NZ622073B2 - Direct read after write for optical storage device - Google Patents
Direct read after write for optical storage device Download PDFInfo
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- NZ622073B2 NZ622073B2 NZ622073A NZ62207312A NZ622073B2 NZ 622073 B2 NZ622073 B2 NZ 622073B2 NZ 622073 A NZ622073 A NZ 622073A NZ 62207312 A NZ62207312 A NZ 62207312A NZ 622073 B2 NZ622073 B2 NZ 622073B2
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- 238000003860 storage Methods 0.000 title claims abstract description 44
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- 238000004519 manufacturing process Methods 0.000 claims description 4
- 238000007374 clinical diagnostic method Methods 0.000 claims description 3
- 238000004590 computer program Methods 0.000 claims 3
- 230000000051 modifying Effects 0.000 description 29
- 238000010586 diagram Methods 0.000 description 11
- 238000000034 method Methods 0.000 description 8
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Classifications
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/002—Recording, reproducing or erasing systems characterised by the shape or form of the carrier
- G11B7/003—Recording, reproducing or erasing systems characterised by the shape or form of the carrier with webs, filaments or wires, e.g. belts, spooled tapes or films of quasi-infinite extent
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
- G11B7/0045—Recording
- G11B7/00458—Verification, i.e. checking data during or after recording
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
- G11B7/1353—Diffractive elements, e.g. holograms or gratings
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
- G11B7/1395—Beam splitters or combiners
Abstract
Systems and methods for data storage on an optical medium (16) having a plurality of tracks (36) include splitting a light beam into a higher power main beam (40) and at least one lower power side beam (44, 48) that form corresponding spots spaced along a selected one of the plurality of tracks (36) and selectively positioning and aligning the beams/spots along the selected one of the plurality of tracks (36) using the higher power main beam (40) to write data while reading previously written data using the at least one lower power side beam (44, 48). The systems and methods may include correlating the read signal with a time-shifted write signal to provide a direct read after write capability to verify data written to the optical medium. In one embodiment, an optical tape drive includes an optical pickup unit (OPU) (20) that generates a lower power satellite beam (44, 48) to read data directly after writing by a higher power main beam (40). and selectively positioning and aligning the beams/spots along the selected one of the plurality of tracks (36) using the higher power main beam (40) to write data while reading previously written data using the at least one lower power side beam (44, 48). The systems and methods may include correlating the read signal with a time-shifted write signal to provide a direct read after write capability to verify data written to the optical medium. In one embodiment, an optical tape drive includes an optical pickup unit (OPU) (20) that generates a lower power satellite beam (44, 48) to read data directly after writing by a higher power main beam (40).
Description
DIRECT READ AFTER WRITE FOR OPTICAL STORAGE DEVICE
TECHNICAL FIELD
This disclosure relates to a system and method for reading data directly
after writing data in an optical storage device.
BACKGROUND
Optical recording devices such as optical disk and optical tape drives
commonly use an Optical Pickup Unit (OPU) or read/write head to write and retrieve data
from associated optical media. Conventional OPUs may utilize different wavelength
semiconductor laser diodes with complex beam path optics and electromechanical
elements to focus and track the optical beam within one or more preformatted tracks on
the medium to write or store the data and subsequently read the data. Data written to the
medium with a laser at higher power may be verified in a separate operation or process
after writing using a lower laser power, or may be verified during the write operation by
another laser or laser beam. The ability to read and verify the data during the write
operation may be referred to as Direct Read After Write (DRAW). One strategy for
providing DRAW functionality is to use multiple independent OPUs with one OPU
writing the data as a second OPU reads the data for write verification, such as disclosed
in U.S. Pat. No. 6,141,312, for example. While this approach may be suitable for some
applications, it increases the cost and complexity of the storage device.
Present OPUs may use a diffraction grating or similar optics in the laser
path to generate three beams from a single laser element including a higher power beam
used for reading/writing data and for focusing, and two lower power satellite beams used
for tracking. The three beams are focused to three corresponding spots on the surface of
the optical storage medium used by the various optical and electromechanical elements of
the OPU. In general, the higher power spot is positioned in the center or middle between
the two satellite spots. In addition to reading/writing data and focusing, the center spot
may also be used for one particular type of tracking operation in some applications. The
lower power satellite spots generated from the lower power side-beams are typically used
for another type of tracking operation for specific types of media.
SUMMARY
Systems and methods for data storage on an optical medium having a
plurality of tracks include splitting a light beam into a higher power main beam and at
least one lower power side beam that form corresponding spots spaced along a selected
one of the plurality of tracks and selectively positioning and aligning the beams/spots
along the selected one of the plurality of tracks using the higher power main beam to
write data while reading previously written data using the at least one lower power side
beam. The systems and methods may include correlating the read signal with a time-
shifted write signal to provide a direct read after write capability while reducing noise
associated with modulation of the write signal to verify data written to the optical
medium.
In one embodiment, an optical tape drive receives an optical tape having a
plurality of tracks that generally span across a width of the tape for storing data and
includes an optical pickup unit (OPU) or head having optics that split a coherent light
beam into a higher power main beam and at least one lower power side beam that form
corresponding spots spaced along a selected one of the plurality of tracks. At least one
controller coupled to the optical head selectively positions and aligns the optical head
and/or beams for writing data along the selected one of the plurality of tracks using the
higher power main beam while reading previously written data from the selected one of
the plurality of tracks using the at least one lower power side beam while the main beam
continues writing data to provide a direct read after write (DRAW) capability.
Various embodiments according to the present disclosure include a
correlation detector that determines similarity between a read signal associated with data
detected by the lower power side beam and a time-shifted write signal associated with the
higher power main beam to verify data written to the selected one of the plurality of
tracks directly after writing. The correlation detector may combine the read signal and
the time-shifted write signal and compares a resulting signal to an associated threshold to
verify integrity of data written to the selected one of the plurality of tracks. In one
embodiment, the correlation detector includes a low-pass filter that filters the resulting
signal before the resulting signal is compared to the associated threshold. Alternatively,
or in combination, a resettable integrator that integrates the resulting signal before the
resulting signal is compared to the associated threshold may be used with the integrator
resetting in response to a data block synchronization signal associated with each block of
data written to the optical medium. Various embodiments may include generating a
predetermined verification pattern for the higher power main beam having alternating
periods of fixed power and random data. The predetermined verification pattern may be
included in a corresponding DRAW field for each block of data written and/or may be
generated in response to a request for diagnostics.
Embodiments according to the present disclosure may provide various
advantages. For example, an optical storage device according to one embodiment of the
present disclosure provides direct read after right functionality for data verification using
a single OPU or optical head. Various embodiments of a system or method according to
the present disclosure use a correlation detector strategy to reliably detect data marks in
the beam reflected from a lower power satellite beam in the presence of main beam
modulation and other noise. The direct read after write functionality and correlation
detector strategy according to embodiments of the present disclosure can also provide
real-time diagnostic information and functionalities for the drive channel of an optical
storage device. For example, systems and methods according to embodiments of the
present disclosure may be used to enhance write strategy, provide information on write
pattern jitter, provide information to adjust and improve OPU performance and laser
power, to anticipate OPU anomalies, and the like.
The above advantages and other advantages and features associated with
various embodiments of the present disclosure will be readily apparent from the
following detailed description when taken in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figures 1A and IB are diagrams illustrating operation of an optical data
storage system or method with direct read after write (DRAW) capability according to
various embodiments of the present disclosure;
Figure 2 is a block diagram illustrating operation of an optical pickup unit
(OPU) having a coherent light beam split or divided into a center beam and two satellite
or side beams to provide DRAW capability according to various embodiments of the
present disclosure;
Figure 3 is a block diagram illustrating operation of a DRAW system or
method for optical data storage according to various embodiments of the present
disclosure;
Figure 4 is a block diagram illustrating one embodiment of a correlation
detector for an optical data storage device according to the present disclosure;
Figures 5A-5D illustrate representative signals in an optical data storage
system or method having DRAW functionality according to various embodiments of the
present disclosure;
Figures 6 and 7 illustrate operation of a DRAW system or method for
optical data storage using a predetermined data verification pattern to provide
deterministic DRAW operation according to embodiments of the present disclosure; and
Figures 8A-8D illustrate representative signals in an optical data storage
system or method having deterministic DRAW operation according to embodiments of
the present disclosure.
DETAILED DESCRIPTION
Various embodiments of the present disclosure are described herein.
However, the disclosed embodiments are merely exemplary and other embodiments may
take various and alternative forms that are not explicitly illustrated or described. The
Figures are not necessarily to scale; some features may be exaggerated or minimized to
show details of particular components. Therefore, specific structural and functional
details disclosed herein are not to be interpreted as limiting, but merely as a
representative basis for teaching one of ordinary skill in the art to variously employ the
present invention. As those of ordinary skill in the art will understand, various features
illustrated and described with reference to any one of the Figures may be combined with
features illustrated in one or more other Figures to produce embodiments that are not
explicitly illustrated or described. The combinations of features illustrated provide
representative embodiments for typical applications. However, various combinations and
modifications of the features consistent with the teachings of this disclosure may be
desired for particular applications or implementations.
The processes, methods, logic, or strategies disclosed may be deliverable
to and/or implemented by a processing device, controller, or computer, which may
include any existing programmable electronic control unit or dedicated electronic control
unit. Similarly, the processes, methods, logic, or strategies may be stored as data and
instructions executable by a controller or computer in many forms including, but not
limited to, information permanently stored on various types of articles of manufacture
that may include persistent non-writable storage media such as ROM devices, as well as
information alterably stored on writeable storage media such as floppy disks, magnetic
tapes, CDs, RAM devices, and other magnetic and optical media. The processes,
methods, logic, or strategies may also be implemented in a software executable object.
Alternatively, they may be embodied in whole or in part using suitable hardware
components, such as Application Specific Integrated Circuits (ASICs), Field-
Programmable Gate Arrays (FPGAs), state machines, controllers or other hardware
components or devices, or a combination of hardware, software and firmware
components.
Referring now to Figures 1A and IB, block diagrams illustrating operation
of an optical data storage system or method with direct read after write (DRAW)
capability according to various embodiments of the present disclosure are shown. Figure
1A is a side view diagram and Figure IB is a top or plan view diagram. In the
representative embodiment illustrated in Figures 1A and IB, optical data storage system
is implemented by an optical tape drive 12 that receives an optical data storage
medium 14 implemented by an optical tape 16. While illustrated and described with
reference to an optical tape drive, those of ordinary skill in the art will recognize that the
teachings of the present disclosure may also be applied to various other types of optical
data storage devices that may use various types of write-once or re-writable optical
media, such as optical discs, for example. In one embodiment, optical tape 16 is a ½ inch
(12.7mm) wide tape having a plurality of tracks generally extending across the width of
the tape and may vary in length depending on the desired storage capacity and
performance characteristics as illustrated and described in greater detail herein. Optical
tape 16 may be wound on an associated spool 30 contained within a protective case or
cartridge 18 that is manually or automatically loaded or mounted in optical tape drive 12.
Transport mechanism 24 moves optical tape 16 through a carriage and past at least one
optical pickup unit (OPU) or optical head 20 to a take-up spool 22 that typically remains
within tape drive 12. OPU 20 writes data to, and reads data from, optical tape 16 as
transport mechanism 24 moves optical tape 16 between cartridge 18 and take-up spool 22
in response to at least one controller and associated electronics 26. As explained in
greater detail below, data may be read/written to optical tape 16 in one or more of the
plurality of tracks in a serpentine fashion as the tape travels in either direction past OPU
, i.e. either from cartridge 18 to take-up spool 22, or from take-up spool 22 to cartridge
Optical head 20 may include associated optics and related
electromechanical servo controlled devices, represented generally by reference numeral
, that split or divide a light beam, such as a laser beam, into two or more beams that are
focused to corresponding spots on the storage medium for reading/writing data as
illustrated and described in greater detail with reference to Figure 2. Various servo
mechanisms (not specifically illustrated) may be used to position/align the beams with a
selected one of the plurality of tracks on optical tape 16.
Figure 2 is a block diagram illustrating operation of an optical pickup unit
(OPU) 20 having a coherent light beam split or divided into a center beam 40 and two
satellite or side beams 44, 48 to provide DRAW capability according to various
embodiments of the present disclosure. Beams 40, 44, and 48 may be generated by a
single or common coherent light source, such as a laser diode, for example. The source
beam travels through associated optics, that may include a diffraction grating, for
example, to divide or split the source beam into center beam 40, first side beam 44, and
second side beam 48 and to focus the beams to corresponding spots 50, 54, and 58,
respectively, on the surface of optical tape 16 within a selected one of the plurality of
tracks 36. The three optical spots 50, 54, and 58 are manipulated by various optical and
electrometrical elements of OPU 20 to write and retrieve data from optical tape 16.
The optical elements used to split the source beam and focus the resulting
beams to spots 50, 54, and 58 may be designed to provide higher power to center beam
40 and center spot 50 with lower power to side beams 44, 48 and associated spots 54, 58.
For example, center spot 40 may contain about 60-70% of the source beam power with
side beams 44, 48 dividing the remaining 40-30% of the source beam power. Center
beam 40 is modulated by OPU 20 to generate write marks 60 during writing of data to
optical tape 16, which may require about ten times more average power than to read
previously stored data (such as about 10 mW to write data and about 0.7 mW to read
data, for example). As such, if the source beam is modulated and produces sufficient
power for writing data using the center beam/spot 40/50, side beams 44, 48 will be
modulated in a like manner but will contain insufficient power to alter tape 16. In the
representative embodiment illustrated, spots 50, 54, and 58 are mechanically aligned in
the OPU manufacturing process to correspond to the axes of data tracks 36 on
Preformatted optical tape media 16. In addition, satellite spots 54, 58 are generally
symmetrically positioned relative to center spot 50 so that transit distance (d) of tape 16
between center spot 50 and either satellite/side spot 54, 58 is substantially the same.
Representative embodiments may include a distance (d) of between about 10-20 mih .
Some conventional optical storage devices use center spot 50 from the
higher power emitting beam 40 for reading, writing, and focusing in addition to one type
of tracking operation. Satellite spots 54, 58 formed by the lower power side-beams 44,
48 are used for another type of tracking for specific types of media. In these applications,
side spots 54, 58 may not be aligned with one another, or with center spot 50 along a
single track 36 of optical tape 16. In contrast to the conventional function of satellite
beams 44, 48, various embodiments according to the present disclosure provide tracking
using light reflected from main spot 50 so that satellite spots 54, 58 can be used to
provide direct read after write (DRAW) functionality as described below. In one
embodiment, light reflected from main beam 40 is used in a differential push/pull
tracking strategy that does not require satellite beams 44, 48 for tracking. Of course, the
satellite beam located upstream of main beam 40 relative to the current direction of media
travel may be available for use in tracking if desired.
As previously described, the source laser beam is operated at a higher
power (relative to operation during a data read/retrieval) and modulated to write data
marks 60 on a selected one of the plurality of tracks 36 on optical tape medium 16.
However, only center beam 40 emits enough power to the optical tape 16 to actually alter
the structure of the optically active layer of as represented by data marks 60. Satellite
beams 44, 48, having much lower power as determined by the diffraction grating power
distribution, do not alter tap 16. As recognized by the present disclosure, satellite beams
44, 48 have enough power after being reflected from optical tape 16 to detect data marks
60. Therefore, depending on the direction of travel of optical tape 16, the reflection from
an associated satellite spot 54, 58 can be detected by OPU 20 and used to verify data
marks 60 directly after being written by main beam/spot 40/50 to provide DRAW
operation.
While the reflected beam associated with one of the satellite beams 44, 48
(depending on the direction of travel of tape 16) contains information associated with the
data marks 60 on tape medium 16, the reflected beam is heavily contaminated by the
modulation of center beam 40 and other noise sources and generally exhibits a very low
signal to noise ratio (SNR). As such, various embodiments of the present disclosure
include a correlation detector to reliably extract the information in the reflected beam
associated with data marks 60 from the reflected satellite spot 54 corresponding to data
immediately previously written by center spot 50 during DRAW operation. In the
representative embodiment illustrated in Figure 2, tape 16 is traveling in a first direction
from right to left as generally represented by arrow 64. The system operates in a similar
fashion when tape 16 is traveling in a second direction that is opposite the first direction
such that data written by center spot 50 is read directly after writing using reflected light
from satellite spot 58, wherein satellite spot 58 and center spot 50 are substantially
aligned with the same selected one of the plurality of tracks 36 as represented by "Track
n" in Figure 2.
Figure 3 is a block diagram illustrating operation of a DRAW system or
method for optical data storage according to various embodiments of the present
disclosure. Controller 26 (Fig. 1) communicates data to a DC-free write pattern coder
100. OPU laser modulator 102 modulates the source laser beam based on the write
pattern received from coder 100 to generate a modulated center beam 104 that is focused
to a corresponding spot on optical media 14 at a first position within a selected one of a
plurality of tracks as optical media 14 moves past. The first position arrives at the
location of a downstream satellite beam spot at a later time (T ) associated with a transit
delay based on the media speed. While center beam 104 is writing data to a second
location of optical media 14, and modulating the satellite beams in a similar fashion
based on the data being written, the beam reflected from the downstream satellite
beam/spot 110 is detected by OPU satellite spot mark detector 112. As such, the
reflected beam contains information associated with data marks immediately previously
written to the first location by center beam 104, as well as the data currently being written
to optical media 14 at the second location.
The signal or related information from OPU satellite spot mark detector
112 is processed by DC-free processor 120 and provided to modulation noise canceller
130 to reduce or eliminate the modulation noise associated with modulation of center
beam 104 for data currently being written at the second location while satellite beam/spot
110 reads the previously written data from the first location. Canceller 130 includes a
discriminator pattern generator 132 that uses information from write pattern coder 100 to
subtract the effect of the modulation of center beam 104 at summing block 134.
As also illustrated in Figure 3, correlation detector 140 determines
similarity between the read signal associated with data detected by the at least one lower
power side beam/spot 110 and a time-shifted write signal provided by write pattern coder
100 and time delay (Td) block 144 associated with the higher power main beam 104 to
verify data written to optical media 14 directly after writing. The time delay T
represents the transit time or transit delay associated with optical media 14 moving
between the main spot 50 and a downstream side spot 54, 58 and may vary based on the
actual or estimated speed of optical media 14. Block 142 combines the modulation noise
canceled read signal from block 134 and the time-shifted write signal from block 144 and
compares the resulting signal to an associated threshold as represented by level detector
148 to verify data written to the selected one of the plurality of tracks. In the
representative embodiment illustrated in Figure 3, system 10 compares the signals by
multiplying or determining a product as represented by block 142 with the resulting
signal provided to resettable integrator or area detector 146 before the resulting signal is
compared to the associated threshold by level detector 148. Resettable area detector or
integrator 146 may be periodically reset to a predetermined value (such as zero or other
designated value) by an associated signal, such as a data synchronization signal
associated with each block of data written to optical media 14. Alternatively, a constant
bleeder or decrementing function may be used to adjust the integrator value over time.
Figure 4 is a block diagram illustrating one embodiment of a correlation
detector in a system or method for optical data storage according to the present
disclosure. In general, the fundamental function of a correlation estimator or detector as
illustrated in the representative embodiments of Figures 3 and 4 is to provide a measure
or estimate of the similarity between two signals or patterns of data. As used in the
representative embodiments illustrated and described in this disclosure, correlation
detectors or estimators detect the presence of a specified pattern of data within a very
noisy signal and provide a corresponding signal or other output that can be used to
measure the degree of correlation or similarity between the two patterns or signals.
In the DRAW embodiment of Figure 4, the data block write pattern 100' is
used to modulate main beam 40 with the data signal represented generally by P (t) and
create corresponding marks on the optical media 14 at the main spot location. Satellite
beam 44 creates a spot a distance "d" downstream relative to main beam 40 to read data
directly after writing as previously described. The signal associated with light reflected
from the satellite beam 44 contains information from the data marks passing by satellite
beam 44 that were just written by main beam 40 Td seconds earlier (as represented by
P (t-T ) in addition to noise from modulation of main beam 40 and other sources as any
additional data is written by main beam 40. This signal is detected by the OPU detectors
and is generally represented by P (t). The "time stamp" of the P (t-Td) data-block
patterns within the P (t) signal is known or can be determined/estimated using the transit
delay 160 based on the media speed and distance "d" between main beam 40 and satellite
beam 44.
After passing through corresponding DC-free processors 162 and 164, the
satellite signal associated with data read by the satellite beam and represented by P (t) is
compared to the signal P (t-T ) provided to the center beam for writing data, but that is
time-shifted based on the transit time of the optical media 14 moving from center or main
beam 40 to satellite beam 44 at block 142'. In this embodiment, block 142' performs
real-time multiplication (analog or digital) of the satellite signal represented by P (t) with
the time adjusted data block write pattern, P (t-T ). This results in a pattern with a DC
value representing the similarity or correlation of the two signals. Any uncorrected
signal or noise in the two signals results in additive patterns with "zero-mean value".
Therefore, application of a low-pass filter block 172 and/or a resettable integrator 146' to
the result of the comparison (multiplication in this example) produces a signal with
magnitude indicative of existence of the written pattern within the satellite signal.
Resettable integrator 146' may be reset to zero or another value in response to a
corresponding signal, such as a data block synchronization pulse 170, for example. The
output from resettable integrator 146' is compared to a corresponding threshold by level
detector 178. If the result exceeds the threshold, then the block write is determined to be
valid. Similarly, the output from low pass filter (LPF) 172 is compared to a
corresponding threshold by level detector 174 with a block write valid signal when the
result exceeds the threshold.
The signal correlation strategies employed by the correlation detectors
illustrated in the representative embodiments of Figures 3 and 4 are generally known in
the signal processing art. As described above, if the detected mark pattern (data) from
the satellite beam 44 is the same or well-correlated to the mark pattern written by the
main beam 40 then the delayed pattern correlation filters or detectors shown in Figures 3
and 4 are capable of detecting the similarities and verifying that data is being written.
However, since the delayed data being read by the satellite spot is greatly contaminated
by the uncorrelated modulations of the main beam, the process of detection of the written
data in these representative embodiments is cumulative over a block of data and the
results are generally statistical rather than deterministic in nature. This is generally not
problematic for data storage devices because they typically buffer and record data in
blocks. In addition, write errors generally result in re-writing an entire block of data.
Figures 5A-5D illustrate representative signals in an optical data storage
system or method having DRAW functionality according to various embodiments of the
present disclosure. The representative signals illustrated were generated using a computer
model of the block diagram of Figure 4, with application of ten consecutive data blocks
of random binary numbers representing the patterns of write data blocks. Line 200
represents the write patterns. Line 200' represents the delayed or time-shifted write
pattern shifted by the transit delay time Td as represented by line 202. Line 206
represents the satellite or side-beam signal. Random write failure periods were
embedded by modifying the patterns in satellite signal 206 at random locations and with
random durations/periods. Also, the effect of uncorrelated modulation of the laser beam
due to the write process was implemented in the model by continued amplitude
modulation of the satellite beam with uncorrelated write data patterns.
Figure 5B illustrates operation of a resettable integrator 146' (Fig. 4) with
line 220 illustrating the integrated value, line 222 representing a correspond threshold,
line 224 representing the embedded error, and line 224 representing data block
synchronization pulses. As shown in Figure 5B, valid data blocks are indicated where the
integrator value 220 exceeds a corresponding threshold 222. Areas where the integrator
value represented by line 220 does not reach threshold 222, such as indicated at 230,
corresponds to an error as indicated by line 224 and is detected as an invalid data block or
write error as represented by correlation signal 260 in Figure 5D. Similarly, Figure 5C
illustrates operation of a low pass filter 172 (Fig. 4) with line 240 representing the output
signal, line 242 representing a corresponding threshold, line 224 representing the
embedded error signal, and line 226 representing the data synchronization pulses. As
shown in Figure 5C, a valid data block write is indicated when output 240 exceeds a
corresponding threshold 242 as determined by level detector 174 (Fig. 4). Depending on
the particular application and implementation, a resettable integrator or low pass filter
may be used alone or in combination.
Figure 6 and 7 illustrate operation of a DRAW system or method for
optical data storage using a predetermined data verification pattern to provide
deterministic DRAW operation according to embodiments of the present disclosure. The
representative signals illustrated were generated using a computer model similar to the
previously described model, but signals modified as described below. The statistical
behavior of correlation detectors as previously described generally results from the
uncorrected modulation present in the satellite beam from the concurrent write process.
To further improve the robustness of the previously described correlation strategies, a
specific data field having a predetermined verification pattern selected to reduce or
eliminate the effect of the main beam write modulation on the satellite beam read signal
may be used in one or more data blocks to provide deterministic DRAW operation.
Figure 6 illustrates representative signals or patterns that may be used to
provide deterministic DRAW operation according to various embodiments of the present
disclosure. Line 300 represents a write pattern having a verification pattern or DRAW
field represented generally by reference numeral 330. Verification pattern or DRAW
field 330 includes fixed power periods indicated at 338 and 340 of write beam (set to read
power value for the appropriate satellite beam or spot) alternating with periods of random
data marks as indicated at 332, 334, and 336. The time-shifted or delayed write pattern
signal is represented by line 300' with corresponding time-shifted periods of generally
constant power alternating with time-shifted periods of random data marks 332', 334',
and 336' during the time-shifted verification period or DRAW field 330'. If the periods
of constant or fixed power substantially correspond to the transit time or delay (Td), the
downstream satellite beam will encounter and detect the random data marks 332' and
334', for example during constant power (no modulation) periods of the main beam at
338, 340, respectively. As such, the effect of main beam modulation is substantially
eliminated from the satellite signal because there are no write pulses during these periods.
Therefore, the result of the correlation detectors and the reset integrator block would be
free of write power modulation as generally illustrated in Figure 7.
Line 400 of Figure 7 represents the time-shifted or delayed write patterns
including alternating periods of constant power 338', 340' and periods of random data
marks 332', 334', and 336'. Line 410 illustrates operation of a resettable integrator with
a corresponding threshold 420 applied by a level detector to determine valid write data.
The integrator may be reset in response to a data synchronization signal as generally
indicated at 430. As indicated in Figure 7, the integrator signal does not detect valid data
during the constant power periods 338' and 340' due to the DC-free processing
previously described. This result may vary depending on the particular coding strategy
employed. However, the system may include appropriate logic that to indicate valid data
or provide another indication during these periods. In one embodiment, a verification
field or DRAW field 330' is provided at least once in every data block to provide a
deterministic status of write process integrity. This method can be utilized by itself or in
conjunction with the previously described correlation detection strategy to improve the
robustness of the OPU. Alternatively, or in combination, a DRAW field or verification
pattern may be generated in response to a signal, such as a request for diagnostics. In one
embodiment, the read/write channel can request such an intermittent DRAW field or
verification operation whenever the integrity of the write function is in question.
Figures 8A-8D illustrate representative signals in an optical data storage
system or method having deterministic DRAW operation according to embodiments of
the present disclosure. Similar to the embodiment described with reference to Figures
5A-5D, the representative signals of Figures 8A-8D were generated using a
corresponding computer model to demonstrate deterministic DRAW operation with a
DRAW field or verification pattern as previously described. In Figure 8A, line 500
represents the write patterns with line 500' representing the time-shifted or delayed write
patterns that include at least one verification pattern or DRAW field. Line 520 represents
the satellite signal. Line 530 of Figure 8B represents the value for the resettable
integrator. Line 560 represents the embedded error signal and line 570 represents the
data block synchronization pulses. Figure 8C illustrates operation of a low pass filter
block with line 580 representing the filter outlet, which is compared to a corresponding
threshold 590 by a level detector with valid data indicated where the output 580 exceeds
the threshold 590. Figure 8D illustrates the output of the correlation detector as
represented by line 660 based on the resettable integrator output and/or the low pass filter
output.
As illustrated in Figures 8A-8D, a system or method for optical data
storage with deterministic direct read after write (DRAW) using a satellite beam
downstream of a main beam may use a DRAW field or verification pattern to reduce or
eliminate the effect of main beam modulation during satellite beam data
reading/verification to improve robustness.
As illustrated and described above, embodiments of an optical data storage
system and/or method according to the present disclosure may provide various
advantages. For example, an optical storage device according to one embodiment of the
present disclosure provides direct read after right functionality for data verification using
a single OPU or optical head. Various embodiments of a system or method according to
the present disclosure use a correlation detector strategy to reliably detect data marks in
the beam reflected from a lower power satellite beam in the presence of main beam
modulation and other noise. The direct read after write functionality and correlation
detector strategy according to embodiments of the present disclosure can also provide
real-time diagnostic information and functionalities for the drive channel of an optical
storage device. For example, systems and methods according to embodiments of the
present disclosure may be used to enhance write strategy, provide information on write
pattern jitter, provide information to adjust and improve OPU performance and laser
power, to anticipate OPU anomalies, and the like.
While exemplary embodiments are described above, it is not intended that
these embodiments describe all possible forms encompassed by the claims. The words
used in the specification are words of description rather than limitation, and it is
understood that various changes may be made without departing from the spirit and scope
of the disclosure and claims. As previously described, the features of various
embodiments may be combined to form further embodiments that may not be explicitly
described or illustrated. While various embodiments may have been described as
providing advantages or being preferred over other embodiments or prior art
implementations with respect to one or more desired characteristics, those of ordinary
skill in the art recognize that one or more features or characteristics may be compromised
to achieve desired overall system attributes, which depend on the specific application and
implementation. These attributes include, but are not limited to: cost, strength, durability,
life cycle cost, marketability, appearance, packaging, size, serviceability, weight,
manufacturability, ease of assembly, etc. As such, embodiments described as less
desirable than other embodiments or prior art implementations with respect to one or
more characteristics are not outside the scope of the disclosure and may be desirable for
particular applications.
Claims (14)
1. An optical storage system that receives an optical medium having a plurality of tracks for storing data, the system comprising: an optical head having optics that split a light beam into a higher power main beam and at least one lower power side beam that form corresponding spots spaced along a selected one of the plurality of tracks; at least one controller coupled to the optical head that selectively positions the optical head for writing data along the selected one of the plurality of tracks using the higher power main beam while reading data directly after writing from the selected one of the plurality of tracks using the at least one lower power side beam; and a correlation detector that determines a correlation between a read signal associated with data detected by the at least one lower power side beam and a time-shifted write signal associated with the higher power main beam to verify data written to the selected one of the plurality of tracks directly after writing.
2. The system of claim 1 wherein the correlation detector combines the read signal and the time-shifted write signal and compares a resulting signal to an associated threshold to verify data written to the selected one of the plurality of tracks.
3. The system of claim 2 further comprising a low-pass filter that filters the resulting signal before the resulting signal is compared to the associated threshold.
4. The system of claim 2 further comprising a resettable integrator that integrates the resulting signal before the resulting signal is compared to the associated threshold, the integrator resetting in response to a data block synchronization signal associated with each block of data written to the optical medium. 206510NZ_claims_20150921_PLH
5. The system of claim 1 further comprising the correlation detector that determines correlation between a write signal provided to the higher power main beam that is time shifted based on transit delay of the optical medium moving between the main beam and the at least one side beam, and a read signal from the at least one lower power side beam after the transit delay, wherein valid data is determined based on the correlation exceeding a corresponding threshold.
6. The system of any preceding claim wherein the optical medium comprises an optical tape with the plurality of tracks extending generally across a width of the optical tape and wherein the system comprises an optical tape drive that receives the optical tape.
7. The system of any preceding claim wherein the controller generates a predetermined verification pattern for the higher power main beam having alternating periods of fixed power and random data.
8. The system of claim 7 wherein the controller generates the predetermined verification pattern for each block of data written to the optical medium.
9. The system of claim 8 or 7 wherein the controller generates the predetermined verification pattern in response to a request for diagnostics.
10. The system of any preceding claim wherein the optical head splits the light beam into a higher power main beam and first and second lower power side beams wherein the first lower power side beam reads data when the optical medium travels in a first direction and the second lower power side beam reads data when the optical medium travels in a second direction opposite the first direction.
11. A method for providing direct read after write functionality for an optical storage device having an optical head that splits a light beam into a center beam and at least one satellite beam that form corresponding spots spaced along a selected one of a plurality of tracks of an optical storage medium, the method comprising: writing data to the selected one of the plurality of tracks using the center beam; 206510NZ_claims_20150921_PLH reading previously written data directly after writing using the at least one satellite beam; comparing a first signal associated with data read by the at least one satellite beam to a second signal provided to the center beam for writing data that is time-shifted based on a transit time of the optical medium moving from the center beam to the at least one satellite beam, wherein comparing comprises multiplying the first and second signals to determine a correlation signal and comparing the correlation signal to a threshold to verify data written to the optical storage medium.
12. The method of claim 11 wherein the optical storage medium comprises an optical tape with the plurality of tracks extending generally across a width of the optical tape.
13. An article of manufacture including a non-transitory computer readable medium having stored thereon computer program logic for providing direct read after write functionality for an optical storage device with an optical head that splits a light beam into a center beam and at least one satellite beam that form corresponding spots spaced along a selected one of a plurality of tracks of an optical storage medium, the article of manufacture comprising computer program logic executed by a computer to perform the following operations: writing data to the selected one of the plurality of tracks using the center beam; reading previously written data directly after writing using the at least one satellite beam; comparing a first signal associated with data read by the at least one satellite beam to a second signal provided to the center beam for writing data that is time-shifted based on a transit time of the optical medium moving from the center beam to the at least one satellite beam, wherein comparing comprises multiplying the first and second signals to determine a correlation signal and comparing the correlation signal to a threshold to verify data written to the optical storage medium.
14. A computer program comprising program instructions for providing direct read after write functionality for an optical storage device with an optical head that splits a light beam into 206510NZ_claims_20150921_PLH a center beam and at least one satellite beam that form corresponding spots spaced along a selected one of a plurality of tracks of an optical storage medium by implementing the method of claim 12 or 11. 206510NZ_claims_20150921_PLH
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US13/214,662 US8451702B2 (en) | 2011-08-22 | 2011-08-22 | Direct read after write for optical storage device |
US13/214,662 | 2011-08-22 | ||
PCT/US2012/049893 WO2013028354A1 (en) | 2011-08-22 | 2012-08-08 | Direct read after write for optical storage device |
Publications (2)
Publication Number | Publication Date |
---|---|
NZ622073A NZ622073A (en) | 2015-10-30 |
NZ622073B2 true NZ622073B2 (en) | 2016-02-02 |
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