Claims
- 1. An information storage system comprising an optical record carrier having a stack of information layers alternating with spacer layers,
- and a device for scanning the information layers, which device is provided with a radiation source and focusing means for selectively focusing a radiation beam from the radiation source on the separate information layers, and a focus servosystem,
- characterized in that the thickness of each spacer layer ranges between 1.5 and 4 times the refractive index of the spacer layer multiplied by the peak-to-peak distance of the S-curve of the focus servosystem.
- 2. A device for scanning information layers of a multi-layer optical record carrier, which device is provided with a radiation source, focusing means for selectively focusing a radiation beam from the radiation source on the separate information layers, and a focus servosystem comprising a focus detection system having a radiation-sensitive surface, characterized in that the radiation-sensitive surface has a largest dimension ranging between 1.5 and 3 times the diameter of the radiation spot formed on the radiation-sensitive surface when the radiation beam is optimally focused on the information layer to be scanned.
- 3. A device for scanning information layers of a multi-layer optical record carrier, which device is provided with a radiation source, focusing means for selectively focusing a radiation beam from the radiation source on the separate information layers, and dividing means located in the optical path between the radiation source and the focusing means for generating two servobeams and one main beam from the radiation beam, characterized in that the power in the main beam is smaller than six times the power in each of the servobeams.
Priority Claims (2)
Number |
Date |
Country |
Kind |
9002841 |
Dec 1990 |
NLX |
|
94202416 |
Aug 1994 |
EPX |
|
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a division of application Ser. No. 08/299,861, filed Sep. 1, 1994, now U.S. Pat. No. 5,677,903 which is a continuation-in-part of co-pending application Ser. No. 07/674,493 filed Mar. 25, 1991 by Antonius H. M. Holtslag for METHOD OF AND APPARATUS FOR OPTICALLY WRITING, READING AND ERASING A MULTI-PLANE RECORD CARRIER, AND RECORD CARRIER SUITABLE FOR SAID METHOD AND APPARATUS, now U.S. Pat. No. 5,408,453.
US Referenced Citations (6)
Divisions (1)
|
Number |
Date |
Country |
Parent |
299861 |
Sep 1994 |
|
Continuation in Parts (1)
|
Number |
Date |
Country |
Parent |
674493 |
Mar 1991 |
|