1. What is the testing principle of optical time domain reflectometer (OTDR)? What is the function?

Answer: OTDR is based on the principle of backscattering and Fresnel reflection of light. It uses the backscattered light generated when light propagates in the optical fiber to obtain attenuation information. It can be used to measure fiber attenuation, joint loss, fiber fault point location and Understanding the loss distribution along the length of optical fiber is an indispensable tool in optical cable construction, maintenance and monitoring. Its main index parameters include: dynamic range, sensitivity, resolution, measurement time and blind zone, etc.

2. What does “1310nm” or “1550nm” in common light test instruments refer to?

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

The working wavelength of optical fiber communication is in the near-infrared region, and the bands are:

O-band: 1260nm to 1310nm

E-band: 1360nm to 1460nm

S-band: 1460nm to 1530nm

C-band: 1535nm to 1565nm

L band: 1565nm to 1625nm

U-band: 1640nm to 1675nm

Single-mode fiber usually operates at 1310nm, 1550nm and 1625nm.

3. Among currently available commercial optical fibers, what wavelength of light has the smallest dispersion? What wavelength of light has the least loss?

Answer: Light with a wavelength of 1310nm has minimum dispersion, and light with a wavelength of 1550nm has minimum loss.

4. How are optical fibers classified according to the different modes of light waves transmitted in optical fibers?

Answer: It can be divided into single-mode fiber and multi-mode fiber. The core diameter of single-mode optical fiber is approximately between 1 and 10 μm. At a given operating wavelength, it only transmits a single fundamental mode and is suitable for large-capacity long-distance communication systems. Multimode optical fiber can transmit multiple modes of light waves, with a core diameter of approximately 50 to 60 μm, and its transmission performance is worse than that of single-mode optical fiber.

5. Optical fiber connectors have two most basic performance parameters. What are they?

Answer: Optical fiber connectors are commonly known as unions. For the optical performance requirements of single-fiber connectors, the focus is on the two most basic performance parameters of insertion loss and return loss.

6. How many types of commonly used optical fiber connectors are there?

Answer: According to different classification methods, fiber optic connectors can be divided into different types.

According to different transmission media, they can be divided into single-mode optical fiber connectors and multi-mode optical fiber connectors;

According to different structures, it can be divided into various types such as FC, SC, ST, D4, DIN, Biconic, MU, LC, MT, etc.; according to the pin end face of the connector, it can be divided into FC, PC (UPC) and APC.

Commonly used optical fiber connectors: FC/PC type optical fiber connector, SC type optical fiber connector, LC type optical fiber connector.

7. What are the connection devices for optical fiber?

1) Optical fiber splicing

2) Optical fiber connector

fiber optic adapter

PC/UPC/APC fiber cross section

The cross-sections of fiber optic connectors should be divided into PC, UPC, and APC.

PC and UPC are optical fiber microsphere end faces that are parallel to the end face of the ceramic body. The industry standard return losses are -35dB and -50dB respectively.

The APC section has an 8-degree tilt angle. In order to reduce reflections, the industry standard return loss is -60dB.

8. What does an optocoupler mean?

Fiber optic coupler (Coupler), also known as splitter (Splitter), is a component that splits optical signals from one optical fiber to multiple optical fibers.

Couplers are bidirectional passive devices, and their basic forms include tree and star.

9. What are the main optical fibers currently used in transmission network construction?

Answer: There are three main types, namely G.652 conventional single-mode fiber, G.653 dispersion-shifted single-mode fiber and G.655 non-zero dispersion-shifted fiber.

10. What is PON (Passive Optical Network)?

Answer: PON is an optical fiber loop optical network in the local user access network, based on passive optical components, such as couplers and optical splitters.

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