Quick question regarding the usage of diffraction gratings in optical pickups

[alanbrito]

Hi guys,

I know you all know where to find good information on the topic. For an experiment, I decided to use a diode sled (SF-AW210) in order to expose photoresist, and it worked very nicely. The question that I had is why is there a diffraction grating right after the BD 405 nm diode, for example, the grating marked as #16 in this image:

Can anyone post some link as to where I can find information on it? For my experiment I removed it since I saw no purpose to it, but I want to be sure.

Thanks in advance!

Alan

 

[alanbrito]

Hmmm, I found this in another thread:

A diffraction grating splits the beam into a main beam and two (first order) side beams. (The higher order beams are not used). The diffraction grating is used to generate multiple beams, not for its more common function of splitting up light into its constituent colors. The side beams are used for tracking and straddle the track which is being read. The tracking servo maintains this centering by keeping the amplitude of the two return beams equalized.)

That may be answering my question, if it is correct.

 

[alanbrito]

And I think this confirms it, as it was posted in Sam's repair FAQ: Notes on the Troubleshooting and Repair of Compact Disc Players and CDROM Drives