Fiber transmission distance

Introduction to Fiber Optic Transmission

Optical fiber transmission, that is, data and signal transmission using optical fiber as a medium. Optical fibers can not only be used to transmit analog and digital signals, but also meet the needs of video transmission. Optical fiber transmission is generally carried out using optical cables. The data transmission rate of a single optical fiber can reach several Gbps, and the transmission distance can reach tens of kilometers without using repeaters.

Advantages of fiber optic transmission

(1) Wide frequency band, large communication capacity and long transmission distance;

(2) The loss is small and the relay distance is long;

(3) Light weight and small size;

(4) Anti-electromagnetic interference, good transmission quality;

(5) No sparks, small leakage and good confidentiality;

(6) Save metal materials and use resources reasonably (quartz SiO2);

(7) It has the characteristics of strong corrosion resistance and radiation resistance.

It can adapt to high salt fog and humid marine environment, and is mainly used in ship video surveillance, network access and underwater underwater acoustic signal transmission in ships.

Optical fiber transmission (communication) is a communication method in which light waves are used as carriers and optical fibers are used as transmission media to transmit information from one place to another, which is called "wired" optical communication. Strictly speaking, it operates in the near-infrared band of the electromagnetic spectrum (usually in the 770-1675nm range), just in the low-loss region of silica glass fibers.

The principle of optical fiber transmission

The law of independent propagation of light holds that when rays from different light sources pass through a certain point in the medium in different directions, the rays do not affect each other, as if other rays do not exist.

The law of straight line propagation, refraction and reflection of light holds that light travels in a straight line in an isotropic homogeneous medium (with constant refractive index n). Reflection and refraction occur when light encounters a smooth interface between two different media during propagation. The propagation speed of light in a homogeneous medium is: V=c/n, where c is the propagation speed of light in a vacuum; n is the refractive index of the medium.

The law of reflection states that the reflection line is located in the plane determined by the incident ray and the normal line, the reflection line and the incident ray are on both sides of the normal line, and the reflection angle is equal to the incident angle.

The law of refraction states that the refracted line lies in the plane determined by the incident ray and the normal, and the refracted and incident ray lie on both sides of the normal.

During the propagation of light, if the light propagates from one medium to the interface of another medium, reflection and refraction will occur at the interface because the refractive indices of the two media are not equal. Generally, a medium with a large refractive index is called an optically dense medium, and a medium with a small refractive index is called an optically thin medium.

In order to ensure the long-distance transmission of the optical signal in the optical fiber, the optical signal must be repeatedly totally reflected in the optical fiber, so as to ensure the minimum attenuation and the minimum dispersion, and reach the far end. The two conditions for achieving total reflection are: the refractive index n1 of the fiber core must be greater than the refractive index N2 of the fiber cladding; when the light entering the fiber is incident on the core-cladding interface, the incident angle should be larger than the tenth critical angle. .

Optical fiber transmission material

The optical fiber used in the integrated wiring system is a glass multi-mode LED with a wavelength of 850nm, the transmission rate is 100Mbps, and the effective range is about 20Km. Its core and cladding are composed of two media with different optical properties. The inner medium has a higher index of refraction for light than the medium surrounding it. It can be known from physics that at the interface of two media, when light is incident from the side with high refractive index to the side with low refractive index, as long as the incident angle is greater than a critical value, a reflection phenomenon will occur, and the energy will not be affected. loss. At this time, the covering layer wrapped around the periphery acts like an opaque substance, preventing light from escaping from the surface during the interpenetration process.

Fibers produced, whether in glass or plastic media, transmit the full visible light and part of the infrared spectrum. Optical cables made of optical fibers have various structural forms. There are two main types of optical cables for short distances:

A layer structure optical cable is to add steel wire or nylon wire in the center, there are several optical fibers in the outer bundle, and a layer of plastic sheath is added on the outside;

The other is a high-density optical cable, which is made of multiple layers of ribbons, and a row of optical fibers is laid in parallel on each layer of ribbons.

Introduction of optical fiber transmission rate and transmission distance

1: Transmission rate 1Gb/s, 850nm

a, Ordinary 50μm multimode fiber transmission distance 550m

b. The transmission distance of ordinary 62.5μm multimode fiber is 275m

c. The transmission distance of the new 50μm multimode fiber is 1100m

2: Transmission rate 10Gb/s, 850nm

a. Ordinary 50μm multimode fiber transmission distance 250m

b. The transmission distance of ordinary 62.5μm multimode fiber is 100m

c. The transmission distance of the new 50μm multimode fiber is 550m

3: Transmission rate 2.5Gb/s, 1550nm

a, g.652 single-mode fiber transmission distance of 100km

b. The transmission distance of g.655 single-mode fiber is 390km (ofstruewave)

4: Transmission rate 10Gb/s, 1550nm

a, g.652 single-mode fiber transmission distance 60km

b. The transmission distance of g.655 single-mode fiber is 240km (ofstruewave)

5: The transmission rate is 40Gb/s, 1550nm

a, g.652 single-mode fiber transmission distance 4km

b. The transmission distance of g.655 single-mode fiber is 16km (ofstruewave)