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Basic knowledge of optical fiber and cable part (2)

Update:22-10-2020
Summary:

   16. In the current commercial optical fiber, what wa […]

   16. In the current commercial optical fiber, what wavelength of light has the smallest dispersion? What wavelength of light has the least loss?
   Answer: Light with a wavelength of 1310nm has the smallest dispersion, and light with a wavelength of 1550nm has the smallest loss.
   17. According to the change of the refractive index of the fiber core, how to classify the fiber?
  Answer: It can be divided into step fiber and graded fiber. Step fiber has a narrow bandwidth and is suitable for small-capacity short-distance communications; graded fiber has a wider bandwidth and is suitable for medium and large-capacity communications.
   18. According to the different modes of light waves transmitted in the optical fiber, how to classify the optical fiber?
  Answer: It can be divided into single-mode fiber and multi-mode fiber. The core diameter of a single-mode fiber is about 1-10μm, and only a single fundamental mode is transmitted at a given operating wavelength, which is suitable for large-capacity long-distance communication systems. Multimode fiber can transmit light waves in multiple modes, and its core diameter is about 50-60μm, and its transmission performance is worse than single-mode fiber.
   When transmitting the current differential protection of multiplex protection, multi-mode optical fiber is used between the photoelectric conversion device installed in the communication room of the substation and the protection device installed in the main control room.
  19. What is the significance of the numerical aperture (NA) of the step index fiber?
  Answer: The numerical aperture (NA) indicates the light-collecting ability of the optical fiber. The larger the NA, the stronger the optical fiber's ability to collect light.
   20. 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 refractive index difference between the two orthogonal polarization modes is It is birefringence.
   21. What are the most common optical cable structures?
  Answer: There are two types: layer twist type and skeleton type
   22. What are the main components of optical cables?
  Answer: It is mainly composed of: fiber core, optical fiber grease, sheath material, PBT (polybutylene terephthalate) and other materials.
  23. What is the armor of the optical cable?
  Answer: 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 optical cable.
   24. What material is used for the cable sheath?
  Answer: The sheath or layer of the optical cable is usually composed of polyethylene (PE) and polyvinyl chloride (PVC) materials, and its function is to protect the cable core from external influences.
  25. Special optical cables used in power systems.
  Answer: There are mainly three types of special optical cables:
   Ground wire composite optical cable (OPGW), the optical fiber is placed in the power line of the steel-clad aluminum strand structure. The application of OPGW optical cable plays the dual functions of ground wire and communication, effectively improving the utilization rate of power poles.
   Wrapped Optical Cable (GWWOP), where there are power transmission lines, the optical cable is wound or suspended on the ground wire.
   Self-supporting optical cable (ADSS) has strong tensile strength and can be hung directly between two power poles with a maximum span of up to 1000m.

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