•P-1100B II
II.
FUNDAMENTALS
5 PICK-UP (PU) AND PU SERVO
5-1 S T R U C T U R E O F A P I C K U P
L i g h t b e a m s e m i t t e d f r o m a s e m i c o n d u c t o r laser are c h a n g e d
t o parallel light ralys by a c o l l i m a t o r lens s y s t e m a n d enter a
p o l a r i z a t i o n p r i s m . S i n c e t h e s e m i c o n d u c t o r laser b e a m s are
linear-polarized in t h e d i r e c t i o n vertical t o t h e plane of i n
c i d e n c e , t h e b e a m s are r e f l e c t e d by t h e polarizing f i l m . T h e
light b e a m s r e f l e c t e d f r o m a n o t h e r p l a n e of t h e polarization
p r i s m pass t h r o u g h a q u a r t e r - w a v e p l a t e , a n d t h e n are c o n
v e r g e d t o a s p o t of nearly
1
.5 /im in d i a m e t e r w i t h the aid of
a n o b j e c t i v e lens.
T h e light r e f l e c t e d f r o m a disc passes a g a i n t h r o u g h t h e o b
jective lens a n d f o l l o w s t h e s a m e p a t h as the f o r w a r d p a t h t o
the polarizing f i l m . By t h e e f f e c t o f t h e q u a r t e r - w a v e p l a t e , t h e
light i n c o m i n g i n t o t h e polarizing f i l m is c h a n g e d so t h a t its
polarizing d i r e c t i o n is p e r p e n d i c u l a r t o t h e polarizing d i r e c t i o n
in t h e f o r w a r d p a t h . T h e r e f o r e , t h e light t r a n s m i t s t h e polariz
ing f i l m a n d d o e s n o t g o b a c k t o t h e s e m i c o n d u c t o r raSer.
N e x t , t h e light i n c o m i n g into a c r i t i c a l a n g l e p r i s m f o r d e t e c
t i o n of a f o u c s p o i n t is r e f l e c t e d t h r e e t i m e s inside t h e p r i s m
a n d t h e n f e d i n t o 4 - d i v i d e d p h o t o d i o d e s . T h e o u t p u t of t h e s e
p h o t o d i o d e s are u s e d f o r c o n t r o l i n g a t r a c k i n g servo coil a n d
a f o c u s servo coil t o o b t a i n an o p t i m u m f o c u s i n g of t h e a b j e c
tive lens o n pits of t h e disc.
4-divided photodiodes
Critical angle prism
Critical angle prism
Collimator lens
Polarized prism
Objective lens
Fig. 5.1
2 7
Laser diode
Monitor photodiode
Disc
Objective
lens
Tracking
servo
coil
Focus
servo
coil
Collimator lens
Polarizing prism
1/4 wavelength plate
Polarization
film
4-divided
photodiodes'
Laser
diodes
Summary of Contents for DP-1100 B
Page 3: ...D P 1 1 0 0 B II D P 1 1 0 0 B II I BLOCK DIAGRAM ...
Page 32: ...D P 1 1 0 0 B II 1 CIRCUIT DESCRIPTION Disc Scratch Dust RFES D C O N D O C K Fig 1 2A 3 5 ...
Page 112: ...2 IC OPERATION OF EACH CIRCUIT AND D P 1 1 0 0 B II PIN DESCRIPTION Fig 2 4 1 G 1 ...
Page 117: ...DP 1100B II I OPERATION OF MAIN MICROPROCESSOR Fig 3 1D Q data reading flow chart ...