Forty-five traditional knowledge of optical fiber and optical fiber cables

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Forty-five traditional knowledge of optical fiber and optical fiber cables

1. Briefly describe the composition of optical fiber.

A: The optical fiber consists of two basic parts: the core, package layer and Coating Layer Made of transparent optical materials.

2. What are the basic parameters used to describe the transmission characteristics of optical fiber lines?

Answer: Includes loss, dispersion, bandwidth, cut-off wavelength, and Mode Field diameter.

3. What are the causes of optical fiber attenuation?

A: optical fiber attenuation refers to the reduction of optical power between two cross sections of an optical fiber, which is related to the wavelength. The main cause of attenuation is scattering, absorption, and optical loss caused by connectors and connectors.

4. How is the attenuation coefficient defined?

A: It is defined by the attenuation (dB/km) per unit length of a uniform fiber in a steady state.

5. What is insertion loss?

Answer: it refers to the Attenuation Caused by the insertion of optical components (such as connectors or coupler) in optical transmission lines.

6. What is the relationship between the bandwidth of the optical fiber?

Answer: in the optical fiber transfer function, the optical fiber amplitude is 50% or less than the zero-frequency amplitude. The bandwidth of an optical fiber is inversely proportional to its length. The product of the bandwidth length is a constant.

7. What kinds of dispersion does the optical fiber have? What is it about?

A: The dispersion of an optical fiber refers to the expansion of the group delay in a fiber, including the mode dispersion, material dispersion, and structural dispersion. Depends on the characteristics of the light source and optical fiber.

8. How do we describe the dispersion characteristics of signals transmitted in optical fiber?

A: You can describe it using three physical parameters: pulse broadening, bandwidth of the optical fiber, and dispersion coefficient of the optical fiber.

9. What is the cutoff wavelength?

Answer: it refers to the shortest wavelength in the optical fiber that can only transmit the base modulus. For a single-mode optical fiber, the cut-off wavelength must be shorter than the wavelength of the conducting light.

10. What is the impact of fiber dispersion on the performance of the optical fiber communication system?

Answer: The dispersion of the optical fiber will make the optical pulse expand during the transmission process of the optical fiber. It affects the error rate, the length of the transmission distance, and the system speed.

11. What is the back scattering method?

A: The Back-to-Back Scattering Method is a method for measuring attenuation along the length of the optical fiber. Most of the optical power in the optical fiber is Forward propagation, but few are scattered from the light emitting device. Observe the back-scattering time curve using the splitter at the light emitting device, and measure the length and attenuation of the connected uniform Optical Fiber from one end, it can also detect local irregularities, breakpoints and optical power loss caused by connectors and connectors.

12. What is the test principle of an OTDR? What are the functions?

A: The OTDR is developed based on the Back-to-Back Scattering and fresh reflection principles of light. It uses the backward scattered light generated when the light is transmitted in the optical fiber to obtain the attenuation information, it can be used to measure the attenuation, joint loss, fault point location of optical fiber, and understand the loss distribution along the length of optical fiber. It is an indispensable tool in the construction, maintenance and monitoring of optical fiber cables. Its main index parameters include dynamic range, sensitivity, resolution, measurement time and blind zone.

13. What is the blind zone of OTDR? What is the impact on testing? How to deal with blind spots in actual tests?

A: It is usually called a blind spot due to the saturation of the OTDR receiving end caused by reflection from characteristic points such as active connectors and mechanical connectors.

Blind spots in optical fiber are divided into two types: the event blind zone and the attenuation blind zone: the reflection peak caused by the intervention of the active connector, the length distance from the start point of the reflection peak to the receiver saturation peak, known as the event blind zone; the distance between the start point of the reflection peak and other event points that can be identified in the optical fiber due to the intervention of active connectors is called the attenuation blind zone.

For OTDR, the smaller the blind zone, the better. The blind area increases with the increase of the pulse width. Although the length of the measurement is increased, the blind area is also increased. Therefore, when the optical fiber is tested, narrow pulses are used for the measurement of optical fiber and adjacent event points attached to the OTDR, while wide pulses are used for the measurement of the far end of the optical fiber.

14. Can OTDR measure different types of optical fibers?

A: If the single-mode OTDR module is used to measure the multimode optical fiber, or a Multimode OTDR module is used to measure the single-mode optical fiber with a core diameter of 62. 5mm, the measurement results of the optical fiber length are not affected, but the results are incorrect, such as the optical fiber loss, optical joint loss, and return loss. Therefore, when measuring the optical fiber, You must select an OTDR that matches the optical fiber to be tested for measurement. In this way, all the performance indicators are correct.

15. What do "1310nm" or "1550nm" in common optical testing instruments mean?

A: it refers to the wavelength of the optical signal. The wavelength range of optical fiber communication is in the near infrared zone, and the wavelength is in the NM ~ Between 1700nm. It is often divided into short wave long band and long wavelength band, The former refers to 850nm wavelength, the latter refers to 1310nm and 1550nm.

16. In the current commercial optical fiber, What wavelength of light has the minimum dispersion? What wavelength of light has a minimum loss?

Answer: The light of 1310nm wavelength has the minimum dispersion, and the light of 1550nm wavelength has the minimum loss.

17. How are optical fibers classified based on the change of the refractive index of the fiber core?

Answer: It can be divided into step optical fiber and gradient optical fiber. Step-by-Step optical fiber bandwidth is narrow, suitable for small-capacity short-distance communication; gradient optical fiber bandwidth is wider, suitable for medium and large-capacity communication.

18. How can optical fiber be classified based on the optical fiber transmission mode?

A: It can be divided into single-mode optical fiber and multi-mode optical fiber. The diameter of the Single-Mode Optical Fiber Core is about 1 ~ A single base mode is transmitted only at a given operating wavelength between 10 μm, which is suitable for large-capacity long-distance communication systems. Multimode Optical Fiber can transmit light waves in multiple modes, with a core diameter of about 50 ~ Between 60 μm, the transmission performance is worse than that of single-mode optical fiber.

Multi-mode optical fiber cables are 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 hole (NA) of the step refractive index optical fiber?

A: The numerical hole (NA) indicates the optical fiber's light receiving capability. The larger the NA, the stronger the optical fiber's light collecting capability.

20. What is the refraction of a Single-Mode Optical Fiber?

A: There are two orthogonal polarization modes in a single-mode optical fiber. When the fiber is not completely symmetrical with a garden column, the two orthogonal polarization modes are not degenerate, the absolute value of the difference between the modulus and refractive indexes of Two Orthogonal Polarization conditions is the refraction.

21. What are the most common types of optical fiber cables?

A: There are two types of applications: layer-twisting and bone-frame.

22. What are the main components of optical cables?

Answer: It is mainly composed of: fiber core, optical fiber oil paste, sheath material, PBT (polyethylene terephthalate) and other materials.

23. What does the optical cable armor mean?

Answer: it refers to the protective components (usually steel wires or steel bands) used in special-purpose optical cables (such as submarine cables ). Armor is attached to the internal sheath of the optical cable.

24. What materials are used for the optical fiber sheath?

Answer: The cable sheath or protection layer is usually composed of polyethylene (PE) and polyvinyl chloride (PVC) materials. Its function is to protect the cable core from external influences.

25. List the special optical cables used in power systems.

A: There are three types of special optical cables:

  • The OPGW is placed in the power line of the aluminum-twisted steel ladle structure. The Application of OPGW Optical Fiber enables both ground and communication, effectively improving the utilization rate of power tower.
  • GWWOP wraps or hangs a GWWOP in a place where a transmission line already exists.
  • The self-built optical cable (ADSS) has a strong anti-tension capability and can be directly mounted between two power towers. Its maximum span is 1000 m.

26. What types of application structures does OPGW have?

Answer: (1) Structure of the plastic tube layer plus the aluminum tube; (2) Structure of the center plastic tube + the aluminum tube; (3) Structure of the aluminum skeleton; (4) Structure of the spiral aluminum tube; (5) single-layer stainless steel tube structure (center stainless steel tube structure, Stainless Steel Tube Layer twisted structure); 6) composite stainless steel tube structure (center stainless steel tube structure, Stainless Steel Tube Layer twisted structure ).

27. What are the main components of twisted wires outside the core of the OPGW optical cable?

Answer: it consists of AA wire (aluminum alloy wire) and AS wire (aluminum clad steel wire.

28. What are the technical conditions for selecting the OPGW optical cable model?

Answer: 1) nominal tensile strength of the OPGW Optical Cable (RTS) (kN); 2) Number of Optical Fiber cores of the OPGW Optical Cable (SM); 3) short-circuit current (kA); 4) short-circuit time (s); 5) temperature range (℃ ).

29. How is the degree of bending Limited?

Answer: The bending radius of the optical cable shall be no less than 20 times the outer diameter of the optical cable, and the bending radius shall not be less than 30 times the outer diameter of the optical cable during construction (non-static state.

30. What should I pay attention to in the ADSS optical cable project?

A: There are three key technologies: mechanical design of optical cables, determination of suspension points, and selection and installation of supporting fittings.

31. What are the main optical fiber fittings?

Answer: Optical Fiber fittings refer to the hardware used to install optical fiber cables. They mainly include tensile cable clips, Suspension Cable clips, and vibration-proofing devices.

32. What are the basic performance parameters of the optical fiber connector?

Answer: fiber optic connectors are commonly known as live connectors. For the optical performance requirements of single fiber connectors, the focus is on the intervention loss and return loss, the two most basic performance parameters.

33. What are the common types of fiber optic connectors?

Answer: according to different classification methods, optical fiber connectors can be divided into different types, and can be divided into single-mode optical fiber connectors and multi-mode optical fiber connectors based on different transmission media; different types of connectors can be divided into FC, SC, ST, D4, DIN, Biconic, MU, LC, and MT. The Pin End Faces of connectors can be divided into FC and PC (UPC) and APC. Common optical fiber connectors: FC/PC optical fiber connectors, SC optical fiber connectors, and LC optical fiber connectors.

34. In the optical fiber communication system, please name the following items.

AFC, FC adapter ST type adapter SC type adapter FC/APC, FC/PC type connector SC type connector ST type connector LC Type jumper MU type jumper single mode or multimode jumper

35. What is the interference loss (or insertion loss) of the optical fiber connector )?

A: What is the return loss (reflection attenuation, return loss, and return loss) of the optical fiber connector )?

36. What is the return loss (or reflection attenuation, return loss, and return loss) of the optical fiber connector )?

A: It is a measure of the input power component returned from the connector and along the input channel. Its typical value should be no less than 25dB.

37. What is the most prominent difference between Light Emitting Diode and semiconductor laser?

Answer: The light produced by the light emitting diode is non-coherent and the spectrum is wide. The light produced by the laser is coherent and the spectrum is narrow.

38. What is the most obvious difference between the operating characteristics of LEDs and LD?

A: If the LED does not have a threshold, the LD has a threshold. A laser is generated only when the injection current exceeds the threshold.

39. What are two common single longitudinal mode semiconductor lasers?

A: Both DFB and DBR are distributed feedback lasers. The optical feedback is provided by the Distribution feedback Prague grating in the optical cavity.

40. What are the two main types of optical receiver?

A: It mainly includes a diode (PIN tube) and an avalanche diode (APD ).

41. What factors are involved in noise generation in optical fiber communication systems?

Answer: noise generated due to unqualified light consumption ratio, random variation of light intensity noise, time jitter noise, receiver point noise and thermal noise, and optical fiber mode noise, the noise produced by the pulse widening caused by dispersion, the mode distribution noise of the LD, the noise produced by the frequency of the LD, and the noise produced by the reflection.

42. What are the main optical fibers used for transmission network construction? What are their main features?

Answer: There are three main types: G.652 standard single-mode optical fiber, G.653 dispersion displacement single-mode optical fiber, and G.655 non-zero dispersion displacement optical fiber.

  • G.652 single-mode optical fiber in the C band 1530 ~ 1565nm and L band 1565 ~ The dispersion of 1625nm is large, generally 17 ~ 22 psnm? If the system speed exceeds 2.5 Gbit/s, dispersion compensation is required. If the system speed is 10 Gbit/s, the System Dispersion Compensation cost is high, it is currently the most common optical fiber laying in the transmission network.
  • The dispersion of G.653 dispersion displacement optical fiber in the C and L bands is generally-1 ~ 3.5 psnm? Km, which is zero dispersion at 1550nm, and the system speed can reach 20 Gbit/s and 40 Gbit/s. It is the best optical fiber for single-wave long-distance transmission. However, due to its zero dispersion, when using DWDM for expansion, there will be a non-linear effect, resulting in Signal Crosstalk and four-wave mixing FWM. Therefore, DWDM is not suitable.
  • G.655 non-zero dispersion displacement Optical Fiber: the dispersion of G.655 non-zero dispersion displacement optical fiber in the C band is 1 ~ 6 psnm? Km, the dispersion in the L band is generally 6 ~ 10 psnm? Km, the dispersion is small, avoiding the zero dispersion zone. It not only suppresses the four-wave mixing FWM, but also can be used for DWDM resizing or enabling high-speed systems. The new G.655 optical fiber can extend the effective area to 1.5 ~ of the average optical fiber ~ 2 times. Large Effective Area can reduce power density and non-linear effect of optical fiber.
  • 43. What is the non-linearity of optical fiber?

A: When the incoming optical power exceeds a certain value, the refractive index of the optical fiber is related to the non-linearity of the optical power and generates Raman Scattering and extensive scattering, changing the incident light frequency.

44. What is the impact of non-linearity on optical fiber transmission?

A: non-linear effects may cause some additional losses and interference, which may degrade the system performance. Nonlinear Distortion is generated because the optical power of the WDM System is large and long-distance along the optical fiber. Nonlinear Distortion includes stimulated scattering and nonlinear refraction. Among them, stimulated scattering involves Raman Scattering and extensive scattering. The above two Scattering Modes reduce the incident energy and cause loss. When the input power is small, it can be ignored.

45. What is PON (Passive Optical Network )?

Answer: PON is an optical Fiber Loop Optical Network in the access network of local users. It is based on passive optical devices, such as coupler and optical splitter.

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