English for Specific Purposes

Electronic Engineering 35

 

SPECIALIST READING B: Optical Fiber

 

14. Read the text and find out what optical fiber is and which types of optical fiber are described. Then reread the text to complete the following chart with relevant information:

 

Optical fiber definition

 

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Optical fiber type 1 description

 

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Optical fiber type 2 description

 

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Single- & multimode optical fiber up-

 

And downsides

 

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Optical fiber is a plastic or glass conduit to transport light. Today this technology has become incredibly important, as communications infrastructure has begun to use optical fiber to transmit data at extremely high rates. Aside from fiber optic communications, optical fiber has a number of applications in medicine, consumer products, and physics.

 

The basic principle behind optical fiber is quite simple: the fiber is coated to make it completely reflective on the inside, so that when light goes in, it reflects without losing any light, passing down the fiber to the other end.

 

Because of its low level of attenuation¹, optical fiber is ideal for long distance communications. While metal wire requires repeaters to be installed at short distances, to make sure the signal stays strong, optical fiber can be stretched for long distances without a repeater. And since optical fiber doesn’t conduct electricity the same way metal wire does, it is safe to use in high voltage environments.

 

There are two basic types of fiber: multimode fiber and single-mode fiber. Multimode fiber is best designed for short transmission distances, and is suited for use in LAN systems and video surveillance. Single-mode fiber is best designed for longer transmission distances, making it suitable for long-distance telephony and multichannel television broadcast systems.

 

Multimode (step-index²) fiber refers to numerous modes or light rays carried simultaneously through the waveguide. Modes result from light only propagating in the fiber core at discrete angles within the cone of acceptance. This fiber type has a much larger core diameter, compared to single-mode fiber, allowing for the larger number of modes, and multimode fiber is easier to couple than single-mode optical fiber.

 

Figure 1 shows how the principle of total internalreflection applies to multimode step-index fiber. Because the core's index of refraction³ is higher than the cladding index of refraction⁴, the light