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What is Optical Fiber?

Views: 5032     Author: Site Editor     Publish Time: 2020-12-02      Origin: Site

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What is Optical Fiber?



An optical fiber is a flexible, transparent glass/fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Transmission is the transfer of a signal as the light pulse along a glass (silica) fiber.

Optical fibers carry light signals down them in what are called modes. Different ways of traveling: a mode is simply the path that a light beam follows down the fiber. One mode is to go straight down the middle of the fiber. Another is to bounce down the fiber at a shallow angle. Other modes involve bouncing down the fiber at other angles, more or less steep.

Types

optical core

                            Optical Core

Single Mode



The simplest type of optical fiber is called single-mode. It has a very thin core about 5-10 microns (millionths of a meter) in diameter. In a single-mode fiber, all signals travel straight down the middle without bouncing off the edges (yellow line in diagram). Single-mode fibers generally carries the Cable TV, Internet, and telephone signals, wrapped together into a huge bundle. Cables like this can send information over 100 km (60 miles).



Multi Mode



Another type of fiber-optic cable is called multi-mode. Each optical fiber in a multi-mode cable is about 10 times bigger than one in a single-mode cable. This means light beams travels through the core at following a variety of different paths (yellow, orange, blue, and cyan lines)—in other words, in multiple different modes. Multi-mode cables can send information only over relatively short distances and are used (among other things) to link computer networks together.

单模多模示意图

Single Mode and Multi Mode Fibers



Even thicker fibers are used in a medical tool called a gastroscope (a type of endoscope), which doctors poke down someone’s throat for detecting illnesses inside their stomach. A gastroscope is a thick fiber-optic cable consisting of many optical fibers. At the top end of a gastroscope, there is an eyepiece and a lamp. The lamp shines its light down one part of the cable into the patient’s stomach. When the light reaches the stomach, it reflects off the stomach walls into a lens at the bottom of the cable. Then it travels back up another part of the cable into the doctor’s eyepiece. Other types of endoscopes work the same way and can be used to inspect different parts of the body. There is also an industrial version of the tool, called a fiberscope, which can be used to examine things like inaccessible pieces of machinery in airplane engines.

Artworks: Above: Light travels in different ways in single-mode and multi-mode fibers. Below: Inside a typical single-mode fiber cable (not drawn to scale). The thin core is surrounded by cladding roughly ten times bigger in diameter, a plastic outer coating (about twice the diameter of the cladding), some strengthening fibers made of a tough material such as Aramid Yarn with a protective outer jacket on the outside.




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