Laser Communication
Three set ups for three communication will be discussed.
1 Communication with a diode laser (Internal modulation)
2 Communication with a HeNe laser using a speaker-mounted strip
3 Communication with a HeNe which is modulated by a mirror attached to a speaker cone.
The last two are the external modulation based experiments. You will be performing communication with all the three set
ups. Each experiment would require a modulator based on an electronic circuit.
The scheme is shown in Fig. 1.
There is a driver circuit with one end connected to a micro-phone and the other end is connected to the three setups:
speaker with a mounted strip, speaker with a mounted mirror and the diode laser. When you speak into the microphone,
the driver circuit modulates the two speakers and the diode laser simultaneously.
This results in modulation of the three laser beams. If you now put a photo detector facing these beams one by one you
can observe the quality of sound transmitted by each laser. There is only one receiver that will be used with all the three
transmitters so that while comparing the quality same receiver remain in use.
Fig. 1
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