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Opto-electronics components

  1. Mar 20, 2010 #1
    This is not a homework question but for a project.

    We are using a laser diode, one that you would normally find in a laser pointer to transfer information to a photo-transistor for a free space optical communications system.

    Now I know the power output is around 5mW, but over a distance will we lose power as the light travels towards the photo-transistor? If so, how do you calculate the power at a certain distance, say 25 m or so?

    Also, could someone also tell me the formula for calculating the spread of the laser light over a distance. This is so we know how much light is missing the photo-transistor and so we can correct this by using lenses to focus the light onto the photo-transistor?

    Thanks in advance.
  2. jcsd
  3. Mar 21, 2010 #2


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    Gold Member

    Well it would still have to obey the inverse-square law. Doubling the distance from the source means a 1/4 reduction in power at the receiver end.
  4. Mar 21, 2010 #3
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