News Column

Researchers Submit Patent Application, "Optical Disk Recording Medium, Optical Disk Device, and Recording Method", for Approval

July 1, 2014



By a News Reporter-Staff News Editor at Information Technology Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Hino, Yasumori (Nara, JP); Nakata, Kohei (Nara, JP); Takahashi, Yoshihisa (Osaka, JP), filed on March 14, 2013, was made available online on June 19, 2014.

The patent's assignee is Panasonic Corporation.

News editors obtained the following quote from the background information supplied by the inventors: "Currently, various types of optical disks including a DVD and a Blu-ray Disc (hereinafter, referred to as a BD) are being used as information recording media for storing images and data. Such optical disks have a higher storage reliability than a hard disk device (hereinafter, referred to as an HDD) or a magnetic tape. Therefore, applications of optical disks are being expanded from conventional applications of recording AV (audio/video) data such as images and sounds to applications of storing data over long periods of time.

"However, the amount of data that can be stored per cubic volume of an optical disk is only around 1/3 of that of an HDD or a magnetic tape. Therefore, from the perspective of space efficiency during storage, there are demands for technological developments that enable an increase in the amount of data that can be stored per cubic volume without raising the cost of optical disks, and research and development are being continuously carried out in an energetic manner. Recently, BDXL (with a recording density of approximately 33.4 GB per layer) is being marketed as an optical disk with the highest volume recording density among BDs.

"Such optical disks are capable of storing data for 50 years or longer. Therefore, from the perspective of long-term storage of data, optical disks have a storage reliability that is 10 or more times longer than the lifespan of HDDs which is around 5 years. Accordingly, by transferring data for long-term storage from an HDD to an optical disk, a balance between long-term storage reliability and a reduction of storage cost can be achieved. In particular, compared to an HDD which consumes power during data storage, an optical disk which does not require power during data storage is capable of reducing carbon dioxide emissions as a green storage and can contribute to reducing power consumption at data centers which has become a major concern in recent years.

"However, even with a BDXL which boasts the highest recording density among optical disks, the amount of data that can be stored per volume is only around 1/3 of that of an HDD. Therefore, optical disks require a greater storage space than HDDs during data storage and, in particular, with applications such as data centers where cost demands related to storage spaces are high, there is a need to improve the recording density per volume of optical disks.

"Techniques for improving the recording density per volume of an optical disk include a land-groove recording/reproducing technique which is capable of improving track recording. This technique is used in DVD-RAMs and increases recording density of a track by recording data, which has conventionally been recorded only on grooves or on tracks, on both grooves and tracks.

"Normally, when the recording density on tracks of an optical disk is increased, diffracted light from a groove track which is necessary for an optical beam to control tracing of the groove becomes smaller and the optical beam becomes unable to trace the track. When .lamda. denotes a wavelength of an optical beam irradiated on an optical disk and NA denotes a numerical aperture of a lens that forms the optical beam, if a track spacing L between grooves or lands becomes smaller than .lamda./NA.times.0.6, diffracted light can no longer be detected from a groove and control for tracing a track cannot be performed. With a DVD whose numerical aperture NA is 0.6 and optical beam wavelength .lamda. is 650 nm, a limit of track spacing L at which diffracted light can be detected is 650 nm. With a DVD-RAM, by recording data on both lands and grooves, a track pitch of 615 nm is realized and track density is increased (for example, refer to Patent Literature 1).

"With an optical disk used to record data in both lands and grooves as described above, in particular, special measures must be taken with respect to addresses recorded on the optical disk in order to access a position where data is to be recorded. This is because recording data on both lands and grooves requires addresses to be allocated at high density. Conventionally, address allocation techniques include CAPA (Complementary Allocated Pit Address) (for example, refer to Patent Literature 2) that is used in DVD-RAMs and a technique that involves wobbling only a groove wall on one side to record address information. In addition, Patent Literature 3 discloses a system which is used in Blu-ray Discs and which only uses grooves as recording tracks.

"Furthermore, a bonding technique in which two optical disks created by a same process are bonded together to form a single optical disk in order to increase volume density has also been put to practical use in DVDs. Since bonding together two optical disks also improves physical properties related to the shape of optical disks such as warping during long-term storage, optical disks having recording surfaces on both sides are being used as optical disks for long-term storage. Reproduction techniques such as changing directions of rotation of a motor are used to reproduce an optical disk having recording surfaces on both sides at high speed (for example, refer to Patent Literature 4).

"Problems that arise when using an optical disk as a medium suitable for long-term storage will be described below.

"The conventional art described in Patent Literature 1 which is used in DVD-RAMs and which has been devised in order to increase recording density in a recording surface of an optical disk will now be described with reference to FIG. 16.

"FIG. 16 is a diagram for describing a format of a conventional optical disk. In FIG. 16, a recording track 1401 is constituted by a land and a recording track 1402 is constituted by a groove. An address area 1403 is an area provided for accessing an area in which data is recorded and is constituted by pre-recorded pits formed on the optical disk. Address parts 1404 and 1405 are referred to as CAPA and are shifted in a radial direction by one-half track pitch from a center of a track. A data recording area 1406 is a recording sector for recording data.

"The address parts 1404 and 1405 are constituted by a VFO (Variable Frequency Oscillator) 1407 for generating a synchronizing clock for decoding an address, an AM (address mark) 1408 for identifying a start of address data, a PID (Physical Identification Data) 1409 which represents address data, a PED (PID Error Detecting code) 1410 for correcting an error in the address data 1409, and a PA (postamble) 1411 which represents an end of address data. Among the series of addresses, same data is recorded twice in the address part 1404 in a first half of the address area 1403, and the same data is also recorded twice in the address part 1405 in a second half of the address area 1403.

"The data recording area 1406 is an area for recording user data. In a similar manner to the address area 1403, the data recording area 1406 is divided into a plurality of areas necessary for reproducing recorded data after the data is recorded. The data recording area 1406 is constituted by a GAP 1412 which is provided for avoiding interference from the address area 1403, a GUARD 1413 which represents an interference area when a recording position of recording data is offset, a VFO (Variable Frequency Oscillator) 1414 for generating a motivation clock for decoding a recording, a PA (postamble) 1415 for identifying a start of recording data, DATA 1416 which represents a recording data area for recording data on the optical disk, a PA (postamble) 1417 for identifying an end of recording data, a GUARD 1418 which represents an interference area when a recording position of recording data is offset, and a BUFFER 1419 which is provided for avoiding interference from the address area 1403.

"With an optical disk which uses DVD-RAM technology and in which data is recorded on both lands and grooves, the address area 1403 for identifying a position where data is to be recorded and the data recording area 1406 for recording data must be separated from one another. The addresses of a groove and a land are shared a address that is shifted in a radial direction by one-half track pitch from a center of a track, because the addresses cannot be independently recorded on both a land and a groove. With an optical disk in which data is only recorded in a groove such as a DVD.+-.R or a Blu-ray Disc, since addresses are multiplexed by wobbling a groove, an address area and a data recording area need not be separated from each other.

"However, when track density is increased by a land-groove technique, a problem is caused that address data cannot be multiplexed in a data recording area and the data recording area ends up being wasted. In addition, with a land-groove technique which reduces track spacing, since the address area 1403 and the data recording area 1406 are separated from each other, address data or recording data must each be independently demodulated.

"Therefore, as shown in FIG. 16, various areas (VFO 1407, AM 1408, PA 1411, GAP 1412, GUARD 1413, VFO 1414, PS 1415, PA 1417, GUARD 1418, and BUFFER 1419) for independently demodulating data must be independently provided in the address area 1403 and the data recording area 1406. These areas are useless as far as the data recording area is concerned and reduce format use efficiency.

"On the other hand, with an optical disk in which data is only recorded in a groove such as a DVD.+-.R or a Blu-ray Disc, addresses necessary for recording data cannot be formed on both a groove and a land. FIG. 17 is a diagram for describing a format of another conventional optical disk. A relationship between address information and recording data in a Blu-ray Disc will be described with reference to FIG. 17. In addition, a reason why conventional techniques are incapable of allocating addresses in both a land and a groove and multiplexing and recording address information and recording data in a same area.

"In FIG. 17, a recording track 1502 is formed by a groove on an optical disk 1501. Data is recorded in a data recording area 1503, and address information for accessing the data recording area 1503 is recorded in address information areas 1504, 1505, and 1506. Address information is allocated in a same area as recording data, and recording data is recorded by being multiplexed on address information. One piece of recording data is recorded in an area constituted by three pieces of address information AD1 (Z05), AD2 (Z06), and AD3 (Z07), and the area constituted by the three pieces of address information becomes the data recording area 1503 that is a recording unit of data. An integral multiple of a length of the data recording area 1503 that is constituted by the three pieces of address information is not consistent with a length of a circumference of a track. Therefore, as shown in FIG. 17, a position on a circumference of the data recording area 1503 between adjacent recording tracks is allocated by being offset every circumference of the optical disk.

"In the recording track 1502, 1 bit of the pieces of address information AD1, AD2, and AD3 is recorded by partially altering a waveform of a groove that is wobbled at a predetermined period. An area 1507 shown enlarged at the bottom of FIG. 17 is a portion corresponding to an address bit and is subjected to modulation that is referred to as MSK (Minimum Shift Keying). In addition, as shown in the bottom of FIG. 17, since an integral multiple of a wobble period is not consistent with a length of one circumference of a recording track, phases of wobbles vary by a predetermined amount between adjacent recording tracks.

"With an optical disk configured as described above, in order to increase track density by recording data on a land (between adjacent recording tracks 1502), address information for accessing a land must also be imparted to the land. However, with a system in which address information is recorded by wobbling a groove, unique address information cannot be imparted to a land. In addition, since the two grooves adjacent to a land are both independently wobbled and pieces of address information are respectively recorded on the grooves, when the land is traced, addresses of both recording tracks are simultaneously reproduced. As a result, demodulation becomes totally impossible.

"Furthermore, with an optical disk configured as described above, while groove width is constant, land width is affected by wobbling of the grooves and therefore varies. As a result, when data is recorded on a land, a variation in groove width adversely affects the land and reproduction performance declines significantly. As shown, with a system in which recording data is recorded multiplexed on a recording track on which address information has been recorded by wobbling of a groove, since an address area need not be independently secured as is the case of DVD-RAMs described earlier, format use efficiency can be improved. However, when increasing recording density in a track direction, since address information cannot be imparted on a land, there is a fundamental problem that the land cannot be used as a recording track and recording density cannot be increased.

"In addition, one way to increase recording density per volume is to bond together two 0.6 mm-thick optical disks to create a single optical disk with a thickness of 1.2 mm as is the case with DVD-RAMS and the like. Accordingly, recording density per volume can be readily doubled. However, bonding together two optical disks with a same format and a same physical structure makes it difficult to simultaneously record data on or reproduce data from both recording surfaces. This problem will now be described with reference to FIG. 18.

"FIG. 18 is a diagram for describing a recording method for a conventional optical disk having two recording surfaces. In FIG. 18, an optical disk 1601 records data. A substrate of the optical disk 1601 has a thickness of 0.6 mm. An optical disk 1602 is created by bonding together two optical disks 1601 and has two recording surfaces. An optical pickup 1603 records data on one recording surface of the optical disk 1602. An optical pickup 1604 records data on the other recording surface of the optical disk 1602. A motor 1605 rotates the optical disk 1602.

"The optical disk 1602 has recording surfaces on both sides as a result of bonding together two optical disks 1601 with a same format and a same physical structure. In this manner, by bonding together two of the same optical disks 1601, a manufacturing process of the two optical disks 1601 prior to bonding is shared. Therefore, the optical disk 1602 having recording surfaces on both sides can be manufactured inexpensively.

"However, as shown in FIG. 18, directions of spirals of recording tracks are opposite to each other between an upper side and a lower side of the optical disk 1602. Therefore, when the optical disk 1602 is rotated in a certain direction, recording tracks rotate in opposite directions between the upper side and the lower side. As a result, as shown in FIG. 18, even if two optical pickups 1603 and 1604 are provided on both recording surfaces of the optical disk 1602, data cannot be recorded on or reproduced from both recording surfaces at the same time.

"With an optical disk structured as described above, in order to record data on or reproduce data from both recording surfaces, an optical pickup is provided only on the side of one of the recording surfaces and the recording surfaces are reversed by removing and inserting the optical disk. Alternatively, the optical pickups 1603 and 1604 are respectively provided on both of the two recording surfaces, and once recording or reproduction of one recording surface ends, a direction of rotation of the motor 1605 is reversed to start recording or reproduction of the other recording surface. If the two optical pickups 1603 and 1604 are capable of recording data on or reproducing data from both recording surfaces at the same time, a recording transfer rate or a reproduction transfer rate can be doubled. However, due to the reasons described above, it is difficult to have the two optical pickups 1603 and 1604 record data on or reproduce data from both recording surfaces at the same time. Therefore, there is a problem that the transfer rate cannot be increased with an optical disk having two recording surfaces."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "The present invention has been made to solve the problems described above, and an object of the present invention is to provide an optical disk recording medium, an optical disk device, and recording method which are capable of increasing recording density.

"An optical disk recording medium according to an aspect of the present invention is an optical disk recording medium which records data and which comprises a groove track formed by a groove and a land track formed between adjacent groove tracks, wherein the groove track records address information representing information on a position within a recording surface of the optical disk recording medium by a predetermined pattern due to wobbling of the groove track, an integral multiple of a wobbling period of a portion of the groove track other than the address information is consistent with a length of one circumference of the groove track, an integral multiple of a period of the address information is consistent with the length of one circumference of the groove track, and pieces of information that differ between adjacent groove tracks among the address information are recorded by at least predetermined wobble patterns that differ between the adjacent groove tracks.

"According to this configuration, a groove track is formed by a groove and a land track is formed between adjacent groove tracks. The groove track records address information representing information on a position within a recording surface of the optical disk recording medium by a predetermined pattern due to wobbling of the groove track. An integral multiple of a wobbling period of a portion of the groove track other than the address information is consistent with a length of one circumference of the groove track. In addition, an integral multiple of a period of the address information is consistent with the length of one circumference of the groove track. Furthermore, pieces of information that differ between adjacent groove tracks among the address information are recorded by at least predetermined wobble patterns that differ between the adjacent groove tracks.

"According to the present invention, since the integral multiple of a wobbling period of a portion of the groove track other than the address information is consistent with a length of one circumference of the groove track and an integral multiple of a period of the address information is consistent with the length of one circumference of the groove track, a width of the land track can be set constant, data can be recorded on both the groove track and the land track, and a recording density of the optical disk recording medium can be increased.

"In addition, since pieces of information that differ between adjacent groove tracks among the address information are recorded by at least predetermined wobble patterns that differ between the adjacent groove tracks, address information can be decoded without mutual interference from adjacent groove tracks, and address information can even be decoded from the land track between the adjacent groove tracks.

"This and other objects, features, and advantages of the present invention will become more apparent as the following detailed description is read with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 is a diagram for describing a format of an optical disk recording medium according to a first embodiment of the present invention.

"FIG. 2 is a diagram for describing a data allocation structure of address information according to the first embodiment of the present invention.

"FIG. 3 is a diagram for describing more desirable allocation conditions of an MSK wobble of adjacent groove tracks.

"FIG. 4 is a diagram showing a structure of address information constituted by a plurality of address unit bits according to the first embodiment of the present invention.

"FIG. 5 is a diagram for describing generation of a recording clock according to the present first embodiment.

"FIG. 6 is a block diagram showing a configuration of an optical disk device according to the first embodiment of the present invention.

"FIG. 7 is a diagram showing a table which represents a division ratio N that is set for a recording clock PLL circuit of each recording zone and a length 1T that corresponds to a recording line density in each record zone used in the present first embodiment.

"FIG. 8 is a diagram showing a sequence of start of recording and additional recording of a PCRA that is a continuous area when data is recorded in a zone.

"FIG. 9 is a diagram showing a sequence of start of recording and additional recording of a PCRA that is a continuous area when data is recorded across a zone boundary.

"FIG. 10 is a diagram showing a specific example of a PCRA table for managing a PCRA.

"FIG. 11 is a diagram for describing an alternate recording process when there is a defect on an optical disk recording medium and recording is interrupted.

"FIG. 12 is a diagram for describing a wobble pattern of an optical disk recording medium according to a second embodiment of the present invention.

"FIG. 13 is a block diagram for describing a configuration of an optical disk device according to the second embodiment of the present invention.

"FIG. 14 is a block diagram for describing a configuration of an optical disk device according to a third embodiment of the present invention.

"FIG. 15 is a diagram showing a configuration of an address reverse-order decoder shown in FIG. 14.

"FIG. 16 is a diagram for describing a format of a conventional optical disk.

"FIG. 17 is a diagram for describing a format of another conventional optical disk.

"FIG. 18 is a diagram for describing a recording method for a conventional optical disk having two recording surfaces."

For additional information on this patent application, see: Hino, Yasumori; Nakata, Kohei; Takahashi, Yoshihisa. Optical Disk Recording Medium, Optical Disk Device, and Recording Method. Filed March 14, 2013 and posted June 19, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=4342&p=87&f=G&l=50&d=PG01&S1=20140612.PD.&OS=PD/20140612&RS=PD/20140612

Keywords for this news article include: Panasonic Corporation, Information Technology, Information and Data Storage.

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