Photodiodes in drivers?

[ZeroPoint]

I've made the decision to try and design/build my own analog driver as I've seen a few people on this forum do but I'm trying to avoid simply copying and reproducing someone else's work. I want to understand how and why they work so I can create my own. So, I've begun my research, on google and on this forum, and in the majority of designs that I've come across (particularly from my google searches) I have noticed the use of photodiodes in line with the laser liodes, which, from what i understand, monitor the light output of the laser as a means of current control. My question is whether this technique is intended for industrial/medical lasers or if it is also used in laser show applications. It has made me wonder since in many (if not most) projectors the drivers may be isolated from laser output. Unless I am understanding it wrong it seems that drivers like the flexmod, die4drive and badpip must not use this photodiode but then I am having a hard time finding material explaining the operation of drivers without it. Can anyone clarify this for me and/or link me to some material (preferably written/explanatory material instead of just schematics) that can help me understand the theory in designing a driver (without the use of photodiodes/detectors if that is the case).




Thanks,
Luke

[lasersbee]

Not All Laser Diodes incorporate a feedback Photo Diode.

It would be a lot of work and setup to tap off a known amount of
a Laser's beam's profile to get a sample of the main beam to apply
to a Photo Diode that is not already mounted inn the LD can.

I'm not saying it can't be done but is much more difficult if the
feedback Photo Diode is not mounted in the can during manufacturing.


Jerry

[ZeroPoint]

Ah, so the photodiode (if used) is already incorporated into the can of the LD and not something on the driver. I started to suspect that after seeing several schematics but I had never heard of photodiodes before so I didn't realize that they were a part of the diode itself. I was thinking that it was something on the driver that was referencing the light which made be believe that the positioning of the driver to the laser diode would have to be pretty crucial. it makes much more sense now.