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: thomasf@iomega.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.