Page 16 - Photonics Essentials an introduction with experiments

Electrons and Photons

10 Introductory Concepts

2.3 Properties of Photons
a. According to Maxwell, light is an electromagnetic wave.
b. According to Michelson and Morley, light always travels at a con-
stant speed, c.
c. speed of light = c = wavelength × frequency = f ~ 3 × 10 10 cm/sec
d. visible light:
400 nm < < 700 nm (400 nm = blue, 700 nm = red)
near infrared:
700 nm < < 2000 nm

There are many important applications in the visible and near-
infrared regions of the spectrum, including the wavelengths that opti-
mize optical fiber communications. The most important properties of
optical fibers for communications are attenuation of the signal by ab-
sorption and distortion of the signal (noise).
High-performance optical fibers are made from glass. Attenuation
is caused by fluctuations in the density of the glass on the atomic
scale and from residual concentrations of water molecules. The water
molecules absorb light near specific wavelengths. In between these
wavelengths, windows of lower attenuation are formed at = 1300
nm and 1500 nm. A good picture of this situation is shown in Fig.
2.2 for state of the art optical fibers. The properties of several types of
fibers, all of which are made by chemical vapor deposition, are shown.
The properties of optical fibers are covered in more detail in Chapter
9.
Another important application for infrared wavelengths is night vi-
sion binoculars. These instruments are composed of detectors that im-
age the infrared heat radiation from objects and convert this signal to
a visible image so that the wearer can see in the dark.
Light beams behave like waves, and the wave properties of light are
easy to observe:

diffraction effects
dispersion effects; for example, a rainbow
interference effects
wavelength
frequency

Light beams also display effects associated with particles. These ef-
fects are not as apparent in everyday experience. In the laboratory,
you will observe this behavior often.

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