Field of Invention
The instant invention relates to an optical storage medium, in particular to a thin optical storage medium. The present invention particularly relates to modifying the design of an optical storage medium by making structural changes in the medium and making it compatible with the current disc players, aiding in the printing process so as to provide a more robust design and reduce the tracking and focusing error.
Background of the Invention
Optical media forms a very important data storage technology. Optical media comes in formats like CD-ROM/ CD-R/CD-RW/ DVD-ROM/ DVD-RW/DVD+RW/DVD-RAM
Digital Video Disc or Digital Versatile Disc (DVD) is an optical storage medium for read-only, recordable and rewritable applications. DVD is considered to be an enhanced version of a compact disc (CD). They denote unified set of standards for high-density optical disc.
DVD-ROM is a circular disc, 120mm in diameter with a hub in center. Like CD, data is recorded on the disc in a spiral trail of tiny pits (of finite lengths), and the discs are read by means of laser beams.
Unlike CD, as shown in figure 1, a DVD is a bonded disc, made of two 0.06mm layers joined together (active and dummy). The active layer (1) stores all the information and the dummy layer (2) is provided to give the disc a mechanical stability. A stacking ring (3) is provided at a predetermined distance from the central region. The 0.6 mm substrate are polycarbonate plastic coated with a much thinner reflective layer of aluminum or gold. Two such discs are glued together to form a 1.2 mm disc that can be designed to read from one side (single sided) or both side (double sided). The substrates are half as thick as the CD to make it possible to use a lens with a higher numerical aperture and therefore use smaller pits and narrower tracks.

Polycarbonate forms a major part of the structural composition of these discs and it is a major cost factor involved in the production.
Also when the thickness of these optical discs is reduced to below 1.2 mm, some optical drives have problems reading the data stored on the optical disc due to problems with clamping/engaging the optical disc and focusing the lasers at the proper depth within the optical disc.
US Patent Application No. 2006/0198281 illustrates an optical disc having a reduced planar thickness. The optical disc according to the disclosure includes several stacker elements coupled to the central clamping area .
However, this disclosure only provides the disposition of the stacker elements only in the clamping area, which does not alleviate the tracking and focusing error. Also the production costs of the optical disc are not reduced as the said optical disc includes both the active layer and dummy layer.
Summary and objects of the present invention:
It is therefore an object of the present invention to provide for a simple, cost-effective and reliable DVD
Another object to the present invention is to remove the dummy layer and compensate for the loss of inertia due the removal of the dummy layer
It is another object of the present invention to provide a thin optical storage medium that is compatible with the existing drives
A further object of the present invention is to alleviate the tracking and focusing error generated due to the thin size of the optical media due to disc fluttering.

It is still another object of the present invention to ensure a smooth printing process.
Still another object of the present invention is to reduce the overall quantity of polycarbonate and hence the cost of manufacturing.
To achieve the aforementioned objects, the present invention provides an optical storage medium with a central clamping area that defines a central aperture and a stacking ring, characterized in that the medium comprises an active layer, the structure of the active layer being modified by varying the thickness of the active layer at a predetermined positions for improving drive compatibility and /or alleviating the tracking error/ focusing error and also smoothen the printing process.
The optical storage medium of the present invention does not include a dummy layer and the thickness of the active layer is 0.6mm±0.1mm.
In order to enhance the robustness, stability of the optical storage medium and reduce the tracking error and focusing error due to the removal of the dummy layer, the thickness of the active layer is varied by increasing its thickness over the periphery of the inner hub of said storage medium or over the data side of the inner hub of said storage medium or over the optic side of the inner hub of said storage medium.
In an alternate embodiment, the thickness of the active layer is varied by providing an additional element over the periphery of inner hub of said storage medium or over the data side of the inner hub of said storage medium or over the optic side of the inner hub of said storage medium.
However, in order to have better manufacturing process and optimize the design of the hub, the hub thickness is adjusted with the minimum raised hub thickness restricted to a value of 0.3 mm and the with the maximum raised hub thickness restricted to a value of 1.40. This is because minimum thickness drives have difficulty in sensing the discs and with maximum thickness, it becomes too difficult to mould the Discs. The preferable thickness of the central hub is between 1.0 mm to 1.40 mm

Brief description of the accompanying drawings
While the specification concludes with the claims, it is believed that the invention be better understood from the following descriptions which are taken in conjunction with the accompanying drawings in which like designations are used to designate substantially identical elements.
Figure 1 relates to the prior art and shows a conventional optical storage device. Figure 2 shows an optical storage device drive wherein the dummy layer is removed. Figure 3 an optical storage device according to the present invention.
Figure 4a and 4b illustrates an optical storage device according to an alternate embodiment
Detailed description of the instant invention
Optical storage devices store information in the form of pits and lands. The drives read the pits and lands by using a laser and sensor. The drive's laser scans the underside of the disc, searching for specific pits and lands that correspond to the command the drive has received. A double-layered DVD has another layer of pits and lands embedded below the top layer. The drive simply refocuses its laser slightly in order to read the other layer.
As illustrated by figure 2, the dummy layer (2) has been removed and the thin optical medium comprises of only the active layer (1). Due to the removal of the dummy layer (2) there is a loss of inertia, which is to be compensated by physical changes in structure of the optical medium. Also, to improve drive compatibility and minimize the tracking error / focusing error due to the relrhoval of the dummy layer, modification have to be made to the design of the optical storage medium.

All the conventional drives are designed for a 1.4mm thick disc. The optical pickup units of all drives clamp a disc from both sides. Therefore a thinner disc would not be held tightly and would not be read by the drive. This is because the clamping heads or the pins, which hold the disc, expect a 1.4mm thick disc and the clamping mechanism of the drive is not suitable for a 0.6mm±0.1 disc .
This would lead to drive compatibility problem and the disc would fail in many drives.
Accordingly the optical disc as per the instant invention is made compatible to be read by the drive.
As shown in the Figure 3, in order to make the disc more robust and simultaneously improve the drive compatibility, the thickness of the active layer is varied by increasing its thickness over the periphery of the inner hub of said storage medium
In an alternate embodiment, as shown in Figure 4(a), an additional element (5) is provided over the periphery of inner hub of said storage medium in order to make the disc more robust and simultaneously improve the drive compatibility.
In Figure 4(b), an additional element (5) is provided over the optic side of the inner hub of said storage medium in order to make the disc more robust and simultaneously improve the drive compatibility.
All documents cited in the description are incorporated herein by reference The present invention is not to be limited in scope by the specific embodiments and examples which are intended as illustrations of a number of aspects of the invention and any embodiments which are functionally equivalent are within the scope of this invention. Those skilled in the art will know, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. These and all other equivalents are intended to be encompassed by the following claims.

We Claim:
1. An optical storage medium with a central a central clamping area that defines a central aperture and a stacking ring, characterized in that the medium comprises an active layer, the structure of the active layer being modified by varying the thickness of the active layer at a predetermined positions for improving drive compatibility, alleviating the tracking error/ focusing error and /or smoothening the printing process
1. An optical storage medium as claimed in claim 1, wherein said medium does not
comprise a dummy layer.
2. An optical storage medium as claimed in claim 1, wherein the thickness of the
active layer is 0.6mm+/- O.lmm.

5. An optical storage medium as claimed in claim I, wherein the thickness of the
active layer is varied by increasing the thickness of the active layer over the
periphery of an inner hub of said storage medium
6. A thin optical storage medium as claimed in claim: 1, wherein the thickness of the
active layer is varied by increasing the thickness of the active layer over the data
side of an inner hub of said storage medium.
7. A thin optical storage medium as claimed in claim 1, wherein the thickness of the
active layer is varied by providing increasing the thickness of the active layer over
the optic side of an inner hub of said storage medium.
8. An optical storage medium as claimed in claim 1, wherein the thickness of the
active layer is varied by providing an additional element over the periphery of an
inner hub of said storage medium
9. A thin optical storage medium as claimed in claim 1, wherein the thickness of the
active layer is varied by providing an additional element of predetermined
thickness over the data side of an inner hub of said storage medium.

10. A thin optical storage medium as claimed in claim 1, wherein the thickness of the
active layer is varied by providing an additional element over the optic side of an
inner hub of said storage medium.
11. A thin optical storage medium as claimed in claim 1 wherein the thickness of the
central hub is further adjusted to a value between 0.3 mm to 1.40 mm
12. A thin optical storage medium as claimed in claim 11 wherein the thickness of the
central hub is further adjusted to a value between 1.0 mm to 1.40 mm