|Publication number||USRE41881 E1|
|Application number||US 09/997,036|
|Publication date||Oct 26, 2010|
|Filing date||Nov 27, 2001|
|Priority date||Jul 24, 1997|
|Also published as||DE69839415D1, DE69839415T2, EP0893793A2, EP0893793A3, EP0893793B1, US6046968|
|Publication number||09997036, 997036, US RE41881 E1, US RE41881E1, US-E1-RE41881, USRE41881 E1, USRE41881E1|
|Inventors||Daniel Y. Abramovitch, David K. Towner|
|Original Assignee||Hewlett-Packard Development Company, L.P.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (22), Non-Patent Citations (1), Referenced by (2), Classifications (38), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is a reissue of U.S. Pat. No. 6,046,968 entitled “Re-Writable Optical Disk Having Reference Clock Information Permanently Formed on the Disk” issued on Apr. 4, 2000 and is related to reissue application Ser. No. 11/416,589 filed on May 3, 2006.
This invention relates generally to storing data on re-writable optical disks. In particular, it relates to an optical disk having servo tracks including a clock reference structure for generating a clock reference signal for accurately controlling the placement of data marks along the servo tracks when writing information to a recording layer of the optical disk, and an optical disk recorder for writing the information to the optical disk.
Typically, data is stored on a recording layer of an optical disk by forming either data pits or data marks on the recording layer of the disk. The data pits or marks are formed along servo tracks on the recording layer of the optical disk. A servo track is a permanent physical feature on the recording layer of the optical disk which provides a track-following reference and defines the path along which stat is written. Servo tracks may be spiral or concentric. A groove is an example of a servo track. In some types of prerecorded optical disks, such as read only memory (ROM) disks, the data pits formed on the recording layer also function as a servo track.
Typically, an optical transducer which includes a focused laser beam is coupled to a servo track on the recording layer of the optical disk. When reading the optical disk, the data pits or marks formed along the servo track pass by the optical transducer as the optical disk rotates, causing the optical transducer to generate data signal representing the data stored on the recording layer of the disk. The optical transducer includes a focus positioner and a tracking positioner for maintaining alignment of the focused laser beam with respect to the servo track in the focus direction and the cross-track direction as the optical disk rotates. The focus and tracking positioners include servo-control systems which respond to focus and tracking error signals produced by the optical transducer.
In a re-writable optical disk, such as a phase change optical disk, data is stored on the recording layer of the optical disk in the form of data marks by controlling the optical characteristics of the recording layer of the disk. Data marks are formed on the recording layer by heating the recording layer of the disk with a focused laser beam at the locations where the data marks are to be written. In phase change recording, the optical reflectivity of the data mark is determined by the crystalline condition of the recording layer. The crystalline condition of the recording layer is determined by controlling the optical power in the focused laser beam. The optical power of the laser beam used to heat the recording layer determines the rate at which the temperature of the recording layer of the optical disk cools where the data mark is located. The rate at which the data mark location of the recording layer cools determines whether the location cools to an amorphous or a crystalline condition. Typically, the recorded data mark is amorphous and the surrounding area is crystalline.
In the prior art, placement of data to be written on a recording layer of a re-writable optical disk is typically determined by including synchronization information between fixed-length data fields. A sector is a repeating unit of pre-determined length.
The edit gap 40 shown in
Presently existing DVD read only memory (ROM) formats do not include physical sectoring of data stored on the recording layer of an optical disk. Therefore, synchronization fields and edit gaps are not provided. When reading a ROM optical disk, a read clock is produced from the data stored on the optical disk. Therefore, no synchronization information is required.
The DVD read only memory (ROM) format specification organizes data into fixed-length data field for error correction code (ECC) purposes. Each data field has an associated header containing synchronization and address information to facilitate data readout. This synchronization and address information is stored on the disk in the form of data pits which are indistinguishable from the data pits used to encode data. Although a DVD-ROM data field, together with its associated header information makes up a “physical sector” for the purposes of a read-only memory, it does not satisfy the requirements of a physical sector for the purposes of a re-writable optical disk memory. For this reason, all sectoring of the DVD format is treated as “logical sectoring.” A logical sector is contained within the data, whereas a physical sector contains the data. Therefore, all synchronization information, addressing and other DVD formatting are treated as if they were data, and are written on the disk in the form of data marks at the same time data is written.
Writing data to the recording layer of a re-writable optical disk which is compatible with DVD-ROM formats therefore requires the data to be written to a disk having no physical sectors on the unwritten disk, and therefore, no address or synchronization information in dedicated ares within the physical sectors. Furthermore, edit gaps can not be included. Without edit gaps, the data marks must be written with sub-bit accuracy during overwriting of pre-existing data.
U.S. Pat. Nos. 4,238,843, 4,363,116, 4,366,564, 4,375,088, 4,972,401 teach methods of permanently providing additional synchronization information along the tracks of an optical disk within data fields. The teachings of these patents also include synchronization information within sync fields between the data fields. Further, the spatial frequency of the synchronization information which is within the data fields must correspond with nulls in the spatial frequency of the data. This requires the data to be encoded using special codes so that nulls in the spatial frequency of the data correspond with the spatial frequency of the synchronization information.
It is desirable to have a re-writable optical disk and an optical disk recorder capable of recording data on the optical disk wherein the recorded disk is compatible with DVD-ROM standard formats, and is readable by a standard DVD reader, and wherein pre-existing data on the optical disk can be re-written (sometimes called over-written) with new data with sub-bit accuracy. The optical disk and optical disk recorder must be capable of generating a write clock which is synchronized with sub-bit accuracy to absolute position along the servo tracks of the optical disk. Further, it is necessary to be able to write standard DVD data formats.
The present invention provides a re-writable optical disk having a recording layer which includes a permanent clock reference structure provides a clock reference signal generated by an optical transducer as the clock reference structure passes by the optical transducer as the optical disk rotates. A write clock is phase-locked to the clock reference signal. The write clock enables new data to be written to the recording layer of the optical disk with sub-bit accuracy. Further, the write clock eliminates the need for sync fields and edit gaps and provides a means for writing and re-writing data in data fields of indeterminate length.
A first embodiment of the invention includes an optical disk. The optical disk includes a recording layer having servo tracks. A clock reference structure is formed along the servo tracks. The clock reference structure permits data to be written to the recording layer in data fields of indeterminate length. The clock reference structure comprises a reference spatial frequency which is greater than a predetermined spatial frequency. An extension of this embodiment includes the predetermined spatial frequency being greater than the maximum spatial frequency detectable by a standard DVD-ROM reader.
Another embodiment of the invention includes an optical disk recorder in which an optical disk is rotatably mounted on the recorder. The optical disk includes a recording layer containing servo tracks. An optical transducer radially follows a servo track as the optical disk rotates. A clock reference structure pre-exists along the servo tracks and provides data fields of indeterminate length. The clock reference structure causes the optical transducer to produce a clock reference signal as the optical disk rotates. The optical disk recorder further includes a means for recording data marks on the recording, layer of the optical disk. The data marks are recorded so that a standard DVD-ROM reader can read the data marks but the optical disk is constructed so that the reader cannot detect the clock reference structure. A write clock determines the physical placement of data marks written on the recording layer of the optical disk. The write clock is phase locked to the clock reference signal.
Another embodiment of the invention includes an optical disk recorder for receiving an optical disk. The optical disk is rotatably mountable on the recorder. The optical disk includes a recording layer having servo tracks and a clock reference structure having a spatial frequency which is too high to be detected by a standard DVD-ROM reader. The clock reference structure is formed along the servo tracks and provides data fields of indeterminate length. The optical disk recorder includes an optical transducer which is optically coupled to the recording layer of the optical disk. The optical transducer follows the servo tracks of the optical disk as the optical disk rotates. The clock reference structure formed along the servo tracks of the optical disk causes the optical transducer further includes a means for writing data marks on the recording layer of the optical disk. A write clock determines the physical placement of data marks written on the recording layer of the optical disk. The write clock is phase locked to the clock reference signal.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
As shown in the drawings for purposes of illustration, the invention is embodied in an optical disk structure and optical disk recorder which enables data to be written or re-written onto the recording layer of the optical disk. The data can be written or re-written with sub-bit accuracy without requiring the unwritten optical disk to be divided into physical sectors. Furthermore, synchronization fields and edit gaps are not required on an optical disk on which data is to be written. The optical disk recorder includes an optical transducer which can resolve and detect a high spatial frequency clock reference structure located on the optical disk. Standard DVD-ROM disk readers are not able to resolve and detect the clock reference structure. Therefore, the optical disk structure and optical disk recorder of this invention allow production of re-writable optical disks which can be read by standard DVD-ROM disk readers. Additionally, the optical disk recorder can read optical disks.
A clock reference structure is permanently formed along servo tracks of the optical disk. An optical transducer is coupled to the clock reference structure and generates a clock reference signal simultaneously with writing new data onto the recording layer of the optical disk. The data is written as data marks along the servo tracks. Each of the data marks includes a first and a second edge. During recording, the edges of the data marks are formed in synchronization with a write clock. Therefore, each time the edge of a data mark is formed, the write clock had completed the dame fraction of a cycle. The write clock is phase-locked to the clock reference signal. Therefore, the edges of the data marks are formed in synchronization with the clock reference signal with sub-bit accuracy. Therefore, the edges of the data marks are accurately aligned with the clock reference structure. The edge of the data mark is only recorded when required by the data written and the data encoding scheme. Many cycles of the clock reference structure will not have a corresponding data mark edge.
FIGS 4a, 4b, 4c illustrate a comparison of the fields of information along the tracks of two prior art optical disks, and the data fields of the present invention.
As shown is
The track address information can be included as a lower spatial frequency modulation superimposed on the higher clock reference structure spatial frequency.
A purpose of the present invention includes the elimination of physical sector information from unrecorded optical disks. The term “physical sectors” for the purposes of the description of the invention refers to permanently embossed structures between the data fields shown in FIG. 4a and FIG. 4b. For the invention, synchronization information can be used to synchronize a clock within an optical disk reader to read data within a data field. Such synchronization information is not present before data has been written to the optical disk. Further, such synchronization information is not required by an optical disk recorder of the invention to generate a reference clock signal. The DVD-ROM specification refers to the segmenting of data and the inclusion of synchronization information within the data as “physical sectoring.” For the description of the invention, this is referred to as “logical sectoring” to distinguish it from permanently embossed synchronization information located between data fields which is formed during manufacturing of a re-writable optical disk.
Alternate configurations of the embodiment shown in
Another embodiment of the invention includes the data marks 58 being formed on the recording layer by heating the recording layer of the optical disk 50 with a focused laser beam at the locations where the data marks 58 are written. In phase-change recording, the optical reflectivity of the data marks 58 is determined by controlling the rate at which the temperature of the recording layer of the optical disk 50 cools where the data marks 58 are located.
The recording layer of an optical disk is characterized by a recording threshold. The recording threshold being the minimum irradiance (optical power per unit area) at the recording layer necessary to alter the recording layer in an optically delectable way; for example by writing data marks. Irradiance levels below the recording threshold do not alter the recording layer and are used for producing the focus and tracking error signals used for maintaining the alignment of the optical transducer with the servo track. Irradiance levels below the recording threshold are also used in an optical disk reader to read recorded data.
As is well known in the art, the optical power emitted by a laser diode can be modulated at very high frequencies by modulating the electrical current used to drive the laser diode. Data recording is accomplished by modulating the laser diode drive current, thereby modulating the optical power emitted by the laser and, consequently, the irradiance at the recording layer. Whenever the irradiance at the recording layer is modulated above the recording threshold the recording layer is altered and a data mark is written. The positions of edges of data marks along the servo track correspond with the times of read signal transitions when the data marks are read by an optical disk reader.
Methods for manufacturing grooved optical disks are well known in the art and are currently employed in the production of most re-writable optical disks. Typically, a smooth glass disk is coated with photoresist and exposed with a focused laser beam as the disk is rotated on a precision spindle under servo control. For a spiral groove, the focused laser beam is continuously translated in the radial direction as the disk rotates. The exposed disk is developed to remove exposed photoresist and to harden unexposed photoresist; the exposed glass disk is then called the master. The master is then heavily plated with a metal (usually nickel), filling the grooves where the photoresist was exposed by the laser. The metal plating is separated from the master and mounted to a metal backing plate to form a sub-master or stamper. The sub-master is used as one surface of a mold used to manufacture grooved disk substrates. Substrates are normally injection molded form transparent polycarbonate plastic and then coated with the recording layer to form re-writable optical disks. The recording layer is then coated with a protective lacquer film. Laser light used for reading and writing data is focused through the substrate. This arrangement protects the recording layer from damage and contamination.
The edges of the grooves can be formed to oscillate in-phase radially deflecting the laser beam while exposing the photoresist in the mastering process. As is well known in the field of optics, high frequency deflections are practical to implement using a galvanometer mirror, an electro-optic deflector or an acousto-optic deflector in the path of the laser beam between the laser and the objective lens.
The edges of the grooves can be formed to oscillate substantially 180 degrees out-of-phase by modulating the power of the laser beam while exposing the photoresist in the mastering process. Numerous practical methods exist for modulating the power of a laser beam at a high frequency. Some lasers can be modulated directly by controlling a current or voltage source connected to the laser. Otherwise, an electro-optic or acousto-optic modulator, can be used in the laser beam path. A variety of modulation methods are also available that operate within the cavity of a gas laser, as is well known in the field of optics. Other methods of forming grooves can be used including a method which forms a clock reference structure which consists of a groove having a single edge which oscillates.
Prior to writing data to an optical disk, the data is encoded. A primary purpose of encoding data is to maximize the data storage capacity of the disk. Using the DVD format as an example,
Clock reference signal shown in
When recording re-writable data on a DVD formal disk, a write clock is needed which has a temporal period which corresponds to a channel bit length of 0.133 um. Thus, one channel bit length passes the optical transducer during each period of the write clock. Since a clock reference structure with a spatial period of 0.133 um can not be resolved by currently available optical transducers, the spatial period of the clock reference structure is selected to be a multiple of the channel bit length. In this example, one period of the clock reference structure has a length of four channel bits, equal to 0.533 um. The frequency of the clock reference signal is then ¼ of the channel bit frequency and the clock reference signal is increased in frequency by a factor of four to produce the write clock.
The rotational motor 84 is generally the same as the rotational motors used in prior art optical disk drives.
The optical power emitted by the laser diode 90 can be modulated at very high frequencies by modulating the electrical current used to drive the laser diode 90. Data recording is accomplished by modulating the laser diode 90 drive current, thereby modulating the optical power emitted by the laser diode 90, and consequently, the irradiance at the recording layer of the optical disk 80. The electrical current used to drive the laser diode 90 is controlled by the write signal.
The ability of an optical system to resolve fine structures like the clock reference structure of the invention is described by the modulation transfer function (MTF) of the optical system. Using methods such as Fourier transforms, the spatial distribution of light leaving an object can be represented as a spatial frequency distribution, in which each spatial frequency component has a particular amplitude and phase. A similar approach is commonly used to represent an electrical signal in terms of the component temporal frequencies of the electrical signal. An optical system such a lens, acts as an optical filter which selectively attenuates each spatial frequency component in an image formed by the lens. For each spatial frequency component, the lens has a transfer factor which determines the ratio of image modulation (lens output) to object modulation (lens input). The MTF of the lens specifies the transfer factor as a function of spatial frequency.
An aberration-free lens such as the objective lens in the optical transducer of an optical disk recorder or reader, has an MTF which is well known in the art of optics as being the appropriately scaled autocorrelation of the pupil function.
Manufacturers of optical disks and optical readers develop and agree to optical data storage industry standards. These standards ensure that any optical disk can be read by any optical disk reader if the optical disk and the reader conform to the same industry standards. DVD is an example of an industry standard. The specifications for DVD define numerous parameters of both DVD disks and DVD readers. The specifications include certain parameters of the optical transducer in the optical disk reader. These parameters include the wavelength (650 nm) and the numerical aperture (0.60) of the light beam focused on the optical disk. Curve 116 represents the MTF for the optical transducer of an industry standard DVD optical disk reader. As illustrated by curve 116, and as calculated above, the cutoff frequency for an industry standard DVD reader is 1.85 cycles/um.
The DVD standard only applies to read-only-memory (ROM). The DVD standard does not specify the design and manufacture of re-writable optical disks that can be read by industry standard DVD optical disk readers. There is a market demand for re-writable DVD disks and for optical disk recorders for writing data to the re-writable DVD disks. An object of this invention is to provide a continuous and permanent clock reference structure for use in recording re-writable DVD disks, wherein the clock reference structure can not be detected by industry standard DVD readers.
Curve 118 of
Curve 118 represents the MTF of an optical transducer having a numerical aperture of 0.8 and a light beam wavelength of 650 nm. However, curve 118 can alternatively represent the MTF of an optical transducer in which the numerical aperture is 0.6 and the light beam wavelength is 488 nm. In either of these example cases, the cutoff frequency 119 is 2.46 cycles/um and the shape of the MTF curve is as represented by the curve 118.
The write clock is synchronized to the recovered clock reference signal using a harmonic locking phase-locked loop shown in
The clock reference signal having a clock reference frequency (fr) is coupled to the phase-locked loop through a zero crossing detector 1012. The zero crossing detector 1012 converts the clock reference signal into a square wave. The square wave is coupled to a phase detector 1014. The write clock is generated at a frequency (N*fr) by a voltage controlled oscillator (VCO) 1016. An output signal (write clock) of the VCO 1016 is frequency divided by a frequency divider 1018. The output of the frequency divider 1018 is coupled to the phase detector 1014. The phase detector 1014 generates a phase detect signal in which the amplitude of the detect signal is proportional to the phase difference between the frequency-divided VCO signal and the square clock reference signal. Various embodiments of the phase detector exist, some of which include charge pump circuitry. The phase detect signal is amplified and filtered by a loop amplifier/filter 1020. The output of the amplifier/filter 1020 is coupled to the VCO and will advance or retard the phase of the VCO output signal.
The harmonic locking phase-locked loop accomplishes two functions. The first function is to generate a write clock which is at N times the frequency (fr) of the detected clock reference signal. The second function is to minimize the phase difference between the clock reference signal and the divided VCO signal.
While there is design flexibility in the choice of the reference multiplier N, it is not arbitrary. As noted on page 202 of Gardner; “the phase jitter at the output includes a component equal to N times that portion of the reference jitter that passes through the loop transfer function. Also, if there is closed-loop baseband noise vn at the phase detector output, then the corresponding VCO jitter is N(vn/Kd) (where Kd is the gain of the VCO), assuming that the spectrum of vn lies in the loop bandwidth. If N is large, the output jitter can be unacceptable, even for respectfully small values of reference jitter on vn. Extreme measures are sometimes needed to suppress stray circuit noises that are ordinarily negligible.”
Essentially, there is a practical limitation to the size of N due to the amplification of jitter and noise in the loop. For this reason, when write clock frequency greater than the clock reference frequency is required, it is most advantageous to maximize the clock reference frequency. Therefore, N is minimized, which minimizes the jitter.
This creates a distinction between clock reference structures having fundamental frequencies significantly lower than the maximum data spatial frequency and the clock reference structure of this invention. That is, the jitter produced by clock reference structures with fundamental spatial frequencies which are significantly lower than the maximum data frequency is likely to be too great to be of practical use in writing to an optical disk unless the data is divided into sectors which include edit gaps within them. However, the clock reference structure of this invention having spatial frequencies comparable to or greater than the maximum fundamental data spatial frequency will have less jitter and noise amplification in the harmonic locking phase-locking loop than a clock reference structure having a spatial frequency less than the maximum fundamental data spatial frequency. Therefore, the clock reference structure of the invention enables the production of a superior write clock.
The data signal and the clock reference signal are both coupled to the optical transducer in both optical disk readers and optical disk writers. Therefore, the data signal and the clock reference signal must be separated. To understand the process of separating the data signal from the clock reference signal, it is important to realize that as the optical disk rotationally passes under the optical transducer at a particular velocity, spatial frequencies of structures on the recording layer of the optical disk are translated into temporal frequencies. For a given spatial frequency (υ) on the optical disk and a given linear velocity (v) of the disk passing under the transducer, there is a specified temporal frequency (f) such that f is equal to υ*v. Therefore, the spatial frequency relationship between the data marks and the clock reference structure is preserved as a temporal frequency relationship between the data signal and the clock reference signal.
In prior art clock generation schemes that use synchronization fields in sector headers, the separation of the data signal and the clock signal is realized by spatially alternating the data and clock signals. The separation is accomplished by only re-synchronizing the write clock during the sector headers and running the write clock open loop while the optical transducer is coupled to data fields of the optical disk. The spatial multiplexing becomes time domain multiplexing as sector headers and data fields alternately pass the optical transducer of an optical disk reader or optical disk recorder.
Spatial multiplexing as previously described, can not be used to obtain a clock reference structure which is coincident with the data structure. Rather, it is necessary that the clock reference signal be separable from the data signal while data is being read or written. Generally, there are three optical storage configurations available for accomplishing the required separation of the clock reference signal and the data signal.
The first configuration includes the clock reference structure having a spatial frequency at which the spatial frequencies of the data have been specifically encoded to be nulled.
A second configuration includes the clock reference structure having a spatial frequency which is greater than the spatial frequency of the data.
A third configuration includes the clock reference structure having a spatial frequency which overlaps the spatial frequency spectrum of the data.
The first configuration constrains the coding of data stored on the optical disk to an extent that this configuration can not be used for writing data to optical disks which are to be read by a DVD-ROM reader.
The second and third configurations are the subject of the invention. The second configurations offers the advantage that the clock reference frequency is greater than the clock reference frequency of the third configuration. As previously described, the greater the frequency of the clock reference signal, the lower the amount of jitter that will be added to the write clock.
The optical disk of the present invention includes construction for producing a data signal with a high signal-to-noise ratio (SNR) when read by an optical disk reader. A clock reference signal is an unwanted source of noise if it appears within the data signal of the reader. The optical and electronic specifications of the optical transducer of a standard DVD optical disk reader are defined by a DVD format specification and are well known. Further, DVD readers are publicly sold. It is possible to determine the extent a clock reference structure formed on a re-writable DVD optical disk produces noise in the data signal of a standard DVD optical disk reader. The optical disk of the present invention includes construction for minimizing such noise.
The optical disk of the invention further includes construction to produce a high SNR clock reference signal while being recorded by an optical disk recorder of the invention. A data signal produced by pre-existing data marks on the disk is an unwanted source of noise if the data signal appears within the clock reference signal of the recorder. The optical disk recorder of the invention includes construction to maximize the clock reference signal while minimizing noise due to pre-existing data marks.
The clock reference structure of the re-writable optical disk of the invention is described by way of three embodiments. Each embodiment substantially eliminates a clock reference signal as a potential noise source in the data signal produced by a standard optical disk reader, and produces a high SNR clock reference signal in an optical disk recorder of the invention. Each of the embodiments enables the optical disk to be recorded in DVD format and subsequently re-written, in whole or in part, such that the disk is readable by a standard DVD reader.
In an optical disk recorder of the invention, the undesired data signal can be separated from the clock reference signal electronically. The frequency of the clock reference signal exceeds the highest fundamental frequency of the data signal, permitting the data signal to be substantially removed by high-pass electronic filtering. Electronic signal separation is enhanced due to the high spectral power and narrow spectral bandwidth of the clock reference signal.
In an optical disk recorder, significant additional rejection of the data signal is obtained by detecting the clock reference signal split detection (sometimes called tangential push-pull detection), an optical detection method well known in the art. In
Split detection produces substantially no signal from the data marks produced by phase change recording wherein data marks primarily affect the amplitude of the reflected light but not its phase. (Note that the name “phase change” applies to the crystalline or amorphous phase of the recording layer, not whether the recorded marks affect the amplitude or phase of the incident light.) The clock pits which constitute the clock reference structure produce a well-modulated clock reference signal when detected using split detection in the transducer of the optical disk recorder. For best SNR of the clock reference signal, the preferred round trip optical depth for the pits is λ/4, where λ is the wavelength of the light used in the optical transducer of the optical disk recorder. The optical depth of structures on the recording layer of an optical disk is defined as physical depth multiplied by the refractive index of the disk substrate material in contact with the recording layer.
In a second embodiment clock reference structure, as depicted in
A prior art standard optical disk reader generates a data signal using central aperture (CAP) detection. CAP detection is a method well known in the art which forms a signal by summing the four quadrant signals produced by a quadrant detector similar to the optical detector 114 of FIG. 17. The CAP detection signal is the (A=B=C=D) where A, B, C, D represent the signals from the detector quadrants. Alternatively, a detector with a single detection area large enough to capture the entire beam diameter is equivalent and may be used. CAP detection is well known in the art to have low sensitivity to structures on the recording layer having a round trip optical depth of λ/4 where λ is the wavelength of the light used in the optical transducer of the reader. This signal rejection characteristic of CAP detection permits the use of clock reference structures such as those shown in
In a preferred configuration, however, the spatial frequency of the clock reference structure exceeds the cutoff frequency of the optical transducer of a standard optical disk reader. In this case, the clock reference signal will be entirely eliminated from the data signal produced by the standard optical disk reader.
In an optical disk recorder, constructed to record data on disks having a reference structure comprising groove edges that oscillate substantially 180 degrees out of phase, the preferred method for detecting the clock reference signal is split detection, as previously described herein. As previously described, split detection produces substantially no signal from data marks, such as phase change marks, which primarily affect the amplitude of the reflected light. As previously noted, and as shown by curve 123 in
In a third embodiment clock reference structure, as depicted in
In an optical disk recorder, constructed to record data on disks having a reference structure comprising groove edges that oscillate in phase, the preferred method for detecting the clock reference signal is radial push-pull detection, an optical method well known in the are of optical data storage. Radial push-pull detection forms a signal according to the formula ((A=B)−(C=D)), which is sometimes normalized by dividing by (A=B=C=D). As previously discussed. A, B, C and D are electrical outputs from quadrants 21, 23, 25 and 27 of detector 114 in FIG. 17. Radial push-pull detection produces substantially no signal from data marks. Data marks are not detected, first because they primarily affect the amplitude of the reflected light, and secondly because they are nominally symmetric about the center of the track. As is well known in the art, radial push-pull detection is sensitive to structures which affect the phase of the reflected light and which are asymmetric about track center. Radial push-pull detection produces a well-modulated signal from groove edges which oscillate in phase, especially when the round trip optical depth of the groove is λ/4. Radial push-pull detection produces a well-modulated signal from groove edges which oscillate in phase, especially when the round trip optical depth of the groove is λ/4. Radial push-pull detection provides sufficient rejection of the undesired data signal to permit recovery of a clock reference signal having frequency within the frequency range of the data. It is desirable to provide the ability to use a clock reference structure with a spatial frequency below the cutoff frequency of a standard optical disk reader because the radial push-pull signal detection method reduces the cutoff frequency of the recorder's optical transducer when recovering a clock reference signal. Curve 125 of
Where the track pitch P is the radial distance between track centers. The MTF curves of
Note that the radial push pull signal contains tracking error information at frequencies substantially below the clock reference signal frequency and may also be used generate a tracking error signal for use by a tracking positioner.
The invention can include other clock reference structures such as a clock reference structure which consists of a groove having a single edge which oscillates. The three clock reference structures described here are by way of example.
Another embodiment of the invention uses a variation of the components shown in FIG. 10 and previously described. As shown in
Although specific embodiments of the invention have been described and illustrated, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated. The invention is limited only by the claims.
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|JPS6074123A *||Title not available|
|1||Borg H J and Duchateau J P W B "High Density Phase-Change Recording beyond 2.6 GByte" Proceedings of SPIE, vol. 3109 pp. 20-25, conference held in Apr. 1997.|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|USRE43788||Mar 16, 2010||Nov 6, 2012||Hewlett-Packard Development Company, L.P.||Re-writable optical disk having reference clock information permanently formed on the disk|
|USRE45292||Sep 19, 2012||Dec 16, 2014||Hewlett-Packard Development Company, L.P.||Re-writable optical disk having reference clock information permanently formed on the disk|
|U.S. Classification||369/47.28, 369/59.2, 369/275.4|
|International Classification||G11B7/007, G11B7/09, G11B20/14, G11B27/30, G11B27/19, G11B7/00, G11B7/0045, G11B7/006, G11B7/24, G11B27/24|
|Cooperative Classification||G11B20/1403, G11B20/10009, G11B2020/1287, G11B2020/1281, G11B7/0045, G11B7/006, G11B7/24082, G11B2020/1239, G11B2220/216, G11B7/00736, G11B20/1217, G11B20/10222, G11B2220/2562, G11B27/24, G11B27/3027, G11B2020/1232|
|European Classification||G11B20/12D, G11B20/10A, G11B20/10A7, G11B7/24082, G11B7/006, G11B27/30C, G11B7/007R, G11B20/14A, G11B27/24|
|Sep 30, 2003||AS||Assignment|
Owner name: HEWLETT-PACKARD DEVELOPMENT COMPANY L.P., TEXAS
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:HEWLETT-PACKARD COMPANY;REEL/FRAME:014061/0492
Effective date: 20030926
|Mar 22, 2011||CC||Certificate of correction|
|Sep 23, 2011||FPAY||Fee payment|
Year of fee payment: 12