Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
2001-02-28
2003-02-18
Mulvaney, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S064400, C428S064800
Reexamination Certificate
active
06521318
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a new type of optical disk and a method for implementing the effects of the new device on existing optical disks, and in particular, to an optical disk with improved digital or analog signal reproduction from the optical disk coding by an optical reading assembly. Both the device and the method of the present invention extend to all forms of optical disk including, but not limited to prerecorded, recordable, rewriteable (magneto-optical) and other forms of optical disk.
BACKGROUND ART
Presently, optical disks consist of a layered structure
1
as shown in FIG.
1
. In an optical disk player, laser light
2
from a laser diode is focused by the action of a series of lenses, and the transparent polycarbonate layer
3
itself, onto a reflective surface
4
. The reflected light is then passed back into the optical system and separated, usually by a quarter-wave polarising plate or a half mirror, then detected by a series of photodiodes. By way of fast action servo systems, voltage levels from photodiodes control an objective lens to keep the focused region of the laser beam in alignment with the desired part of the optical disk.
The depth of the pits
5
is important for the operation of the disk. Pits are generally made a quarter of the laser light wavelength in depth. As the laser light is coherent and the reflected light from the region in-between the pits, defined as the land-region
6
, travels an extra half wavelength compared to light from the reflective surface of the pits
4
which results in a degree of annihilation of the reflected light.
Thus, pit edges and surrounding land-regions are indicated by a low level of reflectance intensity, however, when the laser beam is focused on the reflective coating a strong reflective signal is obtained. This discrimination process leads to the reading of the information on an optical disk.
To further illustrate this,
FIG. 2
shows laser light
2
from a light source positioned over a pit
5
. Reflected laser light from near the pit edge at position
7
is a half-wavelength out of phase with reflected laser light from the position
8
if the depth of the pit
5
is a quarter of the wavelength of the laser light. Hence, reflected laser light from the periphery regions of a pit
5
and corresponding regions adjacent the pit, that is at the edge of land-regions
6
, is low in intensity due to superpositioning of the 180° out of phase reflected coherent laser light. It is these nulls in light intensity which are manifested as the information on the optical disk.
Digital optical disks may use a pit format which uses a master clock to identify information based on time-length. Normally, the master clock period is denoted T, then the smallest pit-length or land-length (that is the region between pits) is denoted 3T, then 4T, 5T, etc. The longest pit-length or land-length is denoted as 11T. These pit-lengths and land-lengths are a common element in present-day digital technology. Normally, the smallest pit-length period 3T is ‘1’ in computer binary; 4T is ‘11’ in computer binary; and so on, they represent the positive waveform. The smallest land-length period 3T is ‘0’ in computer binary; 4T is ‘00’; and so on, they represent the negative waveform. In a typical format, an analog waveform is completely represented by an eighteen digit word.
The protective film
9
, shown in
FIG. 1
, is typically used to prevent damage to the pits which are in close proximity to the surface, and to allow a label to be imprinted onto the disk. The reflective information layer of some optical disk formats allow single-layer, dual-layer or multi-layer films on one side of disk. The analog tracks of an optical disk are recorded with small precise pits having variation in depth in the disk surface.
It is the variation in the intensity of reflected light which allows reproduction of the information contained within the disk as a configuration of pits to be reproduced electronically via the photodiodes. Inherent variations in reflection coefficients in the disk device can introduce undesirable noise levels, which if significant will result in misread or lost information.
Patent document U.S. Pat. No. 5,190,800 teaches of an optical recording medium having a substrate which contains a light absorbent capable of absorbing light other than the light used for recording and reproducing. This light filtering mechanism affects the overall transmittance of various wavelengths of light incident on the substrate but does not provide an enhanced means for edge (pit and land) identification in the optical recording medium. The document does not disclose a means for addressing the effects of reflected or refracted laser light inside the optical disk. Indeed, it is an object of this document to provide an optical recording medium which does not suffer from deterioration by ordinary light, rather than aid in the reproduction of signals by enhanced edge (pit and land) identification from the optical recording medium. Neither does the presence of a recording layer, light reflective layer or protective layer assist in this respect. These components are standard features of optical disks today and are not directed at assisting in edge (pit and land) identification at the recording and light reflective layers.
A brief outline of current optical disk technology, which is applicable to the present invention, follows. A recordable optical disk is typically structured as shown in FIG.
3
. There is a thin exposed layer
10
and a reflecting layer
11
. The reflecting layer
11
is positioned behind the exposed layer
10
and opposite the laser source. The reflecting layer
11
replaces the reflective surface
4
of
FIG. 1. A
short pulse of laser light is used to burn a spot on the exposed layer
10
when the material is in its amorphous state. These spots can create a ‘pit’ of a desired length.
Magneto-optical disks, also called erasable rewriteable-optical disks, are based on a hybrid of optical disk technology and magnetic disk technology. The thin exposed layer
10
, of
FIG. 3
, is in this case a material which allows its magnetic state to be changed when heated to a certain temperature. Thus, this material replaces the thin exposed layer of a recordable laser disk. A low power laser is used to read the ‘pits’ by detecting magnetic spots on the disk. The spots also keep the magnetic field direction they developed when heated. Another higher power laser is used to heat spots which thus change their magnetic state, hence making the ‘pits’ erasable.
Hence, there are different formats of laser optical disk, the structures having different reflecting layers which may reflect a particular wavelength of the incident laser light. Modern lasers for optical disks often have automatic gain control circuits which help the opto-electronics read from the different reflecting layers. The basic format variations of the standard CDs family of optical disks include: Audio CD, CD-ROM, Video CD, CD-I, CD-R, CD-RW, Photo CD, CD-G, MovieCD, etc.
The detecting sensor (photodiode) is very important in laser optical technology. However, the photodiode does not detect what wavelength of light is reflected by the target. Additionally, the photodiode does not discriminate between light that is reflected or refracted by materials outside of the target, thus an ambiguous light signal may be obtained. This is the basis of a large proportion of errors being readout from the information on a disk.
Reduction of noise levels, that is a dither effect from pit reflection, induced by opto-electronics reading optical disks, and by the structure of the optical disks themselves, is an important issue. Besides improving the quality of sound and removing reading errors, improved identification of edge regions will allow a clear contrast between a pit-edge and a land-edge to be observed which may allow a higher density of digital information to be contained within an optical disk.
This identifies a need for an improved optical disk wherein higher reflected optical intensities
Cesari and McKenna LLP
Mulvaney Elizabeth
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