavelength of the light, if the core diameter d1 is in the range of 5 to 10 μm, the fiber only allows one mode (the fundamental mode HE11) to propagate therein, and the remaining high-order modes are all cut off. Such a fiber is called a single mode fiber.
Since it has only one mode of propagation and avoids the problem of modal dispersion, single mode fiber has an extremely wide bandwidth, which is especially suitable for large-capacity fiber-optic communication. Therefore, in order to achieve single-mode transmission, the parameters of the optical fiber must satisfy certain conditions. According to the formula, when the fiber with NA=0.12 is to achieve single-mode transmission above λ=1.3μm, the radius of the fiber core should be ≤ 4.2 μm, that is, its core diameter d1 ≤ 8.4 μm.
Since the core diameter of a single-mode fiber is very small, more stringent requirements are imposed on its manufacturing process.
1. It is necessary to supply power to devices with large power consumption: PoE switches use different standards and different output powers. For example, IEEE802.3af does not exceed 15.4W at maximum. Due to the loss of transmission wires, the maximum power consumption can be no more than 12.95W. The device is powered. A PoE switch that complies with the IEEE802.3at standard can supply power to devices with a maximum power consumption of less than 25W.
2. How many devices can be powered: An important indicator of a PoE switch is the total power of the PoE. Under the IEEE802.3af standard, if the PoE power supply of the PoE switch reaches 370W, then it can supply 24 ports (370/15.4=24), but if it is based on the IEEE802.3at standard, the maximum power supply is 30W. At the same time, it can only power up to 12 ports (370/30=12).
3. Need to pick up, whether with fiber, with no network management, speed (10/100/1000M).
From a technical point of view, PoE technology has been developed for many years and is now in a very mature stage. The standard PoE power supply is stable and safe enough. However, due to the current cost of pressure on the monitoring market, the quality of the selected PoE switch or wire is too low, or the design of the solution itself is unreasonable. The power supply distance is not arranged or the connection of too many high-power devices has caused insufficient power supply (especially nighttime monitoring equipment). When the heating mode is turned on). Therefore, engineering companies generally have the view that PoE power supply is unstable.
The network monitoring project is different from ordinary network integrated wiring. The data transmission volume is very large, the power is high, and it requires all-weather uninterrupted work. The use of quality-guaranteed PoE equipment and wires is the guarantee of the stability of the whole system.
The following are the advantages of POE switches
1. Simplify wiring and save labor costs
A network cable transmits data and power simultaneously. PoE saves time and money by eliminating the need for expensive power and the time it takes to install the power supply.
2. Safe and convenient
The PoE power supply device only supplies power to the devices that need to be powered. Only when the device that needs to be powered is connected, the Ethernet cable will have voltage, thus eliminating the risk of leakage on the line. Users can safely mix legacy devices and PoE devices on the network, which can coexist with existing Ethernet cables.
3. Easy to manage remotely
Like data transmission, PoE can monitor and control the device by using Simple Network Management Protocol (SNMP). This feature provides features such as night shutdown and remote reboot.
