1.Composition of optical fiber
An optical fiber consists of two basic parts: a core and cladding made of a transparent optical material, and a coating layer.
2.What are the basic parameters of optical fiber line transmission characteristics?
Loss, dispersion, bandwidth, cut-off wavelength, mode field diameter and so on.
3. What causes fiber attenuation?
The optical power in the fiber decreases along the vertical axis. The decrease of optical power is related to wavelength. In optical fiber links, the optical power reduction is mainly due to scattering, absorption, and optical power loss caused by connectors and fused joints. The unit of attenuation is dB.
There are many reasons for fiber attenuation,including: absorption attenuation, impurity absorption and intrinsic absorption; Scattering attenuation includes linear scattering, nonlinear scattering and structurally incomplete scattering. Other attenuation, including micro bending attenuation, etc. The main one is attenuation caused by impurity absorption.
4.What is the bandwidth of optical fiber related to?
The bandwidth of the fiber refers to the modulation frequency at which the amplitude of the optical power in the fiber's transfer function is reduced by 50% or 3dB compared to 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.
The broadening of light pulses in optical fibers caused by different group velocities of different wavelengths in the spectral component of the source.
5.How to describe the dispersion characteristics of signal propagation in optical fiber?
It can be described by three physical quantities: pulse broadening, fiber bandwidth and fiber dispersion coefficient.
6.What is the cut-off wavelength?
It is the shortest wavelength in the fiber that can only conduct the fundamental mode. For single-mode fibers, the cut-off wavelength must be shorter than the wavelength of the transmitted light.
7. What is the effect of optical fiber dispersion on the performance of optical fiber communication system?
The dispersion of the fiber will widen the optical pulse during the transmission process in the fiber. It affects the size of the bit error rate, the length of the transmission distance, and the size of the system speed.
8.What is the test principle of optical time domain reflectometer (OTDR)? 
What is its function?
OTDR is based on the backscattering and Fresnel reflection principles of light, using the backscattering light generated when the light propagates in the optical fiber to obtain attenuation information, can be used to measure optical fiber attenuation, connector loss, optical fiber fault location and understand the loss distribution along the length of the optical fiber, is an essential tool in the construction, maintenance and monitoring of optical fiber. The main parameters include dynamic range, sensitivity, resolution, measurement time and blind area.
9.What does "1310nm" or "1550nm" in a common optical test meter refer to?
The operating wavelength of optical fiber communication lies 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 fibers typically operate at 1310nm, 1550nm, and 1625nm.
10.In current commercial optical fibers, what wavelength of light has the minimum dispersion? What wavelength of light has the least loss?
Light with a wavelength of 1310nm has minimum dispersion, and light with a wavelength of 1550nm has minimum loss.
11.How are optical fibers classified according to the modes of light wave transmission in them?
They can be divided into single-mode fiber and multi-mode fiber. The core diameter of single-mode fiber is about 1 ~ 10μm, and only a single fundamental mode is transmitted at a given working wavelength, which is suitable for large-capacity long-distance communication systems. Multi-mode fiber can transmit multiple modes of light waves, and the core diameter is about 50 ~ 60μm, and the transmission performance is worse than that of single-mode fiber.
12.What are the most common fiber optic cable structures?
There are stranding and skeleton.
13.What are the main components of optical cable?
It is mainly composed of fiber core, fiber optic ointment, sheath material, PBT (polybutylene terephthalate) and other materials.
14.What is the armor of optical cable?
It is the protective element (usually steel wire or steel strip) used in special purpose optical cables (such as submarine optical cables, etc.). The armouring is attached to the inner sheath of the cable.
15.What are the two most basic performance parameters of optical fiber connectors?
Optical fiber connectors are commonly known as live connectors. For the optical performance requirements of single-fiber connectors, the focus is on the two most basic performance parameters of the intervention loss and return loss.
16.What types of fiber optic connectors are commonly used?
According to different classification methods, optical fiber connectors can be divided into different types, according to the different transmission media can be divided into single-mode optical fiber connectors and multi-mode optical fiber connectors; According to the different structure can be divided into FC, SC, ST, D4, DIN, Biconic, MU, LC, MT and other types; The connector can be divided into FC, PC (UPC) and APC according to the pin end face of the connector. Commonly used optical fiber connectors: FC/PC optical fiber connectors, SC optical fiber connectors, LC optical fiber connectors.
17.optical coupler
Optical fiber Coupler (Coupler), also known as Splitter (Splitter), is a component that divides optical signals from one optical fiber to multiple optical fibers.
The coupler is a two-way passive device, the basic form of tree, star.
