US5620766A - Magneto-optical disk - Google Patents
This definition explains the meaning of Magneto-Optical Disk and why it matters. The Invention of the Rewritable Magneto-Optical Disk In , three IBM scientists working out of the Thomas J. Watson Research Center in Yorktown, NY, found a combination of two common minerals and a rare earth element that could be easily and repeatedly magnetized to accept large volumes of computer data at high speeds.
An optical disk is primarily used as a portable and secondary storage device. It can store more data than the previous generation of magnetic storage media, and has a relatively longer lifespan.
These disks are generally used to:. By: Todd Wasserman Contributor. By: Kishore Jethanandani Contributor. By: Terri Williams Contributor.
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Follow Connect with us. Sign up. Term of the Day. Best of Techopedia weekly. News and Special Offers occasional. Thank you for subscribing to our newsletter! Connect with us. Optical Disk. Techopedia Explains Optical Disk. What Does Optical Disk Mean? Techopedia Explains Optical Disk An optical disk is primarily used as a portable and secondary storage device. These disks are generally used to: Distribute software to customers Store large amounts of data such as music, images and videos Transfer data to different computers or devices Back up data from a local machine.
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A magneto-optical disc includes a pit forming region and a groove forming region on a surface of a substrate and a recording layer covering the pit and groove forming regions. The pit forming region includes a row of pits having a width of ?m and a depth of A and the groove forming region includes a spiral groove having a width of ?m and a depth of A. The MO drive of the DD is a standard Sony magneto optical drive and will accept any byte/sector optical disk. These inch disks are removable and are encased in a box not much larger than a CD jewel box. The disk has two sides and up to forty MINUTES of stereo audio can be recorded on each side for a total of eighty minutes per disk! HP - Magneto Optical Disk, ", GB, 2, Bytes/Sector, Rewritable J (DMi EA.
Year of fee payment : 4. Year of fee payment : 8. Year of fee payment : A magneto-optical disc includes a pit forming region and a groove forming region on a surface of a substrate and a recording layer covering the pit and groove forming regions.
The pit forming region includes a row of pits having a width of 0. The disc is recorded and read by using an optical head with an objective lens having a numerical aperture of 0. Tracking, seeking and information retrieval can be done with minimal errors using the same laser light beam in both the pit and groove forming regions.
This invention relates to a magneto-optical disc having pits and a groove in a substrate surface. Magneto-optical discs have a magneto-optical recording layer on a grooved substrate. On recording and reading, tracking control signals and focus control signals are detected in terms of the magnitude of reflected light from the disc surface. In pre-formatted magneto-optical discs, some bits of information are previously recorded as pits in a lead-in or lead-out area in addition to the groove, the pre-recorded information including information for allowing the hardware to operate the disc under optimum conditions and discrete value information in the form of pulse signals of a predetermined period.
Therefore, the pre-formatted magneto-optical disc includes both a region where pits are formed and a region where a groove is formed.
In these magneto-optical discs, since such operation as tracking servo, seek servo and pit information retrieval is carried out by means of an optical system using the same laser light in the pit and groove forming regions, the sizes of pits and groove must be optimized for the optical system in order to prevent occurrence of errors in the servo systems and pit information retrieval. An object of the present invention is to provide a novel and improved magneto-optical disc which allows such operation as tracking, seeking and information retrieval to be carried out with minimal errors by means of an optical system using the same laser light in both pit and groove forming regions.
The present invention provides a magneto-optical disc comprising a substrate having a pit forming region and a groove forming region on a surface thereof, and a recording layer covering the pit and groove forming regions. A row of pits having a width of 0. Recording and reading operation is carried out using an optical head having an objective lens having a numerical aperture NA of 0. In one preferred embodiment wherein an optical head having an objective lens having a numerical aperture NA of 0.
In the pit forming region, the push-pull signal level is 0. In the groove forming region, the push-pull signal level is 0. Since the pits having pre-format information recorded therein and the groove for tracking servo operation are sized as defined above, the magneto-optical disc of the present invention allows an optical system to carry out such operation as tracking, seeking and information retrieval with minimal errors. The magneto-optical disc of the present invention includes a substrate and a recording layer on a surface thereof.
The substrate surface includes a pit forming region and a groove forming region. The recording layer covers the pit and groove forming regions.
The pit forming region is located in a lead-in or lead-out area. The pit forming region includes a row of pits bearing bits of information as previously mentioned and serving for tracking too. The groove forming region typically includes a spiral groove serving for tracking of recording and reading light. The groove, when wobbled, can also serve to control the rotation rpm of the disc. The groove may further bear time information and address information.
According to the present invention, a row of pits having a width of 0. These sizes are measurements by a scanning tunnel microscope STM for the depth and a scanning electron microscope SEM for the width.
The magneto-optical disc of the present invention is recorded and read using a drive unit including an optical head having an objective lens having a numerical aperture NA of 0. The recording and reading light in the form of linearly polarized laser light having a wavelength of to nm, preferably to nm is directed to the disc such that its electric field vector may be in a direction perpendicular to the groove and row of pits.
In this way, data are recorded in and retrieved from the magneto-optical disc. Tracking during recording and reading is achieved by directing such laser light to the groove and row of pits. It is to be noted that the magneto-optical disc of the invention is generally designed for in-groove recording.
The magneto-optical disc of the invention has the following features when operated with the optical head and laser light as mentioned above. If the amplitude center position of 3T signal is located below the amplitude center position of 11T signal or on the zero-level side , Asy has a negative value.
With Asy outside the range, a failure would occur in reading out 3T signals. The push-pull signal used herein is a tracking signal used in controlling tracking by a push-pull method. The push-pull method is a method of detecting a tracking error by receiving light reflected and diffracted by the groove or pit on two light-receiving sections of a two-divided photodiode disposed symmetrical with respect to the track center, determining the difference between the outputs of the two light-receiving sections, the output difference giving the tracking error.
Push-pull signal levels below the range would not ensure normal tracking whereas above the range, the balance with other optical properties would be destroyed and some optical heads would produce focus servo signals containing noise. The radial contrast RC in the pit forming region is represented by. The number of tracks that the optical head skipped and the moving direction or polarity of the optical head can be determined from the RC output.
With a radial contrast below the range, there would occur errors in track counting and polarity determination. Beyond the range, the servo system would become unstable due to disturbing noise. The radial contrast RC in the groove forming region is represented by. The components of the magneto-optical disc of the present invention other than the size of the pits and groove are not particularly limited and may be selected from those used in conventional magneto-optical discs.
One preferred embodiment of the magneto-optical disc is illustrated below. Referring to FIG. For recording and reading operation, a magnetic head not shown cooperates with the disc on or above the protective coating 8. The operating system may be either a flying head system which the magnetic head is lifted above the disk surface due to a pneumatic lift by disc rotation or a stationary head system in which the magnetic head is spaced a fixed distance from the disk surface.
The substrate 2 is generally formed of glass or transparent resins such as polycarbonate, acrylic resins, amorphous polyolefins, and styrene resins.
Such a choice is made because the magneto-optical disc of the invention is recorded and read by using an optical head positioned on the rear surface side of the substrate 2 the lower side in FIG. The surface of the substrate 2 on which the recording layer 5 is formed is provided with a groove and pits as previously defined.
It is desired to provide at least one of these protective layers, most desirably both. The protective layers are formed of a dielectric material such as oxides, carbides, nitrides, sulfides and mixtures thereof by any desired gas phase deposition method such as sputtering, evaporation and ion plating.
The recording layer 5 disposed between the first and second dielectric layers 4 and 6 is one in which information can be magnetically recorded using a modulated thermal beam or modulated magnetic field and the recorded information be read through magneto-optical conversion. The recording layer 5 may be formed of any desired material which is capable of such magneto-optical recording. Preferably, it is prepared by depositing an alloy containing a rare earth metal element, especially a rare earth metal-transition metal alloy by sputtering, evaporation or ion plating, preferably by sputtering, to form an amorphous film.
The recording layer is generally about 10 to nm thick. The reflective layer 7 is optionally disposed on the second dielectric layer 6 and formed of any of relatively high reflectivity metal materials which include Au, Ag, Pt, Al, Ti, Cr, Ni and Co and alloys or compounds thereof. The reflective layer may be formed in a similar manner to the recording layer 5.
The reflective layer is generally about 30 to nm thick. The protective coating 8 is optional and provided for protecting the underlying sputtered layers from the first protective layer 4 to the reflective layer 7. The protective coating 8 is preferably formed of a radiation curable resin. More particularly, the coating is made of a material obtained by radiation curing a radiation curable compound or a polymerizable composition thereof. Illustrative are monomers, oligomers and polymers having contained or incorporated in their molecule groups capable of crosslinking or polymerizing upon exposure to radiation, for example, acrylic double bonds as given by acrylic and methacrylic acids and esters thereof having an unsaturated double bond sensitive to ionization energy and capable of radical polymerization, allyl double bonds as given by diallyl phthalate, and unsaturated bonds as given by maleic acid and maleic derivatives.
They are preferably polyfunctional, especially trifunctional or more and used alone or in admixture of two or more. The radiation curable monomers and oligomers used herein preferably have a molecular weight of less than 2, and 2, to 10,, respectively. Other useful radiation curable oligomers are acryl-modified ones of oligoester acrylate and urethane elastomers and derivatives of these having a functional group such as COOH incorporated therein.
In addition to or instead of the above-mentioned compound, there may be used radiation curable compounds obtained by modifying thermoplastic resin to be radiation sensitive. Exemplary radiation curable resins are thermoplastic resins containing or having incorporated in a molecule thereof a group capable of crosslinking or polymerizing upon exposure to radiation, for example, a acrylic double bond as given by acrylic acid, methacrylic acid and esters thereof having an unsaturated double bond capable of radical polymerization, an allyl double bond as given by diallyl phthalate, and an unsaturated bond as given by maleic acid and maleic derivatives.
Examples of the thermoplastic resins which can be modified to be radiation curable include vinyl chloride copolymers, saturated polyester resins, polyvinyl alcohol resins, epoxy resins, phenoxy resins, and cellulosic derivatives. Other resins which can be modified to be radiation curable include polyfunctional polyester resins, polyether ester resins, polyvinyl pyrrolidone resin and derivatives PVP-olefin copolymers , polyamide resins, polyimide resins, phenolic resins, spiro-acetal resins, and acrylic resins containing at least an acrylate and methacrylate having a hydroxyl group as a polymerizable component.
A polymerizable coating composition is cured with radiation, typically ultraviolet radiation and a photo-polymerization initiator or sensitizer is preferably contained in the composition. The photo-polymerization initiator or sensitizer used herein is not critical and may be selected from conventional ones such as acetophenones, benzoins, benzophenones, and thioxanthoins.
The composition may contain about 0. The polymerizable composition may be synthesized by a conventional method or prepared by mixing commercially available compounds. Another composition containing a radiation curable compound from which the protective coating can be formed is one containing an epoxy resin and a cationic photo-polymerization catalyst. Epoxy resins are preferably alicyclic epoxy resins, especially those having two or more epoxy groups in a molecule.
Exemplary alicyclic epoxy resins are 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, bis 3,4-epoxycyclohexylmethyl adipate, bis 3,4-epoxycyclohexyl adipate, 2- 3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy cyclohexane-metadioxane, bis 2,3-epoxycyclopentyl ether, vinylcyclohexene dioxide alone or in admixture. The alicyclic epoxy resins may have any desired epoxy equivalent although an epoxy equivalent of 60 to , especially to is preferred for satisfactory curability.
The cationic photo-polymerization catalyst may be selected from well-known ones. Examples include complexes of metal fluoroborate and boron trifluoride, bis perfluoroalkylsulfonyl methane metal salts, aryl diazonium compounds, aromatic onium salts of Group 6A elements, aromatic onium salts of Group 5A elements, dicarbonyl chelates of Group 3A to 5A elements, thiopyrilium salts, Group 6A elements having MF6 anions wherein M is P, As or Sb, triaryl sulfonium complex salts, aromatic iodoniumcomplex salts, and aromatic sulfonium complex salts.
Preferred are polyaryl sulfonium complex salts, aromatic sulfonium or iodonium salts of halo-containing complex ions, and aromatic onium salts of Group 3A, 5A or 6A elements. Also useful are cationic photo-polymerization catalysts containing an organometallic compound and a photo-decomposable organic silicon compound.
These cationic photo-polymerization catalysts are non-strong acid systems and thus avoid any adverse effect to the corrosion-susceptible recording layer of the magneto-optical recording disc.
Especially preferred are organic aluminum compounds such as trismethoxy aluminum, trispropionato aluminum, tristrifluoroacetyl aluminum, and trisethylacetoacetonato aluminum. The photo-decomposable organic silicon compounds are to form silanols upon exposure to radiation such as ultraviolet radiation. Preferably the composition contains 0. Preferred among the aforementioned compositions is a composition containing a radiation curable compound having an acryl group and a photo-polymerization initiator or sensitizer, which is applied to form a coating and then cured with radiation, especially UV radiation.
Too thick coatings tend to crack due to shrinkage upon curing or cause warpage of the disc. For example, the protective coating 8 is prepared by first applying a resin, preferably a radiation curable resin composition as mentioned above to form a coating. The coating method is not critical and may be selected from well-known ones such as spin coating, screen printing, gravure coating, spray coating and dipping.
Coating conditions may be properly determined by taking into account the viscosity of polymerizable composition, the desired buildup of coating and the like.
Then the coating is exposed to UV radiation for curing. If desired, the coating is heated prior to UV exposure. Instead of UV, electron radiation or the like may be used.