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Optics
Fibroptonic
Ref : 202 012
ENGLISH
4.3 Observations
•
The spectral response of the assembly: optical fibre + photoreceptor is weak in
blue-violet; it is maximum in red and infrared.
•
This experiment shows that there exists radiation outside the visible region, beyond
the red: the infrared.
•
The amplitude of the signal received is dependent on the optical quality and the
state of the surface of the end of the fibre. It must be perfectly polished and
transparent. The amplitude of the signal also depends on the lighting power of the
white light source and on the distance between the projector and optical fibre.
•
To increase the signal we can disconnect the fibre, which absorbs a small fraction
of the electromagnetic radiation and then directly examine the spectrum with a
single receiver module
•
On the other hand, with a diffraction grating as a dispersive system, a large part of
the light emitted is lost in the different orders of the fibre which are not examined.
Furthermore, when we examine the 1
nanometers), it superimposes itself on the 2
(wavelength greater than 400 nm). Thus, it is better to use a prism, which gives a
single very bright spectrum and avoid the problems of overlapping of orders, but it
has the disadvantage of further dispersing the blue instead of the red.
st
order infrared (wavelength greater than 800
nd
order violet-blue radiation
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