2. How to Make FES (Focus Error Signal)1· · · Hologram Foucault Method
Note: The following PD form is slightly different from the actual one. (image only)
(At the time of just focus)
(Close to the disc)
(Far from the disc)
C B A
D + � No error + � + + � �
Actual form has I/V amplifiers here
q
From the deviation of focus, the light shown above (black part) comes back on PD. By receiving the output through a differential amplifier, DC voltage, which responded to defocusing, is output.
3. How to Make Thread Error Signal
When thread does not move..... OL
Bump
PU
Take out the low frequency component for tracking error signals. Tracking Error Signal _ LPF _ Thread Error Signal With this, move the thread to make OL stay around the free neutral point.
