Understanding Fiber Optics and Optical Accessories

Understanding Fiber Optics and Optical Accessories

Optical fibers are small wires and plastic transmitters of visible light and infrared rays. They have three layers: core, cladding and coating.
- In order for the light to reflect completely in the core, the refractive index of the core is greater than the refractive index of the jacket.
- The outer casing protects the fiber from moisture and corrosion, and prevents crosstalk with adjacent fibers.
Coat and jackets are made of glass or plastic, silica, metal, fluorine, crystalline fiber. They are classified into Single Mode (SM) and Multimode (MM) modes that correspond to the number of modes of light passing through the fiber. Wave mode is a steady state of light waves (also known as one ray mode).

Internal structure
The modes are: SM and MM (MM types are 62.5 and 50).
According to the installation environment, there are Outdoor and Indoor.
Outdoor is divided into categories: F8 and Underground
Single Mode and Multi Mode
SM fibers only transmit a waveform due to very small core diameter (about 10 micrometers). Due to the transmission of only one wave mode, SM is not affected by dispersion phenomena and SM is less commonly used than MM.
- MM fibers have a core diameter larger than SM (about 6-8 times), which can transmit many wave modes in the core.
They are also classified into optical fibers with step indexes and class indexes depending on the shape and refractive index of the parts of the fiber core.
The distance between two fiber optic connectors does not specify how much KM. The distance between the two devices is based on the entire line attenuation calculation, transmission power, sensitivity and reserve power of the device.
Normally each device has a recommendation to run at a certain distance, but it is only relative.
The wavelength range for SM and MM devices varies:
MM has the standard wavelengths: 780, 850 and 1300. At present, the devices use less wavelength 780.
SM has wavelengths: 1310, 1550, 1627. Currently SM devices using DWM technology can also use other wavelengths.
Most single-mode fiber is only for backbone, in addition to cost, the technology of single mode cable is very strict, and very difficult to use as well. Reason: The core layer of the single mode cable is very small (about 27 micrometers), and the multi mode is much larger (about 130 micrometers). In addition, due to the single-mode coaxial design for straight line lighting, the cost of fabrication, as well as precision in construction, high technology equipment ... makes Single Mode cables difficult to perform in buildings. Civil.
Distinction: mainly due to the path of light transmitted in the core (which is due to the structure of the core)

In Single mode, light follows a straight line that coincides with the cable axis, while in Multi Mode, light follows a beam of light with a coherent sinusoidal pattern (so that more light can be added). have different wavelengths).
About physical parameters:
Fiber core diameter: Core.
SM: 9/125;
MM: 50/125 and 62.5 / 125.
Shielding diameter: Cladding, both SM and MM are the same 125um.
Coating depends on the type of protection that this layer is made for, but it is common for the Outdoor cable to be 250, with an Indoor cable, it is 900, this does not depend on it's SM cable or MM.
The usage depends on the transmit power, receiver sensitivity, transmission distance, required speed and cost that people decide to use SM or MM.

Connector types of fiber optic cable:

The choice of the connector depends on the choice of ODF Optical (the fixture fixture) and Modular type on the switch or converter.

Plug the connector into fiber optic and then grind to flat head. There are many types of connectors of different manufacturers in Vietnam, mainly AMP connector, this type of head does not need to use glue that is locked in the fiber. This technique is simple but high loss due to manual and repair costs and cable troubleshooting at the initial cost due to the connector used only once.
Tungsten welding technique:
Using a specialized fiber-optic cable welding machine to connect a wire to the cable, the wire is a type of wire already has a built-in connector (patch optical)
This technique has the disadvantage that few people do because the cost of machine investment is quite high (about 12K USD / fiber) but its advantage is the cost of repair and troubleshooting is quite cheap because the wire can use more (each wire extends an average of 2.5 meters, each treatment must cut 3 cm).