Dual Laser Optical Block - Sony DVP-NS300 Training Manual

Dual Laser Optical Block

Disc Playback Characteristics
All fifth generation DVD models, (except basic model DVP-NS300) can play back computer made –R or +RW
discs.
Computer made (burned) –R or +RW discs have different characteristics than machine stamped counterparts
and stamped CDs have different characteristics than DVDs. To insure full compatibility, the optical block uses
two lasers. One is optimized for CDs and the other for DVDs.
To understand how separate lasers insure playback of computer burned discs, some basics are explained here.
The reflected Laser light from the disc to the optical block contains the data. DVD discs (including DVD-R and
+RW discs) reflect best in the 650-635nM wavelength band. CD discs (including –R or +RW discs) reflect light
best at 780nM.
Figure 1-2 shows that maximum CD-R disc reflection (RF) occurs at 780nM. Since –R or +RW discs have lower
reflectivity than stamped discs (reflectivity also varies from brand to brand) output is maximized if two lasers are
used: one operating at 648nM for DVDs and another at 780nM for CDs.
Reflective
Intensity for
CD-R
Optical Pick-up
650nM
780nM
Wavelength
FIGURE 1-2
3
1. What's New?
CD = 1.2cm
DVD=0.6cm
KHM-240
Lens
For CD
For DVD