Communication industry: 29 basic knowledge points of optical fiber communication

- Jul 31, 2017-

Optical fiber communication, refers to the transmission of voice, image and data signal modulation on the optical carrier, optical fiber as a transmission medium communication.

1. Intrinsic loss of fiber: Rayleigh scattering, intrinsic absorption, etc.

2. Bending: Optical fiber bending when the light in part of the optical fiber will be lost due to scattering, resulting in loss.

3. Squeeze: The loss of a small bending of a fiber when squeezed.

4. Impurity: The loss caused by the absorption and scattering of light in the fiber.

5. Uneven: The refractive index of the optical fiber material is not evenly caused by the loss.

6. Butt: The loss of optical fiber docking, such as: different axes (single mode fiber coaxial degree requirements less than 0.8μm), the end surface and the axis are not vertical, end surface uneven, docking heart diameter mismatch and weld quality is poor.

7. Multimode Fiber: Center glass core teaching Coarse (50 or the 5μm), can pass a variety of modes of light. However, the colors is larger, which restricts the frequency of transmitting digital signals, and increases with distance will be more serious. For example, the 600mb/km fiber has only 300MB bandwidth at 2KM. Therefore, multimode fiber transmission distance is relatively near, generally only a few kilometers.

8. Single-mode fiber: center glass core teaching thin (the core diameter is generally 9 or 10μm), only a mode of light. Therefore, the model colors dispersion is very small, suitable for long-distance communication, but its chroma dispersion plays a major role, so the single mode fiber has a high requirement for the spectral width and stability of the light source, which is narrower and the stability is better.

9. Conventional optical fiber: fiber-optic production long home to optimize the frequency of fiber transmission in a single wavelength of light, such as 1300μm.

10. Dispersion-shifted optical fiber: fiber-optic production long home the optical fiber transmission frequency is optimized at two wavelengths of light, such as: 1300μm and 1550μm.

11. Mutant Optical Fiber: The refractive index of the fiber core to the glass cladding is abrupt. Its cost is low, the mold colors disperses high. Suitable for short-distance low-speed communication, such as: industrial control. However, Single-mode fiber is very small because of the colors dispersion, so the single mode fiber adopts mutation type.

12. Tapered Fiber: Fiber core to the glass cladding of the refractive index is gradually becoming smaller, can make Gao in the form of sinusoidal transmission, which can reduce the die colors scattered, increase fiber bandwidth, increase transmission distance, but the cost is higher, now multimode fiber is the gradient type fiber.

13. Electric transmitter: The main task is PCM coding and signal multiplexing.

Multiplexing refers to the combination of multi-channel signals in a physical channel transmission, to the receiving end with special equipment to separate the signals, multiplexing can greatly improve the utilization of communication lines.

14. Sampling: The process of discrete digital signals from the original time and amplitude of a continuous analog signal, and changing into time and amplitude.

15. Code: Refers to the sampling of M-type signals in accordance with a certain rule by a set of binary or other numbers, each signal can be represented by N 22, M and N to meet m=2n. For example, if the quantized amplitude is 8, then each amplitude in the encoding needs to be represented by a 3-binary sequence.

16. Time Division Multiplexing: when the data transmission rate reached by the channel is greater than the total data transmission rate of each signal, you can use the channel time into one of the time slices (time slots), according to a certain rule to allocate these time slices to each signal, each signal can only be in their own time within the exclusive channel transmission, so the signal will not interfere with each other.

17. Frequency Division Multiplexing: When the channel bandwidth is greater than the total bandwidth of each signal, the channel can be divided into several channels, each of which is used to transmit the signal. Or the frequency is divided into different frequency segments, the different signals in different channels of transmission, the various bands will not affect each other, so different road signals can be transmitted at the same time. This is Frequency division multiplexing (FDM).

18. Code Division Multiple Access (CDMA): This technique is used in mobile communications, different mobile stations (or mobile phones) can use the same frequency, but each mobile station (or cell phone) is assigned with a unique "code sequence", the sequence code and all other "code sequences" are not the same, so each user does not interfere with each other. It is called "Code Division Multiple Access" (CDMA) technology because it distinguishes different mobile stations (or mobile phones) by different "code sequences".

19. Space division Multiple Access (SDMA): This technique utilizes spatial partitioning to form different channels. For example, using multiple antennas on a single satellite, the beams of each antenna are fired at different areas of the Earth's surface. Earth stations in different parts of the ground, they work at the same time, even with the same frequency, do not interfere with each other.

20. Line code: Also known as channel coding, fiber jumper function is to eliminate or reduce the digital signal in the DC and low-frequency components, in order to transmit, receive and monitor in optical fiber. Generally can be summed up as three categories: scrambling binary, Word conversion code, insert type code.

21. Modulation mode: Analog communication can use amplitude modulation, FM, modulation of the same type, the use of digital modulations, corresponding to be called the amplitude shift keying (ask), Frequency shift keying (FSK), Phase shift keying (PSK); there are only two kinds of the Ask called On-off keying (ook), the current digital communication system uses OOK-PCM format, belonging to intensity modulation-direct detection (IM-DD) communication mode, is the simplest and most elementary way in communication mode. The coherent communication system can use Ask, FSK or PSK-PCM format, which is a complex and advanced communication mode.

22. Optical receiver sensitivity: defined as the minimum input optical power required by the receiver under the condition that the desired bit rate is guaranteed.

23. Optical coupling: The optical power of the same wavelength is tapped or closed. Through the optical coupler, we can synthesize the two-channel optical signal along the way.

24. Optical isolator: A passive optical device which only allows unidirectional light to pass, its working principle is based on the non reciprocity of Faraday rotation.

25. Fiber optic jumper Magneto-optical isolator: can also be said to be a single wizard, the isolator placed in the front of the laser and optical amplifiers to prevent the system's reflection light on the device performance and even damage.

26. Optical Filter: The instrument used for wavelength selection, which can pick out the desired wavelength from a wide range of wavelengths, and the light other than this wavelength will be rejected. It can be used for wavelength selection, noise filtering of optical amplifiers, gain equalization, retrocession/demultiplexing.

27. Fiber optic connectors: A device for connecting optical fibres. It has an indispensable position in the optical fiber communication system and measuring instrument. It is different from the fiber-optic fixed joint, can be disassembled, flexible to use, so it is also known as fiber-optic active connectors or fiber-optic active connectors. In general, the fiber connector requires small size, small access loss, repeatable disassembly, high reliability, long life, low price and so on.

28. Optical Attenuator: It is used for the attenuation of optical power, it is mainly used in the measurement of fiber optic system, signal attenuation of short distance communication system and system test. Optical fiber jumper light attenuator requires light weight, small size, high precision, good stability, convenient use and so on. It can be divided into fixed, graded variable, continuous adjustable several.

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