Fred C Th...
Technology & Engineering
AO-DVD (Articulated Optical - Digital Versatile Disk) A 20X to 100X Performance Enhancement Path for DVD-ROM Fred Thomas, Chief Technologist Advanced Research & Development, R&D Iomega Corporation 1821 West Iomega Way Roy, Utah 84067 Phone: 801-332-4662, Fax: 801-332-5434 Email: email@example.com Introduction: AO-DVD (Articulated Optical - Digital Versatile Disk) technology is a newly conceived low-cost data distribution and content execution media for integration into mainstream CD and DVD optical data storage drives. It was conceived recently at Iomega Corporation, the removable data storage company that has brought the world such data storage innovations as the Zip Drive, Jaz Drive, PocketZip Drive and Peerless Drive. Iomega has also made a name for itself with several performance enhanced CDRW optical data storage products. AO-DVD can be seen as potentially the next generation of CD-ROM or DVD-ROM for distribution of content. The reason for this statement is that AO-DVD has the potential to support areal densities, which are 20 to 100 times greater than those presently shipping in CD or DVD-ROM formats. AO-DVD technology is also amenable to being designed into the drive architecture of a CD or DVD drive at very low additional cost. This means that it is a high-value augmentation technology for these present mainstream technologies rather than a competing new standard. New AO-DVD-enabled CDRW or DVD-RW format drives will still be able to record data at present CD/DVD densities, but will have access to low-cost AO-DVD/AO-CD content which, for example, is 40X larger than that of these present optical ROM medias. Inherent in the data architecture of AO-DVD or AO-CD is an increase in the transfer rate of data from the media to the drive. This transfer rate increase is due to the massively multi-level encoding of data. With transfer rates an order of magnitude faster than presently available from optical ROM media, a whole array of new applications and markets for both CD and DVD drives with AO-DVD modes is opened. A principal one is the ability to distribute and play high- definition video content at low cost. Others include running interactive software and games directly from one’s optical drive, be it in a computer or Set-Top Box. The implications are exciting. The ability to create low-cost media with the same type cost structure as current CD-ROM and DVD media is believed to be of paramount necessity for the success of AO-DVD technology. In fact, on a per MB, or capacity, basis it can be shown that AO-DVD’s costs to produce are significantly less than CD or DVD-ROM media. Some possible new applications and products that could be enabled by the commercial development of AO-DVD technology would include: • Media the size of a quarter (DataPlay size disk, 32 mm) holding a full-length HDTV movie (20GB). o A micro personal video player the size of a packet of cigarettes to play video content. • A standard size 120 mm AO-DVD disk holding a film studio’s full menu of summer releases (e.g. 10-15 movies) with a core DRM technology built in. This would enable the free distribution of this content to consumers much like the AOL mass marketing of their ISP services through mass CD-ROM mailings. A video rental store on a disk with sufficient compression. • A film artist’s (actor or director’s) complete works supplied and direct marketed to consumers upon the purchase of a single title. A complete TV series on a disk. In this way impulse purchase of films of the same genre are consumer enabled. • AO-DVD can be viewed as a technology to be leveraged in the developing Set-Top Box market share wars. Entire libraries of DRM-accessible films on just a few AO-DVD disks can be supplied to the consumer for production costs of pennies per movie. • A standard size 120 mm AO-DVD disk (>180 GB, single sided/single layer) would be one of the enabling technologies, which would allow for cost-effective distribution of full-length fully digital movies to theaters. • Enhanced CDRW drives with the capability to play full-length DVD movies on AO-DVD media (>20 GB) with lower drive production costs than DVD. This value offering represents the capability to play movies but not record them. AO-DVD opens a whole new vista in content distribution, much like CD-ROM created a whole new model for content distribution in the 1990s and DVD-ROM has over the past couple of years. DVD/CD Compatible Media and Drive Architecture: At a very high level, AO-DVD media can be characterized as a planar disco-ball with microscopic mirror facets. Figure 1 illustrates the general topography of AO-DVD media. Each “optical data element” (ODE) is comprised of an array of miniature reflective mirrors (4), each with a fixed angular tilt orientation relative to the media’s planar orientation. The ODE is sized to be on the order of the laser stylus spot size. The reflective orientation of each individual micro-mirror is such that when reflecting light from a focused interrogating data read beam, the reflection is captured within the numerical aperture of the drive’s objective lens. The captured beam is then optically relayed to one of an array of solid-state position sensitive photo detectors equal to the number of micro-mirrors in the ODE. Figure 1 - AO-DVD Media Topography Data is encoded on AO-DVD in the reflective orientation of each micro-mirror and its relative down-track run-length within the square ODE. Each micro-mirror has three data encode states: a tilt orientation (theta), a rotational orientation (alpha) and a run-length (RL). The combination of any two orientations for angles “alpha” and “theta” and the run-length for the micro-mirrors can be used to represent a specific digital state. The number of combinations, which are possible to resolve with the drive embedded solid-state position-sensitive photo detectors, determines how many bits of data can be encoded with a single ODE array. Equation 1 calculates the number of bits that can be encoded in a single ODE. BitsODE = Log2 [(#RL)DTR • (#α • #θ)#MM] Equation 1 Where, #RL = numbers of micro-mirror run-length states DTR = down-track rows of micro-mirrors within an ODE #α = number of micro-mirror rotational angular states #θ = number of micro-mirror tilt angular states #MM = number of micro-mirrors in an ODE In order to make direct AO comparisons to capacity points on CD and DVD media, it is helpful to calculate the equivalent size of a user data bit for these standards. That calculation reveals that for both CD and DVD, the equivalent size of a user bit on the media is the width of a data track and about 1/3 that dimension in length. This compressed aspect ratio is due largely to the run-length limited encoding implemented in these standards. If, for example, the run-length term in Equation 1 is set to #RL=3 and DTR=2 as with the AO-DVD embodiment described so far, we see this term equals 9 or slightly greater than 3 bits (23). Hence, Equation 1 can be rewritten, dropping this term, for direct capacity increase factor calculation. Capacity Factor = Log2 [(#α • #θ)#MM] Equation 2 For example, for a drive with an NA=0.7, the approximate maximum micro-mirror tilt angle (θ) is 22 degrees. There are 4 micro-mirrors in each ODE; hence, 90 degrees of rotational orientation (α) is allocated to each. The product of alpha and theta is 1024 in Equation 2 if we assume we are able to fabricate micro-mirror angular states about 1.5 degrees apart. Finally, using MM#=4 as described, the calculated “Capacity Factor” is 40X. For this example, remarkably, there are almost 100 trillion (1x1012) more levels or possible combinations encodable in an AO-DVD ODE than is possible in the equivalent media area on a DVD. It should be noted that this “Capacity Factor” calculation assumes that data overhead in the format for error correction, modulation and sector information is equivalent to the standard being compared (DVD or CD). Table 1 shows “Capacity Factor” sensitivity as a function of fabricatable micro-mirror state separation. Table 1 – Angular State Separation Sensitivity Angle State Separation 10° 5° 3° 1.5° 0.5° Capacity Factor 17.3X 25.3X 31.2X 39.2X 51.9X ODE Multi- Levels 1.6x105 4.1x107 2.4x109 6.2x1011 4.1x1015 From Table 1 we should note that if the separation in angular states were to increase from 1.5 degrees to 10 degrees (6.7X), the capacity would only decrease by 2.3X. This benefit is due to the exponential nature of Equations 1 and 2. Figure 2 illustrates the micro-mirror reflective orientation layout of segments of 5 tracks of AO-DVD data in relation to the AO-DVD drive’s solid-state position detector seen on the right of the Figure. In this embodiment 4 quad detectors are used to sense the reflected position of the 4 beams emanating from an individual ODE. The superimposed spots on the detector in Figure 2 illustrate one random 40-bit state. Using a detector architecture like or similar to this one, the AO-DVD drive when in DVD mode would sum A, B, C and D quad detectors to produce traditional DVD signal channels for track-following and focus control. Figure 2 - AO-DVD ODE Micro-Mirror Orientation Structure In Figure 2, AO-DVD media ODEs are illustrated with solid boundary lines. The letters designating each micro-mirror within an ODE correspond to the sub-quadrant (A, B, C, or D) on the detector their reflections are directed at. Looking at Figure 2, we see 5 different laser stylus data-read spot locations superimposed on the media. The top spot location illustrates perfect spot alignment on the center data track and totally within an ODE’s boundary. The next two lower spots in Figure 2 illustrate off-track positional locations that will generate the maximum off-track signal. Note that the orientation of adjacent data-track ODE micro-mirrors creates a continuous push-pull off-track signal. The bottom two spot locations superimposed on the AO- DVD media in Figure 2 illustrate the laser stylus location at positions of equal spot exposure of two adjacent down-track ODEs. The orientation of the micro-mirrors for these exposures creates a maximal difference signal between the summed detector elements A+B and C+D. In this manner a high-resolution data clock signal can be generated. This signal is used for the accurate run-length detection of micro- mirror elements within an ODE discussed previously. Other unique features of the AO-DVD media format include angular calibration ODEs with known orientation micro-mirror facets included in data sector headers. In this manner the AO-DVD drive is able to compensate for fixed and rotation media tilt in the calculation of ODE data states within the sector. Figure 3 - Generalized AO-DVD / (DVD or CD) Hybrid Drive Optical Path Figure 3 shows one embodiment of the proposed optical path for an AO-DVD hybrid drive. Unique components included the corrector plate and hologram to be used to help control such AO-DVD design parameters such as spot size, spot circularization/geometry and spot cross-talk minimization at the detector. A first order estimate of the transfer rate potential for AO- DVD assumes that present 40X DVDs are detector noise limited. Next we shall assume the following: First, the equivalent laser stylus beam power to that of the 40X DVD drive is used in the AO-DVD drive. Next, there are additional reflective path losses due to reflective diffractive effects from an ODE and losses through the additional optical path components, which are on the order of 50% in the AO-DVD drive. Finally, the reflected beam is split into 4 parallel data detection paths. This factoring produces a base-line transfer rate of 5X ((0.5)/4 * 40X). This transfer rate now must be multiplied by the multi-level transfer rate enhancement produced by the “Capacity Factor.” For the example discussed previously, a “Capacity Factor” of 40X is applied. Hence, an AO-DVD transfer rate of 200X DVD, or 277 MB/sec, can be estimated. This is multiple times faster than present state of the art drive interfaces such as Firewire/IEEE-1394. Digital Rights Management (DRM): The unique topography of AO-ROM media, which is not drive laser stylus producible, lends it’s self to robust DRM methodologies. Iomega has developed a cadre of removable media authentication and unique media serial number pipe tamper protection technologies, which have issued or pending patents in place. A robust DRM core is central to the AO-DVD media format and drive design. AO-DVD Media E-Beam Fabrication & Results to Date: AO-DVD media is to be mastered using e-beam gray-scale lithographic methods. Several approaches are being tested. Media is to be produced using essentially the same high- pressure plastic injection molding methods used for DVD- ROM production. Hence, the low cost media production model. Initial lithographic results for 3-micron micro-mirrors facets are illustrated in Figures 4 and 5. Although these initial facets are almost an order of magnitude larger than the target 370 nm x 370 nm facet sizes desired for AO-DVD media, the sectional profile shows facets with exceptional resolution fidelity. Figure 4 - Pyramid Shaped Micro-Mirrors in Resist Figure 5 - Micro-Mirror Facet Sectional Profile A tolerance analysis for direct e-beam writing of gray-scale resists which includes such factors as: e-beam resist contrast, e-beam resist resolution, e-beam stylus size, existing e-beam DVD mastering equipment work piece rotational run-out, scattering effects of the e-beam stylus in work piece required resist depth, and production plastic replication fidelity capabilities was done. This calculation points to being able to produce AO-DVD micro-mirror facets with sub 30 nm resolutions. For the 370 nm square micro- mirror facets AO-DVD requires, this equates to an encouraging 10+ e-beam passes during the gray-scale e- beam mastering process. Conclusions / Path Ahead: Work is presently proceeding on to-scale gray-scale e-beam lithographic fabrication of AO-DVD media. Other areas of focus include analytical and empirical examination of the diffractive component of ODE reflections and associated potential noise source issues. It is understood that the discussion presented here rests principally on geometrical optical arguments. This technology can hence more generally be described as the creation of sub-wavelength mechanical structures whose property, upon reflection of a focused laser spot, is the creation of multiple beam paths each of whose irradiance patterns centroid position in the lens aperture changes predictably and measurably for the storage multi-level encoded information. As these results develop, drive optical path, detector layout and electronics functionality requirements of the AO-DVD hybrid drive are being continually refined.