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Popular science | 20 questions about basic knowledge of optical fiber and cable!
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1. Briefly describe the composition of optical fiber？
Answer: The optical fiber consists of two basic parts: a core made of transparent optical material, a cladding, and a coating.
2. What are the basic parameters describing the transmission characteristics of optical fiber lines?
Answer: Including loss, dispersion, bandwidth, cutoff wavelength, mode field diameter, etc.
3. What are the reasons for fiber attenuation?
Answer: The attenuation of optical fiber refers to the reduction of optical power between two cross-sections of an optical fiber, which is related to wavelength. The main causes of attenuation are scattering, absorption, and optical loss due to connectors and splices.
4. How is the fiber attenuation coefficient defined?
Answer: It is defined by the attenuation (dB/km) per unit length of a uniform optical fiber in a steady state.
5. What is insertion loss?
Answer: It refers to the attenuation caused by inserting optical components (such as inserting connectors or couplers) in the optical transmission line.
6. What is the bandwidth of optical fiber related to?
Answer: The bandwidth of the optical fiber refers to: in the transfer function of the optical fiber, the modulation frequency when the amplitude of the optical power is 50% or 3dB lower than the amplitude of the zero frequency. The bandwidth of an optical fiber is approximately inversely proportional to its length, and the product of the bandwidth length is a constant.
7. How many kinds of dispersion are there in optical fiber? What is it about?
Answer: The dispersion of an optical fiber refers to the broadening of the group delay in an optical fiber, including mode dispersion, material dispersion and structural dispersion. It depends on the characteristics of both the light source and the optical fiber.
8. How to describe the dispersion characteristics of the signal propagating in the optical fiber?
Answer: It can be described by three physical quantities: pulse broadening, optical fiber bandwidth, and optical fiber dispersion coefficient.
9. What is the cut-off wavelength?
Answer: It refers to the shortest wavelength that can only conduct the fundamental mode in the fiber. For single-mode fiber, its cutoff wavelength must be shorter than the wavelength of the transmitted light.
10. What impact will the dispersion of optical fiber have on the performance of optical fiber communication system?
Answer: The dispersion of the optical fiber will cause the light pulse to broaden during transmission in the optical fiber. It affects the size of the bit error rate, the length of the transmission distance, and the size of the system rate.
11. What is backscattering method?
A: The backscatter method is a method of measuring attenuation along the length of an optical fiber. Most of the optical power in the fiber is forward propagating, but a small portion is backscattered towards the emitter. Use the beam splitter at the light emitter to observe the time curve of backscattering. From one end, not only the length and attenuation of the uniform optical fiber connected can be measured, but also the local irregularities, breakpoints and problems caused by joints and connectors can be measured. optical power loss.
12. What is the test principle of Optical Time Domain Reflectometer (OTDR)? What function?
Answer: OTDR is based on the principle of backscattering and Fresnel reflection of light, and uses the backscattering light generated when light propagates in the optical fiber to obtain attenuation information, which can be used to measure fiber attenuation, connector loss, fiber fault location and Knowing the loss distribution of the optical fiber along the length, etc., is an indispensable tool in the construction, maintenance and monitoring of optical cables. Its main index parameters include: dynamic range, sensitivity, resolution, measurement time and blind zone, etc.
13. What is the birefringence of single-mode fiber?
Answer: There are two orthogonal polarization modes in a single-mode fiber. When the fiber is not completely cylindrically symmetric, the two orthogonal polarization modes are not degenerate. The absolute value of the difference in the refractive index of the two orthogonal polarization modes is for double refraction.
14. What are the most common optical cable structures?
Answer: There are two types: layer stranding type and skeleton type.
15. What is the main composition of the optical cable?
Answer: It is mainly composed of: fiber core, fiber optic ointment, sheath material, PBT (polybutylene terephthalate) and other materials.
16. What is the armor of the optical cable?
Answer: It refers to the protective element (usually steel wire or steel belt) used in special-purpose optical cables (such as submarine optical cables, etc.). The armor is attached to the inner sheath of the cable.
17. What material is used for the cable sheath?
Answer: The cable sheath or sheath is usually made of polyethylene (PE) and polyvinyl chloride (PVC) materials, and its function is to protect the cable core from external influences.
18. How many application structures are there for OPGW optical cable?
Answer: There are mainly: 1) structure of layered plastic tube + aluminum tube; 2) structure of central plastic tube + aluminum tube; 3) aluminum skeleton structure; 4) spiral aluminum tube structure; 5) single-layer stainless steel tube structure (center 6) Composite stainless steel tube structure (central stainless steel tube structure, stainless steel tube layer stranded structure).
19. What is the main composition of the stranded wire outside the core of the OPGW optical cable?
Answer: It consists of AA wire (aluminum alloy wire) and AS wire (aluminum clad steel wire).
20. To choose the OPGW optical cable model, what are the technical conditions that should be met?
Answer: 1) Nominal tensile strength (RTS) (kN) of OPGW optical cable; 2) Number of fiber cores (SM) of OPGW optical cable; 3) Short-circuit current (kA); 4) Short-circuit time (s); 5) Temperature Range (°C).
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