U.S. patent application number 12/775590 was filed with the patent office on 2011-11-10 for system and method for improved data storage.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to John Erik Hershey, Brian Lee Lawrence, Victor Petrovich Ostroverkhov, John Anderson Fergus Ross, Milos Todorovic, Kenneth Brakeley Welles, II.
Application Number | 20110273973 12/775590 |
Document ID | / |
Family ID | 44263258 |
Filed Date | 2011-11-10 |
United States Patent
Application |
20110273973 |
Kind Code |
A1 |
Ross; John Anderson Fergus ;
et al. |
November 10, 2011 |
SYSTEM AND METHOD FOR IMPROVED DATA STORAGE
Abstract
A method for storing data on a storage medium is provided. The
method includes receiving a modulated bitstream, wherein the
modulated bitstream comprises a plurality of bits comprising a
bitstate of 1 and 0. The method also includes secondary modulating
each of the pluality of bits comprising the bitstate of 1 to output
a plurality of secondary modulated bits. The method further
includes forming a plurality of marks in the storage medium, the
marks indicative of each of the plurality of secondary modulated
bits and the plurality of bits comprising the bitstate of 0 in the
modulated bitstream.
Inventors: |
Ross; John Anderson Fergus;
(Niskayuna, NY) ; Ostroverkhov; Victor Petrovich;
(Ballston lake, NY) ; Hershey; John Erik;
(Ballston Lake, NY) ; Lawrence; Brian Lee;
(Waunakee, WI) ; Welles, II; Kenneth Brakeley;
(Scotia, NY) ; Todorovic; Milos; (Niskayuna,
NY) |
Assignee: |
GENERAL ELECTRIC COMPANY
SCHENECTADY
NY
|
Family ID: |
44263258 |
Appl. No.: |
12/775590 |
Filed: |
May 7, 2010 |
Current U.S.
Class: |
369/47.19 ;
G9B/20.009 |
Current CPC
Class: |
G11B 7/0065 20130101;
G11B 7/007 20130101 |
Class at
Publication: |
369/47.19 ;
G9B/20.009 |
International
Class: |
G11B 20/10 20060101
G11B020/10 |
Claims
1. A method for storing data on a storage medium, the method
comprising: receiving a modulated bitstream, wherein the modulated
bitstream comprises a plurality of bits comprising a bitstate of 1
and 0; secondary modulating each of the pluality of bits comprising
the bitstate of 1 to output a plurality of secondary modulated
bits; and forming a plurality of marks in the storage medium, the
marks indicative of each of the plurality of secondary modulated
bits and the plurality of bits comprising the bitstate of 0 in the
modulated bitstream, wherein said forming the plurality of marks
comprises forming a stepped pattern of micro-reflectors along
multiple tracks of a single layer of the storage medium.
2. The method of claim 1, comprising primary modulating an optical
signal to output the modulated bitstream.
3. The method of claim 2, wherein said primary modulating comprises
modulating via non-return to zero I (NRZI) modulation.
4. The method of claim 1, wherein said secondary modulating
comprises phase modulating the modulated bitstream.
5. The method of claim 4, wherein said phase modulating comprises
discretely phase modulating the modulated bitstream.
6. The method of claim 5, wherein said discretely phase modulating
comprises employing a lattice code scheme.
7. The method of claim 5, wherein said discretely phase modulating
comprises employing forward error correction coding.
8. (canceled)
9. The method of claim 1, wherein said forming the plurality of
marks comprises forming a stepped pattern of micro-reflectors
across multiple layers of the storage medium.
10. The method of claim 1, wherein said secondary modulating
comprises depth modulating the modulated bitstream.
11. The method of claim 1, wherein said secondary modulating
comprises amplitude modulating the modulated bitstream.
12. A method for storing data on a storage medium, the method
comprising: receiving a modulated bitstream, wherein the modulated
bitstream comprises a plurality of bits comprising a bitstate of 1
and 0; secondary modulating each of the pluality of bits comprising
the bitstate of 1 to output a plurality of secondary modulated
bits; and forming a plurality of marks in the storage medium, the
marks indicative of each of the plurality of secondary modulated
bits and the plurality of bits comprising the bitstate of 0 in the
modulated bitstream, wherein said forming the plurality of marks
comprises forming a stepped pattern of micro-reflectors across
multiple layers of the storage medium.
13. The method of claim 12, further comprising primary modulating
an optical signal to output the modulated bitstream.
14. The method of claim 12, wherein said secondary modulating
comprises phase modulating the modulated bitstream.
15. An optical recording system for a storage medium comprising: a
processor configured to: modulate a channel of bits to output a
modulated bitstream, wherein the modulated bitstream comprises a
plurality of bits comprising a bitstate of 1 and 0; and secondary
modulate each of the pluality of bits comprising the bitstate of 1
to output a plurality of secondary modulated bits; and an optical
drive electronics unit electrically coupled to the processor, the
optical drive electronics unit configured to: receive one or more
command signals from the processor; and actuate one or more optical
components to form a plurality of marks on the storage medium
indicative of the plurality of secondary modulated bits, wherein
the plurality of marks comprise a plurality of micro-holograms.
16. The optical recording system of claim 15, wherein the secondary
modulated bits comprise at least one of a plurality of phase
modulated bits, depth modulated bits, amplitude modulated bits or a
combination thereof.
17. The optical recording system of claim 15, wherein the storage
system comprises a holographic disk.
18. (canceled)
19. An optical reader for a storage medium comprising: an optical
drive electronics unit configured to: detect a reflected light beam
from the storage medium, wherein the storage medium comprises a
plurality of bits in a modulated bitstream comprising a bitstate of
0 and a plurality of secondary modulated bits; and detect in the
reflected light beam either one of: plurality of bits comprising
the bitstate of 0 in the modulated bitstream; or the plurality of
bits comprising the bitstate of 0 in the modulated bitstream and
the plurality of secondary modulated bits, wherein said optical
drive electronics unit comprises a homodyne detector.
20. The optical reader of claim 19, wherein said storage medium
comprises a a holographic disk.
21. An optical recording system for a storage medium comprising: a
processor configured to: modulate a channel of bits to output a
modulated bitstream, wherein the modulated bitstream comprises a
plurality of bits comprising a bitstate of 1 and 0; and secondary
modulate each of the pluality of bits comprising the bitstate of 1
to output a plurality of secondary modulated bits; and an optical
drive electronics unit electrically coupled to the processor, the
optical drive electronics unit configured to: receive one or more
command signals from the processor; and actuate one or more optical
components to form a plurality of marks on the storage medium
indicative of the plurality of secondary modulated bits, wherein
the storage medium comprises a holographic disk.
22. The optical recording system of claim 21, wherein the secondary
modulated bits comprise at least one of a plurality of phase
modulated bits, depth modulated bits, amplitude modulated bits or a
combination thereof.
23. A method for storing data on a storage medium, the method
comprising: receiving a modulated bitstream, wherein the modulated
bitstream comprises a plurality of bits comprising a bitstate of 1
and 0; secondary modulating each of the pluality of bits comprising
the bitstate of 1 to output a plurality of secondary modulated
bits, wherein the secondary modulating comprises phase modulating
the modulated bitstream, wherein the phase modulating comprises
discretely phase modulating the modulated bitstream, wherein said
discretely phase modulating comprises employing a lattice code
scheme; and forming a plurality of marks in the storage medium, the
marks indicative of each of the plurality of secondary modulated
bits and the plurality of bits comprising the bitstate of 0 in the
modulated bitstream
Description
BACKGROUND
[0001] The present techniques relate generally to bit-wise
holographic data storage techniques. More specifically, the
techniques relate to methods and systems for modulating bit streams
for storage on optical disks.
[0002] As computing power has advanced, computing technology has
entered new application areas, such as consumer video, data
archiving, document storage, imaging, and movie production, among
others. These applications have provided a continuing push to
develop data storage techniques that have increased storage
capacity. Further, increases in storage capacity have both enabled
and promoted the development of technologies that have gone far
beyond the initial expectations of the developers, such as gaming,
among others.
[0003] The progressively higher storage capacities for optical
storage systems provide a good example of the developments in data
storage technologies. The compact disk, or CD, format, developed in
the early 1980's, has a capacity of around 650-700 MB of data, or
around 74-80 min. of a two channel audio program. In comparison,
the digital versatile disc (DVD) format, developed in the early
1990's, has a capacity of around 4.7 GB (single layer) or 8.5 GB
(dual layer). The higher storage capacity of the DVD is sufficient
to store full-length feature films at older video resolutions (for
example, PAL at about 720 (h).times.576 (v) pixels, or NTSC at
about 720 (h).times.480 (v) pixels).
[0004] However, as higher resolution video formats, such as
high-definition television (HDTV) (at about 1920 (h).times.1080 (v)
pixels for 1080p), have become popular, storage formats capable of
holding full-length feature films recorded at these resolutions
have become desirable. This has prompted the development of
high-capacity recording formats, such as the Blu-ray Disc.TM.
format, which is capable of holding about 25 GB in a single-layer
disk, or 50 GB in a dual-layer disk. As resolution of video
displays, and other technologies, continue to develop, storage
media with ever-higher capacities will become more important. One
developing storage technology that may better achieve future
capacity requirements in the storage industry is based on
holographic storage.
[0005] Holographic storage is the storage of data in the form of
holograms, which are images of three dimensional interference
patterns created by the intersection of two beams of light in a
photosensitive storage medium. Both page-based holographic
techniques and bit-wise holographic techniques have been pursued.
In page-based holographic data storage, a signal beam which
contains digitally encoded data is superposed on a reference beam
within the volume of the storage medium resulting in a chemical
reaction which, for example, changes or modulates the refractive
index of the medium within the volume. This modulation serves to
record both the intensity and phase information from the signal.
Each bit is therefore generally stored as a part of the
interference pattern. The hologram can later be retrieved by
exposing the storage medium to the reference beam alone, which
interacts with the stored holographic data to generate a
reconstructed signal beam proportional to the initial signal beam
used to store the holographic image.
[0006] In bit-wise holography or micro-holographic data storage,
every bit is written as a micro-hologram, or Bragg reflection
grating, typically generated by two counter-propagating focused
recording beams. The data is then retrieved by using a read beam to
reflect off the micro-hologram to reconstruct the recording beam.
Accordingly, micro-holographic data storage is more similar to
current technologies than page-wise holographic storage. However,
in contrast to the one to a few layers of data storage that may be
used in DVD and Blu-ray Disk.TM. formats, holographic disks may
have 50 or 100 layers of data storage, providing data storage
capacities that may be measured in terabytes (TB).
[0007] With rapid advances in technology, multimedia with enhanced
features are being produced that require high storage capacity and
upgraded technology drives to reproduce the content. Consequently,
this results in increased manufacturing costs. Furthermore, there
is an increasing demand in storage industry in terms of storage
capacity and data transfer rate. Accordingly, there is a need for
an improved storage system that may address one or more of the
aforementioned issues.
BRIEF DESCRIPTION
[0008] In accordance with an embodiment of the invention, a method
for storing data on a storage medium is provided. The method
includes receiving a modulated bitstream, wherein the modulated
bitstream comprises multiple bits comprising a bitstate of 1 and 0.
The method also includes secondary modulating each of the multiple
bits comprising the bitstate of 1 to output multiple secondary
modulated bits. The method further includes forming multiple marks
in the storage medium, the marks indicative of each of the multiple
secondary modulated bits and the plurality of bits comprising the
bitstate of 0 in the modulated bitstream.
[0009] In accordance with another embodiment of the invention, an
optical storage disk is provided. The optical storage disk includes
at least one recording layer, wherein the recording layer comprises
a photosensitive media comprising multiple micro-holograms, wherein
each of the micro-holograms are indicative of multiple secondary
modulated bits.
[0010] In accordance with another embodiment of the invention, an
optical recording system for a storage medium is provided. The
optical recording system includes a processor configured to
modulate a channel of bits to output a modulated bitstream, wherein
the modulated bitstream comprises multiple bits including a
bitstate of 1 and 0. The processor is also configured to secondary
modulate each of the multiple bits comprising the bitstate of 1 to
output multiple secondary modulated bits. The optical recording
system also includes an optical drive electronics unit electrically
coupled to the processor, wherein the optical drive electronics
unit is configured to receive one or more command signals from the
processor. The optical drive electronics unit is also configured to
actuate one or more optical components to form multiple marks on
the storage medium indicative of the multiple secondary modulated
bits.
[0011] In accordance with yet another embodiment of the invention,
an optical reader for a storage medium is provided. The optical
reader includes an optical drive electronics unit configured to
detect a reflected light beam from the storage medium, wherein the
storage medium includes multiple bits in a modulated bitstream
including a bitstate of 0 and multiple secondary modulated bits.
The optical drive electronics unit is also configured to detect in
the reflected light beam either one of multiple bits including the
bitstate of 0 in the modulated bitstream or the multiple bits
including the bitstate of 0 in the modulated bitstream and the
plurality of secondary modulated bits.
DRAWINGS
[0012] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings in which like characters represent like parts throughout
the drawings, wherein:
[0013] FIG. 1 is a block diagram of an optical disk drive in
accordance with an embodiment of the invention.
[0014] FIG. 2 is a block diagram representation of steps employed
by the subsystem of optical disk drive electronics unit and the
processor in FIG. 1 for recording on an optical disk.
[0015] FIG. 3 is a schematic representation of an exemplary grating
on a disk in accordance with an embodiment of the invention
[0016] FIG. 4 is a schematic representation of symbols mapped onto
the grating in FIG. 3.
[0017] FIG. 5 is a schematic representation of the symbols in FIG.
4 mapped onto respective quadrature representations, in accordance
with an embodiment of the invention.
[0018] FIG. 6 is a schematic illustration of the quadrature
representations mapped onto respective bit representations, in
accordance with an embodiment of the invention.
[0019] FIG. 7 is a flow chart representing steps in a method for
recording data on a storage system in accordance with an embodiment
of the invention.
DETAILED DESCRIPTION
[0020] As discussed in detail below, embodiments of the invention
include a system and method for improved data storage. The system
is configured to be backward compatible. The term `backward
compatibility` refers to the ability of system and method to allow
for reading of data on a storage medium such as an optical disk by
first generation drives as well as second generation drives. As
used herein the term `first generation drives` refers to drives
that have read drive electronics to detect only the energy of a
beam reflected from the disk. The term `second generation drives`
as used herein, refers to drives that have read drive electronics
that detects phase and energy of the beam reflected from the
disk.
[0021] One or more embodiments of the present technique will be
described below. In an effort to provide a concise description of
these embodiments, not all features of an actual implementation are
described in the specification. It should be appreciated that in
the development of any such actual implementation, as in any
engineering or design project, numerous implementation-specific
decisions must be made to achieve the developers' specific goals,
such as compliance with system-related and business-related
constraints, which may vary from one implementation to another.
Moreover, it should be appreciated that such a development effort
might be complex and time consuming, but would nevertheless be a
routine undertaking of design, fabrication, and manufacture for one
of ordinary skill having the benefit of this disclosure.
[0022] Optical storage systems typically involve two separate
encodings of the data bits to be stored. A first encoding is
generally a forward error correcting code (FEC), such as the
Reed-Solomon (RS) block-based error correcting code used in compact
disks (CDs). An RS code may protect k data symbols, each containing
s bits, with a codeword that is n symbols long, with each encoded
symbol also comprising s bits. The RS code is capable of correctly
decoding a codeword with up to t corrupted, but unidentified,
symbols where 2t=n-k. RS coding may also deal efficiently with
erasures, e.g., those symbols somehow known to be corrupted. If
there are s errors and r erasures, the RS code may correctly decode
the codeword so long as 2s+r<2t.
[0023] The second encoding generally used in optical storage
systems may be termed "modulation coding." Modulation coding is the
representation of the bits resulting from the first (e.g., RS)
coding in a set of bit-sequences, or symbols, chosen to mitigate
some undesirable effects that may be associated with the reading
process. The symbols are then written to an optical data storage
unit. For optical systems based on variations in height of a
reflective surface, e.g., pits and lands, such as CDs, the symbols
have generally been linear bit-sequences chosen to limit the number
of sequential zeros or ones in a particular data track on an
optical storage disk. Examples of such techniques include the
eight-to-fourteen modulation (EFM), and the EFM+ modulation and
run-length limited (RLL) with NRZI modulation coding. Such
techniques may also be referred herein to as `primary
modulation`.
[0024] The present technique introduces a secondary modulation in
the event of a presence of a micro-reflector, such as, but not
limited to, a micro-hologram in an output of the primary
modulation. Furthermore, the RLL properties of the primary
modulation are retained thus enabling backward compatibility. In
one embodiment, the secondary modulation includes phase modulation
of the writing beams that are employed to record micro-holograms.
In another embodiment, the secondary modulation includes depth
modulation of the micro-holograms. In yet another embodiment, the
secondary modulation includes amplitude modulation of the
micro-holograms.
[0025] Turning now to the figures, FIG. 1 is an exemplary optical
recording/reader system 10 that may be used to write/read data from
an optical storage disk 12. The data stored on the optical data
disc 12 is written/read by a series of optical elements 14, which
project at least one write/read beam 16 onto the optical data disk
12. It should be noted that although only one read/write beam 16
has been illustrated, typically the write process, as is
well-known, includes two beams impinging on the disk 12. The
writing is done by modulating the write beam according to an
encoded bit stream that is being recorded, creating a varied
reflectivity pattern corresponding to a modulation pattern in a
recordable region of the disk 12. Upon readout, a reflected beam 18
is picked up from the optical data disc 12 by the optical elements
14. The optical elements 14 may comprise any number of different
elements designed to generate excitation beams, focus those beams
on the optical data disc 12, and detect the reflection 18 coming
back from the optical data disc 12. The optical elements 14 are
controlled through a coupling 20 to an optical drive electronics
package 22. The optical drive electronics unit 22 may include such
units as power supplies for one or more laser systems, detection
electronics to detect an electronic signal from the detector,
analog-to-digital converters to convert the detected signal into a
digital signal and vice versa, and other units such as a bit
predictor to predict when the detector signal is actually
registering a bit value stored on the optical data disc 12.
[0026] The location of the optical elements 14 over the optical
data disk 12 is controlled by a tracking servo 24 which has a
mechanical actuator 26 configured to move the optical elements back
and forth over the surface of the optical data disc 12. The optical
drive electronics unit 22 and the tracking servo 24 are controlled
by a processor 28. The processor 28 also controls a motor
controller 30 which provides the power 32 to a spindle motor 34.
The spindle motor 34 is coupled to a spindle 36 that controls the
rotational speed of the optical data disc 12. As the optical
elements 14 are moved from the outside edge of the optical data
disc 12 closer to the spindle 36, the rotational speed of the
optical data disc may be increased by the processor 28. This may be
performed to keep the data rate of the data from the optical data
disc 12 essentially the same when the optical elements 14 are at
the outer edge as when the optical elements are at the inner edge.
The maximum rotational speed of the disk may be about 500
revolutions per minute (rpm), 1000 rpm, 1500 rpm, 3000 rpm, 5000
rpm, 10,000 rpm, or higher.
[0027] The processor 28 is connected to random access memory or RAM
38 and read only memory or ROM 40. The ROM 40 contains the programs
that allow the processor 28 to control the tracking servo 24,
optical drive electronics 22, and motor controller 30. Further, the
ROM 40 also contains programs that allow the processor 28 to
analyze data from the optical drive electronics 22, which has been
stored in the RAM 38, among others. As discussed in further detail
herein, such analysis of the data stored in the RAM 38 may include,
for example, modulation/demodulation, coding/decoding or other
functions necessary to convert the information from the optical
data disc 12 into a data stream that may be used by other
units.
[0028] It should be noted that embodiments of the invention are not
limited to any particular processor for performing the processing
tasks of the invention. The term "processor," as that term is used
herein, is intended to denote any machine capable of performing the
calculations, or computations, necessary to perform the tasks of
the invention. The term "processor" is intended to denote any
machine that is capable of accepting a structured input and of
processing the input in accordance with prescribed rules to produce
an output. It should also be noted that the phrase "configured to"
as used herein means that the processor is equipped with a
combination of hardware and software for performing the tasks of
the invention, as will be understood by those skilled in the
art.
[0029] If the optical reader system 10 is a commercial unit, such
as a consumer electronic device, it may have controls to allow the
processor 28 to be accessed and controlled by a user. Such controls
may take the form of panel controls 42, such as keyboards, program
selection switches and the like. Further, control of the processor
28 may be performed by a remote receiver 44. The remote receiver 44
may be configured to receive a control signal 46 from a remote
control 48. The control signal 46 may take the form of an infrared
beam, an acoustic signal, or a radio signal, among others.
[0030] In case of the read system, after the processor 28 has
analyzed the data stored in the RAM 38 to generate a data stream,
the data stream may be provided by the processor 28 to other units.
For example, the data may be provided as a digital data stream
through a network interface 50 to external digital units, such as
computers or other devices located on an external network.
Alternatively, the processor 28 may provide the digital data stream
to a consumer electronics digital interface 52, such as a
high-definition multi-media interface (HDMI), or other high-speed
interfaces, such as a USB port, among others. The processor 28 may
also have other connected interface units such as a
digital-to-analog signal processor 54. The digital-to-analog signal
processor 54 may allow the processor 28 to provide an analog signal
for output to other types of devices, such as to an analog input
signal on a television or to an audio signal input to an
amplification system.
[0031] In case of a write system, the data 56 to be recorded may be
provided to the processor 28 through different units 50, 52, and/or
54. The data is stored in the RAM 38. The processor 28 sends an
appropriate command to the optical drive electronics 22.
Accordingly, the optical drive electronics 22 controls the optical
elements 14 to write appropriate data on to the disk 12. The
details of the algorithm referenced by numeral 64 employed by the
processor 28 and the optical drive electronics 22 are described in
FIG. 2.
[0032] FIG. 2 is a schematic representation of the steps employed
in the subsystem 64 (FIG. 1). The processor 28 receives an input
data stream 56 that undergoes primary modulation 72 to output
primary modulated data 74. In a non-limiting example, the primary
modulation includes RLL such as 17 pp with NRZI modulation. The
processor 28 performs a decision step 76, wherein each of the bits
in the primary modulated data 74 are compared to a `1`, or
otherwise known to be `1`. As used herein, the representation `1`
signifies presence of a mark in the optical disk 12 (FIGS. 1), and
`0` signifies absence of the mark. If the bit is `1`, the bit
undergoes a secondary modulation 82. As mentioned above, the
secondary modulation includes phase modulation, depth modulation or
amplitude modulation of the marks. In an exemplary embodiment, the
marks include micro-holograms. The secondary modulated output 84 is
further recorded on the disk 12 as referenced by 86. If the bit is
`0`, the primary modulated output bit is recorded as is on the disk
12, as referenced by numeral 86.
[0033] In an exemplary embodiment, consider a RLL input data stream
56 into the processor 28. The processor 28 primary modulates the
input data stream 56 via NRZI modulation. The RLL NRZI modulation
coded bitstream, also referred to as primary modulated bitstream,
is checked for presence of `1` or in other words, a mark or a
micro-hologram. In an event of `1`, secondary modulation is
performed. In an event of `0` occurring, secondary modulation is
not performed. Accordingly, a secondary modulated bitstream is
output that is recorded on the optical disk 12 (FIG. 1). Due to
secondary modulation of only the `1` bits, the RLL properties are
retained. This enables backward compatibility, wherein the optical
disk is read by an optical drive system of an existing format. In a
non-limiting example, a drive that does not have the ability to
extract secondary data is able to play a holographic disk recorded
with secondary modulated bits by decoding only the primary data.
For better clarity, referring back to FIG. 1, the optical drive
electronics unit 22 detects in the reflected light beam 18 either
only the primary modulated bits, that includes the bits having
bitstate of 0 in the modulated bitstream, or detects both the
primary modulated bits as well as the secondary modulated `1` bits.
In another example, the disk 12 includes a higher resolution movie
and/or additional features stored in the secondary modulated bits,
while the primary modulated bits include a lower resolution movie.
Thus, an optical drive with upgraded technology, also, second
generation drive, reproduces the higher resolution movie/special
features, whereas an optical drive with existing technology also, a
first generation drive, reproduces only the lower resolution
movie.
[0034] In an example of micro-holograms on a holographic disk,
fringes are formed by interference of two counter-propagating beams
at allocation on the disk. Phase modulation is performed by
shifting fringes of the micro-hologram. In one embodiment, such
phase modulation is achieved by adjusting phases of the two beams
via the optical drive electronics unit 22. In another embodiment,
distance of lenses employed to focus the two beams, from the disk
may be adjusted to alter depth of the fringes and thus, achieve
phase modulation. In a particular embodiment, continuous phase
modulation is employed. In another embodiment, discrete phase
modulation is performed. By way of example, secondary modulation
coding is according to a lattice code scheme or via forward error
correction coding.
[0035] In another exemplary embodiment, amplitude modulation is
performed that increases storage capacity of the storage medium 12
(FIG. 1). Parameters of light used to record micro-holograms may
affect the magnitude of the refractive index modulation and/or size
of the grating produced and consequently amount of diffracted light
during readout. Hence, signal reflected from a `1` mark reaching
the detector during readout varies according to the conditions used
for writing. It should be noted that amplitude modulation does not
affect depth position of the mark. In yet another embodiment, a
combination of phase modulation and amplitude modulation may be
employed. A non-limiting example includes two-dimensional
modulation schemes such as M-PSK/N-PAM.
[0036] FIG. 3 illustrates a grating 104 in the disk after phase or
depth modulation. Each of the lines 103 represents a fringe in a
holographic system. The output 102 includes alternating regions of
`grating` referenced by 104 and `no grating` 106. The `grating`
region 104 indicates presence of a mark or a micro-hologram. As
illustrated herein, the `grating` region includes crests 108 and
troughs 110, wherein the crests 108 indicate a secondary
modulation.
[0037] FIG. 4 illustrates a symbol representation of the grating
104 in FIG. 3. The symbols are indicated by reference numerals 122,
124, 126, 128 and 132. The grating 104 is divided by an internal
bit clock time `T` resulting in 8 symbols, as illustrated.
[0038] FIG. 5 is a schematic representation of the symbols 122,
124, 126, 128 and 132 (FIG. 4) mapped onto respective quadrature
representations 142, 144, 146, 148 and 150. The quadrature
representations indicate location of the symbols relative to four
quadrants. As illustrated, the symbols 142 are located on an X-axis
162 between a first quadrant 164 and a fourth quadrant 172.
Similarly, the symbols 144 are shifted 180 degrees in phase and
located on the X-axis 162 between the second quadrant 166 and the
third quadrant 168. The symbol 146 is located in the first quadrant
164 shifted in phase at an angle between 0 degree and 45 degrees.
Similarly, the symbols 148 are in the third quadrant 168 and the
symbol 150 is on the X-axis at a 0 degree phase shift.
[0039] FIG. 6 is a schematic illustration of the quadrature
representations 142, 144, 146, 148 and 150 mapped onto respective
bit representations 182, 184, 186, 188, and 190. In a particular
embodiment, the bit representations are performed via a look-up
table. As illustrated herein, the symbols 122 located at a 0 degree
phase shift, are represented by `000`. Similarly, the symbols 124
located at a phase shift of 180 degrees are represented by `111`.
Furthermore, the symbols 126, 128 and 132 are represented as `010`,
`101`, and `000` respectively. Thus, a single symbol/micro-hologram
may be mapped into 3 bits after secondary modulation, allowing
increased data storage capability and data transfer rate in the
disk.
[0040] In a particular embodiment, phase modulation is detected
using in-phase and quadrature homodyne detection. Homodyne
detection, as well-known to one skilled in the art, uses optical
interference between signal and reference beams that results in
enhancement or suppression of the detected signal depending on the
relative phase difference between the two beams. Interference of
the signal beam with two reference beams whose phases are separated
by 90.degree. allows one to measure both in-phase and out-of-phase
components. When both in-phase and out-of-phase components are
detected, they can be used to calculate the phase of the signal
beam, which in this example carries the secondary modulation data
stream. It should be noted that phase modulation does not change
intensity of the reflected beam 18 (FIG. 1) from a sample mark in
the optical disk 12 (FIG. 1).
[0041] FIG. 7 is a flow chart representing steps in a method 200
for storing data on a storage medium. The method 200 includes
receiving a modulated bitstream in step 202, wherein the modulated
bitstream comprises a plurality of bits comprising a bitstate of 1
and 0. In a particular embodiment, an optical signal is primary
modulated to output the modulated bitstream. In another embodiment,
the optical signal is primary modulated via NRZI modulation. Each
of the multiple bits including a bitstate of 1 is secondary
modulated to output multiple secondary modulated bits in step 204.
In one embodiment, the multiple bits including a bitstate of 1 are
phase modulated. In an exemplary embodiment, the multiple bits
including a bitstate of 1 are phase modulated discretely. In a
non-limiting example, the discrete phase modulation represents a
lattice code. In another example, the discrete phase modulation
employs forward error correction coding. In another embodiment, the
multiple bits including a bitstate of 1 are depth modulated. In yet
another embodiment, the multiple bits including a bitstate of 1 are
amplitude modulated. Multiple marks are formed in the storage
medium in step 206, wherein the marks are indicative of each of the
multiple secondary modulated bits. Specifically, a single mark is
selected from a set of possible marks and the single selected mark
is written at a given interval of time. In a particular embodiment,
a stepped pattern of micro-reflectors are formed along multiple
tracks of a single layer of the storage medium. In another
embodiment, a stepped pattern of micro-reflectors are formed across
multiple layers of the storage medium.
[0042] The various embodiments of a system and method for improved
data storage described above thus provide a way to produce a disk
with improved features and that can be played using an optical
drive designed for an existing format, also referred to as,
backward compatibility. The system and method enable cost-effective
and efficient manufacturing as the existing manufacturing process
may be employed for production of the discs, which include a
recording format readable by multiple generations of devices)
including additional optional multimedia content. An optical drive
with upgraded technology (second generation drive) reproduces the
additional content, while an optical drive with non-upgraded
technology (first generation drive) reads content excluding the
optional multimedia. Subsequently, these techniques provide a cost
effective means to a manufacturer, distributor and marketing chain,
since a separate accounting, advertising and handling procedures
would have been required in case of additional discs been used for
accommodating different multimedia content. The techniques and
system also enable increased data storage and data rates.
[0043] Of course, it is to be understood that not necessarily all
such objects or advantages described above may be achieved in
accordance with any particular embodiment. Thus, for example, those
skilled in the art will recognize that the systems and techniques
described herein may be embodied or carried out in a manner that
achieves or optimizes one advantage or group of advantages as
taught herein without necessarily achieving other objects or
advantages as may be taught or suggested herein.
[0044] Furthermore, the skilled artisan will recognize the
interchangeability of various features from different embodiments.
For example, a disc including different resolutions of a movie
described with respect to one embodiment can be adapted for use
with an amplitude modulated bitstream, as secondary modulation,
described with respect to another. Similarly, the various features
described, as well as other known equivalents for each feature, can
be mixed and matched by one of ordinary skill in this art to
construct additional systems and techniques in accordance with
principles of this disclo sure.
[0045] While only certain features of the invention have been
illustrated and described herein, many modifications and changes
will occur to those skilled in the art. It is, therefore, to be
understood that the appended claims are intended to cover all such
modifications and changes as fall within the true spirit of the
invention.
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