CN1114770A - Multiple data surface data storage system and method - Google Patents

Abstract

An optical data storage system comprising a multiple data surface medium and an optical head. The medium includes a plurality of substrates separated by a light propagation medium. The data surface is located on a surface of the substrate adjacent to the light-propagating medium. The data surface is substantially light transmissive. The optical head includes an aberration compensator to enable the optical head to focus on different data surfaces and a filter to filter out unwanted reflected light.

Description

Multiple data surface data storage system and method

This invention relates generally to optical data storage systems, and more particularly to storage systems having multiple data storage surfaces.

Optical data storage systems provide a means for storing large amounts of data on disks. The data is accessed by focusing a laser beam on the data layer of the disc and detecting the reflected beam. Various systems are known. In ROM (Read Only Memory), data is permanently loaded into the disc in the form of marks on the disc when the disc is manufactured. Data is detected by detecting the change in reflectivity when a laser beam shines on the data mark. The WORM (Write Once Read Many) system allows users to write data by making marks, such as pits, on the surface of a blank disc. Once data is written onto the disk it cannot be erased. Data in the WORM system is also detected by changes in reflectivity.

Erasable optical systems are also known. These systems use lasers to heat the data layer above a critical temperature to write or erase data. Magneto-optical recording systems record data by orienting magnetic domains at one location up or down. The data is read by shining a low-power laser on the data layer. The difference in the direction of the magnetic domains causes the polarization plane of the beam to deflect in a certain direction, either clockwise or counterclockwise. This change in polarization orientation is detected. Phase change recording utilizes structural changes in 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 different phases.

In order to increase the storage capacity of optical discs, a multi-data layer system has been proposed. In theory, for an optical disc with two or more data layers, the different layers can be accessed by changing the focus position of the lens. Examples include U.S. Patent No. 3,946,367 issued March 23, 1976 to Wohlmul et al.; U.S. Patent No. 4,219,704 issued August 26, 1980 to Russel; U.S. Patent No. 4 issued May 22, 1984 to Holster et al. , No. 450553; U.S. Patent No. 4,905,215 issued February 27, 1990 to llattori et al; Japanese Published Application 63-276732 published November 15, 1988 by Watanabe et al; and "IBM Technical Disclosure", July 1987 Bulletin "Volume 30, No. 2, page 667, Arter et al. (IBM Technical Dlsclosure Bulletin, Vol. 30, NO. 2, P667, July1987).

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

In a preferred embodiment of the present invention, an optical data storage system includes an optical disk drive and a multiple data surface optical medium. The media has a plurality of substrate components separated by air spaces. The surface of the substrate member adjacent to the air space is the data surface. The data surfaces are highly transmissive, except for the last data surface which may contain a reflective layer. Each data surface has trace markers.

Disk drives include lasers that generate laser light. A light transmission channel directs the light to the medium. The transmission channel includes converging components for focusing the light onto the various data surfaces and aberration compensator components for correcting aberrations due to variations in effective substrate thickness. A receiving channel receives reflected light from the medium. The receive channel includes filter components that filter out stray light reflected from surfaces other than the data being read. The receive channel has a detector for receiving reflected light and circuitry for generating data and servo signals responsive to the data.

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

Fig. 1 is the schematic diagram of optical data storage system of the present invention;

Figure 2A is a cross-sectional view of an optical medium of the present invention;

Figure 2B is a cross-sectional view of another optical medium;

Figure 3A is a cross-sectional view of a tracking mark of the medium of Figure 2;

Fig. 3B is a cross-sectional view of another tracking marker;

Fig. 3C is a cross-sectional view of another tracking marker;

Fig. 3D is a cross-sectional view of yet another tracking marker;

Fig. 4 is the schematic diagram of optical head and medium of the present invention;

Figure 5 is a top view of the photodetector in Figure 4;

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

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

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

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

Fig. 8C is a graph of tracking error signal versus optical head displacement in another embodiment;

Fig. 9 is a graph of focus error signal to lens displacement of the present invention;

Fig. 10 is a schematic diagram of the multi-data surface aberration compensator of the present invention;

11 is a schematic diagram of another embodiment of the multi-data surface aberration compensator of the present invention;

12 is a schematic diagram of another embodiment of the multi-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 the multi-data surface compensator of the present invention;

15 is a schematic diagram of another embodiment of the multi-data surface aberration compensator of the present invention;

Figure 16 is a cross-sectional view of the lens in Figure 15;

17 is a schematic diagram of another embodiment of an optical head and a medium of the present invention;

18 is a schematic diagram of another embodiment of the multi-data surface aberration compensator of the present invention;

19 is a schematic diagram of another embodiment of the multi-data surface aberration compensator of the present invention;

Figure 20 is a schematic diagram showing the fabrication process of the compensator of Figures 18 and 19;

Fig. 21 is a schematic diagram of another embodiment of the aberration compensator of the present invention;

Fig. 22 is a schematic diagram of another embodiment of the wooden aberration compensator;

23 is a schematic diagram of a multi-data surface filter of the present invention;

24 is a schematic diagram of another embodiment of the multi-data surface filter of the present invention;

25 is a schematic diagram of another embodiment of the multi-data surface filter of the present invention;

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

FIG. 1 shows a schematic diagram of the optical data storage system of the present invention, generally designated 10 . System 10 includes an optical data storage medium 12, preferably in the form of a disc. Media 12 is removably mounted on positioning shaft 14 as is known in the art. Shaft 14 is connected to shaft motor 16 which in turn is connected to system base 20 . Motor 16 turns shaft 14 and media 12 .

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

FIG. 2A is a cross-sectional view of the media 12 . The medium 12 carries a substrate 50 . The substrate 50 is also called a face plate or cover plate, and is the laser beam entry medium 12 . An outer diameter (OD) edge 52 and an inner diameter (ID) edge 54 are connected between the faceplate 50 and the substrate 56 . Outer rim 58 and inner rim 60 are connected between substrate 56 and substrate 62 . Outer diameter edge 64 and inner diameter edge 66 connect between substrate 62 and substrate 68 . An outer diameter edge 70 and an inner diameter edge 72 are connected between substrate 68 and substrate 74 . Panel 50 and substrates 56, 62, 68 and 74 are made of light transmissive materials such as glass, polycarbonate or other polymers. In a preferred embodiment, face plate 50 is 1.2 mm thick and substrates 56, 62, 68 and 74 are 0.4 mm thick. The thickness of the substrate is optionally 0.2 to 0.8 mm. The inner and outer diameter edges are preferably made of plastic material and have a thickness of about 500 microns. The edge thickness can be selected as 50-500 microns.

The edge can be attached to the panel and substrate with glue, cement or other bonding techniques. The edge can also be made integrally with the substrate. When in place, the rims form a plurality of annular spaces 78 between the substrate and the panel. Shaft bore 80 passes through media 12 in the inner radial rim to receive shaft 14 . A plurality of passages 82 are provided in the inner radial rim for connecting the bore 80 and the space 78 to equalize the pressures of the space 78 and the environment (typically air) surrounding the disc reservoir. Passage 82 is connected to a plurality of low impedance filters 84 to prevent contamination of space 78 by airborne particulate matter. Filter 84 may be quartz or fiberglass. 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 surfaces may be coated with a writable optical storage film (such as WORM) or an erasable optical storage film (such as phase change or magneto-optical). Except optical memory film, data surface does not contain in the prior art (as U.S. Patent No. 4,450, No. 533), known, separate metal reflection layer structure (reflectivity 30～100%), in other words, in ROM In the case of a surface, the data surface may consist of, consist only of, or consist essentially of only the surface itself, whereas in the case of a WORM, phase change, or magneto-optical surface, the data surface may consist of, consist of only, or consist essentially of only the surface and storage film. No additional non-data storage reflective layer is required. The result is a data surface that is very transparent and allows for many data surfaces. Although the middle data surface does not have a 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. The data is permanently recorded in the form of pits formed directly in the substrate during the manufacture of the disc. Different from the prior art, the surface of the ROM of the present invention does not contain a metal reflective layer. The substrate has no coating. The result is a transmittance of approximately 96% per data surface. This 4% reflectance is sufficient for detecting data. The benefit of high transmittance is to allow access to a large number of data surfaces and reduce the effects of unwanted signals from other surfaces. Since there is no covering on these surfaces, they are easier to fabricate and more resistant to corrosion.

Although not required, it is beneficial to increase the reflectivity and thereby reduce the laser power. One way to increase the reflectivity above 4% is to coat it with a thin film of dielectric having a refractive index greater than that of the substrate. The maximum reflectivity of 20% occurs at a dielectric thickness of about λ/4n, and decreases monotonically to 4% at a thickness of λ/2n, where λ is the wavelength of light and n is the refractive index of the dielectric. Examples of such dielectrics are _ZrO2 , ZnS, _SiNx or mixed oxides. The dielectric is deposited by sputtering methods known in the art.

The reflectivity of the data layer can also be reduced by less than 4%. This increases the transmittance and allows more disks to be stacked. The reduction in reflectivity can be achieved by using a dielectric film with a lower refractive index than the substrate. One such dielectric is MnF, which has a refractive index of 1.35. A minimum reflectivity of 1% is achieved when the dielectric thickness is about λ/4n, and it varies monotonically to a maximum reflectance of 4% when the thickness is about λ/2n, where λ is the wavelength of light and n is the refractive index. Various other thin film antireflective materials can also be used. These antireflection films can be applied by sputtering methods known in the art.

Data surfaces can also contain WORM data. A WORM film such as a tellurium-selenium alloy or a phase change WORM film can be applied to 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 any preferred embodiment, the deposition thickness of the tellurium-selenium alloy is 20-800 Angstroms (A).

The data surface may also contain a reversible phase change film. Any type of phase change film can be used, but preferred compounds include those along or close to the connecting line connecting GeTe and Sb ₂ Te ₃ , including Te _{52 5} Ge _{15 3} Sb ₃₃ Ge ₂ Sb ₂ Te ₅ , GeSb ₂ Te ₄ and GeSb ₄ Te ₇ . These films are vacuum deposited on the substrate by sputtering known in the art to a thickness of 20-800 Å. A 3,000 Å thick dielectric protective coating can be formed on the phase change film to prevent erosion.

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

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

FIG. 2R is a cross-sectional view of another embodiment of an optical recording medium, generally indicated at 120 . Elements of media 120 that are similar to media 12 are indicated with primed numerals. Media 120 lacks the rim and space 78 of media 12 . The substrates are separated by a plurality of solid transparent members 122 . Member 122 is made of a material having a different refractive index than the substrate. This is necessary to achieve some reflectivity on the data surface. In a preferred embodiment, member 122 is made of an optical cement which also holds the substrates together. The thickness of member 122 is preferably 100-300 microns. 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, generally designated 130. As shown in FIG. Surface 90 includes a pattern of helical (or concentric) channel grooves 132 . The portion of surface 90 between channels 132 is referred to as land portion 134 . Surface 92 includes a pattern of helical flip channels (ridges) 136 . The portion of surface 92 between inverted grooves 136 is land 138 , and grooves 132 and inverted grooves 136 are also referred to as tracking marks. In a preferred embodiment, the width 140 of the tracking marks is 0.6 microns and the width 140 of the land portions is 1.0 microns. This yields a pitch of (1.0+0.6) = 1.6 microns.

Tracking marks are used to keep the beam on track as the medium 12 rotates. This is detailed below. For the pattern 130, the light beam 144 from the optical head 22 will track the progress of the land portion 134 or 138 depending on the surface on which it is focused. Record data on the land portion. In order for the tracking error signal (TES) to have the same magnitude 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. Light beam 144 is focused on surface 90 through substrate 50 , and light beam 144 is focused on surface 92 through space 78 . In a preferred embodiment, space 78 contains air. To equalize the optical path difference between the land and tracking marks, d1n1 must equal d2n2 (or d2/d1 equals n1/n2), where d1 is the depth (vertical distance) of the mark 132, n1 is the refractive index of the substrate 50, and d2 is the height (vertical distance) of the mark 136, n2 is the refractive index of the space 78, in a comparative embodiment, the space 78 contains air with a refractive index of 1.0, and the refractive index of the substrate 50 (and other substrates) is 1.5 . The ratio d2/d1 is thus equal to 1.5. In a preferred embodiment, d1 is 700 Å and d2 is 1050 Å. The other surfaces of media 12 also have the same tracking mark pattern. The other substrate entrance surfaces 94 , 98 and 102 are similar to surface 92 , while the 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 also be formed in a concentric circular pattern. Furthermore, the spiral pattern of each surface may be the same, ie they are all clockwise or counterclockwise spirals, or the pattern of each data layer may sequentially alternate between clockwise and counterclockwise spirals. This alternation of the spiral pattern is desirable in certain applications that require continuous tracking of data, such as storage of video data and movies. In this case, the beam traces a clockwise helical pattern inward on the first data surface until the helical pattern terminates near the inner radius, then the beam is focused onto the second data surface immediately below and traces a counterclockwise helical pattern outward until it reaches outside diameter.

FIG. 3B shows an enlarged detailed cross-sectional view of another surface pattern of the media 12 and is indicated generally at 150 . Pattern 150 is similar to pattern 130 except that the tracking marks on surface 92 are grooves 152 rather than flipped grooves. Its pitch and ratio d2/d1 are the same as those of pattern 130 . Beam 144 tracks on land 134 on surface 90 , but when beam 144 is focused on surface 92 it will track along groove 152 . In some cases it is desirable to track along the groove 132 . However, as will be described below, beam 144 may also be electronically steered to track land 138 on surface 92. Surface 92 is similar.

FIG. 3C shows an enlarged detailed cross-sectional view of another surface pattern of media 12 , indicated generally at 160 . Pattern 160 is similar to pattern 130 except surface 90 has inverted grooves 162 instead of grooves 132 , and surface 92 has grooves 164 instead of inverted grooves 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 travel along groove 164 when focused on surface 92 (unless it is electron converted to travel along land). Surfaces 94 , 98 and 102 are similar in pattern to 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, indicated generally at 170 . In pattern 170 , surface 90 has a similar structure to surface 90 of pattern 160 . Surface 92 has a similar structure to surface 92 of pattern 130 . The pitch and d2/d1 ratio are the same as for pattern 130. Beam 144 will travel along flip slot 162 when focused on surface 90 (unless its electrons are converted to travel along land) and travel along land 138 when focused on surface 92 . Surfaces 94 , 98 and 102 have a similar pattern to surface 90 , while surfaces 96 , 1000 and 1004 have a similar pattern to surface 92 .

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

The discussion of tracking marks applies to other features of the disc as well. For example, some ROM discs use recesses molded into 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 this medium is used in the multiple data surface form of the present invention, the pockets are formed as pockets or flipped pockets on each data surface in a manner similar to the tracking marks discussed above. The optical path between a land and a pocket or flipped pocket is also similar to a tracking marker. Pockets, flip pockets, troughs, and flip slots are all located at different heights from the land (ie, their vertical distance from the land) and are referred to in this discussion as markers. Tags designed to provide tracking information are called non-data tracking tags. bald head

FIG. 4 shows a schematic diagram of the optical head 22 and the medium 12 . The optical head 22 has a laser diode 200 . Laser 200 may be a gallium-aluminum-arsenide diode laser that produces a main beam 202 having a wavelength of about 780 nanometers. The light beam 202 is collimated by a lens 203 and circularized by a circularizer 204 . The circularizer 204 may be a circularizing prism. Light beam 202 passes through beam splitter 205 . A portion of beam 202 is reflected by beam splitter 205 to converging lens 206 and photodetector 207 . A detector 207 is used to monitor the power of the light beam 202 . The remainder of the light beam 202 reaches and is reflected by a mirror, 208. Light beam 202 then passes through converging lens 210 and a multiple data surface aberration compensator 212 and is focused onto one of the data surfaces of medium 12 (shown as surface 96). The lens 210 is mounted on a bracket 214 . The position of the bracket 214 relative to the medium 12 can be adjusted by a focus motor 216 .

A portion of beam 202 is reflected by the data surface to form reflected beam 220 . Light beam 220 passes through compensator 212 and lens 210 and is reflected by mirror 208 . At beam splitter 205 , light beam 220 is reflected to multi-surface filter 222 . Light beam 220 passes through filter 222 and beam splitter 224 . At beam splitter 224 a first portion 230 of light beam 220 is directed to astigmatic lens 232 and quadrant detector 234 . At beam splitter 224 , second portion 236 of light beam 220 is directed to half wave plate 238 and 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 focuses light beam 242 to light detector 248 , and lens 250 focuses light beam 244 to light detector 252 .

FIG. 5 shows a top view of quadrant detector 234 . The detector 234 is divided into four identical sections 234A, B, C and D.

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

Circuit 264 has a plurality of amplifiers 280, 282, 284 and 286 connected to sections 234A, R, C and D, respectively. Summing amplifier 288 is connected to amplifiers 2800 and 284 and summing amplifier 290 is connected to amplifiers 282 and 286 . Differential amplifier 292 is connected to summing amplifiers 288 and 290 .

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

FIG. 7 is a schematic diagram of the controller system of the present invention and is generally indicated by the reference numeral 3000 . A 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 connected to detector 310 , detector 312 , detector 207 and circuits 262 , 264 and 266 . Controller 314 is a disk drive controller with a microprocessor. Controller 314 is also connected to and controls laser 200 , head motor 26 , axis motor 16 , focus motor 216 , switches 297 and 274 and compensator 212 . A detailed description of the exact structure and operation of compensator 212 is given below.

It can now be seen that system 10 operates. The controller 314 causes the motor 16 to rotate the disc 12 and the motor 26 to move the optical head 22 to the appropriate position under the disc 12 . See Figure 4. Laser 200 to read data from disk 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 used to provide focus and tracking servo information, while beams 242 and 244 are detected by detectors 248 and 252 respectively and used to provide data signals.

See Figure 5. When beam 202 just converges onto data surface 96 , beam 230 has a circular cross-section at detector 234 . This will cause circuit 264 to output a zero focus error signal. If the beam 202 is out of focus in one direction or the other, the beam 230 will appear in an elliptical pattern 352 or 354 on the 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 beam 202 is focused exactly on one track of data surface 96, beam 230 will fall equally on portions A and B and portions D and C with circular cross-sections. If the beam deviates from the course it will land on the boundary between the tracking marker 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, while parts C and D will receive less light, or vice versa.

• FIG. 8A shows a graph of TES generated by circuit 264 versus head 22 displacement. Controller 314 causes VCM 26 to move optical head 22 across the surface of media 12 . TES peak detector 312 counts the peaks (maximum and minimum points) of the TES signal. There are two peaks between the channels. By counting the number of peaks, the controller 314 can position the beam on the appropriate track. The TES signal at land is a positive slope TES signal. Controller 314 uses the positive slope signal to lock the beam onto the track. For example, a positive slope TES signal moves the optical head 22 leftward toward the zero land position, while a negative slope TES signal moves the optical head 22 rightward toward the zero land position. FIG. 8A is a signal derived from the preferred pattern 130 of the medium 12 when the switch 297 is in the initial position shown in FIG. 6 . Surface 90 of pattern 150 and surface 92 of pattern 170 also generate the same signal. The beam is automatically locked to land because of the positive slope there.

8B shows a graph of TES versus displacement of the optical 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 here that the positive slope signal appears at the tracking marker, so the beam is automatically locked on the tracking marker and not the land position. There are occasions when it is desirable to follow trail markers.

8C shows a graph of TES versus head displacement relative to surface 92 of pattern 150, surfaces 90 and 92 of pattern 160, and surface 90 of pattern 170 when inverter switch 297 is activated to invert the TES signal. Now the TES has a positive slope at land and the beam will travel along the land part instead of the tracking marker. Accordingly, controller 314 may track troughs or land by setting switch 297 .

In the preferred embodiment, medium 12 includes a ROM data surface. ROM data is read by detecting reflectivity. In the data circuit 262, a switch 274 is connected to an amplifier 276 when reading a ROM disc. The signals from detectors 248 and 252 are summed. The detected light is weaker when a data point is recorded, and this difference in detected light is the data signal. The setting of switch 274 is the same for reading WORM and phase change data disks. If disc 12 has a magneto-optical data surface, then polarization detection is required to read the data. Switch 274 will be connected to amplifier 278 . The difference in the orthogonally polarized light detected by detectors 248 and 252 will provide the data signal.

FIG. 9 shows a graph of the focus error signal from circuit 264 versus lens 210 displacement. Note that for each data surface of medium 12 a nominally sinusoidal focus error signal is obtained. Between data layers, the focus error signal is zero. During system startup, 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 a positive displacement direction. At each data layer, a peak detector 310 detects two peaks of the focus error signal. Controller 314 will count the peaks, (two per data surface) and determine the exact data surface on which beam 202 is focused. When the desired data surface is reached, controller 314 causes motor 216 to position lens 210 so that the focus error signal is between the two peaks for that particular data surface. The error signal is then used to control the motor 216 to find the zero focus error signal between the two peaks, that is, to lock on the positive slope signal to achieve accurate focus. Controller 314 also adjusts the power of laser 200, switch 297, and aberration compensator 212 as appropriate for the particular data surface.

At startup, the controller 314 also determines the type of disk being read. Switch 274 is first set to the reflectivity detection position, and switch 297 is set to read the land portion of the disc with the preferred pattern 130. The controller 314 searches for and reads the header information of the first track of the first data surface. The header information includes the number of layers, the type of optical medium for each layer (reflectivity or polarization detection), and the pattern of tracking polarization used. Based on this information, controller 314 can properly set switches 274 and 297 to properly read each data surface. For example, a disc may have 4 ROM data surface layers and two ROM data surface layers. Controller 314 will set switch 274 for reflectivity detection for surfaces 1 - 4 and for polarization detection for surfaces 5 - 6 .

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

Alternatively, a disk drive may be dedicated to only one type of media. At this point, the controller 314 is preprogrammed to store information about the data surface, layer number, and tracking mark type. Aberration Compensator

Typically, lenses are designed to converge light in air with a refractive index of 1.0. When such a lens is used to converge light transmitted through materials with different refractive indices, the light suffers from spherical aberration, which distorts and magnifies the beam spot, degrading reading and recording performance.

In typical optical data storage systems, only one converging surface is required. This surface is typically under a 1.2mm thick panel. The lens is generally a 55 numerical aperture (NA) lens, which is specially designed to correct the spherical aberration caused by the 1.2mm panel on the light. The result is good point focus for that particular depth, but blurry focus for other depths. This is a serious problem for any multi-tier system.

The aberration compensator 212 of the present invention can solve this problem. FIG. 10 shows a schematic diagram of an aberration compensator, indicated by the general reference numeral 400 and which can be used as the compensator 212 . The compensator 400 includes a stage block 402 comprising three stages. The first stage 404 is 0.4 mm thick, the second stage 406 is 0.8 mm thick, and the third stage is 1.2 mm thick. The block 402 is made of the same material as the substrate of the faceplate and medium 12 or other similar optical material. Note that the optical thickness increases for these steps are increments of substrate thickness. Block 402 is connected to voice coil motor 410 (or similar actuation device), which in turn is connected to controller 314 . Motor 410 moves block 402 laterally into and out of the optical path of beam 302 .

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

When the beam 202 is focused on one of the surfaces 102 or 104, the mass 402 is completely withdrawn and the beam 202 does not pass through it. Block 402 is positioned such that beam 202 passes through stage 404 when beam 202 is focused on surface 98 or 100 . Block 402 is positioned such that beam 202 passes through stage 406 when beam 202 is focused on surface 94 or 96 . As the beam 202 passes through the surface 90 or 92 , the positioning of the block 402 causes the beam 202 to pass through the steps 408 . The result is that no matter which pair of surfaces is focused, beam 202 passes through material with the same total optical thickness and does not suffer from spherical aberration. Controller 314 controls motor 410 to move mass 402 as needed.

FIG. 11 shows an aberration compensator, indicated by the general reference numeral 430 and usable as the compensator 212. As shown in FIG. 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 faceplate of media 12 or a material with similar optical properties. Block 432 is in a fixed position for light beam 202 to pass through it. Block 434 is connected to a voice coil motor 436 and is slidable along the surface of block 432 . Controller 314 is connected to and controls motor 436 . By moving block 434 relative to block 432 , the overall thickness of material through which beam 202 passes may be adjusted. The result is that beam 202 passes through the same thickness of material regardless of which data surface it is focused on.

12 and 13 show an aberration compensator indicated by the general reference numeral 450, which may be used as the compensator 212. The compensator 450 has a circular stepped member 452 . Part 452 has four sections 454 , 456 , 458 and 460 . Portions 456 458 and 460 have a thickness similar to steps 404 , 406 and 408 of compensator 400 , respectively. Portion 454 has no material and represents an empty space in the circle, as shown in FIG. 13 . The garden member 452 is connected to a stepper motor 462 controlled by the controller 314 . Axis 462 rotates 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 by the general reference numeral 570, which may be used as the compensator 212. As shown in FIG. Compensator 570 includes a stationary convex lens 572 and a movable concave lens 574 . Lens 574 is connected 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 . Light beam 202 reaches medium 12 through lenses 572 , 574 and lens 210 . Moving lens 574 relative to lens 572 changes the spherical aberration of beam 202 and causes it to focus on a different surface. In the preferred embodiment lenses 210, 574 and 572 form a Cooke triplet with movable center member 574. The Cook triplet is described in detail in R. Kingslake's article "Lens Design Fundamentals" ("Lens Design Fundamentals", Academic Press, New York, 1978, pp. 286-295). Although lens 274 is shown as a Moving, also lens 274 can be fixed and lens 572 is used as moving part.In Fig. 4, aberration compensator 212 is between lens 210 and medium 12. But, if used compensator 570 it will be positioned at lens 210 and reflector 208, as shown in FIG. 14 .

FIG. 15 shows an aberration compensator indicated generally at 580 . The compensator 580 includes an aspheric lens component 582 of zero nominal focusing power. Part 582 has a spherical aberration surface 584 and a planar surface 586 . Lens 582 is connected 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 . Light beam 202 reaches medium 12 via lens 210 and lens 582 . Moving lens 582 relative to lens 210 changes the spherical aberration of beam 202 and enables it to be focused onto a different data surface.

FIG. 16 shows a schematic view of the lens 582 relative to the axes Z and P. As shown in FIG. In a preferred embodiment, the surface 584 should correspond to the formula Z=0.00770P ⁴ −0.00154P ⁶ .

FIG. 17 shows a schematic diagram of another optical head according to the present invention, and is indicated by the general reference numeral 600. As shown in FIG. Components of optical head 600 that are similar to optical head 22 are indicated with primed numerals. Note that optical head 6000 is identical to system 10 except that aberration compensator 212 is eliminated and a new aberration compensator 602 is added between beam splitter 206' and mirror 208'. A description of compensator 602 and its operation is given below. Operation of optical head 600 is otherwise the same as optical head 22 . Optical head 600 may replace optical head 22 in system 10 .

FIG. 18 shows an aberration compensator, indicated generally at 610 , which may be used as compensator 602 . The compensator 610 has a substrate 612 with a reflective holographic overlay 614 . The substrate 612 is connected to a stepper motor 616 controlled by the controller 314 . The holographic overlay 614 is recorded with several holograms, each of which causes a specific aberration to the light beam 202'. These holograms are Bragg-like in that they only respond to light of a certain wavelength and angle of incidence. When the substrate 212 is rotated a few degrees, the light beam 202' will encounter a different hologram. The number of recorded holograms corresponds to the number of different spherical aberrations to be corrected. For the medium 12 shown, four different records are required, each corresponding to a pair of data surfaces.

FIG. 19 shows an aberration compensator indicated by the general numeral 620 and usable as the compensator 602 . Compensator 620 includes a substrate 622, a transmissive holographic overlay 624, and a stepper motor 626. Compensator 620 is similar to compensator 610 except that holographic overlay 624 is transmissive rather than reflective. A number of holograms are recorded on the holographic overlay 624, each corresponding to the required spherical aberration compensation amount. As the substrate 622 rotates, the light beam 202' encounters the holograms in sequence.

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

Lens 668 forms an aberration-free point on plane 672 . This beam then passes through block 674, where the thickness represents the sum of the substrate thicknesses encountered while accessing a particular recording layer. Lens 676 is identical in design to lens 210 used in optical memory heads. It collimates light into a beam containing a specific spherical aberration corresponding to a specific thickness. This wavefront is holographically recorded by interfering with the reference beam 662 . If the hologram is oriented approximately in the plane 690 shown, a transmission hologram is recorded. If it is oriented approximately in the plane 692 shown in dashed lines, a reflection hologram is recorded. By rotating the hologram to a new angle and inserting a plate of corresponding thickness in block 674, the wavefront required to correct for aberrations encountered when accessing different pairs of recording layers can be holographically stored. Multiple angle-resolved holograms are recorded, each corresponding to and corrected for a pair of non-simultaneously recorded layers. Holographic overlays can be made with dichromate glue or photopolymerizable materials. Individual holograms can be recorded in angular increments as small as 1 degree without significant interference. This ensures the recording of a large number of holograms and the corresponding use of a large number of data surfaces.

FIG. 21 shows another aberration compensator indicated by the general reference numeral 700 and usable as compensator 602 . The compensator 700 includes a polarizing beam splitter 702, a quarter wavelength 704, a carousel 706 connected to a stepper motor 708, and a plurality of spherical aberration mirrors 710 each capable of providing different spherical aberration corrections. Beam 202' is oriented according to its polarization so that it passes through beam splitter 702 and plate 704 to one of mirrors 710. Mirror 710 imparts appropriate spherical aberration to beam 202', which then returns through plate 704 and is reflected by beam splitter 702 to mirror 208'. Motor 708 under control of controller 314 rotates carousel 706 to select the appropriate mirror for placement. Mirror 710 is a reflective Schmidt correction. See "Optics Principles" by M. Born et al. (M. Born, et al., Principle of 'Optics', Pergonan Press Oxford, 1975, pp. 245-249), pp. 245-249.

FIG. 22 shows another aberration compensator, indicated generally at 720, which may be used as compensator 602. As shown in FIG. The compensator 720 includes a polarizing beam splitter 722 , a quarter wavelength 724 and an electrically controlled deformable mirror 726 . The deformable mirror 726 is controlled by an internal piezoelectric element and is described in more detail in J.P. Gaffarel et al., Applied Optics, Vol. Discussion. The operation of compensator 720 is similar to that of compensator 700, except that mirror 726 is electrically adjusted to provide the appropriate spherical aberration. In other words, mirror 726 is adjusted to form a different Schmidt correction plate 710 phase to that of compensator 700. Corresponding reflective surfaces. The controller 314 controls the adjustment of the mirror 726 as needed.

The operation of aberration compensators 212 and 602 was described above in connection with medium 12 . Due to the air layers between the layers, one aberration compensation setup is applied to a pair of data surfaces. However, when using media 120, each data surface requires an aberration compensation setting. This is due to the lack of air space. Multiple Data Surface Filters

When beam 202 is focused on a particular data surface of medium 12 , reflected beam 230 returns from that surface to optical head 22 . But there are also light beams 202 that are reflected from other data surfaces. These unwanted reflected light must be removed to obtain data and servo signals. The multiple data surface filter 222 of the present invention can achieve this function.

FIG. 23 shows a schematic diagram of a filter 750 that may be used as 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 lens 210 . Light beam 230 is focused to point 760 by lens 752 . Unwanted light 762 is not collimated due to not being properly focused by lens 210 . Light 762 will not be focused to point 760. Plate 764 has a hole 764 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 recollimated by lens 756 . In a preferred embodiment, aperture 764 is circular and has a diameter of approximately λ/(2 ^* (NA)), where In is the wavelength of light and NA is the numerical aperture of lens 752 . The exact diameter is determined by balancing collimation tolerances and interlayer signal rejection requirements. Holes 764 may also be slits with a narrowest gap of λ/(2 ^* (NA)). At this point the plate 764 may be two pieces separated by a slit. Plate 754 may be made of sheet metal or a transparent substrate with a light blocking coating that does not cover aperture 764 .

FIG. 24 shows a filter 800 that may be used as the filter 222 . Filter 800 includes lens 802 , baffle 804 , baffle 806 and lens 808 . The plate 806 has a hole 810 at the focal point 812 of the lens 802 . Plate 804 has a complementary aperture 814 which allows collimated light 230 to pass through aperture 810 but blocks unwanted uncollimated light 820 . The hole 814 can be a pair of parallel slits or an annular hole. In a preferred embodiment, the slit pitch of the hole 814 is greater than the diameter of the hole 810 . The diameter of the hole 810 is approximately λ/(2 ^* (NA)). For an annular hole, the inner diameter of the annular slit should be larger than the diameter of the hole 810 . In both cases, the outer edge of the aperture 814 lies outside the light 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 filter 222. In FIG. The optical filter 830 includes a beam splitter 832 and a holographic plate 834 . The cladding of the holographic plate 834 is tuned to effectively reflect the collimated beam 230 but at the same time pass the uncollimated beam 840 . The desired light beam 230 is reflected by the holographic plate 834 and returns to the beam splitter 832 where it 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 at amplitude beam splitter 856 into two beams 852 and 854 . Beams 852 and 854 are directed towards mirrors 860 and 862 respectively and fall onto holographic plate 834 from opposite directions perpendicular to plate 834 . By means of the interference of light beams 852 and 854 a reflection hologram is recorded. Holographic overlays can be made from dichromate glue or photopolymerizable materials.

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

Although preferred embodiments of the present invention have been described in detail, it will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the scope of the present invention as defined by the appended claims.

Claims (22)

1. optical data storage system comprises:

A medium receiver is used to receive optical data storage medium, and this medium has a plurality of separation data surfaces that are positioned at medium different depth place;

A radiation source is used to produce radiation beam;

A surperficial recognition device is used for discerning the data surface numeral that medium presents;

A focalizer is used to make radiation beam to focus on selected of a plurality of media data surface; With

An optical receiver is used to receive the radiation beam that returns from medium, and produces the data-signal in response to this radiation beam.

2. system according to claim 1 is characterized in that one of all data surfaces contain the information of record to some extent, the data surface numeral that presents in this information representation optical data storage medium.

3. system according to claim 2 is characterized in that the information that is write down is to write down in the boot section of one of all data surfaces.

4. system according to claim 1 is characterized in that surperficial recognition device comprises a controller that is electrically coupled to focalizer.

5. system according to claim 4 is characterized in that this controller is preprogrammed with a numeral, the data surface numeral that presents in this numeral optical data storage medium.

6. system according to claim 5, it is characterized in that one of all data surfaces contain the guidance information of record, the data surface numeral that presents in this information representation optical data storage medium, and controller is in response to the data-signal of a guidance information of reading corresponding to optical receiver.

7. system according to claim 1 is characterized in that focalizer comprises lens that are connected in a linear motion motor.

8. system according to claim 1 is characterized in that radiation source is a laser instrument.

9. system according to claim 1 is characterized in that it also comprises an optical data storage medium, and this medium has a plurality of separation data surfaces that are positioned at the medium different depth.

10. optical data storage system comprises:

A spindle motors is used to receive an optical data storage dish, and this dish has a plurality of separation data surfaces that are arranged in dish different depth place;

A laser instrument is used to produce light beam;

A surperficial recognition device is used for the data surface numeral that the identification dish presents;

A beam motion device is used for light beam is guided in a selected radial position on the dish;

A focalizer is used for making light beam to focus on selected of a plurality of dish data surfaces of dish; With

An optical receiver is used to receive the light beam that returns from dish, and produces the data-signal in response to this light beam.

11. system according to claim 10 is characterized in that one of data surface contains the information of record to some extent, the data surface number that presents in this information representation optical data storage dish.

12. system according to claim 11 is characterized in that the information that is write down is to write down in the boot section of one of data surface.

13. system according to claim 10 is characterized in that surperficial recognition device comprises a controller that is electrically coupled to focalizer.

14. system according to claim 13 is characterized in that controller is preprogrammed with a numeral, the data surface number that presents in this numeral optical data storage dish.

15. system according to claim 14, it is characterized in that one of data surface comprises the guidance information that is write down, the data surface number that presents in this information representation optical data storage dish, and the data-signal of the guidance information read corresponding to optical receiver of one of controller response.

16. system according to claim 10 is characterized in that focalizer comprises lens that are connected in linear motion motor.

17. system according to claim 10 is characterized in that it also comprises an optical data storage dish, this dish has a plurality of separation data surfaces that are arranged in dish different depth place.

18. an optical data storage system comprises:

A spindle motors is used to receive the optical data storage dish, and this dish has a plurality of separation data surfaces that are arranged in dish different depth place, and has the recorded information of data surface number in the indicating panel;

A laser instrument is used to produce light beam;

A beam motion device is used for light beam is guided in the last selected radial position of dish;

A focalizer is used for making light beam to focus on one of a plurality of dish data surfaces of selection:

An optical receiver is used to receive the light beam that returns from dish, and produces the data-signal in response to this light beam; With

A disc drive controller is connected in optical receiver and focalizer, is used for determining dish upward data surface number and control focalizer.

19. system according to claim 18 is characterized in that recorded information is to write down in the boot section of one of data surface.

20. system according to claim 18 is characterized in that controller is preprogrammed with numeral, the data surface number that presents in this numeral CD.

21. system according to claim 18 is characterized in that focalizer comprises lens that are connected in linear motion motor.

22. system according to claim 18 is characterized in that it also comprises an optical data storage dish, this dish has a plurality of separation data surfaces that are arranged in dish different depth place.

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