Optical Fiber Classification

Optical fiber de facto standard in the construction of backbone networks. The length of fiber-optic lines in Russia from major operators reaches> 50 thousand km

Thanks to fiber, we have all the advantages in communication, which has not been before.

That's try to consider the culprit celebration - optical fiber.

This article will try to write just about optical fibers, without the mathematical assumptions and simple human explanation.

Article purely exploratory, that is does not contain any unique knowledge, all of which will be described can be found in the heap of books, but it does not kopipast and vyzhimka of «heap» information only fact.

Classification

The most common fibers are divided into 2 general types of fiber

1. Multimode fiber

2. Single

give an explanation for the «domestic» level that is odnomod and mnogomod.

Imagine a hypothetical system with fiber transmission stuck in it.

We need to transmit binary information. Pulses of electricity in the fiber does not apply, because the dielectric, so we budim transmit light energy.

To do this we need a source of light energy. This may be LEDs and lasers.

Now we know that we use as a transmitter - it is light.

Think like the light is introduced in fiber:

1) light is a spectrum, so if the core of extensive fiber (so multiple fiber), the more spectral components of light falling into the heart.

For example, we pass the light at a wavelength 1300nm, because LED is not able to create such a narrow spectrum of radiation, the heart gets, and 1300nm and 1290, and 1280 and more.

Certain wavelengths is fashion

2) If the heart is small (single fiber), then it gets a narrow spectrum of radiation. Ie get it 1300nm without additional modes. And as more fashion is not, then there will be no mode dispersion (of it below).

This is the main difference and multi-single fiber.

Multimode in turn are divided into fiber step index of refraction (step index multi mode fiber) and Gradient (graded index m / mode fiber).

Single fall into step, standard (standard fiber), offset dispersion (dispersion-shifted) and the displaced non-zero dispersion (non-zero dispersion-shifted)

The design of optical fiber

Each fiber is made up of core and shell with different rates of refraction.

Stone (which is the main medium energy light) is made of optically more dense material, shell - from less.

For example, 50/125 record shows that the core diameter is 50 microns, the envelope - 125mkm.

The diameters of the core equal 50mkm and 62.5 microns are signs of multimode optical fibers, and 8-10mkm, respectively, for one.

The envelope, as a rule, always has a diameter larger 125mkm.

As the diameter of single-core fiber is much smaller than the diameter of multi-. Smaller diameter core reduces mode dispersion (which may be written in a separate article, as well as the propagation of light in the fiber), and hence increase the range transmission. However, when a single fiber replaced mnogomody, thanks to a better «Transport» characteristics, if not need to use expensive lasers with a narrow spectrum of radiation. In multimode fibers used LEDs with a blurred spectrum.

Therefore, for low-cost optical solutions, such as local Internet providers, where the distance between the active network equipment rarely more than 5-15km, the use of mnogomoda very reasonably.

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