I was doing some research on laser drivers and I ran across this simple website that gives a schematic for a laser driver. The author took a small keychain laser and reversed engineered the driver circuit to figure out how it works. Basically the laser head has an emitter and a detector. A small amount of the emitted light is picked up by the detector and can be used to regulate the current through the emitter.
If you connect the switch on this circuit, it will turn on the laser. If you alternatively wanted to transmit data through a laser, you would bypass the switch, and connect one side to the ground of your transmitter circuit, and the data pin you would connect to the other side of the switch. This will turn the laser on and off based on the driving signal. You could also amplitude modulate the laser. If your transmitter circuit is a radio output, then you will amplitude modulate the laser, and can transmit radio through the light. I have not tested this, nor have I seen it done, but I think you could connect it to a RCA cable and transmit RCA composite video. Of course for all of these you need a receiver.
But as far as this circuit goes:
Most common Laser Heads have inside two semiconductors: a LD (laser diode) and a PD (photodiode).
The laser diode will be forward biased and its cathode (LDC) will connect to a driver transistor &/or network to regulate the LD current based on the photodiode current (feedback network).
The photodiode will be reverse biased, its anode (PDA) will feed a driver regulator and thus the control will give a feedback signal for the LD driver.
Of course the feedback is an optical one, part of the laser beam goes backwards to reach the photodiode junction, as shown in figure 2.
3 Responses to “Laser driver circuit”
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http://www.national.com/nationaledge/aug04/article.html has a great article on the feedback circuit involved.
Thanks, that is a good article.
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