Page 49 - Optical Switching And Networking Handbook

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34 Chapter 2

the fiber. This light beam travels down the glass. Along the way, sev-
eral things could happen to the light beam:

1. It could be resisted and lose its signal strength (it gets weaker;
weaker means not as bright).
2. It can be dispersed (spread out, making it less intense; spread
covers a wider area; less focus is a good way to think about it).
Although these two statements sound the same, they are differ-
ent.
As the signal is processed, a detector at the far end sees the light
and converts it back into an electrical signal. The signal is amplified
and given to a demodulator (which has a digital detector) that
decodes the information back into an electrical bit stream that is
passed to the end terminal. This is not a complicated system. How-
ever, the pieces must all work together to produce the desired effect
of high-speed communications.At the input, the information must be
processed fast enough to create the photonic output at a rate of speed
consistent with the fiber. The receiving device must extract the data
equally fast, otherise bottlenecks occur.

Transmitting the Signal
on the Glass

As light is transmitted on the fiber, there is a common goal to under-
stand: What kind of light are we sending? Light exists at many dif-
ferent frequencies (colors). The frequencies (you will hear people
refer to this as wavelength) range from visible to invisible light in the
ultraviolet range. Figure 2-5 lists the frequencies of the spectrum.
When we use these light waves for transmitting in a communica-
tions system, we use the infrared spectrum, as shown in Figure 2-5.
The light is invisible and can be created with a LED or an infrared
laser. Loss in the glass will be a concern; therefore, infrared is a
better choice for transmission. This obviously dispels the myth
that you can see the light inside the fiber, because all the communi-
cations systems today use invisible light frequencies.Ah, the glory of
technology!