HK1023208B - Multiple data surface data storage system and method - Google Patents

Description

Multiple data surface data storage system and method

The present application is a divisional application of the Chinese patent application No. 95101436.6.

Technical Field

The present invention relates generally to optical data storage systems and more particularly to storage systems having multiple data storage surfaces.

Background

Optical data storage systems provide a means of storing large amounts of data on a disc. The data are accessed by focusing a laser beam onto the data layer of the disc and detecting the reflected beam. There are various known systems in which, in ROM (read only memory), data is permanently loaded into the disc in the form of marks within the disc at the time of disc manufacture. The data is detected by detecting a change in reflectivity when the laser beam strikes the data mark. WORM (write once read many) systems allow a user to write data by making marks, such as pits, on the surface of a blank disc. Once the data is written to the disc it cannot be erased. Data in WORM systems is also detected by changes in reflectivity.

Erasable optical systems are also known. These systems use a laser to heat the data layer above a critical temperature to write or erase data. Magneto-optical recording systems record data by orienting one magnetic domain in an up or down position. Data is read by directing a low power laser beam onto the data layer. The difference in domain orientation causes the plane of polarization of the beam to be deflected in either a clockwise or counterclockwise direction. This change in polarization orientation is detected. Phase change recording uses the structural change of the data layer itself (amorphous/crystalline are two common phases) to record data. Data is detected by detecting the change in reflectivity as the beam passes through the different phases.

To increase the storage capacity of optical discs, multiple data layer systems have been proposed. In theory, for an optical disc having two or more data layers, different layers can be accessed by changing the focal position of the lens. Examples of this include U.S. patent No. 3,946,367 to Wohluml et al, published on 23/3/1976; U.S. patent No. 4,219,704 to Russel at 26.8.1980; U.S. patent No. 4,450,553 issued to Holster et al, 5/22/1984; U.S. patent No. 4,905,215 to Hattori et al on day 27 of 1990; japanese published application No. 63-276732, published by Watanabe et al on 11/15 1988; and "IBM technical Disclosure Bulletin" volume 30, No.2, page 667, Arter et al (IBMTtechnical Disclosure Bulletin, Vol, 30, NO.2, P667, July1987), 7.1987.

A problem with these prior art systems is that it is difficult to clearly read the recorded data when there is more than one data layer. The interference signals from other layers greatly reduce the read capability. In addition, there are many problems in focusing at different depths and in generating tracking signals. There is a need for an optical data storage system that overcomes these problems.

Disclosure of Invention

It is therefore an object of the present invention to provide an optical data storage system that overcomes the problems of the prior art.

The present invention provides an optical data storage system comprising:

an electromagnetic radiation source for generating a beam of electromagnetic radiation;

an optical medium having a plurality of data surfaces;

a focusing device for focusing the beam of electromagnetic radiation on a selected one of the data surfaces;

an optical detector for receiving a returned beam of electromagnetic radiation from the medium and generating a focus error signal therefrom; and

a focus control device coupled to the focusing assembly, the focus control device including a peak detector for detecting peaks in the focus error signal, and a controller for counting the peaks detected by the peak detector and determining a data surface on which to focus the beam of electromagnetic radiation.

The present invention also provides an optical data storage system comprising:

a laser for generating a light beam;

an optical disc medium having a plurality of data surfaces;

a rotating device connected to the optical disc medium for rotating the optical disc medium;

a focusing means for focusing the light beam on a selected one of the data surfaces;

an optical detector for receiving a returned light beam from the medium and generating a focus error signal therefrom; and

a focus control device coupled to the focusing assembly, the focus control device including a peak detector for detecting peaks in the focus error signal, and a controller for counting the peaks detected by the peak detector and for determining a data surface on which to focus the light beam.

Specifically, the technical scheme of the invention is as follows. An optical data storage system comprising: a media receiver for receiving an optical data storage medium having a plurality of spaced data surfaces at different depths in the medium; a radiation source for generating a radiation beam; and an optical receiver for receiving the radiation beam returned from the medium and generating a data signal in response thereto, characterized by further comprising:

surface recognition means, connected to the light receiver, for recognizing the data surface numbers present in the medium; a focusing device, coupled to the surface identification device, for focusing the beam of radiation onto a selected one of the plurality of media data surfaces.

In a preferred embodiment of the present invention, an optical data storage system includes an optical disc drive and a multiple data surface optical medium. The medium has a plurality of substrate members separated by air spaces. The surface of the substrate assembly adjacent to the air space is a data surface. The data surface is highly transmissive except for the last data surface and may include a reflective layer. Each data surface has tracking marks.

The disc drive includes a laser that generates laser light. An optical transmission channel directs light to the medium, the transmission channel including converging means for converging the light onto different data surfaces and aberration compensator means for correcting aberrations caused by variations in effective substrate thickness. A receiving channel receives reflected light from the medium. The receiving channel includes a filter member that filters out stray light reflected from surfaces other than the data surface being read. The receive channel has a detector for receiving the reflected light and circuitry for generating data and servo signals responsive to the data.

Drawings

A more particular understanding of the nature and advantages of the present invention may be derived from the following detailed description when taken in conjunction with the accompanying drawings.

FIG. 1 is a schematic diagram of an optical data storage system of the present invention;

FIG. 2A is a cross-sectional view of an optical media of the present invention;

FIG. 2B is a cross-sectional view of another optical media;

FIG. 3A is a cross-sectional view of a tracking mark of the media of FIG. 2;

FIG. 3B is a cross-sectional view of another tracking mark;

FIG. 3C is a cross-sectional view of yet another tracking mark;

FIG. 3D is a cross-sectional view of yet another tracking mark;

FIG. 4 is a schematic view of an optical head and medium of the present invention;

FIG. 5 is a top view of the light detector of FIG. 4;

FIG. 6 is a circuit diagram of a channel circuit of the present invention;

FIG. 7 is a schematic diagram of the control circuit of the present invention;

FIG. 8A is a graph of tracking error signal versus head displacement;

FIG. 8B is a graph of tracking error signal versus displacement of the optical head in another embodiment;

FIG. 8C is a graph of tracking error signal versus head displacement for yet another embodiment;

FIG. 9 is a graph of focus error signal versus lens shift in accordance with the present invention;

FIG. 10 is a schematic diagram of a multiple data surface aberration compensator of the present invention;

FIG. 11 is a schematic diagram of another embodiment of a multiple data surface aberration compensator of the present invention;

FIG. 12 is a schematic diagram of yet another embodiment of a multiple data surface aberration compensator of the present invention;

FIG. 13 is a top view of the compensator of FIG. 12;

FIG. 14 is a schematic diagram of yet another embodiment of a multiple data surface compensator of the present invention;

fig. 15 is a schematic diagram of another embodiment of a multiple data surface aberration compensator of the present invention;

FIG. 16 is a cross-sectional view of the lens of FIG. 15;

FIG. 17 is a schematic view of another embodiment of an optical head and medium according to the invention;

FIG. 18 is a schematic diagram of another embodiment of a multiple data surface aberration compensator of the present invention;

FIG. 19 is a schematic diagram of another embodiment of a multiple data surface aberration compensator of the present invention;

FIG. 20 is a schematic diagram showing a process of fabricating the compensator of FIGS. 18 and 19;

fig. 21 is a schematic view of another embodiment of an aberration compensator of the present invention;

fig. 22 is a schematic view of another embodiment of an aberration compensator of the present invention;

FIG. 23 is a schematic diagram of a multiple data surface filter of the present invention;

FIG. 24 is a schematic diagram of another embodiment of a multiple data surface filter of the present invention;

FIG. 25 is a schematic diagram of another embodiment of a multiple data surface filter of the present invention;

FIG. 26 is a schematic diagram showing a process of fabricating the optical filter of FIG. 25.

Detailed Description

Fig. 1 shows a schematic diagram of an optical data storage system of the present invention, generally designated by the reference numeral 10. The system 10 comprises an optical data storage medium 12 preferably formed in the shape of a disc. The media 12 is removably mounted on a positioning shaft 14 as is known in the art. The shaft 14 is connected to a shaft motor 16, which motor 16 is in turn connected to a system base 20. The motor 16 rotates the shaft 14 and the medium 12.

The head 22 is positioned below the medium 12. The head 22 is connected to an arm 24, and the arm 24 is in turn connected to the base 20 with actuation means, such as a voice coil motor 26. The motor 26 moves the arm 24 and head 22 radially beneath the media 12.

Optical medium

Fig. 2A is a cross-sectional view of the media 12. The medium 12 carries a substrate 50. Substrate 50 is also called a panel or cover plate and the laser beam enters medium 12 therefrom. An Outer Diameter (OD) rim 52 and an Inner Diameter (ID) rim 54 are attached between the faceplate 50 and a substrate 56. The outer and inner diameter rims 58, 60 are attached between the substrate 56 and the substrate 62. The outer diameter edge 64 and the inner diameter edge 66 are connected between the substrate 62 and the substrate 68. Outer diameter rim 70 and inner diameter rim 72 are attached between substrate 68 and substrate 74. The faceplate 50 and substrates 56, 62, 68 and 74 are made of a material that is transparent to light, such as glass, polycarbonate or other polymers. In a preferred embodiment, the panel 50 is 1.2mm thick and the substrates 56, 62, 68 and 74 are 0.4mm thick. The thickness of the substrate may be selected to be 0.2 to 0.8 mm. The inner and outer rims are preferably made of a plastic material and are about 500 microns thick, and optionally 50-500 microns thick.

The rim may be attached to the panel and substrate using glue, cement or other bonding process. The rim may also be integrally formed with the substrate. With this in place, the rim forms a plurality of annular spaces 78 between the substrate and the face plate. Shaft bore 80 passes through media 12 in the inner diameter rim to accommodate shaft 14. A plurality of passages 82 are provided in the inner diameter rim for connecting the apertures 80 and the space 78 to equalize the pressure of the space 78 and the environment (typically air) surrounding the disk storage. A plurality of low impedance filters 84 are connected to the passageway 82 to prevent contamination of the space 78 by particulate matter in the air. The filter 84 may be quartz or fiberglass. The channel 82 and filter 84 may also be located on the outer diameter rim.

Surfaces 90, 92, 94, 96, 98, 100, 102 and 104 are data surfaces and are adjacent to space 78. These data surfaces may contain ROM data formed directly on the substrate surface; alternatively, the data surface may be coated with a writable optical storage film (e.g. WORM) or an erasable optical storage film (e.g. phase change or magneto-optical). The data surface is free of a separate metallic reflective layer structure (reflectivity of 30-100%) as known in the prior art (e.g., U.S. patent No. 4,450,533), except for the optical storage film, i.e., in the case of a ROM surface, the data surface may include, consist of, or consist essentially of only the surface itself, and in the case of a WORM, phase change, or magneto-optical surface, the data surface may include, consist of, or consist essentially of only the surface and the optical storage film. No additional non-data storing reflective layer is required. The result is a data surface which is very light-transmitting and which can be provided with a large number of data surfaces. Although the middle data surface has no reflective layer, a reflective layer may be placed behind the last data surface 104 to obtain greater reflection from the last data surface 104.

In a preferred embodiment, the data surface is a ROM surface. Data is permanently recorded in the form of a recess and formed directly in the substrate when the disc is manufactured. Unlike the prior art, the ROM surface of the present invention does not contain a metallic reflective layer. The substrate is uncoated. The result is a transmission of about 96% per data surface. The 4% reflectivity is sufficient for detecting data. The benefit of high transmission is to allow access to a large number of data surfaces and to reduce the effect of unwanted signals from other surfaces. Because there is no coating on these surfaces, they are easier to fabricate and more corrosion resistant.

It is beneficial, although not necessary, to increase the reflectivity and thus decrease the laser power. One way to increase the reflectivity above 4% is to apply a thin film coating of a dielectric having a refractive index greater than that of the substrate. The maximum reflectivity of 20% occurs at a dielectric thickness of approximately lambda-4n and monotonically decreases to 4% of the thickness λ/2n, where λ is the wavelength of the light and n is the refractive index of the dielectric. An example of such a dielectric is ZrO₂ZnS, SiNx or mixed oxides. The dielectric is deposited by sputtering as known in the art.

The reflectivity of the data layer can also be reduced to below 4%. This increases the transmittance and allows stacking of more discs. The reduction in reflectivity can be achieved by using a dielectric film having a refractive index less than that of the substrate. One such dielectric is MnF, which has a refractive index of 1.35. The minimum reflectivity of 1% is achieved when the dielectric is about λ/4n thick and varies monotonically to 4% of the maximum reflectivity at a thickness of about λ/2n, where λ is the wavelength of light and n is the refractive index. Various other thin film antireflective materials may also be used. These anti-reflective films can be coated by sputtering methods known in the art.

The data surface may also contain WORM data. A WORM film, such as a tellurium-selenium alloy or a phase change WORM film, may be coated onto the data surface. These films can be vacuum deposited by sputtering or evaporation methods known in the art. The amount of reflection, absorption and transmission of each film is related to its thickness and optical constants. In either preferred embodiment, the tellurium-selenium alloy is deposited to a thickness of 20-800 angstroms (*).

The data surface may also include a reversible phase change film. Any type of phase change film may be used, but preferred compounds include those along or near the junction GeTe and Sb₂Te₃Of the connecting wire of (1), comprising Te_52.5Ge_15.3Sb₃₃、Ge₂Sb₂Te₅、GeSb₂Te₄And GeSb₄Te₇. These films are vacuum deposited onto the substrate using sputtering methods known in the art to a thickness of 20 to 800 * a. A dielectric protective coating layer of 3,000 * a thick may be formed on the phase change film to prevent ablation.

The data surface may also include a magneto-optical film. Magneto-optical films such as rare earth transition metals can be vacuum deposited onto the substrate to a thickness of 20-800 * using sputtering methods known in the art.

Another variation is to have those data surfaces contain a combination of ROM, WORM, or erasable media. Higher transmission surfaces such as ROM are preferably closer to the light source, while lower transmission surfaces such as WORM, phase change and magneto-optical surfaces are preferably further apart. The above-described dielectric and anti-reflective films for ROM surfaces can also be used for WORM and erasable media.

Fig. 2B is a cross-sectional view of another embodiment of an optical recording medium, and is indicated generally by the reference numeral 120. Like elements of media 120 to media 12 are indicated with primed numbers. The media 120 is devoid of the rim and space 78 of the media 12. The substrates are separated by a plurality of solid transparent members 122. The member 122 is made of a material having a different refractive index from the substrate. This is necessary to achieve some reflection at the data surface and in a preferred embodiment the member 122 is made with an optical cement which also holds the substrates together. The thickness of the member 122 is preferably 100 to 300 μm. Media 120 may replace media 12 in system 10.

Fig. 3A shows an enlarged detailed cross-sectional view of a preferred data surface pattern of media 12 and is generally designated 130. The surface 90 includes a pattern of helical (or concentric) guide grooves 132. The portion of the surface 90 between the channels 132 is referred to as a land portion 134. Surface 92 includes a pattern of helically-inverted channels (ridges) 136. The portion of the surface 92 between the inversion channels 136 is a land 138. The grooves 132 and the flipping grooves 136 are also referred to as tracking marks. In the preferred embodiment, the width 140 of the tracking marks is 0.6 microns and the width 140 of the land portions is 1.0 micron. This produces a pitch of (1.0+0.6) ═ 1.6 microns.

Tracking marks are used to keep the beam on track as the media 12 rotates. This is described in detail below. For pattern 130, beam 144 from head 22 will track land portion 134 or 138 depending on the surface on which it is focused. The data is recorded on the land portion. In order for the Tracking Error Signal (TES) to have the same amplitude for both surfaces 90 and 92, the optical path difference of the reflected light from the land and tracking marks must be the same for both surfaces. The beam 144 is focused through the substrate 50 onto the surface 90 and the beam 144 is focused through the space 78 onto the surface 92. In the preferred embodiment, the space 78 contains air. To equalize the optical path differences between the land and tracking marks, d1n1 must be equal to d2n2 (or d2/d1 equal to n1/n2), where d1 is the depth (vertical distance) of mark 132, n1 is the index of refraction of substrate 50, d2 is the height (vertical distance) of mark 136, n2 is the index of refraction of space 78, and in a preferred embodiment, space 78 contains air with an index of refraction of 1.0, and substrate 50 (and the other substrates) have an index of refraction of 1.5. Thus the ratio d2/d1 equals 1.5. In the preferred embodiment, d1 is 700 * and d2 is 1050 *. The other surfaces of the medium 12 also have the same tracking mark pattern. Other substrate entrance surfaces 94, 98 and 102 are similar to surface 92, while other spatial entrance surfaces 96, 100 and 104 are similar to surface 92.

Although the tracking marks are preferably formed in a spiral shape, they may be formed in a concentric pattern. Further, the spiral patterns of the respective surfaces may be identical, i.e. they are all clockwise or counter-clockwise spirals, or the pattern of the respective data layer may alternate sequentially between clockwise and counter-clockwise spirals. Such alternation of spiral patterns is desirable in certain applications requiring continuous tracking of data, such as storage of video data and movies. In this case, the beam traces a clockwise spiral pattern on the first data surface inwardly until the spiral pattern terminates near the inner diameter, and then the beam is focused on the second data surface immediately below and traces a counterclockwise spiral pattern outwardly until the outer diameter is reached.

FIG. 3B shows an enlarged detailed cross-sectional view of another surface pattern of media 12 and is indicated generally by reference numeral 150. Pattern 150 is similar to pattern 130 except that the tracking indicia of surface 92 are grooves 152 rather than inverted grooves. The pitch and ratio d2/d1 is the same as for pattern 130. The beam 144 tracks on land 134 of surface 90, but when the beam 144 is focused on surface 92, it will track along groove 152. There are situations where tracking along the groove 132 is desirable. However, as will be described below, beam 144 may also be electronically controlled to track the tracking marks on land 138 surfaces 94, 98 and 102 on surface 92 similar to surface 90, and surfaces 96, 100 and 104 similar to surface 92.

Fig. 3C shows an enlarged detailed cross-sectional view of another surface pattern of media 12, media 12 being indicated generally by reference numeral 160. Pattern 160 is similar to pattern 130 except that surface 90 has an inversion channel 162 instead of channel 132 and surface 92 has a channel 164 instead of inversion channel 136. The pitch and ratio d2/d1 are the same as for pattern 130. Beam 144 will travel along flip groove 162 when focused on surface 90, and it will travel along groove 164 when focused on surface 92 (unless electronically converted to travel along land). The pattern of surfaces 94, 98 and 102 is similar to that of surface 90, while surfaces 96, 100 and 104 are similar to surface 92.

Fig. 3D shows an enlarged detailed cross-sectional view of another surface pattern, which is indicated by the general reference numeral 170. In pattern 170, surface 90 has a similar structure to surface 90 of pattern 160. Surface 92 is similarly structured to surface 92 having pattern 130. The pitch and d2/d1 ratio are the same as for pattern 130. The beam 144 will travel along the flipping slot 162 when focused on the surface 90 (unless electronically converted to travel along land) and along the land 138 when focused on the surface 92. Surfaces 94, 98 and 102 have a similar pattern as surface 90, while surfaces 96, 100 and 104 have a similar pattern as surface 92.

For all of the patterns 130, 150, 160, and 170, the tracking marks are formed on the substrate by a photopolymer process or injection molding method known in the art when the substrate is fabricated. It should be noted that the optical film is deposited on the substrate after the tracking marks are formed, as described above.

The discussion of tracking marks also applies to other features of the optical disc. For example, some ROM disks use pockets molded in the substrate to record data and/or provide tracking information. Other optical media use pockets to emboss sector header information. Some media also use these header pockets to provide tracking information. When such media is used in the multidata surface form of the present invention, the pockets are formed as pockets or flip pockets on each data surface in a manner similar to the tracking marks discussed above. The optical path between the land and the pocket or flip pocket is also similar to the tracking mark. The pockets, inverted pockets, troughs and inverted troughs are all located at different heights from the land (i.e., their vertical distance from the land) and are all referred to as markers in this discussion. The markers that are dedicated to providing tracking information are referred to as non-data tracking markers.

Optical head

Fig. 4 shows a schematic view of the head 22 and the medium 12, the head 22 having a laser diode 200. The laser 200 may be a gallium-aluminum-arsenide diode laser that generates a main beam 202 having a wavelength of about 780 nanometers. The beam 202 is collimated by a lens 203 and rounded by a rounder 204. The rounder 204 may be a rounding prism. The light beam 202 passes through a beam splitter 205. A portion of the light beam 202 is reflected by the beam splitter 205 to the converging lens 206 and the light detector 207. The detector 207 is used to monitor the power of the beam 202. The remainder of the beam 202 reaches and reflects the mirror 208. The light beam 202 then passes through a converging lens 210 and a multiple data surface aberration compensator 212 and is converged onto one of the data surfaces (shown as surface 96) of the medium 12. The lens 210 is mounted on a support 214. The position of the support 214 relative to the medium 12 is adjustable by a focus motor 216.

A portion of the light beam 202 is reflected by the data surface reflective surface to form a reflected light beam 220. The light beam 220 passes through the compensator 212 and the lens 210 and is reflected by the mirror 208. At beam splitter 205, beam 220 is reflected to multi-data surface filter 222. Light beam 220 passes through filter 222 and beam splitter 224. A first portion 230 of beam 220 at beam splitter 224 is directed to a dispersing lens 232 and a quad optical detector 234. At beam splitter 224, a second portion 236 of beam 220 is directed to a half-wave plate 238 and a polarizing beam splitter 240. Beam splitter 240 splits light beam 236 into a first orthogonally polarized light component 242 and a second orthogonally polarized light component 244. Lens 246 converges light beam 242 to light detector 248, and lens 250 converges light beam 244 to light detector 252.

Fig. 5 shows a top view of quad detector 234. The detector 234 is divided into four identical portions 234A, B, C and D.

Fig. 6 shows a circuit diagram of the channel circuit 260. The circuit 260 includes a data circuit 262, a focus error circuit 264, and a tracking error circuit 266. The data circuit 262 includes an amplifier 270 coupled to the detector 248 and an amplifier 272 coupled to the detector 252. Amplifiers 270 and 272 are connected to a double pole double throw electronic switch 274. The switch 274 is coupled to a summing amplifier 276 and a differential amplifier 278.

Circuit 264 has a plurality of amplifiers 280,282, 284 and 286 coupled to portions 234A, B, C and D, respectively. Summing amplifier 288 is coupled to amplifiers 280 and 284 and summing amplifier 290 is coupled to amplifiers 282 and 286. Differential amplifier 292 is coupled to summing amplifiers 288 and 290.

The circuit 266 has a pair of summing amplifiers 294 and 296 and a differential amplifier 298. The summing amplifier 294 is coupled to the amplifiers 280 and 282 and the summing amplifier 296 is coupled to the amplifiers 284 and 286. Differential amplifier 298 is connected to summing amplifiers 294 and 296 through a double pole double throw electronic switch 297. Switch 297 inverts the input signal of amplifier 298.

Fig. 7 is a schematic diagram of a controller system of the present invention and is generally designated by the reference numeral 300. The Focus Error Signal (FES) peak detector 310 is coupled to the focus error signal circuit 264. Tracking Error Signal (TES) peak detector 312 is coupled to tracking error signal circuit 266. Controller 314 is coupled to detector 310, detector 312, detector 207, and circuits 262, 264, and 266. The controller 314 is a disk drive controller with a microprocessor. The controller 314 is also coupled to and controls the laser 200, the head motor 26, the axis motor 16, the focus motor 216, the switches 297 and 274, and the compensator 212. A detailed description of the exact construction and operation of compensator 212 will be given below.

It can now be appreciated that the system 10 is operational. The controller 314 causes the motor 16 to rotate the disc 12 and the motor 26 to move the head 22 to the appropriate position under the disc 12. See fig. 4. The laser 200 is energized to read data from the disc 12. Light beam 202 is focused by lens 210 onto data surface 96. The returning reflected beam 220 is split into beams 230, 242, and 244. Beam 230 is detected by detector 234 and is used to provide focus and tracking servo information, while beams 242 and 244 are detected by detectors 248 and 252, respectively, and are used to provide data signals.

Referring to fig. 5, beam 230 has a circular cross-section at detector 234 when beam 202 has just converged on data surface 96. This will cause circuit 264 to output a zero focus error signal. If beam 202 is out of focus in one direction or the other, beam 230 will appear as an elliptical pattern 352 or 354 on detector 234. This will cause circuit 264 to output a positive or negative focus error signal. The controller 314 will use the focus error signal to control the motor 216 to move the lens 210 until a zero focus error signal is reached.

If the beam 202 is focused exactly on a track of the data surface 96, the beam 230 will fall equally on the portions a and B and the portions D and C with a circular cross-section. If the beam deviates from the track, it will fall on the boundary between the tracking mark and the land. As a result, the beam will be diffracted and the cross-section 350 will move up or down. Parts a and B will receive more light and parts C and D will receive less light, or vice versa.

Fig. 8A shows a graph of TES displacement relative to the head 22 produced by the circuit 264. The controller 314 causes the VCM26 to move the head 22 across the surface of the medium 12. The TES peak detector 312 counts the peaks (maximum and minimum points) of the TES signal. There are two peaks between each of the tracks. By counting the number of peaks, controller 314 can position the beam on the appropriate track where the TES signal at land is a positively sloped TES signal. The positively sloped signal is used by the controller 314 to lock the beam to the track, e.g., the positively sloped TES signal moves the head 22 to the left toward the zero land position, and the negatively sloped TES signal moves the head 22 to the right toward the zero land position. Fig. 8A is a signal derived from preferred pattern 130 of medium 12 when switch 297 is in the initial position shown in fig. 6. The same signal is generated by surface 90 of pattern 150 and surface 92 of pattern 170. The beam is automatically locked to land because there is a positive slope.

FIG. 8B shows a graph of the displacement of the TES and head relative to surface 92 of pattern 150, surfaces 90 and 92 of pattern 160, and surface 90 of pattern 170 when switch 297 is in its initial position. Note that here the positive slope signal occurs at the tracking marker and thus the beam is automatically locked at the tracking marker and not at the land location. It may be desirable to follow the tracking marks in some circumstances.

FIG. 8C shows a graph of the displacement of TES and head relative to surface 92 of pattern 150, surfaces 90 and 92 of pattern 160, and surface 90 of pattern 170 when the TES signal is reversed by actuating inverter switch 297. Now the TES has a positive slope at the land and the beam will travel along the land portion instead of the tracking marks. Thus, controller 314 may track a groove or land by setting switch 297.

In the preferred embodiment, the medium 12 comprises a ROM data surface. The ROM data is read by detecting the reflectivity. In data circuit 262, switch 274 is connected to amplifier 276 when reading a ROM disk. The signals from detectors 248 and 252 are summed. The detected light is weak when data points are recorded, and the difference between the detected light is the data signal. The settings of switch 274 when reading WORM and phase change data disks are the same. If the disk 12 has a magneto-optical data surface, polarization sensing is required to read the data. The switch 274 will be coupled to the amplifier 278. The difference in the orthogonally polarized light detected by detectors 248 and 252 will provide a data signal.

Fig. 9 shows a plot of the focus error signal from circuit 264 versus the displacement of lens 210. Note that a nominally sinusoidal focus error signal is obtained for each data surface of medium 12. Between the data layers the focus error signal is zero. During system start-up, the controller 314 first causes the motor 216 to position the lens 210 at zero displacement. The controller 314 then seeks the desired data surface by causing the motor 216 to move the lens 210 in the positive displacement direction. At each data layer, the peak detector 310 detects two peaks of the focus error signal. The controller 314 will count the peaks (two per data surface) and determine the exact data surface on which the beam 202 is focused. When the desired data surface is reached, the controller 314 causes the motor 216 to position the lens 210 so that the focus error signal is between the two peaks for that particular data surface. This error signal is then used to control the motor 216 to find the zero focus error signal between the two peaks, i.e., locked onto the positive slope signal to achieve accurate focus. The controller 314 also adjusts the power of the laser 200, the switch 297, and the aberration compensator 212 to suit the particular data surface.

At startup, the controller 314 also determines the type of disk being read. Switch 274 is first placed at the reflectivity detection location and switch 297 is placed at the location where the land portion of the disc at the preferred pattern 130 is read. The controller 314 looks for and reads the header information of the first track of the first data surface. The header information contains the layer number, the type of optical medium (reflectivity or polarization detection) for each layer, and the type of tracking mark pattern used. Based on this information, controller 314 may set switches 274 and 297 appropriately to read the respective data surfaces correctly. For example, a disc may have 4 ROM data surface layers and two MO data surface layers. The controller 314 will set the switch 274 to detect the reflectivity of surfaces 1-4 and the polarization of surfaces 5-6.

If the controller 314 is unable to read the first track of the first data surface (perhaps the first layer has a different pattern of tracking marks), the controller 314 will place the switch 297 in the other state and again attempt to read the first track of the first data surface. If this is not sufficient (perhaps the first data surface is magneto-optical and requires polarization detection), the controller will place switch 274 in polarization detection and try again, placing switch 297 in one position and then in another position. In summary, the controller 314 will attempt to read the header information of the first track of the first data surface with four different combinations of switches 274 and 297 until the track is successfully read. Once the controller 314 has the header information, it can set the switches 274 and 297 correctly for the other data surfaces.

Alternatively, the disk drive may be dedicated to only one medium. At this point, the controller 314 is pre-programmed to store information about the data surface type, layer number, and tracking mark type.

Aberration compensator

Typically, the lenses are designed to converge light in air with a refractive index of 1.0. When light transmitted through materials having different refractive indices is condensed by such a lens, the light rays undergo spherical aberration, which distorts and enlarges the beam spot, degrading the performance of reading and recording.

In a typical optical data storage system, there is only one surface that needs to be focused. This surface is typically located below a 1.2mm thick panel. The lens is typically a 55 Numerical Aperture (NA) lens designed to correct for spherical aberration in the light caused by a 1.2mm panel. The result is that good point focus is obtained for that particular depth, but the focus becomes blurred for other depths. This is a serious problem for any multiple data layer system.

The aberration compensator 212 of the present invention solves this problem. Fig. 10 shows a schematic diagram of an aberration compensator, generally indicated by the reference numeral 400, which may be used as the compensator 212. Compensator 400 includes a stage 402 having three stages. The first step 404 is 0.4mm thick, the second step 406 is 0.8mm thick and the third step is 1.2mm thick. The block 402 is made of the same material as the faceplate and substrate of the medium 12 or other similar optical material. Note that the optical thickness of these steps increases by an increment of the substrate thickness. The block 402 is coupled to a voice coil motor 410 (or similar actuator), which motor 410 is in turn coupled to the controller 314. The motor 410 moves the block 402 laterally into and out of the optical path of the beam 302.

Lens 210 is designed to focus on the lowest data surface of medium 12. In other words, the lens 210 is used to compensate for spherical aberration caused by the combined thickness of the panel and intervening substrate. For the present invention, beam 202 must pass through panel 50 and substrates 56, 62 and 68 (substrate material having a combined thickness of 2.4 mm) in order to be focused on surface 102 or 104. Note that the air spaces 78 are not considered here because they are not configured to produce additional spherical aberration. Lens 210 is thus designed to focus light passing through 2.4mm polycarbonate and can be equally effectively focused on surfaces 102 and 104.

When the beam 202 is focused on one of the surfaces 102 or 104, the block 402 is completely withdrawn and the beam 202 does not pass through it. When beam 202 is focused on surface 98 or 100, block 402 is positioned such that beam 202 passes through stage 404. When the beam 202 is focused on a surface 94 or 96, the block 402 is positioned such that the beam 202 passes through the step 406. As beam 202 passes through surface 90 or 92, block 402 is positioned such that beam 202 passes through step 408. The result is that the beam 202 passes through the same total optical thickness of material and does not create spherical aberration problems regardless of which pair of surfaces is focused on. The controller 314 controls the motor 410 to move the block 402 as needed.

Fig. 11 shows an aberration compensator, indicated generally by the reference numeral 430, which may be used as the compensator 212. The compensator 430 has a pair of complementary triangular blocks 432 and 434. Blocks 432 and 434 are made of the same material as the substrate and face plate of medium 12 or a material with similar optical properties. Block 432 is in a fixed position so that beam 202 passes through it. The block 434 is attached to a voice coil motor 436 and is slidable along the surface of the block 432. The controller 314 is coupled to and controls a motor 436 that moves a mass 434 relative to a mass 432 to adjust the total thickness of material through which the beam 202 passes. The result is that the beam 202 passes through the same thickness of material regardless of which data surface it is focused on.

Fig. 12 and 13 show an aberration compensator, indicated generally by the reference numeral 450, which may be used as the compensator 212. The compensator 450 has a circular stepped member 452. The member 452 has four portions 454, 456, 458, and 460. Portions 456, 458, and 460 have similar thicknesses as steps 404, 406, and 408, respectively, which complement 400. The portion 454 is devoid of material and represents an empty space in a circle, as shown in fig. 13, and the circular member 452 is attached to a stepper motor 462 controlled by the controller 314. Shaft 462 pivots member 452 so that beam 202 passes through the same thickness of material regardless of which data surface it is focused on.

Fig. 14 shows an aberration compensator, indicated generally by the reference numeral 570, which can be used as the compensator 212. The compensator 570 includes a stationary convex lens 572 and a movable concave lens 574. The lens 574 is coupled to a voice coil motor 576. The voice coil motor 576 moves the lens 574 relative to the lens 572 under the control of the controller 314. The light beam 202 reaches the medium 12 via lenses 572, 574 and lens 210. Moving the lens 574 with respect to the lens 572 changes the spherical aberration of the light beam 202 and focuses it on a different surface. In the preferred embodiment, the lenses 210, 574, and 572 form a Coker (Cooke) triplet lens with a movable central member 574. Cocksane lenses are described in detail in R.Kingslake, article "Lens Design Fundamentals", Academic Press, New York, 1978, PP.286-295. Although the lens 274 is shown as being movable, the lens 274 may be fixed and the lens 572 used as the moving member. In fig. 4, the aberration compensator 212 is between the lens 210 and the medium 12. However, if a compensator 570 is used, it will be located between the lens 210 and the mirror 208, as shown in FIG. 14.

Fig. 15 shows an aberration compensator, indicated generally by the reference numeral 580. The compensator 580 comprises an aspheric lens component 582 of zero nominal focusing power. The member 582 has a spherical aberration surface 584 and a planar surface 586. The lens 582 is coupled to a voice coil motor 588. The voice coil motor 588 moves the lens 582 relative to the lens 512 under the control of the controller 314. Beam 202 passes through lens 210 and lens 582 to medium 12. Moving the lens 582 relative to the lens 210 changes the spherical aberration of the beam 202 and enables it to be focused onto different data surfaces.

Fig. 16 shows a schematic view of the lens 582 about axes Z and P. In a preferred embodiment, the surface 584 should correspond to the formula Z0.00770P₄-0.00154 P₆。

Fig. 17 shows a schematic view of another optical head according to the invention and is indicated by the general reference character 600. Parts of the head 600 similar to those of the head 22 are indicated with prime numbers. Note that the optical head 600 is the same as the system 10 except that the aberration compensator 212 is eliminated and a new aberration compensator 602 is added between the beam splitter 206 'and the mirror 208'. A description of the compensator 602 and its operation will be given below. The operation of the head 600 is otherwise identical to that of the head 22. The head 600 may replace the head 22 in the system 10.

Fig. 18 shows an aberration compensator, indicated generally by the reference numeral 610, which can be used as the compensator 602. Compensator 610 has a substrate 612 with a reflective holographic overlay 614. Substrate 612 is connected to a stepper motor 616 controlled by controller 314. Holographic overlay 614 records a number of holograms, each of which causes a particular aberration to beam 202'. These holograms are of the Bragg type and they react only to light of a specific wavelength and angle of incidence. When the substrate 212 is rotated a few degrees, the beam 202' will encounter a different hologram. The number of holograms recorded corresponds to the number of different spherical aberration to be corrected. For the medium 12 shown, four different recordings are required, each corresponding to a pair of data surfaces.

Fig. 19 shows an aberration compensator, indicated by the general reference 620 and usable as the compensator 602. Compensator 620 includes a substrate 622, a transmissive holographic cladding 624, and a stepper motor 626, and compensator 620 is similar to compensator 610 except that holographic cladding 624 is transmissive rather than reflective. The holographic overlay 624 has a number of holograms recorded thereon, each corresponding to a desired amount of spherical aberration compensation. As the substrate 622 rotates, the beam 202' encounters the holograms in turn.

FIG. 20 shows a schematic diagram of a recording system, generally designated 650, for making holographic overlays 614 and 624. System 650 has a laser 652 that produces a beam 654 at a frequency similar to that of laser 200. Beam 654 is collimated by lens 656 and reaches beam splitter 658. Beam splitter 658 splits the beam into beams 660 and 662. Light beam 660 is reflected by mirrors 664 and 666 and focused by lens 668 to a point 670 at a plane 672. The beam 660 passes through a stepped block 674 similar to block 402. Beam 660 is then re-collimated by lens 676 and strikes holographic overlay 680 of substrate 682. The substrate 682 is rotatably mounted on a stepper motor 684. Beam 662 strikes cladding 680 at a 90 angle to beam 660.

Lens 668 is at an aberration point on plane 672. This light then passes through block 674, the thickness of block 674 representing the sum of the substrate thicknesses encountered in accessing a particular recording layer. The lens 676 is identical in design to the lens 210 used in the optical memory head. Which collimates the light into a beam containing a specific spherical aberration corresponding to a specific thickness. This wavefront is holographically recorded by interference with reference beam 662. If the hologram is oriented substantially in the plane 690 as shown, a transmission hologram is recorded. If it is oriented at 692 generally in the plane shown by the dashed line, a reflection hologram is recorded. By rotating the hologram to a new angle and inserting the plate of the corresponding thickness of block 674, the wavefront needed to correct the aberrations encountered when accessing different pairs of recording layers can be stored holographically. A plurality of angle-resolved holograms are recorded, each corresponding to and modifying a pair of different recording layers. The holographic overlay may be made of dichromic acid glue or a photopolymerizable material. Each hologram can be recorded in angular increments as small as 1 degree without significant interference. This may ensure that a large number of holograms are recorded and a correspondingly large number of data surfaces are employed.

Fig. 21 shows another aberration compensator, indicated generally by the reference numeral 700, which may be used as the compensator 602. The compensator 700 includes a polarizing beam splitter 702, a quarter wave 704, a carousel 706 coupled to a stepper motor 708, and a plurality of spherical aberration mirrors 710 that can each provide different spherical aberration corrections. The beam 202' is oriented with its polarization such that it passes through the beam splitter 702 and the plate 704 to one of the mirrors 710. The mirror 710 causes the appropriate spherical aberration to the beam 202 ', and then the beam 202 ' returns through the plate 704 and reflects off the beam splitter 702 to the mirror 208 '. The motor 708, under the control of the controller 314, rotates the carousel 706 to select the appropriate mirror position. Mirror 710 is a reflective schmitt correction plate. See M.Born et al, "optical principles" (M.Born, et., Princible of Optics, Pergonan pressure Oxford, 1975, pp.245-249) at page 245-249.

Fig. 22 shows another aberration compensator, indicated generally by the reference numeral 720 and usable as the compensator 602. Compensator 720 includes a polarizing beam splitter 722, a quarter wave length 724, and an electrically controlled deformable mirror 726. The deformable mirror 726 is controlled by an internal piezoelectric element and is discussed in more detail in J.P. Gaffarel et al, Applied Optics, Vol.26, pp 3772 & 3777 (1987), Vol.26, pp 3772 & 3777, Vol.26, Vol.p.. Compensator 720 operates similarly to compensator 700 except that mirror 726 is electrically adjusted to provide the appropriate spherical aberration. In other words, the mirror 726 is adjusted to form a reflective surface corresponding to different schmitt correction patches 710 of the compensator 700. The controller 314 controls the adjustment of the mirror 726 as needed.

The operation of the aberration compensators 212 and 602 is described above in connection with medium 12. An aberration compensation arrangement is suitable for a pair of data surfaces due to the air layer between the layers. However, each data surface requires an aberration compensation arrangement when using the medium 120. This is due to the absence of air spaces.

Multiple data surface filters

When beam 202 is focused on a particular data surface of medium 12, reflected beam 230 is returned from the surface to head 22. But some of the light beam 202 is reflected from other data surfaces. These unwanted reflections must be removed to obtain the data and servo signals. The multiple data surface filters 222 of the present invention may perform this function.

Fig. 23 shows a schematic diagram of an optical filter 750 that may be used as the optical filter 222. The filter 750 includes a baffle 754 and a lens 756. The desired beam 230 is collimated because it is properly converged by the mirror 210. Beam 230 is focused by lens 752 to point 760. Unwanted light 762 is not collimated by not being properly focused by lens 210. Light 762 will not be focused to point 760. Plate 764 has an aperture 764 located at point 760 to allow light 230 to pass through. Most of the unwanted light 762 is blocked by the plate 754. Light 230 is re-collimated by lens 756. In a preferred embodiment, the aperture 764 is circular and has a diameter of about λ/(2 × (NA)), where λ is the wavelength of light and NA is the numerical aperture of the lens 752. The exact diameter is determined by a combination of balanced alignment tolerances and interlayer signal rejection requirements. The aperture 764 may also be a slit with a narrowest gap of λ/(2 × NA). The plate 764 may now be two pieces separated by a slit. The plate 754 may be made of a metal sheet or a transparent substrate with a light-blocking coating that does not cover the aperture 764.

Fig. 24 shows a filter 800 that may be used as the filter 222. The filter 800 includes a lens 802, a baffle 804, a baffle 806, and a lens 808. The plate 806 has an aperture 810 located at the focal point 812 of the lens 802. The plate 804 has a complementary aperture 814 that allows collimated light 230 to pass through the aperture 810 but blocks unwanted uncollimated light 820. The aperture 814 may be a pair of parallel slits or an annular aperture. In a preferred embodiment, the slit spacing of the holes 814 is greater than the diameter of the holes 810. The diameter of the aperture 810 is approximately λ/(2 × NA). For an annular aperture, the inner diameter of the annular slit should be greater than the diameter of the aperture 810. In both cases, the outer edge of the hole 814 is located outside the beam 230. The baffles 804 and 806 may be made of sheet metal or a transparent substrate with a light blocking coating that does not cover the holes 810 and 814.

Fig. 25 shows another filter 830 that may be used as the filter 222. The filter 830 includes a beam splitter 832 and a hologram plate 834. The cladding of the holographic plate 834 is tuned to effectively reflect the collimated beam 230 but pass the uncollimated beam 840 at the same time. The desired light beam 230 is reflected by the holographic plate 834 and back to the beam splitter 832, and is reflected to the beam splitter 224.

Fig. 26 is a schematic diagram showing the fabrication of the hologram plate 834. A collimated laser beam 850 having the same wavelength as laser 200 is split into two beams 852 and 854 at amplitude splitter 856. Beams 852 and 854 are directed to mirrors 860 and 862, respectively, and fall onto holographic plate 834 from opposite directions perpendicular to plate 834. A reflection hologram is recorded by interference of beams 852 and 854. The holographic overlay may be made of dichromic acid glue or a photopolymerizable material.

In fig. 4, a filter 222 of the present invention is located in the path of light beam 220. However, one or more filters may be placed in the optical path of servo beam 230 or data beam 236.

While the preferred embodiments of the present invention have been illustrated in detail, it should be apparent that modifications and adaptations to those embodiments may occur to one skilled in the art without departing from the scope of the present invention as set forth in the following claims.

Claims (17)

1. An optical data storage system comprising:

an electromagnetic radiation source for generating a beam of electromagnetic radiation;

an optical medium having a plurality of data surfaces;

focusing means for focusing the beam of electromagnetic radiation on a selected one of the data surfaces;

an optical detector for receiving a returned beam of electromagnetic radiation from the medium and generating a focus error signal therefrom; and

a focus control device connected to the focusing device, the focus control device including a peak detector for detecting a peak in the focus error signal; and a controller for counting peaks detected by the peak detector and determining a data surface on which to focus the beam of electromagnetic radiation.

2. The system of claim 1, wherein: the optical detector is a segmented optical detector.

3. The system of claim 2, wherein: the segmented optical detector is comprised of at least 4 segments.

4. The system of claim 1, wherein: the optical detector is composed of 4 segments, and the 4 segments are segmented by crossing two boundary lines into 4 sectors; the method for generating the focus error signal comprises the following steps: the output signals from each diagonally opposite pair of sectors are summed and then the two sums of each other are subtracted.

5. The system of claim 1, wherein: the focusing means comprises a lens coupled to a linear movement means which moves the lens in a direction substantially perpendicular to the data surface.

6. The system of claim 1, wherein: the detection of two peaks in the focus error signal may specify the position of the data surface.

7. The system of claim 6, wherein: the focus control means may control the focusing means such that the focus error signal is maintained at a zero point between the two peak values.

8. The system of claim 1, wherein: the optical medium is an optical disc and the system further comprises a rotating means for rotating the optical disc.

9. The system of claim 1, wherein: the optical medium contains information identifying the number of data layers present in the medium.

10. An optical data storage system comprising:

a laser for generating a light beam;

an optical disc medium having a plurality of data surfaces;

a rotating device connected to the optical disc medium for rotating the optical disc medium;

a focusing means for focusing the light beam on a selected one of the data surfaces;

an optical detector for receiving a returned light beam from the medium and generating a focus error signal therefrom; and

a focus control device coupled to the focusing assembly, the focus control device including a peak detector for detecting peaks in the focus error signal, and a controller for counting the peaks detected by the peak detector and for determining a data surface on which to focus the light beam.

11. The system of claim 10, wherein: the optical detector is a segmented optical detector.

12. The system of claim 11, wherein: the segmented optical detector is comprised of at least 4 segments.

13. The system of claim 10, wherein: the optical detector is composed of 4 segments, and the 4 segments are segmented by crossing two boundary lines into 4 sectors; the method for generating the focus error signal comprises the following steps: the signals output from each diagonally opposite pair of sectors are added and then the two sums of each other are subtracted.

14. The system of claim 10, wherein: the focusing means comprises a lens coupled to a linear movement means which moves the lens in a direction substantially perpendicular to the data surface.

15. The system of claim 10, wherein: the detection of two peaks in the focus error signal may specify the position of one data surface.

16. The system of claim 15, wherein: the focus control means may control the focusing means such that the focus error signal is maintained at a zero point between the two peak values.

17. The system of claim 10, wherein: the optical medium contains information identifying the number of data layers stored in the medium.