1. What is the blind spot of OTDR? What is the impact on testing? How to deal with the dead zone in the actual test?

Typically, a series of blind spots caused by saturation of an OTDR receiver is called a blind spot.

The dead zone in the fiber can be divided into the event dead zone and the attenuation dead zone: the distance from the starting point of the reflection peak caused by the interference of the active connector to the receiver saturation peak is called the event dead zone; from the starting point of the reflection peak to the active connector in the fiber The distance from the point at which other events due to interference can be identified is called the attenuation dead zone

For OTDR, the smaller the dead zone, the better. As the pulse width increases, the dead zone increases. While increasing the pulse width increases the measurement length, it also increases the measurement dead zone. Therefore, when testing optical fibers, narrow pulses should be used for the measurement of the OTDR and its adjacent event points, and wide pulses should be used for the measurement of the far end of the optical fiber.

2. Can OTDR measure different types of fibers?

If a single-mode OTDR module is used to measure a multi-mode fiber, or a multi-mode OTDR module is used to measure a single-mode fiber with a core diameter of 62.5mm, the measurement results of the fiber length are not affected, but the results such as fiber loss, optical connector loss and return loss Incorrect. Therefore, when measuring optical fibers, it is necessary to select an OTDR that matches the measured optical fiber for measurement, so as to obtain the correct results of various performance indicators.

3. What does "1310nm" or "1550nm" mean in ordinary optical test instruments?

It refers to the wavelength of an optical signal. The wavelength range of optical fiber communication is in the near-infrared region, with wavelengths between 800nm and 1700nm. It is usually divided into short-band and long-band, the former refers to the 850nm wavelength, and the latter refers to the 1310nm and 1550nm wavelengths.

4. Which wavelength of light has the least chromatic dispersion in current commercial fibers? What wavelength has the least loss of light?

The 1310nm wavelength has the smallest optical dispersion and the 1550nm wavelength has the smallest optical loss.

5. How to classify the fiber according to the change of the refractive index of the fiber core?

Divided into stepped fibers and gradient fibers. The stepped fiber has a narrow bandwidth and is suitable for short-distance communication with small capacity; the tapered fiber has a wide bandwidth and is suitable for large and medium-capacity communication.

6. How to classify fibers according to the different modes of light wave transmission in fibers?

Divided into single-mode fiber and multi-mode fiber. The core diameter of a single-mode fiber is about 1-10 μM, and at a given wavelength, only one fundamental mode is transmitted, which is suitable for large-capacity long-distance communication systems. Multimode fiber can transmit multimode light waves, and its core diameter is about 50-60 μM, and its transmission performance is worse than that of single mode fiber. When transmitting the current differential protection of multiple protection, multi-mode optical fiber is used between the photoelectric conversion device in the communication room of the substation and the protection device in the main control room.

7. What is the meaning of numerical aperture (NA) of step index fiber?

The Numerical Aperture (NA) represents the light-gathering ability of the fiber. The larger the NA, the stronger the light-gathering ability of the fiber.

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