And now there is just one more challenge that must be dealt with: keeping the laser "on track."
To do this, a transparent diffraction grating is added just in front of the laser. Most of the beam passes straight through. But small amounts of light are diffracted forward and back to form two new side beams.
These new beams look out for the lane markers which are additional dashed lines of pits on either side of the data track. If the laser beams are properly centered on the data track, the side beams miss the lane markers.
