Multi-dimensional optical disk

Abstract: The present invention provides an optical disk with pits and/or bumps which each contain a plurality of facets. Each facet of each pit and/or bump is intended for separate read back as an individual 'side' of the optical disk (much as vinyl records had two 'sides' for separate playback). The separate 'sides' of the optical disk formed by separate facets of each pit and/or bump can be read back either simultaneously or serially, either by a corresponding plurality of laser beams, or by a common laser beam which is positioned to a first orientation with respect to a rotating track to focus on a first set of facets of each pit and/or bump, and then repositioned to focus on a second set of facets of the same set of pits and/or bumps and thus to read a second 'side' of the optical disk. The technique may be extended to provide a single optical disk and even a single track of the optical disk with even more than two 'sides' by using three-, four- or five-sided pyramidal-shaped pits and/or bumps.

Description: Field Of The Invention This invention relates generally to optical disks. More particularly, it relates to a technique and method for achieving higher density data storage in an optical disk such as a compact disk (CD) or digital video disk (DVD). Background Of Related Art Conventional optical disk players (e.g., a CD ROM player, music CD player, DVD player, etc.) contain data bits within pits and/or bumps formed along tracks in the surface of one side of an optical disk (e.g., a compact disk (CD) or digital video disk (DVD). In these conventional systems, the traveling distance of a laser beam is changed in accordance with a the presence or absence of a pit in certain technologies, and/or the presence of a bump using other technologies. Fig. 7 shows a cross sectional view of a conventional optical disk 740 containing a series of pits 702, 704, 706, 708 along a track path. In particular, in Fig. 7, a plurality of pits 702-708 are presented one-by-one to a focal point of a laser beam. The laser 700 outputs a particular laser beam, e.g., 780 nm laser beam, and senses the distance to a reflection point of the laser beam upon its return back to the laser 700. If the pit 702-708 is a deep pit, e.g., as shown in pits 702, 704 and 708, the data point is determined to be of a particular logic level (e.g., a logic '0'). Conversely, if the pit is either non-existent at a data point, or of another depth, as shown in pit 706 , the data point is determined to be of the opposite logic level (e.g., a logic '1'). Fig. 8 shows the bit density in a conventional optical disk, wherein each pit represents a single bit. More recently, advances have been made in an attempt to increase the density of an optical disk. For instance, more advanced techniques use a variably adjustable depth of a pit or height of a bump to represent a plurality of bits in a digitally encoded signal. As examples, U.S. Pat. No. 5,724,339 to Ogawa discloses the use of pits having a cross-sectional shape viewed from a direction perpendicular to the laser, selected from at least two different shapes. The different cross-sectional shapes are determined based on an amount of reflected light. U.S. Pat. No. 5,359,591 to Nomoto similarly discloses the use of pits having different cross-sectional shapes, as does U.S. Pat. No. 5,572,508 to Satoh et al. U.S. Pat. No. 5,559,787 uses polarization of reflected light depending upon the depth of the pit to increase data bit density in each pit. U.S. Pat. No. 5,471,455 to Jabr provides a track with a continuous pit having variable depth surface steps, and U.S. Pat. No. 5,577,016 to Inagaki et al. discloses changing the wavelength of a laser depending upon the depth of measured pits. Unfortunately, the use of different cross-sectional pit shapes with respect to the laser beam, and/or the use of variable-depth pits, requires a complicated laser system which is not only capable of determining whether or not a reflection has been detected from a particular data point, but also which must distinguish between slight differences in reflective qualities. Other patents, such as U.S. Pat. No. 5,995,481 to Mecca control the depth of pits and/or bumps to be equal to one-half the wavelength of the laser light. General improvements in the quality of reflective properties of pits were disclosed in U.S. Pat. No. 5,696,758 to Yanagimachi et al. U.S. Pat. No. 5,357,499 to Nomoto discloses angling of the bottom of single-bit pits toward the laser. While these patents disclose improvements which might improve the reliability of reading each pit as a bit, they do not provide a significant increase in the data density of an optical disk. There is a need for a technique and apparatus for increasing the density of an optical disk without requiring complicated reflection level sensitivity in a laser system otherwise required to measure multiple levels of reflection of a laser beam. DE-A-197 09 522 discloses a storage medium which has information stored as pits in tracks or rows on a substrate, a carrier or other medium, e.g. CD, CD-ROM, optical image plate. An individual data value from a total of more than two different data values can be written into or readout of each information pit. The pits have different states or structures corresponding to the different data values. The different states are differentiated by different associated surface areas by modification of the physical properties. The total number of different states corresponding to the total number of different data values. US-A-5 923 634 discloses an optical disk having angled bumps, the angle of any one bump being in one of 16 possible positions, thus resulting in the representation of 8 bits (or 1 byte) of data by each bump. Summary of the Invention A system, and optical disk, apparatus and methods according to the invention are as set out in the independent claims. Preferred forms are set out in the dependent claims. Brief Description Of The Drawings Features and advantages of the present invention will become apparent to those skilled in the art from the following description with reference to the drawings, in which: Fig. 1A shows a cross-sectional view of a portion of a track of an optical disk including a plurality of multi-faceted pits, in accordance with the principles of the present invention. Fig. 1B shows a bottom view of the optical disk shown in Fig. 1A (presuming that the pits open toward the bottom of the optical disk). Figs. 2A to 2D depict the positioning of two separate laser beams to separately read the individual facets of each pit, in accordance with the principles of the present invention. In particular, Fig. 2A shows the separate read back of two facets of a multi-faceted pit including both opposing 45° angled facets, Fig. 2B shows the separate read back of two facets of a multi-faceted pit including only a first 45° angled facet, Fig. 2C shows the separate read back of two facets of a multi-faceted pit including only a second 45° angled facet, and Fig. 2D shows the separate read back of two facets of a multi-faceted pit including neither opposing 45° angled facet. Fig. 3 shows that for the same area of contact of the laser beam on the optical disk, the use of multi-faceted pits and/or bumps can result in marked improvements in data density, e.g., a 141% improvement as compared with certain prior art techniques. Fig. 4 depicts a track comprising a plurality of multi-faceted pits, each multi-faceted pit having a four-sided pyramidal shape, in accordance with the principles of the present invention. Fig. 5 shows an example embodiment simultaneously positioning four separate lasers having four laser beams adapted to read a reflection or non-reflection from each of four corresponding four facets of a four-sided pyramidal pit, in accordance with the principles of the present invention. Fig. 6 shows the positioning of two lasers (or the re-positioning of a single laser) to detect the multi-bit information from each multi-faceted bump of a track formed on the surface of an optical disk, in accordance with the principles of the present invention. Fig. 7 shows a cross sectional view of a conventional optical disk containing a series of pits along a track path. Fig. 8 shows the bit density in a conventional optical disk, wherein each pit represents a single bit. Detailed Description Of Illustrative Embodiments The present invention provides an optical disk with tracks which are formed by multi-faceted pits (and/or bumps) which each contain a plurality of facets. Each pit (or bump) is multifaceted, i.e., they each have at least two sides, e.g., relatively flat and reflective sides. Each side of the pit (or bump), depending upon its shape, represents either a HIGH bit level, or a LOW bit level. Each facet of each pit and/or bump is intended for separate playback as individual data streams, either substantially simultaneously or serially to provide two bits of data from each pit or bump. A plurality of laser beams are directed at respective sides of the pit (or bump), one toward a corresponding side of the pit (or bump) on the optical disk to determine a bit condition of each side. The separate facets of the pits or bumps can be read back using the corresponding plurality of laser beams appropriately placed to each measure a reflection or non-reflection of a laser beam from the same facet position of each pit or bump. Alternatively, a common laser beam can be moveable between positions. A first position places the laser beam in position (e.g., a 0° orientation with respect to the rotation of the track) to measure reflection from a first facet position of each pit or bump as it rotates through a focal point of the laser, and a second position (e.g., a 180° orientation with respect to the rotation of the track) to place the laser beam in an opposite position to measure reflection from a second, opposite facet position of each pit or bump. Thus, a first 'side' of an optical disk can be played by positioning the laser in a first orientation, and then a second 'side' of the optical disk can be played without removing the optical disk by repositioning the laser in a second orientation. The technique and apparatus in accordance with the principles of the present invention may be extended to provide a single optical disk and even a single track of the optical disk with even more than two 'sides' by using three-, four- or five-sided pyramidal-shaped pits and/or bumps. Fig. 1A shows a cross-sectional view of a portion of a track of an optical disk including a plurality of multi-faceted pits, in accordance with the principles of the present invention. Fig. 1 B shows a bottom view of the optical disk shown in Fig. 1A (presuming that the pits open toward the bottom of the optical disk). In particular, in Figs. 1A and 1B, an optical disk 140 includes a track comprising a plurality of multi-faceted pits 191-197 . For instance, a first pit 191 is formed by a triangular-shaped pit having two opposing 45° angled facets 102, 104. This pit 191 comprises two bits of data information, e.g., a '00'. A second pit 192 comprising two similarly angled facets 106, 108 also includes two bits of data information, e.g., a '00'. The third pit 193 includes a first 45° angled facet 110 , but is missing an opposing 45° angled facet and instead includes a 90° facet (i.e., is missing the 45° angled facet). Thus, the third pit 193 indicates, e.g., a '01'. The fourth pit 194 is missing the first 45° angled facet, but includes the opposing 45° angled facet 116 , indicating, e.g., a '10'. The fifth pit 195 includes both opposing 45° angled facets 118, 120, indicating, e.g., a '00'. The sixth pit 196 includes only the second 45° angled facet 124 , and thus indicates, e.g., a '01'. The seventh pit 197 shown in Figs. 1A and 1B is missing both opposing 45° angled facets, indicating, e.g., a '11'. Figs. 2A to 2D depict the positioning of two separate laser beams to separately read the individual facets of each multi-faceted pit, in accordance with the principles of the present invention. In particular, Fig. 2A shows the separate read back of two facets 102 , 104 of a multi-faceted pit including both opposing 45° angled facets 102, 104 . The two facets 102, 104 may be simultaneously read by two separate lasers 201, 202 as shown in Fig. 2A. Alternatively, a singular laser beam may be repositioned between the position of the first laser beam 210 and the position of the second laser beam 220 to separately read a stream of data bits (one from each pit) comprised in the first facet 102 of a plurality of multi-faceted pits of a track. Then, at a later time, a second 'side' of the optical disk can be read by reading a stream of data bits (one from each pit) comprised in the second facet 104 of the plurality of multi-faceted pits of a track. Fig. 2B shows the separate read back of two facets 110, 112 of a multi-faceted pit including only a first 45° angled facet 110 , and the absence of a second angled facet indicated by the presence of a 90° lip 112 . Fig. 2C shows the separate read back of two facets 114, 116 of a multi-faceted pit including only a second 45° angled facet 116 , and the absence of a first angled facet indicated by the presence of a 90° lip 114 . Fig. 2D shows the separate read back of two facets 126, 128 of a multi-faceted pit including neither opposing 45° angled facet indicated by the presence of essentially no pit. Note that it is desirable to avoid interference in the reception of a reflected laser beam by the opposing laser because of the approximately 90° relationship between laser beams 210, 220 . One technique is to use lasers of differing wavelengths. Another technique is to laterally rotate the laser beams to avoid direct reflections from impinging on the detector of the opposite laser system. Of course, if a single laser beam is used and repositioned for separate read back of only one set of facets (first or second facets) at a time, interference between separate laser systems will not be a design consideration. Individual bits are encoded two at a time into two-sided triangular-shaped pits or bumps. Thus, two bits are represented within a single pit or on a single bump. In another embodiment, four-sided pyramidal-shaped pits or bumps are used to encode four bits of digital data within each pyramidal-shaped pit or bump. The technique and apparatus can be implemented using three-sided pyramidal-shaped pits or bumps, five-sided pyramidal shaped pits or bumps, etc., allowing a plurality of bits to be represented within each pit or bump. The plurality of bits in each pit or bump are read back by a corresponding number of laser beams. Thus, with a same density of pits or bumps used in conventional optical disks, twice the amount of information can be contained within an optical disk using two-sided triangular-shaped pits and two laser beams, or even four times the amount of information can be achieved using four-sided pyramidal-shaped pits or bumps. In accordance with the principles of the present invention, the multiple sides of each pit or bump may be read by separate laser beams either simultaneously, or in quick sequence allowing greater flexibility in placement of the lasers and corresponding optics. Preferably, the laser beams from the plurality of laser beams are arranged non-orthogonal with respect to the surface of the optical disk In another embodiment, an optical disk may be made to have a plurality of 'side' by changing a direction of a laser beam with respect to the rotation of the optical disk. For instance, a laser beam may be placed in a 0° orientation with respect to the rotation of the track such that a first side of each pit or bump can be read. In this position, the laser beam will be used to read only one side of each pit or bump. Thereafter, to read a second 'side' of the optical disk, the laser beam is moved to an opposite orientation, e.g., a 180° orientation with respect to the rotation of the track such that a second side of each pit or bump can be read. Fig. 3 shows that for the same area of contact of the laser beam on the optical disk, the use of multi-faceted pits and/or bumps can result in marked improvements in data density, e.g., a 141% improvement as compared with certain prior art techniques. In particular, as shown in Fig. 3, because of the 45° angling of the reflective portion of the pit: α=4χ β=χ 2 According, the single laser embodiment (using only one facet of the multi-faceted pit and a single laser beam) improves data density by 141% as follows: 1 2 α β x 100% ≅141% Utilizing the full advantage of the invention by either implementing two laser systems or by implementing a repositionable single laser system, the data density can be improved 282% based on a similarly sized conventional optical disk, shown as follows: α β x 100% = 4χ 2 γ x100% ≅ 282% Fig. 4 depicts a track comprising a plurality of multi-faceted pits 470 , 472, 474, 476, each multi-faceted pit 470-476 having a four-sided pyramidal shape, in accordance with the principles of the present invention. While Fig. 4 depicts a four-sided pyramidal shape, the principles of the present invention relate equally to other shaped polygonal pits or bumps, e.g., to three-sided, five-sided, etc. pyramidal shaped pits or bumps. The presence or formation of a particular facet in any pit represents a particular logic level of a data bit, while the absence of a particular facet in any pit represents the opposite logic level of a data bit. Using a four-sided pyramidal shaped pit, each pit can contain four bits of data (i.e., a half byte, or a nibble). As shown in Fig. 4, the first pit 470 includes all four facets 402, 404, 406, 408, representing corresponding bits (e.g., a logic '0') of four separate 'sides' of the optical disk. Alternatively, the four facets may represent four bits or a symbol in a serial data stream, e.g., '0000'. Similarly, as shown in Fig. 4, the second pit 472 does not include a first facet 414, but does include the remaining three facets 416, 418, 412 . Thus, the second pit 472 might represent the symbol '1000'. Likewise, the third pit 474 might represent the symbol '0001', and the fourth pit 476 the symbol '0100'. Fig. 5 shows an example embodiment simultaneously positioning four separate lasers 501-504 having four laser beams 551-554 adapted to read a reflection or non-reflection from each of four corresponding four facets 404, 408, 402, 406 of a four-sided pyramidal pit, in accordance with the principles of the present invention. While the four lasers 501-504 are shown in simultaneous positioning, the principles of the present invention relate equally to any or all of the four lasers 501-504 being positionable in the shown position, with a retreat position allowing operation of the opposing laser. Alternatively, Fig. 5 can be used to depict the approximate orientation of the various lasers 501-504 with respect to the traveling direction of the track of the optical disk, depicted by the arrow in Fig. 5. If using bump technology, the four laser beams can be arranged to not cross paths. Moreover, it is preferred to angle the facets at 45° with respect to the surface of the optical disk, such that the opposing laser beams will cross orthogonally to one another. To further or alternatively minimize interference between opposing lasers (e.g., between laser #1 and laser #2), lasers of different wavelengths may be implemented. Note that the distance between any laser and its corresponding facet can be the same for each of the multiple facets of a multiple-facet pit, in accordance with the principles of the present invention. If a three-sided, four-sided, five-sided, etc. pyramidal pit or bump structure is used in the optical disk, a third, fourth and/or fifth side, respectively, can be read by corresponding re-positioning of the laser beam relative to the side of each pit or bump which is to be read. Preferably, the shape of each pit or bump will take into account the relationship with the rotation of the track. For instance, when the laser beam is in a 0° or 180° orientation with respect to the rotation of the track, the track will be coming directly at or receding directly from the source of the laser beam, allowing a flat reflective surface to be used as the corresponding side of the-pit or bump. However, when the laser beam is in a 90° or 270° orientation to read, e.g., the third and fourth sides of each pit or bump and thus a third and fourth side of the optical disk, the sides may need to be lengthened depending upon the speed of the rotation. Fig. 6 shows the positioning of two lasers (or the re-positioning of a single laser) to detect the multi-bit information from each multi-faceted bump of a track formed on the surface of an optical disk, in accordance with the principles of the present invention. In particular, in Fig. 6, a first laser 601 is positioned to measure a first facet position of each bump on an optical laser disk 640 , while a second laser 602 is positioned to measure a second facet position of each bump on the laser disk. As shown in Fig. 6, the presence of a 45° angled facet in a particular facet position indicates a particular bit level, e.g., a logic '1', while the absence of the 45° angled facet in the particular facet position indicates the opposite bit level, e.g., a logic '0'. While the invention has been described with reference to the exemplary embodiments thereof, those skilled in the art will be able to make various modifications to the described embodiments of the invention within the scope of the claims.

Claims: An optical disk reading system, comprising: an optical disk (140); a laser having at least two different reading positions; a first reading position of said laser being adapted for presenting a laser beam (210) to a first facet (104) of each of a plurality of multi-faceted pits of a data track formed in said optical disk (140), wherein each pit comprises a multi-faceted structure or form, said first reading position of said laser reading a first stream of data of said optical disk for separate playback; and a second reading position of said laser being adapted for presenting said laser beam (220) to a second facet (102) of each of said plurality of multi-faceted pits of said data track, said second reading position of said laser reading a second stream of data of said optical disk for separate playback. An optical disk (FIG. 6), comprising: a plurality of multi-faceted bumps forming a data track, wherein each pit comprises a multi-faceted structure or form; and a plurality of different facets on each multi-faceted bump, each of said plurality of different facets being encoded with a data bit by an angling of said facet with respect to a surface of said optical disk, each particularly angled facet on all of said plurality of multi-faceted bumps comprising a first stream of data of said optical disk; wherein a second stream of data of said optical disk comprises a second particularly angled facet on all of said plurality of multi-faceted bumps; and wherein said first stream of data and said second stream of data of said optical disk are both on a same physical surface of said optical disk. The optical disk according to claim 2, wherein: said optical disk is a compact disk (CD). The optical disk according to claim 2, wherein: said optical disk is a digital video disk (DVD). A method of reading separate data streams from an optical disk (140), comprising: positioning a laser beam (210) to read a status of a first facet (104) of each of a plurality of pits in a track of said optical disk, wherein each pit comprises a multi-faceted structure or form, said first facet of each of said plurality of pits comprising a first data stream of said optical disk for separate playback; and repositioning said laser beam (220) to read a status of a second facet (102) of each of said plurality of pits, said second facet of each of said plurality of pits being different from said first facet of each of said plurality of pits, said second facet of each of said plurality of pits comprising a second data stream of said optical disk for separate playback. The method of reading separate data streams from an optical disk according to claim 5, wherein: said status read by said laser beam relates to an angle of said first facet.

Inventors: KERMANI BAHRAM GHAFFARZADEH, KERMANI, BAHRAM GHAFFARZADEH
Applicants: LUCENT TECHNOLOGIES INC, LUCENT TECHNOLOGIES INC.
Application year: 2000
Main classification: G11B7
IPC codes: G11B7