Apparatus and method to store information in multiple holographic data storage media

A method is disclosed to store information in multiple holographic data storage media. The method supplies a first holographic data storage medium, defines an inner storage portion of that first holographic data storage medium, and defines an outer storage portion of that first holographic data storage medium. The method further supplies a second holographic data storage medium, defines an inner storage portion of that second holographic data storage medium and defines an outer storage portion of that second holographic data storage medium. The method provides information, encodes a hologram comprising that information into the outer storage portion of the first holographic data storage medium, and encodes the information in the inner storage portion of the second holographic data storage medium.

FIELD OF THE INVENTION

This invention relates to an apparatus and method to store information in multiple holographic data storage media.

BACKGROUND OF THE INVENTION

In holographic information storage, an entire page of information is stored at once as an optical interference pattern within a thick, photosensitive optical material. This is done by intersecting two coherent laser beams within the storage material. The first, called the data beam, contains the information to be stored; the second, called the reference beam, is designed to be simple to reproduce, for example a simple collimated beam with a planar wavefront.

The resulting optical interference pattern causes chemical and/or physical changes in the photosensitive medium: a replica of the interference pattern is stored as a change in the absorption, refractive index, or thickness of the photosensitive medium. When the stored interference pattern is illuminated with one of the two waves that were used during recording, some of this incident light is diffracted by the stored interference pattern in such a fashion that the other wave is reconstructed. Illuminating the stored interference pattern with the reference wave reconstructs the data beam, and vice versa.

A large number of these interference patterns can be superimposed in the same thick piece of media and can be accessed independently, as long as they are distinguishable by the direction or the spacing of the patterns. Such separation can be accomplished by changing the angle between the object and reference wave or by changing the laser wavelength. Any particular data page can then be read out independently by illuminating the stored patterns with the reference wave that was used to store that page. Because of the thickness of the hologram, this reference wave is diffracted by the interference patterns in such a fashion that only the desired object beam is significantly reconstructed and imaged on an electronic camera. The theoretical limits for the storage density of this technique are on the order of tens of terabits per cubic centimeter.

SUMMARY OF THE INVENTION

Applicants' invention comprises a method to store information in multiple holographic data storage media. The method supplies a first holographic data storage medium, defines an inner storage portion of that first holographic data storage medium, and defines an outer storage portion of that first holographic data storage medium. The method further supplies a second holographic data storage medium, defines an inner storage portion of that second holographic data storage medium and defines an outer storage portion of that second holographic data storage medium. The method provides information, encodes a hologram comprising that information into the outer storage portion of the first holographic data storage medium, and encodes the information in the inner storage portion of the second holographic data storage medium.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now toFIGS. 3 and 5, holographic data storage system300comprises laser light source205, beam splitter210, reflective spatial light modulator310, holographic storage medium100, and optical sensor array510(FIGS. 4,6) which comprises input screen520(FIGS. 4,5,6,9,10,11). The light generated by source205is split by beam splitter210into reference beam320, and carrier beam330.

In the illustrated embodiment ofFIG. 3, reflective spatial light modulator (“RSLM”)310displays image240. In certain embodiments, reflective spatial light modulator310comprises an assembly comprising a plurality of micro mirrors. In other embodiments, reflective spatial light modulator310comprises a liquid crystal on silicon (“LCOS”) display device. In contrast to nematic twisted liquid crystals used in LCDs, in which the crystals and electrodes are sandwiched between polarized glass plates, LCOS devices have the liquid crystals coated over the surface of a silicon chip. The electronic circuits that drive the formation of the image are etched into the chip, which is coated with a reflective (aluminized) surface. The polarizers are located in the light path both before and after the light bounces off the chip. LCOS devices are easier to manufacture than conventional LCD displays. LCOS devices have higher resolution because several million pixels can be etched onto one chip. LCOS devices can be much smaller than conventional LCD displays.

Carrier beam330picks up image240as the light is reflected off reflective spatial light modulator310to form reflected data beam340comprising image240. Unreflected reference beam320interferes with reflected data beam340to form hologram160within holographic storage medium100. Hologram160is encoded into holographic data storage medium100as an interference pattern.

FIG. 5illustrates holographic data storage system300decoding the interference pattern comprising the encoded hologram160stored in media100. Input screen520(FIGS. 4,5,6,9,10,11) is disposed a distance away from holographic storage medium100sufficient to digitally capture the reconstructed data beam550projected upon it. To decode the interference pattern comprising hologram160(FIGS. 4,5,6,10), reference beam320is incident on the encoded holographic storage medium100. As the reference beam320interferes with the interference pattern, a reconstructed data beam550is generated, wherein that reconstructed data beam550comprises an image540resembling the original image240. Optical sensor array510(FIGS. 4,6) digitally captures the information comprising image540on input screen520.

Referring now toFIGS. 4 and 6, in certain embodiments laser light source205, beam splitter210, reflective spatial light modulator310, and optical sensor array510, are disposed within holographic drive apparatus400. In the illustrated embodiment ofFIGS. 4 and 6, holographic drive apparatus400further comprises housing405.

In certain embodiments, holographic data storage medium100can be removeably disposed within housing405. In the illustrated embodiment ofFIGS. 4 and 6, holographic data storage medium100is releaseably attached to a drive servo mechanism comprising drive servo440and rotatable shaft450. Drive servo440rotates rotatable shaft450thereby causing holographic data storage medium100to rotate also.

Optical sensor array510comprises rotation-error-servo (“RES”)470. As those skilled in the art will appreciate, a servo comprises a device comprising an external shaft, such as rotatable shaft480. Rotatable shaft480can be positioned to specific angular positions by sending RES470a pre-defined coded signal. As long as that coded signal exists on input line415, RES470will maintain the associated angular position of shaft480. As the coded signal changes, the angular position of the shaft480changes.

RES470is interconnected by rotatable shaft480to rear portion of input screen520(FIGS. 4,5,6,9,10,11). RES470can cause input screen520to rotate in a first direction, i.e. clockwise, or to rotate in a second and opposite direction, i.e. counter-clockwise, by causing rotatable shaft480to rotate in the first direction or in the second direction, respectively.

In the illustrated embodiment ofFIGS. 4 and 6, holographic drive apparatus400further comprises drive controller410. Drive controller410comprises processor420, memory430, and microcode435written to memory430. Drive controller410is interconnected with drive servo440via communication link460, and with RES470via communication link415. Drive controller410, using processor420and microcode435, can cause holographic data storage medium100to rotate at a first rotation rate, and can simultaneously cause input screen520(FIGS. 4,5,6,9,10,11) to rotate at a second rotation rate, wherein the first rotation rate may equal the second rotation rate, and wherein the first rotation rate may differ from the second rotation rate.

In certain embodiments, memory430comprises non-volatile memory, such as and without limitation, battery backed-up RAM; a magnetic disk in combination with the associated software, firmware, and hardware, to read information from, and write information to, that magnetic disk; an optical disk in combination with the associated software, firmware, and hardware, to read information from, and write information to, that optical disk; an electronic storage medium; and the like. By “electronic storage medium,” Applicants mean, for example, a device such as a PROM, EPROM, EEPROM, Flash PROM, compactflash, smartmedia, and the like.

FIG. 4shows holographic drive apparatus400being used to encode hologram160as an interference pattern in holographic data storage medium100.FIG. 6shows holographic drive apparatus400being used to decode the interference pattern comprising hologram160. In the illustrated embodiment ofFIGS. 4 and 6, sensor array510outputs information using communication link490. In certain embodiments, communication link490is interconnected with one or more host computers. In certain embodiments, communication link490is interconnected with a storage controller, such as for example storage controller760(FIG. 7).

FIG. 7illustrates one embodiment of Applicants' data storage and retrieval system700. In the illustrated embodiment ofFIG. 7, data storage and retrieval system700communicates with computing devices710,720, and730. In the illustrated embodiment ofFIG. 7, computing devices710,720, and730communicate with storage controller760through a data communication fabric740. In certain embodiments, fabric740comprises one or more data switches750. Further in the illustrated embodiment ofFIG. 7, storage controller760communicates with one or more holographic data storage systems. In the illustrated embodiment ofFIG. 7, data storage and retrieval system700comprises holographic data storage system300(FIGS. 3,5), holographic drive400(FIGS. 4,6), and holographic drive900(FIGS. 9,10,11).

In certain embodiments, computing devices710,720, and730, are selected from the group consisting of an application server, a web server, a work station, a host computer, or other like device from which information is likely to originate. In certain embodiments, one or more of computing devices710,720, and/or730are interconnected with fabric740using Small Computer Systems Interface (“SCSI”) protocol running over a Fibre Channel (“FC”) physical layer. In other embodiments, the connections between computing devices710,720, and730, comprise other protocols, such as Infiniband, Ethernet, or Internet SCSI (“iSCSI”). In certain embodiments, switches750are configured to route traffic from the computing devices710,720, and/or730, directly to the storage controller760.

In the illustrated embodiment ofFIG. 7, storage controller760comprises a data controller762, memory763, microcode822, instructions824, processor764, and data caches766,767, and768, wherein these components communicate through a data bus765. In certain embodiments, memory763comprises a magnetic information storage medium, an optical information storage medium, an electronic information storage medium, and the like. By “electronic storage medium,” Applicants mean, for example, a device such as a PROM, EPROM, EEPROM, Flash PROM, compactflash, smartmedia, and the like.

In certain embodiments, the storage controller760is configured to read data signals from and write data signals to a serial data bus on one or more of the computing devices710,720, and/or730. Alternatively, in other embodiments the storage controller760is configured to read data signals from and write data signals to one or more of the computing devices710,720, and/or730, through the data bus765and the fabric740.

In certain embodiments, storage controller760converts a serial data stream into convolution encoded images. Those images are transferred to RSLM310(FIGS. 3,4,6).

FIG. 1illustrates holographic data storage medium100comprising geometric center-of-disk105. A plurality of interference patterns can be encoded within holographic data storage medium between the inner radius RI110and the outer radius RO120. RAID-Mirror boundary radius RRM130comprises the half-capacity radius of holographic data storage medium100, wherein that RRM is calculated using Equation (1).
RRM=[(RO2−RI2)/2]1/2(1)

Applicants' method to store information encodes a first copy of a hologram between the RRMand the ROof a first holographic data storage medium. Outer storage portion150of holographic data storage medium100is defined by RAID-Mirror boundary radius RRM130and outer radius RO120. For purposes of this Application, a hologram encoded within portion150comprises a “RAID Hologram.”

Applicants' method also encodes a second copy of the hologram between the RIand the RRMof a second holographic data storage medium. Inner storage portion140of holographic data storage medium100is defined by RAID-Mirror boundary radius RRM130and inner radius RI110. For purposes of this Application, a hologram encoded within portion140comprises a “Mirror Hologram.”

In certain embodiments, Applicants' holographic drive400(FIGS. 4,6) and holographic drive900(FIGS. 9,10,11) utilize a constant-linear-velocity (“CLV”) wherein the angular velocity of the holographic data storage medium is inversely proportional to the radius. As a result, the angular velocity of the holographic data storage medium is lower during read operations because Applicants' method encodes the RAID Holograms in the outer storage portion150(FIG. 1) of the holographic data storage medium, where the power consumption by drive servo440is lower due to this lower angular velocity.

FIG. 8illustrates Applicants' Holographic RAID 50 storage protocol. Using this protocol, a file, such as for example file810, is written to holographic data storage media as two data holograms810A and810B, and wherein the parity for the information comprising holograms810A and810B is encoded in parity hologram810C.

Referring now toFIG. 8, RAID Holograms810A,820A,830A, and840A, are encoded in the outer storage portion of holographic data storage medium802. Mirror Holograms810A,820A,830A, and840A, are encoded in the inner storage portion of holographic data storage medium804.

RAID Holograms810B,820B,830B, and840B, are encoded in the outer storage portion of holographic data storage medium804. Mirror Holograms810B,820B,830B, and840B, are encoded in the inner storage portion of holographic data storage medium806.

RAID Holograms810C,820C,830C, and840C, are encoded in the outer storage portion of holographic data storage medium806. Mirror Holograms810C,820C,830C, and840C, are encoded in the inner storage portion of holographic data storage medium802.

Only two of holographic data storage media802,804, and806, need to be mounted in holographic data storage system300(FIGS. 3,5), or in Applicants' holographic data storage drive400(FIGS. 4,6), or in Applicants' holographic data storage drive900(FIGS. 9,10,11), for a read of all four files encoded therein. For example RAID Hologram810A and Mirror Hologram810C, can be read from medium802. The remaining component hologram810B can be read from medium804as a RAID Hologram, or from medium806as a Mirror Hologram.

Moreover, if any two of holographic data storage media802,804, and806, are totally destroyed or missing, each of the four original files can still be retrieved. For example, if media804and806are destroyed or missing, file810can be reconstructed by reading RAID Hologram810A and Mirror Hologram810C from medium802. The remaining element, namely hologram820B, can be restored using an Exclusive OR (“XOR”) parity calculation between the information in data hologram810A and parity hologram810C.

Referring now toFIG. 9, in certain embodiments Applicants' holographic drive900comprises member920attached to solenoid/motor910, wherein drive controller410can cause solenoid/motor910to extend member920outwardly. Laser light source205, beam splitter210, and optical sensor array520(FIGS. 4,5,6,9,10,11), are disposed on member920. Member920in combination with Laser light source205, beam splitter210, and optical sensor array520, comprise holographic read head950.

In the illustrated embodiment ofFIG. 10, holographic read head950has been moved laterally by extension member930. Further in the illustrated embodiment ofFIG. 10, reference beam320is shown interfering with an interference pattern comprising RAID Hologram160(FIGS. 2,10) to form reconstructed data beam550(FIGS. 5,6,10) which comprises the image encoded in RAID Hologram160. Reconstructed data beam550is projected onto input screen520(FIGS. 4,5,6,9,10,11).

In the illustrated embodiment ofFIG. 11, holographic read head950has been moved further laterally by extension members930and940. Further in the illustrated embodiment ofFIG. 11, reference beam320is shown interfering with encoded Mirror Hologram170(FIG. 2) to form reconstructed data beam550(FIGS. 5,10) which comprises the image encoded in Mirror Hologram170. Reconstructed data beam550is projected onto input screen520(FIGS. 4,5,6,9,10,11).

Referring now toFIG. 12, in certain embodiments, Applicants' method positions Applicants' holographic read head950(FIGS. 9,10,11) above Read-Loiter radius RL1210. Radius RLcomprises the mid-capacity point between outer radius RO120and RAID-Mirror boundary radius RRM130. Applicants have found that radius RL1210comprises the optimal position for Applicants' holographic read head for random reads of RAID Holograms encoded in the outer storage portion150of holographic data storage medium100. If Applicants' holographic read head is positioned at radius RL, then the directional-probability of a seek to a random file is 50% inwards from, and 50% outwards from, that loitering position.

For a holographic data storage medium comprising no unused storage capacity, i.e. a “filled” storage medium, the Read-Loiter radius RL1210is defined by Equation (2).
RL=[(RO2−RRM2)/2]1/2(2)
If the holographic data storage medium is not filled, radius RRM is assigned a value corresponding to the innermost radius at which a RAID Hologram is encoded. Thus, RL1210will vary as holographic data storage medium100has RAID Holograms encoded therein.

Applicants' invention comprises a method to store information in multiple holographic data storage media.FIG. 13summarizes one embodiment of Applicants' method. Referring toFIG. 13, in step1310the method supplies a plurality of holographic data storage media and a holographic data storage system, such as and without limitation holographic data storage system300(FIGS. 3,5), data storage and retrieval system700(FIG. 7), holographic drive400(FIGS. 4,6), and/or holographic drive900(FIGS. 9,10,11).

In step1320, the method defines an inner storage portion and an outer storage portion for each of the plurality of holographic data storage media of step1310. In certain embodiments, the method in step1320calculates a RAID-Mirror radius RRMfor each of the holographic data storage media using equation (1) to define the inner storage portion and the outer storage portion. In certain embodiments, step1320is performed by a storage controller, such as storage controller760(FIG. 7). In certain embodiments, step1320is performed by a drive controller, such as drive controller410(FIGS. 4,6,9,10,11).

In step1330, the method provides information. In certain embodiments, step1330is performed by one or more host computers, such as and without limitation one or more of host computers710(FIG. 7),720(FIG. 7), and/or730(FIG. 7). Step1330further comprises receiving the information. In certain embodiments, the information is received by a storage controller, such as storage controller760. In certain embodiments, the information is received by a drive controller, such as drive controller410.

In step1340, the method displays an image of the information on an RSLM, such as and without limitation RSLM310(FIGS. 3,4,6). In certain embodiments, step1340is performed by a storage controller, such as storage controller760(FIG. 7). In certain embodiments, step1340is performed by a drive controller, such as drive controller410(FIGS. 4,6,9,10,1).

In step1350, the method forms a hologram comprising the image of step1340. In certain embodiments, step1350is performed by a storage controller, such as storage controller760(FIG. 7). In certain embodiments, step1350is performed by a drive controller, such as drive controller410(FIGS. 4,6,9,10,11).

In step1360, the method encodes the hologram of step1340into the outer storage portion of a first holographic data storage medium. In certain embodiments, step1360is performed by a storage controller, such as storage controller760(FIG. 7). In certain embodiments, step1360is performed by a drive controller, such as drive controller410(FIGS. 4,6,9,10,11).

In step1370, the method again forms a hologram comprising the image of step1340. In certain embodiments, step1370is performed by a storage controller, such as storage controller760(FIG. 7). In certain embodiments, step1370is performed by a drive controller, such as drive controller410(FIGS. 4,6,9,10,11).

In step1380, the method encodes the hologram of step1370into the inner storage portion of a second holographic data storage medium. In certain embodiments, step1380is performed by a storage controller, such as storage controller760(FIG. 7). In certain embodiments, step1380is performed by a drive controller, such as drive controller410(FIGS. 4,6,9,10,11).

FIGS. 14 and 15summarize the steps of a second embodiment of Applicants' method to store information in multiple holographic data storage media using a holographic RAID storage protocol. Referring toFIG. 14, in step1410the method supplies a plurality of holographic data storage media and a holographic data storage system, such as and without limitation holographic data storage system300(FIGS. 3,5), data storage and retrieval system700(FIG. 7), holographic drive400(FIGS. 4,6), and/or holographic drive900(FIGS. 9,10,11).

In step1420, the method defines an inner storage portion and an outer storage portion for each of the plurality of holographic data storage media of step1310. In certain embodiments, the method calculates a RAID-Mirror radius RRMfor each of the holographic data storage media using equation (1) to define the inner storage portion and the outer storage portion. In certain embodiments, step1420is performed by a storage controller, such as storage controller760(FIG. 7). In certain embodiments, step1420is performed by a drive controller, such as drive controller410(FIGS. 4,6,9,10,11).

In step1430, the method provides information. In certain embodiments, step1430is performed by one or more host computers, such as and without limitation one or more of host computers710(FIG. 7),720(FIG. 7), and/or730(FIG. 7). Step1430further comprises receiving the information. In certain embodiments, the information is received by a storage controller, such as storage controller760. In certain embodiments, the information is received by a drive controller, such as drive controller410.

In step1440, the method displays on an RSLM, such as and without limitation RSLM310(FIGS. 3,4,6), a first image comprising a first portion of the information of step1430. In certain embodiments, step1440is performed by a storage controller, such as storage controller760(FIG. 7). In certain embodiments, step1440is performed by a drive controller, such as drive controller410(FIGS. 4,6,9,10,11).

In step1450, the method forms a first hologram comprising the first image of step1440. In certain embodiments, step1450is performed by a storage controller, such as storage controller760(FIG. 7). In certain embodiments, step1450is performed by a drive controller, such as drive controller410(FIGS. 4,6,9,10,11).

In step1460, the method encodes the first hologram of step1440into the outer storage portion of a first holographic data storage medium. In certain embodiments, step1460is performed by a storage controller, such as storage controller760(FIG. 7). In certain embodiments, step1460is performed by a drive controller, such as drive controller410(FIGS. 4,6,9,10,11).

In step1470, the method encodes the first hologram of step1440into the inner storage portion of a second holographic data storage medium. In certain embodiments, step1470is performed by a storage controller, such as storage controller760(FIG. 7). In certain embodiments, step1470is performed by a drive controller, such as drive controller410(FIGS. 4,6,9,10,11). Applicants' method transitions from step1470to step1510(FIG. 15).

Referring now toFIG. 15, in step1510, the method displays on an RSLM, such as and without limitation RSLM310(FIGS. 3,4,6), a second image comprising a second portion of the information of step1430. In certain embodiments, step1510is performed by a storage controller, such as storage controller760(FIG. 7). In certain embodiments, step1510is performed by a drive controller, such as drive controller410(FIGS. 4,6,9,10,11).

In step1520, the method forms a second hologram comprising the second image of step1510. In certain embodiments, step1520is performed by a storage controller, such as storage controller760(FIG. 7). In certain embodiments, step1520is performed by a drive controller, such as drive controller410(FIGS. 4,6,9,10,11).

In step1530, the method encodes the second hologram of step1520into the outer storage portion of the second holographic data storage medium. In certain embodiments, step1530is performed by a storage controller, such as storage controller760(FIG. 7). In certain embodiments, step1530is performed by a drive controller, such as drive controller410(FIGS. 4,6,9,10,11).

In step1540, the method encodes the second hologram of step1520into the inner storage portion of a third holographic data storage medium. In certain embodiments, step1540is performed by a storage controller, such as storage controller760(FIG. 7). In certain embodiments, step1540is performed by a drive controller, such as drive controller410(FIGS. 4,6,9,10,11).

In step1550, the method displays on an RSLM, such as and without limitation RSLM310(FIGS. 3,4,6), a third image comprising a third portion of the information of step1430. In certain embodiments, step1550is performed by a storage controller, such as storage controller760(FIG. 7). In certain embodiments, step1550is performed by a drive controller, such as drive controller410(FIGS. 4,6,9,10,11).

In step1560, the method forms a third hologram comprising the third image of step1550. In certain embodiments, step1560is performed by a storage controller, such as storage controller760(FIG. 7). In certain embodiments, step1560is performed by a drive controller, such as drive controller410(FIGS. 4,6,9,10,11).

In step1570, the method encodes the third hologram of step1560into the outer storage portion of the third holographic data storage medium. In certain embodiments, step1570is performed by a storage controller, such as storage controller760(FIG. 7). In certain embodiments, step1570is performed by a drive controller, such as drive controller410(FIGS. 4,6,9,10,11).

In step1580, the method encodes the third hologram of step1560into the inner storage portion of the first holographic data storage medium. In certain embodiments, step1580is performed by a storage controller, such as storage controller760(FIG. 7). In certain embodiments, step1580is performed by a drive controller, such as drive controller410(FIGS. 4,6,9,10,11).

In certain embodiments, Applicants' invention includes instructions, such as instructions824(FIG. 7), encoded in memory763(FIG. 7), and/or memory instructions435(FIGS. 4,6,9,10,11) encoded in memory430, where those instructions are executed by a processor, such as processor764(FIG. 7) and/or processor420(FIGS. 4,6,9,10,11), to perform one or more of steps1320,1330,1340,1350,1360,1370, and/or1380, recited inFIG. 13, and/or one or more to steps1420,1430,1440,1450,1460, and/or1470, recited inFIG. 14, and/or one or more of steps1510,1520,1530,1540,1550,1560,1570, and/or1580, recited inFIG. 15.

In certain embodiments, Applicants' invention includes instructions residing in any other computer program product, where those instructions are executed by a computer external to, or internal to holographic data storage system300(FIGS. 3,5), holographic drive400(FIGS. 4,6), data storage and retrieval system700(FIG. 7), and/or holographic drive900(FIGS. 9,10,11), to perform one or more of steps1320,1330,1340,1350,1360,1370, and/or1380, recited inFIG. 13, and/or one or more to steps1420,1430,1440,1450,1460, and/or1470, recited inFIG. 14, and/or one or more of steps1510,1520,1530,1540,1550,1560,1570, and/or1580, recited inFIG. 15. In either case, the instructions may be encoded in an information storage medium comprising, for example, a magnetic information storage medium, an optical information storage medium, an electronic information storage medium, and the like. By “electronic storage medium,” Applicants mean, for example, a device such as a PROM, EPROM, EEPROM, Flash PROM, compactflash, smartmedia, and the like.