1. Field of the Invention
The present invention relates to a magneto-optical recording medium serving as both a ROM (Read Only Memory) made of phase pits formed on a substrate and a RAM (Random Access Memory) made of a magneto-optical recording layer, and to a magneto-optical recording medium drive therefor. In particular, the invention relates to a magneto-optical recording medium and a magneto-optical recording medium drive contributing to a superior readout of information from both the ROM and RAM.
2. Description of the Prior Art
A laser beam of a smaller intensity is applied to the user area 73 in readout of magneto-optical signals. The plane of polarization is rotated in the laser beam in response to the magnetization in the recording layer based on the polar Kerr effect. The signals are determined based on the intensity of the polarization component of the reflected beam. The RAM information is thus read out.
The research has been developed to utilize the aforementioned characterized features of the magneto-optical disk. As disclosed in Japanese Patent Publication No. 6-202850, for example, a so-called concurrent ROM-RAM optical disk has been proposed for simultaneous reproduction of ROM and RAM information.
As shown in
The modulation of optical intensity required to accomplish the read out of the ROM information is one of the factors to generate noise in the reproduction signals of the RAM information. The present applicant proposed a solution in the International PCT application PCT/JP02/00159, filed Jan. 11, 2002. The feedback of an optical intensity modulation signal obtained from the readout of the ROM information is input to a laser diode for readout of information. This is believed to reduce noise in the modulation of optical intensity. However, noise cannot sufficiently be reduced if the modulation degree of optical intensity gets larger for the ROM information. In addition, it is difficult to feedback control the intensity of the laser at a higher speed.
The modulation degree of the optical intensity for the ROM information may be reduced to minimize noise from the phase pits, so that noise is intended to get reduced in the aforementioned RAM signals. However, the reproduction signals of a sufficient level can be obtained for the RAM information only if the intensity of the ROM signals gets extremely smaller. The readout of the ROM information is in this manner hindered. In other words, simultaneous readout of the ROM and RAM signals cannot be achieved even if the modulation degree of the optical intensity for the ROM information is adjusted.
It is accordingly an object of the present invention to provide a magneto-optical recording medium and a magneto-optical recording medium drive contributing to a reliable achievement of simultaneous readout of the ROM information in the form of phase pits and the RAM information based on the magneto-optical recording. It is also an object of the present invention to provide a magneto-optical recording medium and a magneto-optical recording medium drive capable of suppressing jitter within a predetermined range in the reproduction signals of the ROM and RAM information.
According to the present invention, a difference, namely a birefringent difference is set equal to or smaller than 47 nm between first and second birefringent values, said first birefringent value being measured for a single pass of an optical beam passing through the substrate of an attitude rotated, relative to a reference plane perpendicular to the optical beam, by 20 degrees around a tangent line tangent to the sequence of phase pits at the projection of the optical beam on the substrate, said second birefringent value being measured for a single pass of the optical beam passing through the substrate of an attitude rotated, relative to the reference plane, by 20 degrees around a straight line extending within a plane including the surface of the substrate in a direction perpendicular to the sequence of phase pits.
When the birefringent difference is set equal to or smaller than 47 nm, jitter can sufficiently be suppressed in the readout of data from a magnetic recording film. In particular, the birefringent difference is preferably set equal to or smaller than 30 nm. The substrates may be made of polycarbonate or amorphous polyolefin, for example.
The optical depth of the phase pits may be set in a range between 0.06λ and 0.14λ, where λ is the wavelength of an optical beam for the readout of data. In general, the ROM information is recorded in the magneto-optical recording medium based on the phase pits. The deeper phase pits contribute to a reliable readout of the ROM information. The RAM information may be recorded in the magneto-optical recording medium based on the magnetization in the magnetic recording film. The shallower phase pits contribute to a reliable readout of the RAM information. The optical depth of the phase pits in a range as mentioned above contributes to a reliable readout of both the ROM and RAM information. In particular, the optical depth of the phase pits is preferably set in a range between 0.073λ and 0.105λ, where λ is the wavelength of an optical beam for the readout of data.
The phase pits may be set to have a modulation degree ranging from 8% to 55%, for example. The degree of modulation in the set range contributes to a reduced jitter equal to or less than 15% and a reliable tracking.
Injection molding is employed to form the mentioned recording medium made of polycarbonate or amorphous polyolefin. The substrate may be subjected to annealing treatment at the temperature equal to or higher than 90 degrees Celsius. The annealing treatment serves to suppress the birefringent difference of the substrates at a level equal to or smaller than 37 nm. In particular, the temperature equal to or higher than 100 degrees Celsius contributes to establishment of the birefringent difference equal to or smaller than 32 nm. In this case, jitter can be suppressed to a level equal to or less than 8% in the readout of the RAM information. It should be noted that the temperature should not exceed 130 degrees Celsius. If the temperature exceeds 130 degrees Celsius, the substrate may suffer from warp. The warp hinders a reliable readout of the RAM information. A magnetic recording film or layer is formed on the substrate after the annealing treatment.
A specific magneto-optical recording medium drive may be provided for realization of the aforementioned recording medium. The drive may include a light source emitting an optical beam; a spindle supporting a recording medium; and an optical system designed to direct the optical beam to the recording medium, said optical beam having the plane of polarization perpendicular to a recording track defining the sequence of phase pits. This drive enables a superior reduction in jitter as compared with the case where an optical beam is irradiated to have the plane of polarization in parallel with the recording track. The magneto-optical recording medium drive may further comprise: a first optical detector detecting a rotation of the plane of polarization between an optical beam reflected from the recording medium and an optical beam prior to reflection; and a second optical detector detecting the intensity of an optical beam reflected from the recording medium. The first optical detector is utilized for the readout of the RAM information. The second optical detector is utilized for the readout of the ROM information.
The above and other objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiment in conjunction with the accompanying drawings, wherein:
Phase pits 13 are formed on the surface of the substrate 12 based on a transfer from the molding die. The phase pits 13 correspond to depressions formed on the surface of the substrate 12. The substrate of the type is hereinafter referred to as “phase pit substrate”. An undercoat film 14, a magnetic recording film 15, an auxiliary magnetic film 16, an overcoat film 17, a reflection film 18 and a protection film 19 are sequentially formed on the surface of the substrate 12. The undercoat film 14, the magnetic recording film 15, the auxiliary magnetic film 16, the overcoat film 17, the reflection film 18 and the protection film 19 are all overlaid on the phase pits 13. User data is held in the magnetic recording film 15 over the phase pits 13 in the magneto-optical disk 11.
A difference is set equal to or smaller than 47 nm between first and second birefringent values. This difference is hereinafter referred to as “birefringent difference”. In this case, the first birefringent value is obtained based on measurement on the substrate 12 for a single pass of a first inclined incident optical beam. The second birefringent value is likewise obtained based on measurement on the substrate 12 for a single pass of a second inclined incident optical beam. As shown in
The inventors prepared phase pit substrates having the thickness of 1.2 mm. The phase pit substrate includes, as shown in
Next, magneto-optical disks were formed based on the aforementioned phase pit and continuous groove substrates. Various conditions were set for annealing treatment effected on the phase pit and continuous groove substrates. The phase pit and continuous groove substrates were then set in a sputtering apparatus. A vacuum equal to or smaller than 5xe−5 [Pa] was set in the chambers of the sputtering apparatus. A Si target is set in a first chamber. The phase pit and continuous groove substrates were transported into the first chamber. Ar gas and N2 gas were introduced into the first chamber. Reactive sputtering was effected in the first chamber. The undercoat film 14 made of a SiN film having the thickness of 80 nm was formed on the substrates.
Next, the phase pit and continuous groove substrates were transported into a second chamber of the sputtering apparatus. The magnetic recording film 15 made of a Tb22(FeCo12)78 film having the thickness of 30 nm and the auxiliary magnetic film 16 made of a Gd19(FeCo20) film having the thickness of 4 nm were sequentially formed in the second chamber. The phase pit and continuous groove substrates were then transported into the first chamber. The overcoat film 17 made of a SiN film having the thickness of 5 nm and the reflection film 18 made of an aluminum film having the thickness of 50 nm were formed in the first chamber. The protection film 19 made of an ultraviolet setting resin coating was subsequently formed on the reflection film 18. The magneto-optical disks were prepared in this manner.
The magneto-optical disks were sequentially set in a recording/reproducing apparatus. ROM jitter was measured based on the sequence of phase pits in the recording/reproducing apparatus. RAM jitter was also measured based on the reproduction of the magneto-optical recording over the sequence of the phase pits in the recording/reproducing apparatus. The wavelength of the laser beam was set at 650 nm in the recording/reproducing apparatus. The numerical aperture NA was set at 0.55. The linear velocity was set at 4.8 [m/s]. Magnetic field modulation recording was employed to establish a predetermined data of the eight to fourteen modulation in the magnetic recording films on the magneto-optical disks. The shortest length of the mark was set at 0.832 μm. The reproduction power of the laser was set at 1.5 [mW] in the measurement of jitter for both the ROM and RAM information. The DC radiation having the laser power Pw of 8.0 [mW] was employed in the magnetic field modulation recording. The plane of polarization was set in the direction perpendicular to the tracking line in the laser beam in the reproduction process. It should be noted that the same effect can be achieved in the optical modulation recording in place of the magnetic field modulation recording.
As shown in
[Equation 1]
y=0.082X2+0.324X (1)
Next, the inventors prepared the phase pit substrates in the aforementioned manner. Here, the optical depth of the phase pits were set at 0.095λ, equal to the substantial depth of 40 nm. Panlite® ST-3000 polycarbonate was employed as the material for the phase pit substrates. Injection molding was employed to form the phase pit substrates. As shown in
Next, the inventors prepared the phase pit substrates in the aforementioned manner. Panlite® ST-3000 polycarbonate was employed as the material of the phase pit substrates. The temperature was set at 130 degrees Celsius for the annealing treatment. As shown in
Next, the inventors prepared the phase pit substrates in the aforementioned manner. Panlite® ST-3000 polycarbonate was employed as the material for the phase pit substrates. Injection molding was employed to form the phase pit substrates. Various optical depths were set for the phase pits on the phase pit substrates. The annealing treatment was effected on the individual phase pit substrates at the temperature of 130 degrees Celsius for the duration of 30 minutes. Magneto-optical disks were prepared based on the phase pit substrates in the aforementioned manner. The degree of modulation and the jitter were measured for the prepared magneto-optical disks. The magneto-optical disks were sequentially set in a tester. The ROM information was reproduced from the phase pits based on the tracking servo of the phase pits. The wavelength of the laser beam was set at 650 nm. The numerical aperture NA was set at 0.55. The linear velocity was set at 4.8 [m/s]. Magnetic field modulation recording was employed to establish a predetermined data of the eight to fourteen modulation in the magnetic recording films on the magneto-optical disks. The shortest length of the mark was set at 0.832 μm. The ROM information was likewise established based on the phase pits having the shortest length of the mark equal to 0.832 μm of the eight to fourteen modulation. ROM jitter was measured based on the sequence of phase pits. RAM jitter was also measured based on the reproduction of the magneto-optical recording over the sequence of the phase pits. The reproduction power of the laser was set at 1.5 [mW] in the measurement of jitter for both the ROM and RAM information. The DC radiation having the laser power Pw of 8.0 [mW] was employed in the magnetic field modulation recording. The plane of polarization was set in the direction perpendicular to the tracking line in the laser beam in the reproduction process.
The intensity of the laser beam reflected from the magneto-optical disk was measured to calculate the degree of modulation. The optical intensity of the laser beam is detected at the divided photodetector for the perpendicular planes of polarization as described later in detail. Electric signals output from the photodetector are added at an addition amplifier. The intensity is in this manner detected for the overall laser beam. The electric signal after the addition is input into an oscilloscope. As shown in
As is apparent from
As described above, if the optical depth and the degree of modulation are adjusted in a condition where the birefringent difference is set as mentioned above between the first and second inclined incident optical beams, the jitter can sufficiently be suppressed for the ROM and RAM for substantial purposes. If the birefringent difference deviates from the aforementioned range, the jitter cannot be reduced enough even if the optical depth and the degree of modulation are adjusted.
A magneto-optical disk drive 31 is employed to effect recording/reproducing operations on the magneto-optical disk 11. The magneto-optical disk 31 includes a spindle 32 designed to support the magneto-optical disk 11, as shown in
The magneto-optical disk drives 31 includes a light source or semiconductor laser diode 33. The semiconductor laser diode 33 is designed to emit an optical beam or laser beam 34 of a linear polarization. When the magneto-optical disk 11 is mounted on the spindle 32, a so-called optical system 35 serves to direct the laser beam 34 to the magneto-optical disk 11.
The optical system 35 includes an objective lens 36 opposed to the surface of the magneto-optical disk 11, for example. A beam splitter 37 is located between the semiconductor laser diode 33 and the objective lens 36, for example. The laser beam 34 from the semiconductor laser diode 33 passes through the beam splitter 37. The laser beam 34 passing through the beam splitter 37 is irradiated to the magneto-optical disk 11 through the objective lens 36. The objective lens 36 serves to form a minute beam spot on the surface of the magneto-optical disk 11. The laser beam 34 passes through the substrate 12, the undercoat film 14, the magnetic recording film 15, the auxiliary magnetic film 16 and the overcoat film 17 so as to reach the reflection film 18. The reflection film 18 reflects the laser beam 34. The reflected laser beam 34 is directed to the beam splitter 37 through the objective lens 36.
A two-beam Wollaston 38 is opposed to the beam splitter 37. The beam splitter 37 serves to reflect the returned laser beam 34 from the magneto-optical disk 11. The laser beam 34 is directed to the two-beam Wollaston 38 through the beam splitter 37. The two-beam Wollaston 38 resolves the laser beam 34 into components corresponding to planes of polarization perpendicular to each other.
A divided photodetector 41 is placed behind the two-beam Wollaston 38. The laser beams 34 is then detected for the respective planes of polarization at the divided photodetector 41 after the resolution at the two-beam Wollaston 38. The laser beam 34 is converted into electric signals for the respective planes of polarization. The electric signals for the planes of polarization are then summed at an addition amplifier 42. The intensity is detected for the overall laser beam 34. The ROM information is in this manner read out based on the output from the addition amplifier 42. The electric signals are subjected to subtraction at a subtraction amplifier 43. The rotation is detected between the plane of polarization of the laser beam 34 reflected from the magneto-optical disk 11 and the plane of polarization of the laser beam 34 before the reflection. The RAM information is in this manner read out based on the output from the subtraction amplifier 43.
A magnetic head slider 44 is opposed to the objective lens 36. An electromagnetic transducer is mounted on the magnetic head slider 44. The electromagnetic transducer may be located on the extension of the path of the laser beam 34 directed from the objective lends 36 to the magneto-optical disk 11. When the laser beam 34 is irradiated, the temperature of the magnetic recording film 15 rises. The electromagnetic transducer serves to apply a magnetic field for recordation to the magnetic recording film 15. The rise in the temperature allows the magnetization to rotate in the magnetic recording film 15 in response to the direction of the magnetic field for recordation. The RAM information is in this manner written into the magnetic recording film 15. It should be noted that the optical modulation recording may be employed in place of the aforementioned magnetic field modulation recording.
As shown in
The inventors prepared six magneto-optical disks 11 in the aforementioned manner. The inventors measured the jitter for the respective examples. First and second laser beams were prepared. The perpendicular polarization was established in the first laser beam irradiated on the magneto-optical disk 11 in the same manner as the aforementioned magneto-optical disk drive 31. The plane of polarization was set in parallel with the recording track on the magneto-optical disk 11 in the second laser beam. Specifically, a so-called horizontal polarization was established in the second laser beam irradiated on the phase pits 13 and the magnetic recording film 15. As shown in
Number | Date | Country | |
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Parent | PCT/JP03/06452 | May 2003 | US |
Child | 11119986 | May 2005 | US |