Various basic knowledge of fiber optic cable

1. Optical fiber

Optical fiber, the full name is optical fiber, it is a fiber made of glass or plastic that can be used as a light transmission tool.

The main use of optical fiber is communication. At present, the optical fibers used for communication are basically silica-based optical fibers, the main component of which is high-purity silica glass, namely silicon dioxide (SiO2).

Optical fiber communication systems use optical fibers to transmit light waves that carry information to achieve the purpose of communication.

Features of Optical Fiber Communication

huge communication capacity

In theory, one fiber can transmit 10 billion voice channels at the same time. At present, the experiment of transmitting 500,000 voice channels at the same time has been successful, which is thousands or even hundreds of thousands times higher than traditional coaxial cables and microwaves.

long relay distance

Optical fiber has a very low attenuation coefficient, and with appropriate optical transmission, optical receiving equipment, optical amplifier, forward error correction and RZ coding modulation technology, etc., can make its relay distance reach more than thousands of kilometers, while traditional cables can only Transmission 1.5km, microwave 50km, can't compare with it at all.

good confidentiality

Adaptable

It has the advantages of not afraid of the interference of strong external electromagnetic fields, corrosion resistance, etc.

Small size and light weight

Abundant sources of raw materials and low prices

How Fiber Optics Work

The principle of total reflection

If the light beam is directed from an optically denser medium to an optically sparser medium, the angle of refraction is greater than the angle of incidence, as shown in the figure.

If θ0 is continuously increased, the refraction angle θ1 can reach 90°, and the θ1 at this time is called the critical angle.

Total reflection occurs when light rays are directed from an optically denser medium to an optically sparser medium and the angle of incidence is greater than the critical angle.

Optical fibers use this total reflection to transmit optical signals.

Classification of optical fibers

step fiber

In the core and cladding regions, the distribution of the refractive index is uniform, n1 and n2, respectively, and at the boundary between the core and the cladding, the refractive index change is a step (n2>n1).

graded fiber

The refractive index at the fiber axis is the largest (n1), but it gradually decreases with the increase of the radial direction of the cross-section. At the boundary between the core and the cladding, it just drops to the refractive index n2 with the cladding region.

Multimode fiber (MMF, multimode fiber)

Can transmit multiple modes of light. But its intermodal dispersion is large, which limits the frequency of transmitting digital signals, and it will be more serious with the increase of distance.

Single-mode fiber (SMF, single-mode fiber)

Only one mode of light can be transmitted, so its inter-modal dispersion is very small, which is suitable for long-distance communication.

fiber optic interface

There are the following types of fiber optic interfaces:

FC round threaded (most used on patch panels)

ST snap-on round

SC card connection type (the most used on router switches)

The LC connector is similar in shape to the SC connector, but smaller than the SC connector

MT-RJ square, one dual-fiber transceiver

MPO/MTP type

BFOC type

DIN type

FDDI type

MU type

Common representation methods, such as "FC/PC", "SC/PC", "SC/APC" mean?

The front part of "/" indicates the connector model of the pigtail, FC, SC are as described above, omitted;

The part after "/" indicates the cross-section process of the optical fiber connector, that is, the grinding method.

"PC: Physical Contact":

The joint section is flat, in fact, the microsphere is ground and polished, which is the most widely used in the equipment of telecom operators.

"APC":

At an 8-degree angle, the microsphere is ground and polished. It is used more in radio, television and early CATV. Light modulation, when the coupling surface of the joint is vertical, the reflected light returns along the original path.

"UPC":

The attenuation is smaller than that of "PC", and is generally used for equipment with special needs. Some foreign manufacturers use FC/UPC for the internal jumper of the ODF frame, mainly to improve the index of the ODF equipment itself.

Fiber Module

Optical transceiver, the full name of which is called optical transceiver, is an important device in the optical fiber communication system.

Generally, network equipment includes the following categories:

SFP (Small Form-factor Pluggable transceiver ):

Small package pluggable transceiver (LC interface), the speed supported by SFP is 100M, 155M, 622M, 1000M, 1250M, 2500M.

GBIC (GigaBit Interface Converter):

Gigabit Ethernet Interface Converter (SC Interface)

XFP (10-Gigabit small Form-factor Pluggable transceiver ):

10 Gigabit Ethernet Interface Small Form Factor Pluggable Transceiver (LC Interface)

XENPAK (10 Gigabit EtherNet Transceiver PAcKage ):

10 Gigabit Ethernet Interface Transceiver Set Package (SC Interface)

2. Optical cable

Use appropriate materials and cable structures to accommodate and protect the communication optical fibers, so that the optical fibers are protected from mechanical and environmental influences and damages, and are suitable for use in different occasions.

Typical structure of fiber optic cable

Commonly used optical cable structures are layered, skeleton, central tube and ribbon.

Stranded fiber optic cable structure

Skeleton cable structure

Central bundle tube cable structure

Ribbon Cable Structure

Classification of optical cables

outdoor fiber optic cable

Mainly used for direct burial, pipeline and overhead construction of trunk lines and metropolitan area networks.

ribbon cable

Mainly used for the construction of large-core and highly dense metropolitan area backbone networks.

"8" fiber optic cable

The optical fiber cable integrates the cable core part and the steel wire suspension wire into a "8"-shaped PE sheath to form a self-supporting structure. During the laying process, there is no need to erect suspension wires and hooks, and the construction efficiency is high and the construction cost is low. The overhead laying between poles and poles, between poles and buildings, between buildings and buildings, etc. can be realized very simply.

Indoor fiber optic cable

Mainly used in building LAN construction, vertical wiring in buildings

model of fiber optic cable

According to the relevant recommendations of ITU-T, the current type of optical cable is composed of two parts: the type code of the optical cable and the specification code of the optical fiber, separated by a short horizontal line in the middle.

The type code of optical cable consists of five parts: classification, strengthening member, derived feature, sheath and outer layer.

Optical cable classification code and its meaning

GY: Communication room (field) outdoor optical cable

GM: mobile optical cable for communication

GJ: Optical cable in communication room (office)

GS: Optical cable in communication equipment

GH: submarine optical cable for communication

GT: special optical cable for communication

The code name of the reinforcement member and its meaning

No symbol: Metal reinforcement member

F: Non-metallic reinforcing member

The code names of derived features and their meanings

The cable structure features should be able to show the main types of cable cores and the derived structure of the cable. When the optical cable type has several structural features that need to be noted, it can be represented by a combination code, and the combination code is arranged in the order from top to bottom according to the following corresponding codes.

D: Optical fiber ribbon structure

Unsigned: Fiber Loose Covering Structure

J: Optical fiber tight sleeve coating structure

Unsigned: Stranded structure

G: Skeleton groove structure

X: Central beam tube structure

T: ointment filled structure

Z: Self-supporting structure

B: Flat shape

Z: flame retardant

The code name of the sheath and its meaning

Y: polyethylene sheath

V: PVC sheath

U: Polyurethane sheath

A: Aluminum-Polyethylene Bonded Sheath (A Sheath)

S: Steel-Polyethylene Bonded Sheath (S Sheath)

W: Steel-polyethylene bonded jacket with parallel wires (W jacket)

L: Aluminum sheath

G: Steel sheath

Q: Lead sheath

Outer sheath code and its meaning

The outer sheath refers to the armor layer and the outer quilt outside the armor layer.

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