Page 17 - Photonics Essentials an introduction with experiments

Electrons and Photons

Electrons and Photons 11

Figure 2.2. Optical fibers are made of glass and can be very transparent if the glass is
pure. At 1500 nm, the loss is about 0.2 dB per kilometer. This means that a kilometer of
optical fiber is about as transparent as an ordinary windowpane. Fibers are drawn like taffy
from a preform. The properties of preforms made in three different ways are shown: vapor
axial deposition, outside vapor deposition, and inside vapor deposition. The large loss
peak at 1400 nm is the result of absorption by the first harmonic of residual OH molecules
in the glass. Please see Chapter 9 for more details. (Adapted from D. Keck et al., Proc.
SPIE, by permission.

Let us look at Planck’s study of incandescent radiation.
Observation: when things get hot, they begin to glow. As they get
hotter, (1) they glow more brightly and (2) the color of the glow
changes. We can measure the color of the glow by the frequency of the
light. So there seems to be a relationship between temperature and
frequency (color).

Exercise 2.1
If you have an electric heating appliance, you can try the following ex-
periment. After turning off the room lights, turn on the appliance and
watch it as it heats up. Record your observations.
Note: Some people have sensitivity to infrared wavelengths beyond
the range of normal vision. According to Edwin Land, inventor of the
Polaroid camera, who studied this effect, the “color” associated with

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