The present invention relates generally to optical discs. In particular,
the present invention includes an optical disc having high-contrast images within
the disc information area, and a method of forming such discs. The method may include
forming high-contrast images into the diffraction grating in lead-out areas of
a pre-recorded master optical disc using an image mask.
Background of the Invention
Optical discs, such as CD-ROM (Compact Disc-Read Only Memory) or
DVD (Digital Versatile Disc or Digital Video Disc) media, have data stored as a
series of lower "pits" formed within a plane of higher "lands". The pits are arranged
in a spiral track originating at the disc center hub and ending at the disc outer
rim. The data may be considered to lie in a series of tracks spaced radially from
the center hub.
The track typically begins in a "pre-user data" area near the center
hub. The pre-user area contains descriptor information of the disc itself. A "user-data"
area follows the pre-user data area, and contains the data of the disc. A "lead-out"
area follows the user-data area, lying closer to the outer edge of the disc. The
lead-out area contains no user data, but may contain a pattern of pits which can
be a repeating pattern or a random pattern having no data readout value or information
content. The pre-user data area, user-data area, and lead-out area collectively
comprise the "information area" of the disc.
The information content is encoded in the length of the slightly
arcuate, circumferential pits. Microscopically, the track consists of a series
of pits. When viewed with the naked eye, the aligned pits appear to form a continual
groove, with the spiral groove forming a diffraction grating. The diffraction
grating reflects light of varying colors, as described by Bragg's law.
In the lead-out area, the spiral track may be a continuous spiral
groove, having a very long pit, formed not for information content but for appearance.
Thus, while the optical disc may contain a spiral pattern to the outer rim, there
may be very little user-data present, with the lead-out area comprising a majority
of the disc surface in a sparsely populated disc. In even a fully populated disc,
the lead-out area comprises a few millimeters near the outer rim.
A master optical disc is typically manufactured by coating a glass
substrate with a photosensitive layer (e.g., photoresist), followed by baking the
coated substrate. A laser is thereafter used to expose portions of the photoresist
in a spiral pattern of circumferential arcs of varying length, corresponding to
the later formed pits. The master disc is thereafter developed, with the exposed
areas being washed away, forming pits. The unexposed areas remain, forming a plane
of higher "lands." As such, the master disc is said to be a "pre-recorded" optical
disc. For example, pre-recorded optical media may include CD-ROM, DVD, laser vision,
The master disc is used as a mold to form one or more harder, metallised,
"stampers", having bumps corresponding to the pits in the master disc. The stampers
are used to form the optical discs via injection molding, the final discs having
pits corresponding to the bumps in the stampers corresponding to the pits in the
In CD-ROMs, the readable side includes a transparent polycarbonate
bottom layer having the reflective layer thereover, which in turn has a protective
"lacquer" layer thereover, which can include a label. The readable side is typically
placed face down over a laser reader which penetrates the transparent layer to
the single reflective layer having pits. As an example, in pre-recorded media,
pits are formed in such a way to give a high contrast signal relative to the land.
DVDs are optical discs having increased capacity relative to CD-ROMs.
In one example, this is achieved in part by having double sided discs. Double sided
DVDs have two reflective layers, each facing outward, requiring flipping the disc
to read each side or an additional device to read the second side. Double sided
media such as DVDs require each side to be transparent, and thus have a special
labelling requirement, as covering one side with lacquer and label is no longer
possible. Any label or image on the disc must be both visible, and transparent
to a laser in the region containing data.
Labelling of the previously described optical discs is important.
Labelling can operate as a deterrent to piracy. The data on optical discs, being
digital, can be read perfectly, and reproduced perfectly, in unlimited quantities.
Standard printed labels on the lacquer side of CD-ROMs can also easily be reproduced,
using techniques similar to those used to produce the original labels. Labelling
requiring the creation of art-work on the master discs or stampers themselves
would require significantly more effort and/or specialized equipment to produce
copies capable of passing as the original discs.
One known method of labeling optical discs is described in U.S. Patent
No. 5,607,188, issued March 4, 1997, entitled "Marking of Optical Disc for Customized
Identification". The above referenced patent includes an optical disc which is
labeled by incorporating a low contrast image, such as a "watermark"; into the
optical disc substrate. The image is a low contrast image which is located in the
user-data area of the disc and includes optically readable data encoded therein.
In one known optical disc described in WO 94/10684, an optically readable
information disc is suggested which includes an optically transparent disc-shaped
substrate including concentric data in hologram areas. The data area contains an
optically viewable information signal. The hologram area contains at least one
visible, ornamental hologram.
US-A-5 608 718 discloses a disc with an optically viewable image in
the information area including lead-out area by reducing the hight of the loads
up to a maximum of 30%. Outside that area the reduction can have any value.
It would be desirable to mark a disc in a way that would identify
a disc as being authentic, that is, as having been manufactured by an authorized
source. It is desirable to have an optical disc, which includes high-contrast
images, such as a logo, alphanumeric characters or symbols, in the information
area of the disc. Further, it is desirable to have a method for high-contrast
labeling or putting high-contrast images within the information area of the disc
which is accomplished at the master disc level and does not require the use of
Summary of the Invention
The present invention is an optical disc having high-contrast images
in the information area of the disc and a method for creating high-contrast images
in the information area of optical discs as recited in the claims. The present
invention, including a method of creating high-contrast images in the lead-out
area of master optical discs, may include using an image mask and a light source.
In one preferred embodiment, the present invention includes an optical
disc having high-contrast images formed therein. The optical disc includes an
information area, wherein the information area is defined as an area capable of
containing data readable by an optical disc player. An optically viewable high-contrast
image is formed within the information area. The information area includes a plurality
of lands and pits, wherein the optically viewable high-contrast image is defined
by an absence of lands located within the area including lands and pits. Further,
user data may be contained within the information area. In one embodiment, the
user data is located adjacent the high-contrast image.
The information area includes a data content area and a lead-out
area, wherein the optically viewable high-contrast image is located within the
lead-out area. The information area may further comprise a pre-user data area.
In one embodiment, the user data is located within the data content area.
The method can include providing a glass substrate covered by a photosensitive
layer. In one embodiment, a diffraction pattern mask having a spiral pattern or
pattern of concentric circles is used as a pattern mask. In another embodiment,
a random pattern of dots is used as a pattern mask. The pattern mask is interposed
between the master disc and a light source, and the photosensitive layer exposed
for a desired period of time to lead to a subsequent pattern on the master disc.
Light is then projected through an image mask onto the photosensitive layer, for
a sufficient duration to lead to subsequent total or nearly total removal of the
photosensitive layer down to the substrate level. The exposed master disc is developed,
removing the photosensitive layer in areas corresponding to the pattern and image
masks. In one embodiment, the pattern and image masks are combined.
The resulting master disc, in a single sided embodiment, can have
an information area including an inner pre-user data area, a user-data area, and
an outer lead-out area. The image may be located within the information area,
and in particular may be located within the lead-out area. The user-data consists
of circumferential pits within the photosensitive layer, lying along a spiral
path, resembling a continuous spiral. The high-contrast image can consist of areas
in the diffraction pattern where the diffraction pattern grating is removed, substantially
down to the glass substrate level, and/or even with the bottom of the master data
The resulting high-contrast images are easier to read to the unaided
eye than aforementioned low contrast images within the user-data area. The high-contrast
images may be used on the sparsely populated side of a double sided disc to list
the disc contents. The images may also be used as a difficult to reproduce indicia
of origin, for making counterfeiting more difficult. The method of producing a
master disc having a high-contrast image located within the information area does
not require the use of a time consuming laser process for burning the image therein.
Brief Description of the Drawings
Other objects of the present invention and many of the attendant
advantages of the present invention will be readily appreciated as the same becomes
better understood by reference to the following detailed description when considered
in connection with the accompanying drawings, in which like reference numerals
designate like parts throughout the figures thereof, and wherein:
Detailed Description of the Preferred Embodiments
- Figure 1 is a plan view of a readable side of an optical disc having a high-contrast
image in the information area of the disc;
- Figure 2 is a partial cross-sectional view taken along line 2-2 of Figure 1;
- Figure 2A is a partial cross-sectional view taken along line 2-2 of Figure
1, showing a dual sided optical disc having high-contrast images located within
the information area in accordance with the present invention;
- Figure 3 is a diagram illustrating a step in the method of creating a master
disc in accordance with the present invention;
- Figure 4 is a diagram illustrating another step in the method of creating a
master disc in accordance with the present invention;
- Figure 5 is a cross-sectional view of the master disc of Figures 3 and 4 after
- Figure 6 is a diagram illustrating another method of creating a master disc
in accordance with the present invention.
Although a CD ROM optical disc is used in the exemplary embodiment
described herein, it is recognized that the field to which this invention pertains
includes all types of optical data discs having information contained in data structures
therein as data features, and the referenced plan for the data features. In various
formats of optical data discs, the data features may include data pits, grooves,
bumps or ridges, and lands or land area in between. This includes current formats
of audio CD, CD-R, CD-ROM, and video discs, DVD, as well as future formats which
use data features described herein. The definition of optical discs also includes
various types of magneto-optical discs, which commonly use data features, such
as grooves or pits, for tracking and address identification, even though data is
subsequently recorded magneto-optically.
As previously described herein, the production of optical data discs
usually includes the three general steps of producing a master, a stamper, and
the replicas, which are the final product. Although there are variations in specifics
of processing steps, these three steps are almost always involved. The master is
often made on a glass disc coated with photoresist, and exposed by a modulated
laser beam which writes the data on the master by selectively exposing areas of
the photoresist, which, after development, become the optically encoded data features
with respect to a reference plane which may be formed by the unexposed areas.
A stamper is then made from the master, having a mirror-image pattern of the data
features. The stamper is then used to mass produce the replicas, by various injection
molding or pressing processes. Each replica disc has the same data patterns which
were originally created on the master disc (or their inverse, i.e., bumps instead
of pits, depending on which side of the disc is to be read).
The present invention creates high-contrast markings, including labels,
images or authenticity markings (in the information area of the disc) on the master
disc through special processing steps described herein. Because this is done at
the master level, it is not necessary to alter the steps of making the stamper
and replicas, and in this way, pre-existing stamper and replica production operations
can then be used to produce replica optical data discs having a high-contrast
image therein within the information area of the disc.
One preferred embodiment of the invention uses a high-contrast visible
diffraction effect on the surface of the master disc in the information area of
the disc to create the image, which will subsequently be transferred to the final
optical data disc during replication. The data features on the disc give the appearance
of a high-contrast periodic diffraction grating, visible to the unaided eye. This
embodiment of the invention places a unique image, pattern or patterns on the
optical disc within the information area which can be observed as contrasting to
the normal or background diffraction grating effect due to the data features,
giving the image appearance in the selected area.
Figure 1 illustrates a readable side of an optical disc 20 having
a high-contrast image 22 in accordance with the present invention. Although the
Imation logo is shown, it is recognized that almost any image or character may
be produced within the disc substrate. The side shown is capable of being illuminated
by a laser and read. Disc 20 may be an optical disc, such as CD-ROM or a DVD optical
disc. The opposite side (not shown in Figure 1) may be either an opaque, labelled,
lacquer side, or a second, readable side. Disc 20 includes an inner rim 23, an
inner annular ring 24, an information area 25, an outer annular ring 32 and an
outer rim 34.
The information area 25 is defined as the area on the disc capable
of containing user data. The information area 25 includes a pre-user data area
26, a user-data area 28, and a lead-out area 30. Pre-user data area 26 typically
contains information about the disc contents, such as descriptor information. User-data
area 28 contains the user accessible contents of the disc. Lead-out area 30 typically
appears as a spiral track similar to that in the user-data area, but may contain
no information readable by an optical disc player.
The information area 25 is the area available for information storage,
even though much of it may be taken up with lead-out area 30 when the disc has
little user-data encoded. The information area 25 contains high-contrast image
22, such as the Imation logo shown consisting of a design and alphanumeric characters.
As shown, the high-contrast image 22 is located in the lead-out area 30 of the
information area 25.
In Figure 2, a partial cross-sectional view of optical disc 20 (including
image 22) taken through 2-2 of Figure 1 is shown. Disc 20 includes a data substrate
40, a reflective layer 41 and a protective substrate 42. The reflective layer 41
is interposed between the data substrate 40 and the protective substrate 42.
The data substrate 40 is generally transparent and includes a series
of lands 50 and pits 52. The lands 50 and pits 52 are located within data region
54. The data substrate 40 further includes image region 56 which forms a portion
of the image 22.
Image region 56, containing a portion of image 22, has no lands 52 located therein.
The absence of lands 52 in image region 56 results in the optically visible high-contrast
Regions 54 and 56 are visibly different, as region 56 is devoid of
the diffraction pattern. The image 22 formed by region 56 contrasted with region
54 results in a "high-contrast" image, as region 54 consists of pits 52 and region
56 has no lands 50, the lands 50 being substantially, if not completely, absent.
The reflective layer 41 extends over the data substrate 40. Specifically,
the reflective layer 41 is deposited over data region 54 and image region 56,
including lands 50 and pits 52. Protective layer 42 covers the reflective layer
The optical disc 30 is read through the data substrate 40, indicated
by read side arrow 58. In a single sided disc, the opposite side, defined as non-read
side 59, may be clear or include a disc label.
In one preferred embodiment, the data substrate 40 is clear and formed of a polycarbonate.
The reflective layer 41 is formed of a reflective material, such as aluminum or
gold, having an approximate reflectivity rating of 70 percent. The protective substrate
42 is formed of a lacquer which may be opaque or clear. If the lacquer is clear,
and no label is contained on non-read side 59, the reverse of image 22 may be
viewed through non-read side 59.
A reference plane may be defined through the disc, such as pits 52.
The height difference between lands 50 and pits 52 relative to the reference plane
forms data feature patterns sufficiently high to be optically readable for data
in the user-data area 54.
In the image area 56, the lands 50 and pits 52 are no longer optically
readable, but are optically viewable, with the substantial absence of lands 50
forming high-contrast image 22. In one preferred embodiment, the lands 50 are
removed at least to the level of the pits 52.
In Figure 2A, a partial cross-sectional view of a dual sided optical
disc 20 in accordance with the present invention is generally shown. The dual sided
optical disc 20 is formed by securing two single layer optical discs together,
each single layer optical disc being similar to the single layer optical disc 20
previously described. As shown, the two single layer optical discs are secured
together using an adhesive layer 57. The dual sided optical disc 20 includes a
second read side 58a, and a second data substrate 40a. Similar to data substrate
40, the data substrate 40a includes lands 50a and pits 52a. Further, the second
side 58a includes a second data region 54a and a second image region 56a, which
forms a high-contrast image therein. With this embodiment, a high-contrast image
may be provided within the information area on each side of the dual sided optical
disc 20. For example, the first side of the dual sided optical disc 20 may include
user data and the disc name within the information area, and the second side may
include additional user data and a high-contrast image showing the table of contents
of the disc 20.
As previously discussed, a replica optical disc is created from a
master disc via a metalized stamper disc. Figures 3-6 illustrate a master disc
60 in accordance with the present invention and a method of creating a master
disc 60 having a diffraction pattern for producing the replica disc 20 having a
high-contrast image 22 in the information area 25 of the disc 20.
In Figure 3, the process of creating master disc 60 includes providing
a glass substrate 62 coated with a photosensitive layer 64. In one exemplary embodiment,
the photosensitive layer 64 may be secured to the substrate 62 using a primer layer
(not shown). The photosensitive layer 64 is responsive to a light source. In one
embodiment, the substrate 62 is formed of glass or quartz and the photosensitive
layer 64 is formed of photoresist.
A pattern mask 66 is placed over and parallel to the plane of photosensitive
layer 64. In one embodiment, the pattern mask 66 may include a chrome pattern
on a glass substrate. The glass substrate has an absence of chrome corresponding
to the desired pattern. In a preferred embodiment, pattern mask 66 is a diffraction
pattern mask. The spiral track which will result is similar to the spiral track
of pits in the user-data area, but with the spiral track being a continuous groove.
In another embodiment, pattern mask 66 is a random pattern mask. A random pattern
mask in one embodiment is a pattern of seemingly random dots.
A light source 68 is used for transferring the mask 66 pattern to
the master disc 60. In one embodiment, the light source is a UV light source. In
one exemplary embodiment, the UV light source may include a mercury lamp or a
laser light source. The pattern mask 66 is positioned between the master disc
60 and the light source 68. In operation, the light source 68 emitting light 71
is placed over pattern mask 66, and photosensitive layer 64 is exposed to the
light 71 for a period of time sufficient to create the desired reaction. The amount
of exposure reaction is dependent upon the light source and the duration of the
exposure to the light source.
In one preferred embodiment, master disc 60 is a pre-recorded master,
meaning it has user-data already encoded on the disc. In one method, the master
disc 60 is prerecorded using a laser beam writer to record data by exposing photoresist
in regions corresponding to future data pits as is well known in the art. Upon
the further exposure of master disc 60 in accordance with the present invention,
both user-data, diffraction patterns, and images may be developed in a development
It is also recognized that master disc 60 may not be prerecorded,
and may have pre-user data and user-data portions encoded using a mask similar
to pattern mask 66, but encoding for data pits rather than simply an arbitrary
diffraction pattern. In this embodiment, a laser beam is not required to either
write data or form images on the disc.
Figure 4 illustrates further processing of master disc 60 to form
an image in master disc 60, corresponding to the high-contrast image 22. An image
mask 67 is placed over and parallel to the plane of photosensitive layer 64. Light
71 is used to further expose photosensitive layer 64. Image mask 67 is used to
form the image such as the image 22 of Figure 1, on master disc 60. In one embodiment,
the image mask 67 is formed of any material opaque to UV light in the form of
an image. The substrate has an absence of material corresponding to the desired
image pattern. Exposure time and intensity are sufficient to insure that no lands,
or lands of only very small height, will remain in exposed areas (such as an open
mask area 65). In the preferred embodiment shown, the photosensitive layer 64
below the openings in mask 67 is removed entirely down to the glass substrate.
The previous exposure from the pattern mask is thus added to in area 65. In closed
mask areas such as area 63, no light reaches the photosensitive layer 64, leaving
the previous pattern mask 66 exposure unchanged.
Referring to Fig. 5, master disc 60 is developed, leaving only portions
of photosensitive layer 64. Photosensitive layer 64 now includes a pattern region
74 corresponding to mask area 63 (Figure 4) and a low, flat region 75 corresponding
to transparent mask region 65. In one embodiment, pattern region 74 is a diffraction
pattern including a series of master lands 72 and master pits 70.
The master disc 60 is a master of the replica discs (such as optical
disc 20) which will be formed from the master disc 60 in a stamper/disc molding
process. Region 75 corresponds to a portion of the image 22 on replica optical
discs 20. A plane may be generally defined by the bottom of the master pits 70.
Within region 75, the master lands 72 have been totally removed using the above
image mask process, down to the plane defined by the bottom of the pits 70. In
one preferred embodiment, the master lands 72 are totally removed within region
75, exposing the substrate 62 (and/or the adhesive layer between the photosensitive
layer 64 and the substrate 62). By removing master lands 72 in a pattern corresponding
to the desired image 22, a replica disc 20 formed using master disc 60 will have
a high-contrast image located therein.
Master disc 60 is used to form a metalized stamper as previously
described. The stampers will have ridges or stamper bumps corresponding to master
pits 70. The stampers can be used to produce replica discs such as disc 20 in
Figure 1, having pits 52 corresponding to master pits 70 in Figure 5. To form
a dual sided optical disc, two separately stamped single layer optical discs may
be secured together at their nonreadable sides using an adhesive (as shown in
Referring to Fig. 6, an alternate method of forming master disc 60
in accordance with the present invention is shown. The invention includes combining
the functions of the pattern mask 66 (Fig. 3) and the image mask 67 (Fig. 4) into
one combination mask 73. The combination mask 73 can be utilized to eliminate
one of the two light exposure steps previously described herein.
The images formed are high-contrast as they are the result of differences
between the high land surfaces and the low surfaces level with the bottom of the
pits, and absence of pits within the image area. The area of the disc containing
the image does not allow user data to be readable by an optical disc player. The
resulting high-contrast images can be used to produce more easily readable labels
and images on optical discs in the disc information area relative to the images
resulting from only light exposure which are optically readable. The high-contrast
images are formed by reducing the height of the lands to nothing or nearly nothing,
at least down to the level of the bottom of the pits. This is not possible in areas
containing user data, as the data resides in the lands separating the pits. For
this reason, the present method is appropriate in the information area lead-out
area, which typically has a diffraction pattern, but no user data. The present
invention can be practiced in the information area of the disc, but outside of
the area containing user-data.
The high-contrast image can be used to both verify authenticity and
describe the disc contents. In a dual sided optical disc embodiment having little
or no data on one side, the high-contrast image can be used as a label, and list
the disc contents on that sparsely populated side. The image may be located within
a periodic diffraction pattern or a random pattern area.
The high-contrast image 22 in the resulting surface structure of
the optical disc 20 is visible to the human eye. This is because the high-contrast
image 22 has obliterated entire sections of land surface structure, including
any position information.
The above method of forming high-contrast images in the information
area of a disc does not require the use of a time-consuming laser beam recording
Further, since the images formed are high-contrast images, the lead-out
area on a disc may be utilized for containing important information therein, such
as a disc table of contents, logo, or other information.
The master disc resulting from the image mask process allows conventional
disc molding processes to be used for forming replica discs.
Although the process described herein refers to a "positive" image
forming process, it is recognized that a master disc could be formed having a negative
image therein utilizing the same masking techniques. Specifically, the image portion
of the mask would not allow light to pass through to the photosensitive layer,
such that when the master disc is developed, the remaining photosensitive layer
is in the form of the image, with the remaining portion being the washed away
portion down to the master disc substrate.
Numerous characteristics and advantages of the invention covered
by this document have been set forth in the foregoing description. It will be understood,
however, that this disclosure is, in many respects, only illustrative. Changes
may be made in details, particularly in matters of shape, size, and arrangement
of parts without exceeding the scope of the invention. The invention's scope is,
of course, defined in the language in which the appended claims are expressed.