Re: Digital laser drive circuit (transmitter)

There are tons of different combination of circuit available.  However
the key is different;

1/ using the PD pin of the laser as a feedback to the circuit, to make
sure the driving current is adjusted for different operating
temperature to maintain same output power.

2/ adware the Voltage supply is enough for the driving (forward)
voltage of the laser.  Without it, no matter how much current you
pump, the laser wont lase.

3/ beware the maximum driving current through the laser, it will be
killed instantously if u over drive it.

4/ noisce issue - noise can be a hazard to the laser as transient can
kill the laser.  Proper capacitor must be used to protect the circuit.
 Depends on ur circuit layout and design, coupling cap of ~10uF and
0.1uF should be enough for this purpose.  Observe it in scope is the
way to tell, ie. experimental approach.

If you can find some, find some cheap visible laser from laser pointer
for experiment.  It could be $$ if you ruin the VCSEL laser for your
application.

hope it helps.  I experienced your stage where we need to design a
circuit for the laser during my 4th yr course few yrs ago.

PCF




[EMAIL PROTECTED] (matt lyons) wrote in message news:<[EMAIL PROTECTED]>...
> Hello all,
> 
> I am a fourth year electronic engineer student , and am currently
> trying to get started on my final year project(which is tramsmission
> and recieving of a PWM signal via free space optics). I must first
> build a laser drive circuit, and am told that this is a difficult
> task.I have got what seems to be a suitable circuit for my
> transmitter, but am unaware of how to get the appropriate resistor and
> capacitor values.
> 
> I would be very gratefull if some one could tell me how the circuit
> works, or better still, how i will find the resistor and capacitor
> values(the data sheet of the laser being used is attached)
> 
> CIRCUIT: The circuit is on the web at :
>                     
>                     
> http://www.fiber-optics.info/articles/laser-diode.htm FIG8b
> 
>  Q's: how does the differential amplifier work?
>       what is "modulation current", and what value should it be?
>       how does the "servo loop" work?
>       how do i calculate the resistor values?)
> 
> 
> LASER SPEC::http://www.thorlabs.com/Thorcat/6300/6310-S01.pdf
> 
> 
> I would be very gratefull for any help,
> 
> regards,
> Matt, 
> Ireland.