Re: laser FM detector

On Feb 23, 1:32 pm, MooseFET <kensm...@xxxxxxxxx> wrote:
On Feb 23, 8:39 am, John Larkin



<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
On Sat, 23 Feb 2008 06:18:53 -0800 (PST), j2.macali...@xxxxxxxxx
wrote:

Greetings! I'm a fresh college student currently learning electronic
communications. I have been planning on a project that makes use of
lasers to transmit signals through the laser beam, shifting a beam
using a mirror mounted on a vibrating speaker cone.

For the receiving end, I'll be making a simple slope detector + audio
amp circuit that would hopefully demodulate the signal. But instead of
an antenna (which is particularly useless in my project), I will be
using a simple photodiode that would change the frequency of a signal
(from an AC source, most likely a signal gen) according to the angle
shifting of the beam, even though there's a little difference.

How can a photodiode change the frequency of a signal from a signal
generator?

You use a thin one and work at too long of wavelengths for the
detector. If you apply a forward current to the PIN junction, the
carrier density in the diode changes its index of refraction and speed
of light. By modulating the density, you can phase modulate the
signal passing through. If you integrate the modulation signal, you
have frequency modulation.

I hope this helps :)

Using a photodiode to modulate a laser is news to me. If I follow you
correctly, you are making the laser appear to move back and front,
i.e. appear to change the distance to the receiver. How great is this
modulation in terms of distance?

When I first read this post, I had envisioned a laser beam moving from
side to side, falling on a photodector with a tapered mask painted on
it. As the beam moves, the position on the mask changes, and thus the
output voltage due to the attenuation of the mask. Think of the mask
as a V.

How do laser printers move their spot around?
.

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