Storage medium having a layer of micro-optical lenses each lens generating an evanescent field

A medium suitable for the optical storage and retrieval of information comprising a substrate, an active layer for retention of the data, and an overlying optical layer, or layers for double-sided. The optical layer serves to produce an evanescent field in or adjacent to the active layer in response to an incident beam of radiation. The evanescent field is frustrated or attenuated by the data in the active layer and produces a signal.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention in general relates to the field of optical recording systems 
and media and, in particular, to storage media comprising integral 
near-field optics by which means a greater resolution and storage density 
is attained in the processes of writing to and reading from a recording 
layer. 
2. Description of the Prior Art 
The following technical articles and authors are relevant to the present 
application: 
Newton 
McCutchen 
Kino 
Gaudiana, R. A., et al, High Refractive Index Polymers, U.S. Pat. No. 
5,132,430, Jul. 21, 1992, assigned to Polaroid. 
Guerra, J. M., "Photon tunneling microscopy," in Proceedings from Surface 
Measurement and Characterization Meeting, Hamburg, SPIE Vol. 1009, pp. 
254-262, 1988. 
Guerra, J. M., "Photon tunneling microscope," Paper Summaries, SPSE 42nd 
Annual Conference, Boston, pp. 11-15, 1989. 
Guerra, J. M., "Photon tunneling microscopy," Applied Optics, Vol. 29, No. 
26, pp. 3741-3752, 1990. 
Guerra, J. M., "Super-resolution through Diffraction-born Evanescent 
Waves," Appl. Phys. Lett. 66 (26), p. 3555. 1995. 
Guerra, J. M., Plummer, W. T., Optical proximity imaging method and 
apparatus, U.S. Pat. No. 4,681,451, Jul. 21, 1987. Assigned to Polaroid 
Corp. 
Cronin, D. V., Guerra, J. M., Sullivan, P. F., Mokry, P. A., Clark, P. P., 
Cocco, V. L., Data storage apparatus using optical servo tracks, U.S. Pat. 
No. 4,843,494, Jun. 27, 1989. Assigned to Polaroid Corp. 
Guerra, J. M., Apparatus and Methods Employing Phase Control and Analysis 
of Evanescent Illumination for Imaging and Metrology of Subwavelength 
Lateral Surface Topography, U.S. Pat. No. 5,666,197, Sep. 9, 1997. 
Assigned to Polaroid Corp. 
Guerra, J. M., Dark Field, Photon Tunneling Imaging System and Methods, 
Patent Allowed, June, 1997. 
Guerra, J. M., Dark Field, Photon Tunneling Imaging Probes, Patent Allowed, 
June, 1997. 
Guerra, J. M., Dark Field, Photon Tunneling Imaging System and Methods for 
Measuring Flying Height of Read/Write Heads, Patent Allowed, June, 1997. 
Guerra, J. M., Dark Field, Photon Tunneling Imaging System and Methods for 
Optical Recording and Retrieval, Patent Pending. 
Guerra, J. M., Apparatus and Methods for Providing Phase Controlled 
Evanescent Illumination, Patent Allowed. 
Guerra, J. M., Phase Controlled Evanescent Field Systems and Methods for 
Optical Recording and Retrieval, Patent Allowed, Sept. 1997. 
N. Bloembergen and C. H. Lee, Phys. Rev. Letters 19, 835 (1967). 
Mirabella, F. M. Jr., and N. J. Harrick, Internal Reflection Spectroscopy: 
Review and Supplement, Harrick Scientific Corp., Ossining, N.Y. 1985. 
A. Yariv, P. Yeh, Optical Waves in Crystals, John Wiley & Sons, N. Y., 
1984. Bragg reflection p. 175. Gaussian beams, p. 25. Coupled mode theory, 
p. 177. Coupled mode theory of Bragg reflectors, p. 194. Form 
birefringence, p. 205. Electromagnetic surface waves, p. 209. Guided waves 
and integrated optics, p. 405. Surface plasmons, p. 489. Nonlinear optics, 
p. 504. Phase conjugate optics, p. 549. 
A. Yariv, Optical Electronics, Holt, Rinehart and Winston, New York (1985). 
p. 88, Optical resonators, like their low-frequency, radio frequency, and 
microwave counterparts, are used primarily to build up large field 
intensities with moderate power inputs. A universal measure of this 
property is the quality factor Q of the resonator 
P. Yeh, Introduction to Photorefractive Nonlinear Optics, John Wiley & 
Sons, Inc., New York, 1993. 
A. Otto, "Excitation of nonradiative surface plasma waves by the method of 
frustrated total reflection," Z. Phys. (216), 398 (1968) and (219), 227 
(1969). 
Integrating optics and even micro-optics with a photo sensitive material is 
known in other applications not involving data storage, high spatial 
resolution, or even near-field integration. For example, Polavision.TM. 
film incorporated temporary lenticular lenses during production for the 
purpose of exposing color filter stripes on the emulsion. In the present 
state of the art, micro-optic elements may be added to a CCD imager so as 
to increase light efficiency by directing incident light away from the 
"dead" gate structures and into the photo-active areas. Many light 
detectors for light measurement or security devices use micro-optic arrays 
placed near the detector in order to increase the field of view of the 
detector. 
In near-field optical applications, splitting off the total internal 
reflection (TIR) surface from the aplanatic immersion lens in an imaging 
objective and integrating it with the object to be viewed is taught in 
Guerra, Applied Optics 1990 and SPIE 1988, and in a flexible form 
(transducer) in Guerra, J. M., Flexible Transducers for Photon Tunneling 
Microscopes and Methods for Making and Using Same, U.S. Pat. No. 
5,349,443, Sep. 20, 1994 assigned to Polaroid Corp., Guerra, J. M., 
Stereoscopic Photon Tunneling Microscope, U.S. Pat. No. 5,442,443, Aug. 
15, 1995 assigned to Polaroid Corp, and Guerra, J. M., Method for Making 
Flexible Transducers for Use with Photon Tunneling Microscopes, U.S. Pat. 
No. 5,484,558, Jan. 16, 1996. Assigned to Polaroid Corp. Improvements and 
extensions of that split TIR concept are claimed and will be shown herein. 
While the art describes a variety of optical storage media, there remains a 
need for improvements that offer advantages and capabilities not found in 
presently available instruments, and it is a primary object of this 
invention to provide such improvements. 
It is another object of the invention to provide for a method of reading 
and writing utilizing evanescent field resolution. 
It is another object of the invention to facilitate use of the near field 
to attain super-resolution in all axes for optical data storage reading, 
writing, erasing, where the data is stored as index changes (complex, may 
include absorption), polarization or other phase changes, topographic 
height changes, etc. 
It is another object of the invention to fully utilize the whole-field 
optical capability for the purposes of: multi-tasking, multi-track 
encoding, faster data-transfer rates, faster random access time, more 
robust data through redundancy, elimination of radial actuator mechanisms, 
lower required disc rotation speed, higher track density through reduced 
cross talk in absence of Gaussian, robustness through redundancy, 
multi-channel encoding for higher data density, and multiple program 
simultaneous/interactive play. 
It is another object of the invention to eliminate close-flying requirement 
of near-field head by miniaturizing, pluralizing, and integrating 
near-field optics to media. 
It is another object of the invention to have better control over the 
flying and have a more stable near field that is integral with the medium 
by integrating near-field optics to the medium housing. 
It is another object of the invention to improve the NA and signal-to-noise 
of propagating light optical data storage systems and media by integrating 
optical elements with the medium and/or the medium housing. 
It is another object of the invention to integrate an internal reflection 
surface with a recording medium whereby the active layer can be protected 
by an overlying surface, such as a diamond-like coating, and whereby full 
factor of n.sup.2 is retained. 
It is another object of the invention to provide removable, economic 
high-density, near-field media. 
It is another object of the invention to provide removable, economic, 
high-density media with integrated optics for an increase in resolution 
and storage density by at least a factor of n with or without near-field 
or an immersion medium. 
It is another object of the invention to provide a medium in which 
interaction of an integral near-field and the integral active recording, 
erasable, or ROM layer is either through frustration of TIR or attenuation 
of TIR. 
It is another object of the invention to provide a medium in which integral 
micro-optics are used for optical discerning of data through interference, 
absorption, fluorescence, wavelength, size, height, or reflection 
differences. 
It is another object of the invention to provide a medium in which the 
integrated optics are formed by gradient index in a substantially planar 
surface. 
It is another object of the invention to provide a medium in which the 
integrated optics are holographic optical elements (HOEs). 
It is another object of the invention to provide a medium in which the 
integrated optics can be molded in by injection, injection compression, or 
compression molding. 
It is another object of the invention to provide a medium in which the 
integrated optics may be emplaced by means of embossing with heat or 
solvent. 
It is another object of the invention to provide a medium in which the 
integrated optics can be internal, external, or part of an optical window 
in a protective housing. 
It is another object of the invention to produce a near-field in the medium 
such that its characteristics can be precisely controlled. 
It is another object of the invention to allow full use of the attributes 
of the near-field, including the vertical direction, where the stability 
of it being integral to the medium and not dependent on flying height 
variations and surface topography. 
It is another object of the invention to facilitate use of the said stable 
integral evanescent field for multilevel, multi-layer, surface plasmon, 
resonant near-field, diffractive near-field, phase-resolved, wavelength 
(spectral, fluorescence) and/or other writing and reading techniques. 
It is another object of the invention to provide for an increase in 
resolution by illuminating the micro-optic integrated medium either 
inside, outside, or at the critical angle, thereby using either 
propagating light or evanescent near-field. 
It is another object of the invention to cause an increase in illumination 
intensity by: forming a smaller spot, and constructive interference in the 
standing wave that gives rise to the field. 
It is another object of the invention to place the active recording surface 
or ROM surface internal to the medium for data protection. 
It is another object of the invention to place the micro-optics either 
internal to the medium or integral to a housing. 
It is another object of the invention to provide the prisms in a 
retro-reflective arrangement such that the photo-active layer resides on 
all TIR surfaces. 
It is another object of the invention to fill micro-prism cavities with a 
high index polymer of about 1.9-2.1, or to planarize with a sol-gel 
process. 
It is another object of the invention to provide a system that can be 
either epi-illuminated, dark-field illuminated, or phase-controlled 
illuminated. 
It is another object of the invention to provide a small-format system for 
nomadic personal digital applications. 
It is another object of the invention to provide an optical storage system 
that rivals or surpasses the data access speed and density of 
non-removable hard disc drives. 
It is another object of the invention to provide integral optics that by 
virtue of their small size reduce aberrations normally introduced by 
substitution of a prism for an aplanatic sphere, while enjoying the full 
field of the prism. 
It is another object of the invention to provide, in the case of the close 
packed array in the window of the cassette, optics with full axis of 
revolution, thereby regaining factor of n.sup.2. 
It is another object of the invention to provide a plate, either flexible 
or rigid, having integral, internal, or external micro-optics in the form 
of a close-packed lens array that can be used for lithography and other 
energy delivery purposes, microscopic observation, metrology, or other in 
an oil-less immersion microscope that is low cost and regains large 
working distance, which can be used for interferometry as well as 
near-field depending on the NA. 
It is another object of the invention to provide an integral medium that 
includes diffractive micro-optics which are much smaller than the 
wavelength and are planes in a crystal, thin film vertical layers, 
molecular scale polymers, phase gratings induced by holography or ion 
implantation or other, with the diffractive optics working alone or in 
tandem with refractive micro optics, said diffractive optics being 1, 2, 
or 3 dimensional, in order to produce evanescent fields with 
quasi-wavelengths much smaller than achievable with refractive index 
alone. 
It is another object of the invention to provide two or more matched sets 
of diffractive optics, such that one acts as a reference and the other, 
when altered by light, creates interference between the two and a signal. 
It is another object of the invention to encode the information from said 
diffractive structures in an analog form. 
It is another object of the invention to encode the information from said 
diffractive structures in a digital form. 
It is another object of the invention to provide media with integral optics 
that works well with staggered detector array for reduction or elimination 
of actuator, and subpixel resolution of data, and parallel processing. 
It is another object of the invention to provide the foregoing features to 
any of a disc, a tape, or a photo-active layer. 
It is another object of the invention to integrate light source, optics, 
diffraction grating, detector, into a flying head. 
It is another object of the invention to take integration to its ultimate, 
an integrated optical chip or macro device in which is contained some or 
all of the following components: detector array, illumination array, total 
internal reflection interface, micro-optics, diffraction subwavelength 
optics, writeable erasable active layer, resonance layer structure, 
surface plasmon metal layer, phase resolution or shifting means, and so on 
for a true solid state storage device. 
It is another object of the invention to use said integrated head in other 
applications, such as in lithography, in a print head in graphic arts, or 
as a medical sensor, or as a medical energy delivery device. 
Other objects of the invention will be obvious, in part, and, in part, will 
become apparent when reading the detailed description to follow. 
SUMMARY OF THE INVENTION 
The present invention results from the observation that evanescent field, 
or near-field, illumination and imaging brings a number of advantages to 
optical data storage but the downside is that a flying near-field head is 
normally required, which makes removable media hard to achieve, and may be 
susceptible to head crashes in portable nomadic devices. Further, a flying 
near-field head is sensitive to topographic noise in the medium, which 
reduces the signal to noise available for data. Moreover, for the 
next-generation near-field embodiments using diffraction near-field, 
phase-controlled near-field, and multilevel near-field, a controlled and 
confined near-field is required. The present invention, therefore, 
integrates the near-field optics, and thus the near field itself, with the 
medium, so that parameters important to near-field performance can be more 
precisely controlled, and the medium can be made removable. 
There are two general embodiments of integrating the near field with the 
medium. In one, the near-field optics are integrated with the cartridge. 
While the downside is that close-proximity flying is required as with the 
discrete flying head, the advantage is that the flying is more easily 
controlled, the flying interface is sealed within the cartridge so that 
the medium is easily removable, and the full NA.sup.2 factor in areal 
density is achieved. Further, radial actuation is reduced or eliminated, 
with the advantages that that entails. 
In the second, the near-field optics are integrated with the medium proper. 
The advantage is that flying is completely eliminated, and also that the 
near-field is very well controlled so that increases in data storage 
density by means of the various near-field tools used individually or in 
combination (diffraction, phase, multilevel, etc.) can be achieved, again 
in a removable medium. The downside is that only a factor of NA ratio (vs. 
NA.sup.2) is achieved in areal density, but this is more than made up for 
by the increases otherwise gained. Other improvements include whole-field 
imaging, high SNR, among others, that are common to either. 
Finally, integrating micro-optics with the medium is useful even in the 
propagating-light case, where modest increases in areal resolution are 
gained along with large increases in data transfer rates and reduced 
random access time from the whole-field imaging. 
It is difficult for the magnetic data storage industry to achieve 
whole-field data storage and reading because of the nature of the magnetic 
read/write transducer. Even hybrids of magnetic and optical (i.e., the 
magneto-optical technique) suffer from the need for a physical magnetic 
coil. While multiple read/write arrays are in use, they cannot be placed 
so close as to eliminate head movement. 
Optical data storage, however, can achieve whole-field capability because 
light passes through itself, and multiple photons can be made to exist in 
any density of a given space. However, the dependence upon interference as 
the optical contrast mechanism, and the transfer of the mindset of 
magnetic sequential track recording to optical recording, has missed the 
opportunity to capitalize on perhaps this most important feature of 
optical recording--the ability to image multiple tracks and whole fields 
at one time. This innovation, preferably with near-field but also even 
with propagating light, ends the forced magnetic recording restrictions on 
optical recording and frees it to enjoy its full potential. 
Other features of the invention will be readily apparent when the following 
detailed description is read in connection with the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Background of the Invention 
There is shown in FIGS. 1 and 2 a standard optical storage system 10 
comprising an objective lens 11, such as found in a Digital Versatile Disc 
(DVD) head, and a conventional recording medium 20, such as an optical or 
magneto-optical recording disc. Recording medium 20 typically comprises a 
recording layer 23 disposed upon a substrate 21, with data recorded by 
means of optical artifacts 27 formed in medium surface 25 as it moves 
relative to objective lens 11, as indicated by arrow 19. 
Recording medium 20 may further comprise a transparent protective layer 29 
disposed on medium surface 25. The reading of data is accomplished by 
means of incident illumination 13 of wavelength .lambda., a portion of 
which is returned to a detector (not shown) as reflected radiation 15 
depending on the presence or absence of optical artifacts 27. When using 
"epi" (i.e., "from above"), or "oblique," illumination, the resolution of 
a system such as optical storage system 10 is typically no greater than 
##EQU1## 
where NA is the numerical aperture of objective lens 11, and .lambda. is 
the wavelength of the illumination. The working distance for optical 
storage system 10 is typically on the order of 10 mm. 
The numerical aperture is given by the product of the index of refraction 
of the medium (in which recording layer 23 is immersed) with the sine of 
half of the angle that the illumination subtends in that medium. The 
numerical aperture is invariant (e.g., the value remains constant) when 
the optical path crosses a planar boundary between two medium of differing 
refractive indices. The numerical aperture can be increased by means of: 
i) increasing the subtended angle through refraction at an interface with 
an optical element such as a prism or aplanat, or ii) increasing the index 
of refraction in the immersion medium which may be the prism or aplanat, 
or iii) both of the former. This results in a larger numerical aperture 
and a correspondingly higher resolution. 
Information in the form of optical data is typically written to medium 
surface 25 with incident illumination 13 provided essentially 
perpendicular to medium surface 25. As shown in FIG. 3, incident 
illumination 13 is diffracted from medium surface 25 when the size of 
optical artifacts 27 (i.e., data) is approximately the same as 
illumination wavelength .lambda.. The diffraction angle depends on both 
the illumination wavelength .lambda. (i.e., a longer wavelength results in 
a larger diffraction angle) and the spatial period of the data (i.e., a 
smaller spatial period results in a larger diffraction angle). The spatial 
period of the data is the center-to-center separation "P" of optical 
artifacts 27 as shown. 
For the data to be resolved and measured, such that a first optical 
artifact 27 is distinguishable from a neighboring artifact 28, it is 
required that: i) objective lens 11 be sufficiently large in diameter (or 
in numerical aperture) to intercept at least a first order diffraction 
15b, at the minimum diffraction angle .theta., and ii) there be sufficient 
intensity difference between first optical artifact 27 and neighboring 
artifact 28 for first optical artifact 27 to be visible (i.e., modulation 
is present). First order diffraction 15b combines with a zeroth order 
diffraction 15a to form an image. (This description follows the 
diffraction theory of image formation for a microscope in accordance with 
Abbe and Zernike). Interception of even higher orders, if present, serves 
to contribute to image quality. The numerical aperture can also be thought 
of as the bandpass which allows only certain spatial frequencies to pass. 
(It should be understood that, in the examples provided, illumination 
perpendicular to the recording surface is shown for purposes of clarity 
and that practice of the invention is not limited to such perpendicular 
illumination. Oblique illumination, when used, allows the second order 
diffraction (not shown) into the numerical aperture for about a factor of 
two better resolution.) 
As the density of stored information is increased, it becomes necessary to 
utilize a smaller optical artifact 27' in the process of writing to or 
reading from recording medium 20, as illustrated in FIG. 4. The separation 
between optical artifacts 27' is correspondingly decreased as well. 
However, because diffraction angle .theta.' has increased, objective lens 
11 here does not intercept first order diffraction 15d. One solution is to 
use a larger objective lens 11' (indicated by dotted lines). As is 
well-known in the relevant art, storage density increases as the factor 
NA.sup.2 (i.e., the square of the numerical aperture). In the conventional 
DVD optical storage system, for example, the objective lens used has an NA 
of 0.65 rather than the conventional NA of 0.4 so as to provide for an 
increase in storage density. However, this approach results in an increase 
in cost and more critical tolerances resulting from a shallower depth of 
field. 
Alternatively, decreasing the wavelength of incident illumination 13 will 
decrease diffraction angle .theta. such that first order diffraction 15d 
intercepts objective lens 11, and optical artifacts 27' are resolved. As 
can be appreciated by one skilled in the relevant art, the search for an 
illumination source of ever shorter wavelength will continue in view of 
the fact that storage density can be increased in proportion to the square 
of the ratio of conventional (e.g., red) wavelength to a shorter (e.g., 
blue) wavelength. 
As the density of stored information is further increased, an even smaller 
optical artifact 27" is utlilized in the process of writing to or reading 
from recording medium 20, as illustrated in FIG. 5. A first order 
diffraction 15e results and is parallel to medium surface 25. This 
diffracted illumination is in the form of an evanescent field 39, or 
near-field. This non-propagating, non-radiating illumination does not 
leave medium surface 25. As is understood by one skilled in the relevant 
art, the amplitude of the illumination decreases exponentially with 
distance from medium surface 25. For still smaller optical artifacts, the 
exponential decay is more rapid. 
FIG. 6 illustrates the use of an aplanatic sphere 31 in combination with 
objective lens 11 for the detection of artifacts 27" by means of 
evanescent field 39. Numerical aperture and resolution are defined and 
determined by the extreme ray in the illumination cone. For a "pure" 
spatial frequency object as substantially embodied by the diffraction 
grating formed by the optical data tracks, the first and primary 
diffracted order angle can be made to coincide with the extreme ray of the 
numerical aperture, which allows the optical approximation of the 
aplanatic sphere with prismatic elements, such as an array of prism 
micro-optics. 
FIG. 7 illustrates the use of an array of prismatic elements 115 in 
conjunction with objective lens 11 to provide for detection of artifacts 
27" by means of evanescent field 39. The resulting field of view is 
improved over the aplanat configuration as each prismatic element 115 
allows every part of the active optical layer occluded by its base to be 
viewed. In comparison, the aplanat configuration allows only the central 
50 to 75% of the underlying active optical area to be viewed. The aplanat 
has the better resolution, however, because it is optimized to eliminate 
spherical aberration. Therefore, the aplanat is preferred, in either its 
lenticular form or its close-packed two-dimensional form for use in a 
configuration integral to a housing (discussed in greater detail below). 
In such configurations, the fields of view of adjacent aplanatic optical 
elements can be made to overlap, forming an essentially complete field of 
view with little or no loss of recording capability or real estate. 
The two-dimensional aplanat increases the areal storage density by the 
square of the ratio of the increase in numerical aperture NA. The 
lenticular aplanat, on the other hand, increases the areal storage density 
in the track pitch dimension by only the ratio of the increase in 
numerical aperture compared to the objective without the integral 
micro-optic. As can be appreciated by one skilled in the relevant art, an 
aplanat configuration is not the preferred choice for integration with the 
medium proper because of the loss of field of view, and a prism form would 
be used. From an optical standpoint, this is acceptable because, given the 
micro scale of the optics, the aberrations introduced by the planar facets 
of the prism are minimal compared to the curved surface of the aplanat. 
Only the first order diffraction from the spatially pure optical data 
structure is required, and it easily passes from prismatic element 115 to 
objective lens 11. 
It has been proposed that resolution can be increased with a configuration 
such as that exemplified by a near-field optical storage system 30, shown 
in FIGS. 8 and 9, comprising an objective lens 11' and an aplanatic sphere 
31 having a substantially planar surface 32 positioned at a distance "d" 
from medium surface 25 of a conventional recording medium 20'. Because the 
illumination wavelength .lambda. is reduced by a factor equal to the index 
of refraction of aplanatic sphere 31, the resolution of optical storage 
system 30 is increased over that of optical storage system 10 such that 
proportionately smaller optical artifacts 47 can be read. Incident 
illumination 33 is directed into aplanatic sphere 31 at an angle greater 
than critical angle .THETA..sub.C (here measured relative to an optical 
axis normal denoted by O.sub.A). An evanescent field 39, generated at 
surface 32, provides for the operation of optical storage system 30. 
Incident illumination 33 is totally internally reflected at surface 32 to 
emerge as either totally-reflected radiation 37 or frustrated to produce 
propagating radiation 35 by the process of, for example, absorption, 
refraction, diffraction, or scattering, by optical artifacts 47 present in 
recording layer 23. In practical applications, "d" is less than a 
wavelength .lambda.. Accordingly, there is typically provided little or no 
protective layer in recording medium 20' so as to enable placement of 
aplanatic sphere 31 at the requisite distance. Where a protective layer is 
used, this is commonly done solely to prevent oxidation of, for example, 
magneto-optical (MO) surfaces. Because the illumination wavelength 
.lambda. is reduced by a factor equal to the index of refraction of 
aplanatic sphere 31, the resolution of optical storage system 30 is 
increased over that of optical storage system 10 such that proportionately 
smaller optical artifacts 47 can be read. 
Optical storage system 30 incurs several disadvantages when operating as a 
dynamic system in which there is relative movement between aplanatic 
sphere 31 and recording medium 20. Most problematic is that the operations 
of reading and writing are adversely affected by the presence of 
contamination on medium surface 25 because the flying height of aplanatic 
sphere 31 is made to exceed the sensible extent of evanescent field 39. 
This may require that optical storage system 30 be a costly, sealed 
system. Additionally, because there is no protective layer, active layer 
23 is exposed to ambient atmosphere and is vulnerable to oxidation or head 
crashes. 
Propagating and Evanescent-Field Illumination: 
With propagating illumination, the highest NA possible at a medium (e.g., 
greater than one and typically as high as 1.25) is achieved in the case 
where the micro-optic array is directly on the medium. For a split flying 
integrated micro-optic (described below) and with propagating 
illumination, an NA of approximately 0.95 can be realized with a flying 
height much larger than for the near-field case. In either case, 
propagating illumination requires a contrast mechanism such as 
interference or polarization analysis, for example, to detect the optical 
data. The evanescent field micro-optic enjoys an NA of greater than one 
and typically about 1.25 or more, and also brings all the attributes of 
near-field illumination to bear, as discussed in greater detail below. 
As shown in the diagram of FIG. 10, an evanescent field, having an 
intensity described by graph 80, arises at the boundary between surface 32 
and the adjacent lower index medium (usually air or another low-index 
medium). Evanescent field 80 is a continuation of the internal standing 
wave in aplanatic sphere 31 that in turn is a result of constructive 
interference of incident and reflected illumination at surface 32 (i.e., 
the TIR interface) that gives rise to evanescent field 80. Therefore, 
immediately at the active layer or low-index side of surface 32, the 
resultant intensity 38 can be four times as much as the intensity of 
incident radiation (see FIG. 11). Because of this higher intensity, less 
sensitive active layers, lower power sources, or lower cost sources can be 
used in the associated optical storage system. For writing, the power 
levels provided by coherent laser diodes may still be desirable for 
presently-available active optical materials. 
"Near-field" is traditionally understood to include both propagating and 
non-propagating radiation near (i.e., within a wavelength of) a surface. 
The non-propagating field is also known as an evanescent field, comprised 
of inhomogenous or surface bound waves. The evanescent field arises in the 
condition of total internal reflection (TIR) at a boundary between a high 
and low refractive index media, where the parent field in the higher index 
medium penetrates into the lower index medium (i.e., the refraction angle 
becomes imaginary). Because the time average of this penetration of energy 
(represented by the Poynting vector) is zero, total reflection is 
indicated. In the quantum mechanical view, this penetration of the TIR 
barrier is called photon tunneling. Evanescent fields also arise in other 
situations, such as when propagating illumination is diffracted by a 
grating with grating period smaller than the wavelength, discussed below, 
such that the diffracted orders are evanescent (i.e., the diffraction 
angle becomes imaginary). 
For p-polarized coherent illumination at the critical angle .theta..sub.C 
and for total reflection: 
EQU .theta..sub.C =sin .sup.-1 n.sub.21 (1 
where n.sub.21 .ident.n.sub.2 /n.sub.1 .ident.N, the ratio of the indices 
of refraction in medium 2 and medium 1, respectively, the reflected beam 
is shifted in phase by .pi., as with reflection by a perfect conductor. 
(In fact, the total reflection surface can be treated as a lossless 
metal.) Littman showed that, for an absorbing rarer medium, there is no 
longer a particular angle for total reflection, but a transition of finite 
angular width. Accordingly, it should be understood that for the present 
application, when the active layer is an absorber, reference to the 
critical angle takes into account this finite angular width. Many physical 
optics textbooks (e.g., Born and Wolf) proceed from Maxwell's equations to 
show that standing waves are established normal to this totally reflecting 
surface, internal to the denser medium, because of the superposition of 
the incoming and reflected waves. This results in a net field at the 
surface in the rarer medium, normal everywhere to the surface in the Z 
axis, with intensity E due to coherent addition (net) of the incident and 
reflected beams, evanescent wavelength .lambda. .sub.e and phase angle 
.alpha.: 
EQU E=2 cos (2.pi.z/.lambda..sub.e +.alpha.) (2 
Evanescent field 80 has an amplitude that decays exponentially with 
distance from surface 32. The strength of available evanescent field 80 is 
given by: 
##EQU2## 
where E.sub.o is the phase dependent amplitude of the electric field 
associated with the photon in the medium comprising aplanatic sphere 31 
and, d.sub.p, is the penetration depth in the less dense medium at which 
E.sub.o decreases to E.sub.o /e and where: 
##EQU3## 
and .lambda..sub.1 is the wavelength in the denser medium, .theta. is the 
incidence angle, and n.sub.21 in the ratio of denser to lower indices of 
refraction at the boundary surface 32. The actual penetration depth, where 
E.sub.evanescent falls to the limit of detectability, is dependent on 
these variables as well as both the photodetector sensitivity and the 
sample optical properties, and is typically approximately 0.75. However, 
the evanescent field, however small in intensity, can exist sensibly for 
tens of wavelengths, if the parameters in equation (2) are optimized. The 
evanescent field has electromagnetic field vectors in all spatial 
directions, so that coupling is made to dipoles in any spatial 
orientation. This fact is used to advantage in spectroscopy and also here, 
in optical data storage, for more efficient coupling into the active 
layer. 
The evanescent field can exist in the active optical layer. In the relevant 
art, this is denoted as attenuated total reflection (ATR). Alternatively, 
the evanescent field can exist adjacent to the active optical layer, 
denoted as frustrated total reflection (FTR or FTIR). In either case, the 
evanescent field is partly or totally converted into propagating 
illumination by the active optical layer, which then forms an image. Both 
ATR and FTR, as well as propagating, are claimed in the present invention 
in combination with micro-optics integral to the medium. 
If evanescent field 39 can be accessed and converted back into propagating 
illumination so that it contributes to image formation, it follows that 
optical artifacts of a size much smaller than illumination wavelength 
.lambda. can be resolved. To access this evanescent field requires close 
proximity to the medium surface because evanescent field 39 decays over a 
distance of only a fraction of a micron--hence the term "near-field." 
Moreover, the smaller the size of the optical artifacts, the smaller the 
required distance to the medium surface. 
To convert evanescent field 39 back into propagating, it is required that 
one is close to the surface with: i) a high-refractive index dielectric 
material, or ii) a diffraction grating with grating period similar in size 
to the otical artifact spatial period. The more evanescent the field 
(i.e., the smaller the optical artifacts), the higher the refractive index 
that is required. Ultimately, there is a practical limit (imposed by the 
index of refraction of available materials) of about 2.4 in the visible 
spectrum to about 3.5 in the near infra-red spectrum. Conversion by 
diffraction is limited only by the diffraction grating spatial period. In 
the present state of the art, for example, a diffraction grating spatial 
period of less than 40 nanometers has been achieved. 
Also of importance to optical storage density is the contribution of the 
exponential vertical decay of the near-field. This exponential decay makes 
the contrast of the written optical artifacts extremely high, as the 
signal changes from total reflection of the illumination to almost total 
transmission with, in the case of actual optical artifacts, a depth change 
of only 0.2 microns. In the case of the phase change material, the 
contrast is also increased. The near-field illumination reduces surface or 
Fresnel reflection, and is strongly controlled by the absorption part of 
the complex refractive index of the phase change material. This causes the 
signal-to-noise, or contrast, of the optical artifacts to be greatly 
enhanced over viewing in normal illumination. FIG. 12B illustrates the 
increase in signal-to-noise ratio for information in a phase change medium 
read by means of near-field methods as compared to a conventional 
propagating illumination method using bright-field microscopy shown in 
FIG. 12A. 
Description of the Preferred Embodiments 
There is shown in FIGS. 13 and 14 a generalized diagrammatical view of an 
optical storage system 100 comprising an objective lens 111, an epi 
illumination section 110, and a storage medium 120 in accordance with the 
present invention. Objective lens 111 may be the objective of an optical 
disc drive or other similar device, such as the objective of a microscope. 
Storage medium 120, which may be flexible or rigid, comprises an optical 
layer 113 overlying an active layer 123 and may comprise a substrate 121, 
such as polycarbonate disc or card, or a mylar-based tape, to provide 
physical support to active layer 123. Optical layer 113 comprises a 
reflection surface 117, disposed on or adjacent to a data surface 125 of 
active layer 123, and a distributed structure of micro-optical elements 
115, preferably configured as prismatic elements. Alternatively, active 
layer 113 and substrate 121 may comprise a single layer. It should be 
understood that storage medium 120 may include an enclosing housing or 
cartridge (described below) to provide protection for the enclosed medium 
proper and to facilitate loading into and removal from a storage drive 
device. 
Active layer 123 may comprise a "write once" material, a read only 
material, or a material in which the written data can be "erased" (i.e., a 
rewriteable material). For example, active layer 113 may comprise any of 
the optically-active materials used in conventional optical storage media, 
such as magneto-optical (MO), phase change materials, and laser ablation 
surfaces (resulting in surface "pits" or "bumps"). As can be appreciated 
by one skilled in the relevant art, additional optically-active materials 
that would benefit from integration with micro-optical elements, in 
accordance with the present invention, include: photoresist, 
photorefractive polymers or crystals, photopolymers, chalcogenide glasses 
and compounds, photographic silver halide or other emulsions, 
fluorescently active materials, and semiconductor structures such as CCD 
or CMOS silicon detectors. Examples of photo-refractive materials include 
LiNbO.sub.3 and BaTiO.sub.3. Example of a phase change material is an 
alloy such as Te.sub.x Sb.sub.y Ge.sub.z or Te.sub.x Sb.sub.y Ge.sub.2 
Se.sub.w (which is erasable). 
The optical layer is, in one embodiment, the distributed structure of 
micro-optical elements 155, which may comprise an array of lenticular 
lenses (i.e., lenses having facets curved in one meridian), prism-like 
optics, or holographic optical elements, for example, or an array of 
micro-lenses (i.e., lenses having facets curved in at least two 
meridians), or one or more planar optical layers used in conjunction with 
said elements or, for example, an external aplanat, as described in 
greater detail below. 
A data bit, represented by the presence or absence of one or more optical 
artifacts 127, is written to or read from data surface 125 by means of 
radiant energy transmitted into optical layer 113. This radiant energy 
produces an evanescent field 139 which is used to either read from data 
surface 125 or, when increased to an appropriate intensity or duration, to 
write to data surface 125. Reading and writing are performed as storage 
medium 120 is moved with respect to objective lens 111 and illumination 
section 110. Optical artifacts 127 comprise a local portion with change in 
polarization (Kerr rotation), optical phase, index of refraction, 
absorption, scatter, diffraction angle, critical angle, reflection, 
material phase state (e.g., crystalline to amorphous), or topography, in 
comparison to surrounding material. 
Illumination section 110 comprises a radiation source 101 and is typically 
transmitted by means of a beam splitter 102. Epi illumination beam 133 is 
incident upon one or more micro-optical element 115 at an angle of 
incidence .THETA..sub.E with respect to the optical axis of optical layer 
113. For angles of incidence .THETA..sub.E greater than the critical angle 
.THETA..sub.C of optical layer 113, there will be produced evanescent 
field 139 adjacent reflection surface 117 and local to micro-optical 
element 115, at least a portion of which field will lie within active 
layer 123. Evanescent field 139 provides the means by which optical 
artifacts 127 are detected (i.e., read) or produced (i.e., written). That 
is, the presence of optical artifact 127 will produce a detectable 
attenuation or frustration of evanescent field 139 as evanescent field 139 
passes over optical artifact 127, and may result in the conversion of 
evanescent field 139 into propagating radiation 135 as described in 
greater detail below. Accordingly, the detection of optical artifacts 127 
is preferably accomplished by means of one or more detectors 104, which 
may comprise, for example, a detector array or one or more charge-coupled 
devices (CCDs), which sense propagating radiation 135 passing through beam 
splitter 102. 
Radiation source 101 is preferably of narrow bandwidth and may, for 
example, comprise a light-emitting diode such as a blue LED, a laser, a 
laser diode, or a broadband source of radiation optically coupled to one 
or more narrow bandpass filters or a monochromator, so as to limit the 
transmitted wavelengths to predetermined ranges. A coherent light source, 
such as a laser, produces an output with side lobes which is not desirable 
for use in reading because of cross-talk with adjacent tracks. The 
preferred source for reading is an incoherent source because it allows the 
full theoretical resolution of the optics and provides for whole-field 
imaging. Typically, an illumination source for the process of reading will 
comprise an LED because of the relatively low power level required. For 
the process of writing, a laser source is generally used because of a 
higher level of power required. Because the present system has whole-field 
capability, it becomes possible to use a plurality of laser sources to 
write multiple tracks concurrently. Where there is an erasable (i.e., 
rewritable) storage medium used, the process of erasing is accomplished by 
modulating both the intensity and duration of the illumination incident 
upon the active layer. 
Incoherent illumination may be provided by low-cost LEDs, such as currently 
available high-resolution blue LEDs. The incoherence reduces the ringing 
of coherent sources that is the cause of cross-talk between data tracks. 
Cross-talk prevents propagating coherent systems from using the full 
theoretical resolution derived from considering the NA and wavelength 
alone, so that, for example, the new DVD format, with coherent laser diode 
illumination, has a track pitch of 0.74 microns while at the wavelength 
and NA of the format, a track pitch of 0.4 microns would be possible with 
incoherent light. Is can be appreciated by one skilled in the relevant art 
that, while incoherent light results in the highest spatial resolution, 
incoherent light can be used in near-field optics and cannot be used in 
interference-based optical systems. Similarly, coherent light makes 
imaging multiple tracks and large fields difficult to achieve, while the 
incoherent light used in near-field allows whole-field multi-track 
imaging. FIG. 15 is a photomicrograph of a portion of an audio compact 
disc illustrating a plurality of encoded tracks as seen in near-field 
illumination. 
Illumination section 110 may further comprise a phase controller 103 for 
controlling the phase of direct illumination beam 133 as it impinges upon 
optical layer 113. As described in greater detail below, phase controller 
103 and its functions may be provided by a number of different means and 
preferably operates in response to external electronic circuitry (not 
shown). Accordingly, when phase controller 103 is used in optical storage 
system 100, detector 104 comprises a phase analyzer. 
Oblique Illumination and Imaging: 
In a preferred embodiment, best seen in FIG. 16, illumination section 110 
is not used. Rather, read/write illumination is provided by means of an 
illumination section 112. Illumination section 112 comprises a radiation 
source 101', a focusing lens 119 for providing an illumination beam 134 
oblique to optical layer 113 and, optionally, a phase controller 103'. 
There is also shown an oblique objective 119', an optional phase 
controller 123', and detector 121' when used with illumination section 
112. 
In this embodiment, the illumination is again reflected light from above, 
as in the epi illumination, but the illumination and imaging axes are not 
coaxial and are equally oblique to the optical normal axis, and, unlike 
the tilting objective in the propagating case where the integral optical 
layer is a lenticular aplanatic cross section, the obliquity here is 
fixed. The entire base of the prism is seen at once, and the tilt and 
defocus introduced are very small according to the small size of the 
integral optical element. If the oblique objective is actuated radially, 
then all defocus is removed as it traverses the integral optical element. 
While the actual NA of the objective is considerably less than one, the 
oblique incidence and viewing angle provide for an effective numerical 
aperture of considerably greater than one, because the NA is defined and 
measured at the sample plane, in this case the base of the integral 
optical element. If the oblique head (where the head comprises both the 
imaging/detection objective lens as well as the opposed illumination 
source) is incident at less than the critical angle, the illumination is 
propagating and can be used in the normal fashion, such as interference, 
for example. If the incidence is at greater than the critical angle, the 
illumination is evanescent with all the attributes discussed brought to 
bear. At each of the extremes of the prism base, one or the other of the 
first order diffraction is occulted by the prism itself or by a 
neighboring prism, but the remaining first order is sufficient to form an 
image with the zero order. For this arrangement, the cone subtended by the 
objective need not match the angle subtended by the prisms. For example, 
the integral prism elements may be 45.degree.-90.degree.-45.degree. 
prisms, with the objective being NA 0.65. 
Dihedral Reflector Elements 
In yet another embodiment, shown in FIG. 17, the integral optical layer 
comprises dihedral reflector elements 116, wherein incident and exiting 
light from the reflector elements undergoes at least two internal 
reflections from the surfaces forming the dihedral angle, one or both of 
which reflections may be a total internal reflection. The active layer is 
coated onto the external faces of the dihedral reflector elements, with 
optional intervening layers disposed for resonance or other purposes as 
discussed earlier. The external head is incident normal (perpendicular) to 
the plane of the medium. Data 114 is stored on, preferably, only one of 
the internally reflecting surfaces. The optical artifact either restores 
total internal reflection in an otherwise frustrated TIR field, or 
frustrated total internal reflection in an otherwise totally reflecting 
field, or is simply a propagating light effect. The advantage in this 
embodiment is that it eliminates the need for planarizing the internal 
integral micro-optics with a high-index material as before, while 
providing the same internalizing and protection of both the optics and the 
data associated with the active layer. While one of the surface pairs is 
sacrificed for reflection of the data, the data surface area is increased 
by a factor of the square root of 2, for only a small total reduction of 
data surface area. With polarization differentiation, data may be stored 
on both of the internal reflection surfaces. 
Fabrication of Optical Layer 
The masters for the micro-optic arrays can be fabricated by any one of a 
number of well-known techniques, including precision computer-controlled 
diamond turning, photolithography, multiple-beam laser lithography, laser 
mastering lathe, or e-beam lithography. As shown in FIGS. 18, 19, and 20A, 
a master 201 is fabricated from which an inverse master 203 is formed. 
Master 201 can be replicated either directly or in a material such as 
electro-less nickel, for example, to form inverse master 203. Inverse 
master 203 would be used in a fabrication process such as compression, 
injection, or sequential injection/compression molding of any of a number 
of plastics such as polycarbonate, acrylic, and others. Alternatively, 
inverse master 203 can be used for embossing micro-optics into a polymer 
web. 
In fabricating master 201, a servo structure (not shown) can be formed to 
produce a corresponding servo pattern 211 in inverse master 203 to be 
replicated onto a micro-optical structure 213. In this manner, there is 
assured accurate registration between servo pattern 211, which is used for 
tracking in the reading and writing operations, and micro-optical 
structure 213. Alternatively, servo pattern 211 can be embossed, stamped, 
or otherwise formed into micro-optical structure 213 in a secondary 
operation in which registration is achieved by known optical alignment 
methods, including Moire interferometry. Following the formation of 
micro-optical structure 213, there can be added an active layer such as a 
phase change layer 217 and a protective layer 219, for example, as well as 
an optional resonant structure layers or a low-index FTIR layer. In an 
alternative embodiment, shown in FIG. 20B, a micro-optical structure 213' 
comprises truncated prism-like elements. 
Fabrication of Micro-Optics 
Internal micro-optics that have been formed by embossing, stamping, 
molding, or otherwise must be filled with an optical material having an 
index of refraction sufficiently larger than the host substrate material 
to maintain the critical angle for TIR. So, for a host substrate of 
polycarbonate with an index of refraction of 1.5, the concave micro-optics 
may be filled with a high index polymer of about 1.9 to 2.1 (see Gaudiana 
'430). This may be done in a two-shot molding operation, or the high index 
polymer may be spin-coated onto the substrate. Other alternatives include 
depositing ZrO.sub.2, ZnS, or other high-index material into the 
micro-cavities by magnetron sputtering or other vacuum deposition 
technique, followed by a planarizing operation as is known in the 
microelectronics industry. Here, the small amount of material deposited 
requires the micro-cavities to be very small, on the order of a micron in 
pitch. Many high-index materials may be applied with a sol-gel technique, 
although the host substrate will have to be of a plastic that can 
withstand the required solvents and high temperatures. For specialized 
non-rotational applications, the internal micro-optics structure may be 
formed from a preform drawn down to the required dimensions. 
The optimum size of the micro-optic is determined by mastering, 
manufacturing, and optical design considerations. Mastering techniques now 
available suggest a pitch size of not too much below 3 to 5 microns, while 
embossing techniques become problematic with sizes greater than about 50 
microns. Optical aberrations in the prismatic approximation of the 
aplanatic sphere are minimized as the optic becomes smaller, while the 
number of data tracks per optic is optimized for the larger optic sizes. 
Storage Medium with Integral Optical Layer 
In a first embodiment, as best seen in FIGS. 21 and 22, data is written to 
or read from a storage medium 140 comprising an optical layer 153 integral 
with an active layer 143 preferably disposed upon a substrate 141. In the 
configuration shown, storage medium 140 is disc-shaped, and optical layer 
153 comprises a plurality of concentric or spiral lenticular lenses (see 
for example, FIG. 23) wherein storage medium 140 is rotated for the 
reading and writing of data. In an alternative embodiment (see FIG. 24), 
storage medium 140 may be rectangular in shape with data retrieval and 
storage accomplished by means of rotation or rectilinear motion, for 
example. Alternatively, storage medium 140 can be stationary with data 
retrieval accomplished by means of a whole-field imaging detector array. 
Storage medium 140 may be disposed within an optional protective housing 
105, as shown. Housing 105, which serves to minimize the possible 
contamination of active layer 143, comprises an optically-transparent 
window 106 to provide for access for the writing of data to and the 
reading of data from active layer 143. 
As best seen in FIG. 25, active layer 143 comprises a material having an 
optical property that change state to produce an optical artifact 147 
within a data surface 145 upon exposure to a sufficient intensity and 
duration of direct illumination beam 133. In the preferred mode, direct 
illumination beam 133 is incident on a reflection surface 157 at an angle 
of incidence greater than critical angle .THETA..sub.C of a truncated 
prismatic micro-optical element 155 such that there is generated an 
evanescent field 159, at reflection surface 157 proximate illuminated 
micro-optical element 155, extending into active layer 143. It should be 
understood that there may be more than one optical artifact 147 in data 
surface 145 lying beneath one micro-optical element 155, and that reading 
or writing of data would be performed as objective lens 111 and 
illumination beam 133 are translated relative to optical layer 153. 
The index of refraction n.sub.1 of optical layer 153 is preferably greater 
than either the index of refraction n.sub.2 of active layer 143 or the 
index of refraction n.sub.3 of optical artifact 147. The change in state 
of optical property resulting in the production of optical artifact 147 
can be a change in index of refraction (e.g., from n.sub.2 to n.sub.3). 
Alternatively, there may be a change of state in polarization, in phase, 
in scatter, or in topography. These changes in optical property may be 
produced by the application of direct illumination beam 133 
contemporaneously with the application of an external magnetic field (not 
shown). The process of reading, or detection, makes use of the fact that, 
in the absence of optical artifact 147, direct illumination beam 133 is 
emitted from micro-optical element 155 as reflected radiation 137, and 
where optical artifact 147 is present, there is produced an attenuation of 
total internal reflection and propagating radiation 135 is emitted to 
objective lens 111. In an alternative embodiment, objective lens 111 may 
comprise a bifocal feature 231. 
In an alternative mode, the illumination source comprises a direct 
illumination beam 133' incident at an angle less than critical angle 
.THETA..sub.C. In this alternative mode, evanescent field 159 is not 
produced, but the resulting resolution is still greater than that of a 
conventional optical storage system. 
Storage Medium with Optical Window 
In a second embodiment, as best seen in FIGS. 26 and 27, data is written to 
or read from a storage medium 160 comprising a housing 171, an 
optical-layer window 173, and an active layer 163 preferably disposed upon 
a substrate 161. As best seen in FIG. 28A, a data bit is represented by 
the presence or absence of one or more optical artifacts 167 detected 
within a data surface 165. Active layer 163 and substrate 161 are disposed 
within housing 171. Optical-layer window 173 comprises a distributed 
structure of micro-optical elements 175, such as an array of lenticular 
lenses (as shown) or alternatively, an array of micro-lenses. During the 
process of detecting or producing optical artifacts 167, active layer 163 
is translated relative to objective lens 111, as indicated by arrow 19, 
and data is written to or read from active layer 163 through optical-layer 
window 173. 
During the read/write processes, reflection surface 177 of optical-layer 
window 173 is retained at a substantially fixed distance .DELTA.z from 
data surface 165, preferably on the order of one wavelength of direct 
illumination beam 133. In the preferred mode, direct illumination beam 133 
is totally internally reflected from reflection surface 177 at an angle of 
incidence greater than critical angle .THETA..sub.C of micro-optical 
element 175 such that there is produced evanescent field 179 at reflection 
surface 177 extending away from illuminated micro-optical element 175 and 
into active layer 163. In the configuration shown, evanescent field 179 is 
frustrated by the presence of optical artifact 167 encountered within 
active layer 163. The complex index of refraction (n+ik) of active layer 
163 is greater than the index of refraction (n.sub.o) of the material 
(typically air) present between reflection surface 177 and data surface 
165. 
In one alternative embodiment, shown in FIG. 28B, storage medium 160 
comprises optical-layer window 173' comprising a distal surface with 
concave curvature (with respect to the medium) for optical correction. In 
another alternative embodiment, shown in FIG. 28C, storage medium 160 
comprises optical-layer window 173" comprising a distal surface with 
convex curvature for facilitating proximal flying. 
Propagating Case 
While a medium with integral near-field optics is preferably used to 
realize the many attributes and applications, many, but not all of which 
have been described here, of the evanescent field component of the 
near-field, there are also benefits to be gained by using the integral 
near-field optics for only the propagating illumination component of the 
near-field. This is accomplished by i) illuminating the integral 
micro-optics with an incident angle no greater than the critical angle 
within the micro-optics, such that there is no total internal reflection 
within the micro-optics and hence no evanescent field, or ii) by changing 
the index of refraction of one or more of the following: micro-optic 
optical layer, active optical layer, intervening optical layers if 
present, such that there is no critical angle, or the critical angle is so 
large as to be outside of the illumination cone. In either of the former, 
all light is propagating and no evanescent fields exist. 
If the integral micro-optics are integral to the medium proper, numerical 
apertures of greater than 1 can still be achieved as in the evanescent 
field case, but the other attributes of the evanescent field are absent. 
The optical operation in this case is simply that of an immersion 
microscope as invented by Abbe in the 1880's. Resolution, and therefore 
data storage density, is increased over that of the original objective in 
air by a factor of the ratio of the numerical apertures, for the 
lenticular micro-optics, and by that ratio squared when the micro-optics 
comprise full figures of rotation. 
If the micro-optics are integral to the medium cartridge such that there is 
a layer of air between the optics and the medium proper, the numerical 
aperture can be no greater than 1 in this propagating light case. All 
light at greater numerical apertures would be totally internally 
reflected. Here the layer of air can be much greater in thickness than in 
the case of the evanescent field. Flying heights of many wavelengths 
become allowable, because the light is propagating. Each of the 
micro-optic elements in combination with the external objective or 
objective array comprise a conventional high numerical aperture "dry" 
objective, as they are known in microscopy. For best optical performance, 
the surface of the micro-optic elements facing the active optical layer 
may be concave, and all surfaces may have aspheric curvatures which are 
easily molded into, for example, plastic optics. As in the evanescent 
field case, the micro-optic elements are preferably full figures of 
rotation and are staggered in an array such that their fields of view 
overlap so that there are no areas of the active optical surface that are 
not imaged. 
In both of these cases the advantage is an increase in optical data 
density, with a larger flying height in the latter and some reduction of 
noise from topographic roughness of the active optical layer, if present, 
in the former. However, the optical contrast and signal to noise 
enhancement contributed by the evanescent field illumination is absent. 
Contrast can be regained by reverting to, in the case of read-only-media, 
an interference detection method, requiring topographic pits coated with 
an aluminum layer, as is well known and practiced now. Other active 
optical layers, such as magneto-optical, phase change, or other, would 
exhibit the same degree of optical contrast as they do now in propagating 
light, which is to say less contrast than with evanescent field 
illumination but sufficient contrast to work. The micro-optics, by virtue 
of increasing the numerical aperture and reducing the writing spot size, 
also function as light intensifiers, which can be utilized in faster 
writing speeds or lower power laser diodes. 
Propagating configuration of optics integrated with housing 
In a configuration wherein the medium is illuminated by propagating 
illumination, each of the optical elements comprising the micro-optic 
array in the housing can have the required optical power and surface 
disposed on both sides of the optic. This configuration will allow the 
maximization of numerical aperture, resolution, and field-of-view while 
keeping optical aberrations to a minimum by methods generally well 
understood and known to one skilled in the relevant art. 
Integrating a micro-optic array to the cartridge housing the new DVD 
medium, for example, would increase the numerical aperture from the 
existing 0.6 to about 0.95 for a substantial increase in areal density, 
and is backward compatible with the DVD system. 
Integral Optical Layer as Interference Reference 
The optical layer integral to the medium has been generally discussed 
herein is used, among other things, to increase the areal storage density 
whether the evanescent or propagating illumination is used. There is also 
an increase in optical contrast and signal to noise enjoyed in the former, 
while in the latter the optical contrast is much lower but sufficient. For 
ROM or other media where the optical artifacts are read by optical 
interference techniques, and propagating illumination is used, the 
integral optical layer may function as a contact or proximal interference 
reference plate, such that the interference is of the first order that is 
the black center in the colored Newton interference fringes, for example. 
While the vertical range is not as large as for the evanescent field case, 
the contrast is similar. This is sometimes known as contact interference 
microscopy, but has not been applied to optical data storage heretofore 
because of the absence of a proximal interference reference at the medium. 
In this way, even with propagating light the signal to noise ratio can be 
enhanced, while eliminating the need for a metallic reflecting layer in 
the medium and phase analysis optics in the drive. 
In fact, while the first order interference provides the highest contrast 
with broadband and white light, additional vertical range and vertical 
data encoding can be obtained with this interference when the colored 
interference fringes are included. With the use of appropriate narrowband 
color filtration anywhere in the optical path, or alternately the use of 
plural light sources of different illumination wavelengths, data of only a 
specific wavelength may be passed to the exclusion of the others. Thus, 
information from multiple vertical layers, or even overlapping optical 
artifacts in the same layer, may be separated. The surface of the optical 
layer facing the drive may, as before, be prismatic, lenticular, or 
planar, and may be used in combination with an optical lens array, a 
single lens, or a flying optical head. 
Near-field form of optics integrated with cartridge 
For the near-field illumination, the side of the micro-optic array integral 
to the cartridge and facing the medium can be planar, but preferably will 
have slight convex curvature in order to optimize the low-flying 
characteristics required by the exponential decay of the near-field. 
Flying heights for the micro-optic array integral to the cartridge. 
Near-field requires flying heights of typically 0.1 microns for high 
coupling strength. That the intensity is increased by the constructive 
interference in the parent wave allows some tolerance here, in that even a 
higher flying height will still result in adequate signal. 
For the propagating illumination, flying height can be several orders of 
magnitude greater than for the near-field. 
The micro-optic array integral to the cartridge can be on the surface of 
the window and protected by a moveable shutter, or can be internal to the 
window and filled and substantially planarized with a high-index optical 
material (see Gaudiana polymer patent). 
Optical Window Configuration 
FIG. 29A illustrates a window configuration wherein lenticular lenses 221 
are oriented at an acute angle to data tracks 223, and FIG. 29B 
illustrates a window comprising an array of micro-optical lenses 225 
oriented at an acute angle relative to adjacent data tracks 223. 
Storage Medium with "Split" Optics 
In this embodiment, as best seen in FIGS. 30 and 31, there is shown a 
storage medium 180 comprising a housing 191, an aplanat layer 185, and an 
active layer 183, which is preferably disposed upon a substrate 181. An 
opening 193 is provided in housing 191 to allow access to active layer 
183. Storage medium 180 may further comprise a sliding cover 195 (shown in 
FIG. 30 only, for clarity) as a means of minimizing the entry of 
contaminants into housing 191. Data is written to or read from storage 
medium 180 by means of a flying split aplanat 109 disposed between active 
layer 183 and objective lens 111 in a configuration best explained with 
reference to FIG. 32. 
Reading and writing of data is accomplished by positioning flying split 
aplanat 109 within opening 193 such that an aplanat surface 108 is 
positioned substantially within 0.1 .mu.m of optical surface 186. Direct 
illumination beam 133 is totally reflected at aplanat surface 108 and an 
evanescent field 107 is generated. Evanescent field 107 is optically 
coupled into split-optical layer 185 to produce a secondary evanescent 
field 107'. Split aplanat 109 combines with split-optical layer 185 to 
form an equivalent aplanat, as indicated by dotted lines at 109'. A data 
bit is represented by the presence or absence of one or more optical 
artifacts 187 detected within a data surface 184. During the processes of 
detecting or of producing optical artifacts 187, active layer 183 is 
translated relative to flying split aplanat 109, as indicated by arrow 19. 
The advantage of this configuration is that the greater spacing between 
head and medium allows for relative movement. The evanescent field is 
buried in the medium. It then becomes possible to use a high-index 
material, such as diamond, for the top part of the split head to take 
advantage of this greater index value and achieve a higher NA, with 
diamond-like carbon (DLC) coating on the medium. 
In the above manner, the TIR surface portion of the flying head is 
integrated with the medium. The flying head may be part of a drive, or may 
be a lens array in the housing. The flying height is less than a 
wavelength such that the coupling between the flying head and the layer in 
the medium is via the evanescent field, and FTIR. In this way, there is no 
need for spherical aberration correction, because none is introduced by 
such a small split. Further, numerical apertures of greater than 1 can 
occur in the medium. Further still, these numerical apertures can be used 
for either propagating light immersion imaging, or evanescent field 
illumination with the attributes already discussed. Others knowledgeable 
in the relevant art had proposed a split where a portion of the flying 
aplanatic sphere head is removed, and the optical equivalent added to the 
medium. However, the flying heights are on the order of many wavelengths, 
such that (1) all the light is propagating--no use of evanescent fields is 
made, (2) numerical apertures are restricted to less than one, and (3) the 
large split and the absence of evanescent coupling introduces spherical 
aberration which must be corrected for. The see Guerra 1994 patent and 
1988 paper showed how the TIR portion can be split from the head, or 
objective, with the coupling between the two, in one embodiment, being 
immersion oil, but need not be. Accordingly, in another paper (MRS, 1994), 
Guerra showed that the coupling between the TIR surface and the next TIR 
surface can be via the evanescent field (Mica image). So, there are at 
least two evanescent field couplings here, the first being between the 
partitioned head and a first layer in the medium (FTIR), and the second 
and subsequent being between the optical layer(s) and the active layer(s) 
via FTIR or ATR. 
In a near-field optical data storage system where the near-field head is 
flying, this invention allows the optical data surface (ROM or WORM or 
rewriteable) to be internal to the medium disc (floppy or rigid) rather 
than on the surface of the disc. The optical data is protected, and is 
also very planar, thereby removing the noise contributed by topographic 
variation of surface data in the near-field and increasing the 
signal-to-noise of the system. All the advantages of the integral 
micro-optic media configuration are enjoyed, along with the higher storage 
density that comes from the numerical aperture being high along the track 
direction as well as perpendicular to the track direction, and with a disc 
that is simpler in construction and therefore less costly to make. This 
split near-field flying head invention is compatible and can be combined 
with dark-field, dark-field near-field, phase near-field resolution, 
diffraction near-field, optical track discrimination, sub-pixel synthesis 
detector, vacuum surface head, multi-level, multi-layer, and other aspects 
of our near-field storage technology, as well as with the Isis phase 
change material or topographic pits. 
A flying near-field head, which is an optically transparent body in the 
form of a prism or, preferably, an aplanatic sphere that is flying at 
substantially sub-micron height proximal to a disc or other geometry 
surface, is disclosed in our 1987 patent as well as later patents from 
others (Stanford, IBM, Matsushita). Typically, the head is illuminated 
beyond the critical angle to generate an evanescent or near field which is 
then used to write on and read an optical data surface immersed in the 
field. 
In the present invention, the near-field head is physically split into two 
parts along a plane parallel to the total reflection surface. The larger 
part may be considered the refractive element, and the remaining thin 
plate part contains the total reflection surface. The two parts are placed 
very close together, without touching, so that they are optically coupled 
by the evanescent field between them. The thin plate part is then extended 
and made integral to the medium disc, so that there can be relative 
movement between the remaining head and disc, and thus flying. At flying 
heights of less than 0.1 micron, the coupling loss is minor and tolerable. 
The thin plate may be polycarbonate cut from a web, or may be a 
diamond-like carbon or other material layer for higher index of refraction 
and better durability. The thin plate and flying head are of like indices 
of refraction. 
The near-field and the optical data surface(s) are internal to the disc, 
with the robustness and precision control inherent to that configuration. 
However, here only the bottom planar portion of the optic is integral to 
the disc, while the refractive part is flying. In this sense it is similar 
to the patented flexible transducer, in which the bottom total reflection 
surface is a separate flexible sheet placed on the sample, except that in 
that case the coupling of the sheet to the refractive optic in the 
objective is with oil immersion, while in this case the coupling is via 
the evanescent field from the flying head. Thus an evanescent field is 
generated twice, once at the head/medium interface, and then at the medium 
top sheet/recording layer interface. 
Now, the head is flying above a very smooth polycarbonate or other material 
planar surface so that flying height is much more uniform. Also, the 
optical data layer is no longer on the surface, vulnerable to head 
contact, finger contact, or other hazards. Further, in the case of phase 
change data layers, the phase change material is deposited against the 
internal smooth polycarbonate or other surface (there may be other layers 
of other refractive indices deposited first) so that there is no 
topographic noise source. Full resolution inherent to a discrete flying 
near-field head is enjoyed along with the robustness of the integral 
micro-optic media, but without the difficulty of making such media. No 
storage area is lost to field-of-view. 
Resonant structure: 
It is well known in the relevant art that evanescent field 80 can be 
enhanced by orders of magnitude with a resonant structure 34. Typically, 
resonant structure 34 comprises two layers added to the total internal 
reflection surface of the near-field optic, such as a prism or aplanatic 
sphere 31, for example. For a prismatic element comprising a material 
having an index of refraction of 1.5, one added layer will comprise a 
lower index of refraction (e.g., 1.0) and the other layer will comprise a 
higher index layer waveguide of over 2.0. An absorber adjacent to the high 
index waveguide will exhibit enhanced absorption. This technique and 
structure is well known and is used in spectroscopy, for example. Harrick 
shows such a structure, seen in FIG. 33, comprising an absorber layer 36a, 
a cavity film 36b comprising a high-index material such as silicon, a film 
reflector 36c comprising a material such as quartz, and a hemicylinder 
36d. Yariv and Yeh discuss such resonant structures in depth. Guerra 1994 
patent claims a resonant layer structure in combination with a flexible 
transducer for use in photon tunneling microscope devices, which utilize 
the evanescent or near field. Guerra additionally claims a resonant 
structure with a flying near-field head and also integral to a medium, 
both for optical data storage in 1997 patents, but in combination with 
phase controlled evanescent fields. Kino shows a thin film on top of the 
active recording layer (1992 optical data storage patent) but the film is 
not claimed for resonance, and is of an index matching that of a flying 
head. 
Here, the resonant structure may be either part of the near-field optical 
array integral to the cartridge, or may be integral to the medium proper. 
In either case, an advantage gained is the large enhancement of the 
near-field for much higher signal to noise ratio SNR and absorption. Thus, 
even very small optical effects (polarization, refractive index, or other 
changes) in the active optical data recording layer are amplified. 
In an application wherein the micro-optics are configured as part of a 
housing structure for an enclosed optical medium, another advantage is 
that the optical array may be molded in plastic, with the performance and 
cost benefits inherent to that technique (e.g., mass production methods to 
provide complicated aspheric surfaces by which to reduce aberrations). 
However, because the waveguide layer in the resonant structure (which is 
added to the plastic optical array with the usual vapor deposition 
techniques) is of a significantly higher index, the spatial resolution and 
thus areal density of a higher index near-field optic are enjoyed. 
In the case of the resonant structure added to the medium proper, the 
active optical layer is protected by the added structure from 
environmental damage. In addition, the application of these layers 
typically has a smoothing effect on the topography of the active optical 
layer, in the case of MO or phase-change materials, for example, thus 
reducing the noise from that factor. The relative refractive indices of 
the layers, and their optical thickness, as well as the incident 
illumination angle and wavelength, are optimized in well known relations 
for resonance conditions, with many possible variations which are outside 
the scope of this invention. Coherence is required for this resonance. 
Alternatively, a surface plasmon resonant field (which also decays 
exponentially) may be formed when a layer of about 200 angstroms of 
aluminum, gold or silver, disposed between the optical layer and the 
active layer, is optically pumped by the evanescent field, and can achieve 
at least ten times the sensitivity of the evanescent field alone because 
resonance is easily "detuned" by small changes in the adjacent optically 
active layer. Ref: Otto. 
Further Embodiments 
As was disclosed above, to convert evanescent field 39 back into 
propagating, it is required that one is close to the surface with i) a 
high refractive index dielectric material, or ii) a diffraction grating 
with grating period similar in size to the artifact spatial period. The 
more evanescent the field (i.e., the smaller the optical artifacts), the 
higher the refractive index that is required. Ultimately, there is a 
practical limit (imposed by the index of refraction of available 
materials) of about 2.4 in the visible spectrum to about 3.5 in the near 
infra-red spectrum. 
Conversion by diffraction, on the other hand, is limited only by the 
diffraction grating spatial period. In this case, the diffraction grating 
period is less than the illumination wavelength .lambda., where the 
grating can be a phase grating, an amplitude grating, or an index grating. 
The use of evanescent fields generated by diffractive structures for 
optical heterodyning beyond the limitations set by the light wavelength 
and refractive index has been disclosed before in Refs. 1-3 and 
particularly regarding optical data storage capacity in Refs. 4 and 5. Ref 
Guerra 1995 APL paper, and '97 phase patent. Any heterodyning technique 
responds best to global (i.e., multi-element), or semi-global, changes 
rather than local changes (i.e., a single element) in either the reference 
or unknown frequencies, where an element is a single line pair in the case 
of a grating, for example. 
Encoding diffraction near-field information: 
This is a preferred method of making use of the super-resolved optical 
storage capacity of diffraction-born evanescent field optical heterodyning 
disclosed previously. 
A reference frequency in the form of a substantially sub-wavelength optical 
grating placed within the evanescent field distance to an optical storage 
medium replaces the electronic reference frequency now used in analog 
optical video storage, thereby allowing optical data to be stored at 
similar substantially sub-wavelength dimensions. 
Recording and playback of video images (and soundtrack) requires enormous 
data storage capability that is best accomplished with a frequency 
modulation (FM) analog readout and heterodyning technique. On the 
successful laser video discs, for example, the information is stored 
optically as pits of constant length in the track direction, but whose 
pitch varies about some nominal pitch. The analog signal thus generated is 
heterodyned with an electronic signal of the constant nominal pitch, or 
frequency. (Audio, with the less stringent storage demand, is encoded 
digitally as pits of varying length.) 
In the present invention, the reference electronic signal of constant 
frequency is replaced with a reference evanescent field. This is 
accomplished with a grating whose period is smaller than the illumination 
wavelength. The reference grating can take at least two forms. The first 
would be a series of pits of constant length and pitch, illustrated in 
FIGS. 34A and B, against which the recorded pit pitch would vary along the 
track, causing the heterodyne signal to vary. This is the closest 
evanescent, or near-field, analog to what is practiced now, except that it 
is all optical and extends the storage density a magnitude or more. The 
second reference pattern is a simple parallel line pattern of constant 
pitch, illustrated in FIGS. 35A and B, with the recorded lines varying in 
pitch perpendicular to the track direction. The typical track pitch of 
laser discs is about 1.6 microns (DVD is less). As shown in Ref. 4, a 
track pitch of 0.1 microns has been easily demonstrated in the evanescent 
field. A track pitch of 0.05 microns is certainly attainable, so that even 
allowing for a redundancy of about 3 tracks, required for a good 
signal-to-noise in the heterodyning, yields 0.15 microns, or a factor of 
ten over the current technique. Soundtracks can be recorded by modulating 
the grayscale of the tracks, or other dimension, as is done now. 
This reference sub-wavelength grating may be in the form of topography 
added to the total reflection distal surface of a discrete flying optical 
head, or may be integral to the optical recording medium itself. The 
sub-wavelength diffractive grating may be part of the optical layer in the 
medium (as in FIG. 10, for example) and may be illuminated with either 
propagating or evanescent illumination. There may also be a second 
reference sub-wavelength diffractive grating disposed between the active 
layer and the optical layer. Writing with a diffraction-borne near-field 
requires the phase control of the evanescent field as taught in U.S. Pat. 
No. 5,666,197 issued to Guerra. 
As can be appreciated by one skilled in the relevant art, any of the 
above-described embodiments may comprise one or more additional features 
as may be desired to enhance implementation of the disclosed invention. 
For example, the cartridge may have internal non-woven fabric wipers to 
keep the flying interface clean, and may have the usual sliding shutter to 
protect the integral micro-optic window, as is known in the art. 
Similarly, abrasion resistant optical hard-coats such as diamond-like 
carbon (DLC) can be applied to all exposed and tribological surfaces, such 
as the medium proper, both side of the integral micro-optic array in the 
cartridge, and the top surface of the micro-optic integral to the medium 
proper. Further, a head or back plate opposite the medium from the flying 
integral near-field optics may be provided to facilitate proximity flying. 
Critical angle method: 
In this method, optical artifacts are formed and read when total internal 
reflection is locally frustrated or locally enabled by change in the 
refractive index of the base or active layer, and illumination and/or 
imaging is restricted to just at the critical angle. This method is 
sensitive to changes in index of refraction occurring out to the third 
decimal place. Changing incident and imaging angle slightly switches 
channels to whole new set of data at a different index and corresponding 
critical angle. The illumination can be restricted to the immediate 
neighborhood of the critical angle by placing an annular aperture 227 in 
the illuminator, as shown in FIG. 36. When used in wholefield writing, a 
laser diode array 229 may be emplaced as shown. Alternatively, laser diode 
array 229 may be replaced by a mask (not shown) when used for lithography 
or other such methods of whole-field writing. 
Principal Angle Method 
The s- and p-polarization components have generally different phase 
.alpha..sub..perp. and .alpha..sub..vertline..vertline. respectively: 
##EQU4## 
where i.ident..sqroot.-1, .lambda..sub.o is the freespace wavelength of 
the illumination, .beta.=(N.sup.2 sin.sup.2 .theta.-1).sup.1/2, 
.lambda..sub.1 is the wavelength in medium 1, and .mu..ident.n.sub.2 
/n.sub.1 .ident.n.sub.21 .ident.N, the ratio of the indices of refraction 
in medium 2 and medium 1, respectively. 
Equations (5) and (6) indicate that phase shifting of the incident 
illumination can be accomplished in a number of ways that include 
wavelength shift, incident angle shift, azimuthal incident angle shift, 
polarization shift, or shifting of the incident phase in the Z axis. The 
illumination may be coherent, or simply filtered white light. The method 
used in some interferometer microscopes, for example, can be used, where 
piezo-controlled nanometer physical manipulation of the wavefront phase is 
effected, which has the advantage of decoupling phase shift from amplitude 
variation. All this is prior art, described in (ref 1997 Guerra phase 
patents). 
The difference in (5) and (6) results in the elliptical polarization seen 
in totally-reflected illumination. There exists a Principal angle at 
greater than the critical angle and less than .pi./2 where the two 
polarizations are equal; in this sense it is complementary to the Brewster 
angle for propagating illumination. 
Adjusting the aperture in the illumination such that only illumination at 
or near the principal angle reaches the active optical layer will result 
in the highest sensitivity to induced or existing polarization 
differences, representing optical data, in the optically active layer. 
Systems: 
Objective lens 111 is preferably articulated to enable motion in several 
degrees of freedom such as transverse motion, longitudinal focusing, and 
tilt. Although prisms are the preferred embodiment, aplanats can be used 
and articulating the objective lens would increase the field of view for 
the case when optics are aplanatic and integral to the medium proper. 
The integrated micro-optics in either form (part of medium proper or part 
of medium cartridge) could be read with a substantially conventional 
radially actuated traversing head/objective, and still enjoy a degree of 
whole-field and multi-track imaging and the resultant attributes described 
earlier. 
The objective can be a conventional DVD objective, but a more optimized 
system would include an aspheric objective that corrects for the 
anamorphic optics of the integrated micro-optics in the medium proper, and 
corrects for the spherical aberration and astigmatism introduced by the 
substitution of prisms for aplanats. Also, the optimized objective may be 
bifocal, with the central part of the numerical aperture corresponding to 
the NA less than 1 at the active optical layer focused on the lands 
between the truncated prisms. These lands may contain servo tracking 
structure spaced about 0.9 microns apart. 
The micro-optics integrated with the medium proper can be typically 
anywhere from 5 microns to 50 microns or more in pitch, with the data 
tracks on the order of 0.1 micron or so, so each element of the 
micro-optic looks at many tracks. 
However, the integration of micro-optics and the medium allows the 
opportunity for an improved way of reading and writing optical data which 
reduces or eliminates the need for radial actuation, and ultimately, even 
the need for spinning circular media and data tracks. 
Radial actuation reduces the speed of random access of data. Additionally, 
in systems that utilize a flying head, whether near-field, optical, 
magneto-optical, or magnetic, most head crashes and resulting data loss 
occur during radial movement of the head. 
For whole-field imaging, a secondary array of objective optics may be used 
in conjunction with the integrated array. Similarly, the detector is not a 
single element but instead may be an array of elements, with a single or 
multiple elements dedicated to each of the optical array elements. Just as 
with the integrated micro-optic array, the optics in the secondary array 
can be optimized by aspherizing and can have optical power on either side 
in order to optimize the combined microscopic array system. 
If the diameter of the field of view of each of the optical elements in the 
array is 50% of the physical diameter of each optic, then it follows that 
at least two rows of elements are required, staggered such that full 
coverage is achieved. Additional rows may be included for more highly 
optically optimized coverage, or the elements may have discrete focal 
properties to eliminate the need for focus actuation. 
If the detector array is skewed with respect to the optical array, or if 
the elements themselves are offset by a known amount, sub-pixel resolution 
results and then the secondary optical array can even be eliminated. 
For writing, the power levels provided by coherent laser diodes are still 
required at this time for the existing active optical materials. However, 
writing multiple tracks can be achieved through the same secondary 
objective optical array if a laser diode array is used in conjunction with 
it. 
Array Objective 
So far, it has been assumed that there is a conventional objective in the 
drive into which the medium with integral optics is inserted. Further, the 
objective associated with the drive may not be conventional, but may be 
fully articulated to include tilt, and may have a bifocal design to better 
image the servo tracks. Further still, the objective associated with the 
drive may be an array of close-packed and staggered lenses arranged so as 
to cover the entire area of the medium when the medium is spinning, or 
when the medium is stationary and smaller. 
However, the objective in the drive may be eliminated by transferring its 
optical functionality to the optics integral to the medium. This may be 
done for either the evanescent field illumination embodiment or the 
propagating illumination embodiment. 
To this point, the optics have been integral to the medium proper, or to a 
cartridge in which the medium proper is housed. In the case of propagating 
light, when the optics were integral only to the cartridge, they served 
the purpose of working with the external drive objective to increase 
numerical aperture to near 1. Here, the optics are again integral to the 
cartridge, but serve as stand-alone objectives having a numerical aperture 
of about 0.6, in order to eliminate the need for the drive objective. 
A better embodiment, however, is to use integral optics both at the medium 
proper and at the cartridge, so that the two sets of optics work together 
as a high numerical aperture objective. Whether the illumination is 
propagating or evanescent, the numerical aperture will be greater than 1 
and typically 1.3 or higher. 
The optics integral to the media are preferably, as before, circumferential 
in form, while the optics in the cartridge are either an array of close 
packed lenses, staggered so that their fields of view overlap and 
completely cover the medium radius, or an array of lenticules, skewed with 
respect to the tracks in the medium so as to cover the entire data area 
(see FIGS. 29A and 29B). 
The detector can be a single detector that is actuated radially to receive 
the signal from the various elements in the optical array, or may be a 
small detector array that is similarly actuated. However, a preferred 
detector arrangement, in which radial actuation is eliminated, follows. 
Skewed Detector Array 
Whether the optical array is integral to the medium cartridge or is in the 
drive, and whether this array is combined with additional integral optics 
in the medium proper, the resulting image from each of the array elements 
contains information from many data tracks simultaneously. A detector 
array may be placed along and oriented parallel to the longitudinal axis 
of the optical element, in the focal plane of the optical element, as seen 
in FIG. 37. Each of the individual detector pixels 194 in the array then 
receive the signal from a given data track 192 within the image from the 
optical element. Therefore, by monitoring the signal from each of detector 
pixels 194 either switching between one at a time or several at once, the 
data from multiple tracks can be read simultaneously and at high speed. 
For the higher track pitches reached with the evanescent field 
illumination, for example, the size of the detector pixel should be as 
small as possible. At present, the CCD (including CMOS) industry makes 
pixels as small as 6 microns square. However, substantially sub-pixel 
resolution can be synthesized by aligning the boundary between two 
detector columns with the optical axis of the optical array element, such 
that each of the optical artifacts in the image plane of the optical 
element is swept in a skewed trajectory across the detector boundary. By 
analyzing the signal output from several contiguous detector pixels in 
those two rows, and because the amount of skew between the detector 
columns, optical array element, and data track are preset and known, 
optical artifacts that are significantly smaller than the detector pixel 
are detected and resolved from neighboring optical artifacts. 
Pixels in a CCD, CMOS, or other detector are usually arranged in an 
architecture of straight rows and columns. Resolution of such a detector 
or display with this architecture is determined by, and on the order of, 
the size of the pixel in each axis relative to the image or other light 
pattern presented to it or displayed. Should a part of the light pattern 
overlap several pixels, the centroid of the light pattern can be 
determined to a fraction of a pixel. However, should a light pattern be 
smaller than a pixel, it is not resolved whether it falls within a pixel 
or straddles plural pixels. 
In the case of detection, the skewed pixel columns allow the kind of 
sub-pixel centroid resolution described above, except that the sub-pixel 
sized object itself is resolved rather than its centroid alone. 
Because the size of the offset from one pixel to another is known, the 
relative signal levels from each of the pixel "channels" can be compared 
and analyzed to detect, resolve, and determine the size of the sub-pixel 
light pattern as it traverses the terminator boundary between the 
neighboring pixel columns. The optimum way of doing this depends on 
whether speed or resolution or noise reduction is the over riding concern. 
The pixel to pixel analysis algorithm can be as simple as (A-B)/(A+B), in 
the typical quad-cell detector mode, or can be much more sophisticated as 
iterations involving a larger number of pixels is involved. 
A mask 196 may be added that is an array of apertures centered on the pixel 
column boundaries. The width of the apertures is on the order of the 
resolution required. Such a mask 196 may also be centered on the pixel 
columns, but the benefit of the pixel detection arithmetic is eliminated. 
This method and means is somewhat analogous to a Vernier scale, which is to 
say a Moire or heterodyning technique, where resolution on a scale much 
smaller than the fiducials on the Vernier or the grating pitch in Moire is 
achieved. However, it also shares elements of the centroid resolution of 
the quad-cell, and even some elements of a knife-edge approach. 
This skewed array architecture can be applied to an entire 2-D detector 
chip, or to a bi, tri, or multi-linear array. In optical data storage, 
reduces or eliminates the need for servo tracks (acts as wobble pit 
servo); reduces or eliminates radial movement and actuator in optical 
drive: a tri-linear array of about a 20 mm length would cover the entire 
area of a spinning 50 mm (e.g., Polaroid Mini Disc), thereby making for a 
drive nearly the size of the medium with reduced mechanisms and cost, and 
allows parallel data readout, multi-channel encoding, and extremely fast 
readout and data transfer rates. Where smaller storage capacity is 
sufficient, a staggered architecture CCD or CMOS detector could even 
eliminate spinning the medium as well, so that a rectangular data chip 
could be read out directly (with or without near-field). 
A further advantage can be gained by adding a small fixed slope to the 
detector plane and/or to the optical array plane, relative to the plane of 
the medium, such that the center point of the slope is vertically at and 
intersects the plane of best focus. This eliminates the need for a focus 
servo because the slope is calculated such that the amount of possible 
defocus from vertical movement of the medium or other reasons is 
encompassed by the total slope. In other words, the optical artifact will 
always be in focus somewhere along the detector column length. 
Whole-Field Imaging 
Whole-field imaging can be used in many ways as exemplified by the system 
diagram of FIG. 38. New encoding schemes in which multiple tracks are used 
together would allow even more density in data storage. With the existing 
encoding, multitasking from the same disc is possible, as several software 
programs can be read from the same disc at the same time. Rotation speed 
can be reduced because data transfer is occurring from several tracks at 
once, rather than having to wait for the disc to progress a full rotation. 
Therefore, data transfer rates can be as high or higher than hard disk 
drives, for example. At present, removable media storage devices that are 
not based on the Winchesters hard disc technology are much slower in data 
transfer times, so they cannot compete for that part of the desktop PC 
market. 
The whole-field imaging advantage brought by the integrated micro--optic 
array is best realized with near-field illumination and optics. However, 
even propagating illumination techniques will enjoy a good increase in 
effective NA up to but less than 1 for the media cartridge integration, 
and more for integration to the medium proper. 
For some applications, data can be read from a non-rotating medium, whether 
that medium is circular in form or rectangular or other, by combination 
and extension of this invention of integrating micro-optics with the 
medium and the system combination with a secondary array of optics and a 
multi-element areal detector array. The data is scanned from the disc 
without mechanical movement of any kind, by reading out the detector array 
signal. Writing would require a similar array of laser diodes and at least 
a linear movement relative between the medium and the laser diode array. 
When optical active layers become more sensitive, however, a whole-field 
approach can be applied to the writing aspect as well, where a whole-field 
illumination source is spatially modulated by an optical gating device 
such as a liquid crystal matrix, placed at the focus plane conjugate to 
the detector plane. 
In the embodiment of the optical array with a non-actuated single 
illumination source for reading and or writing, additional optics not 
shown are inserted between the source and the array in order to make the 
system optically telecentric. Otherwise, a multiple source array may be 
used. 
Other applications: 
In addition to optical data storage applications, the integration of 
micro-optic arrays with a surface or photo-active surface has other 
applications not anticipated prior to this. The micro-optic array can be 
flexible, semi-rigid, or rigid. 
For example, in the mastering of the stamper for ROM discs, integration of 
a film of micro-lenticulars with the photoresist would increase the 
mastering resolution, allowing a wider choice of laser wavelengths and 
therefore a wider variety of photoresists. The micro-lenticulars would be 
removed along with the resist later in the process. 
Resolution in micro-lithography of, for example, micro-electronic circuits 
and devices would be improved by integration of a micro-optic array with 
the photo-resist coated semiconductor wafer, thereby allowing smaller line 
widths and more powerful, faster chips, without resorting to a single, 
costly, large immersion objective. In this application, the micro-optics 
could be aligned with the line pattern itself. 
Similarly, a micro-optic array could be applied to a finished processed 
wafer in order to measure line widths with high resolution. The 
micro-optic array would preferably consist of micro--aplanatic lenses used 
either in immersion mode or in near-field mode, and would allow the same 
or better resolution as an oil immersion objective but without the 
immersion oil, which could contaminate a clean room and ruin an expensive 
micro-electronic wafer. 
That same micro-optic array can be integrated to many surfaces and samples 
other than wafers, so that even inexpensive microscopes with, for example, 
an objective with NA of 0.65 or so would be converted to immersion 
microscopes with NAs of better than 1 and typically NAs of about 1.3, 
without oil and with the high working distance of the NA 0.65 objective. 
While an immersion objective lens can cost several hundred to several 
thousands of dollars, the flexible micro-optic arrays would be 
mass-produced by, for example, compression molding or web-embossing, and 
so would be repeatable yet inexpensive and disposable. 
Flexible immersion lenses: 
The present invention removes the need for immersion oil in photon 
tunneling microscopy as well as immersion microscopy, eliminates the 
expensive immersion objective, and allows photon tunneling with a dry, 
long working distance, lower NA objective. 
In the Guerra flexible transducer patents of 1994 and 1996, the rigid total 
internal reflection surface is eliminated and replaced with a disposable, 
inexpensive, precision transducer. However, an oil immersion objective 
must still be oil-contacted to the transducer. This invention takes the 
flexible transducer a step further, and eliminates the oil immersion 
objective by incorporating integral micro-aplanatic lenses, arranged in a 
close-packed array into the upper transducer surface. With this flexible 
optical sheet placed on the sample in the teaching of the transducer 
patents, a dry long working distance objective of numerical aperture 0.6 
will function together with the integral aplanatic lenses as an oil 
immersion objective of NA 1.25 or higher. In this way photon tunneling, or 
even just immersion microscopy, is accomplished without oil and with a 
large working distance. Of course, what is lost is the ability to move the 
aplanat with respect to the sample, but with the close packed array most 
of the sample will be made visible by moving the dry objective relative to 
the micro-lenses. 
This flexible lens array brings affordable photon tunneling and immersion 
microscopy to the classroom, for example, or to applications where the 
immersion oil is thought to be a problem, such as in the semi-conductor 
industry when used for lithography or metrology. It is easily molded or 
embossed into web, or the lenses can be holographic elements. 
The present invention removes the need for immersion oil in photon 
tunneling microscopy as well as immersion microscopy, eliminates the 
expensive immersion objective, and allows photon tunneling with a dry, 
long working distance, lower NA objective. 
In the Guerra flexible transducer patents of 1994 and 1996, the rigid total 
internal reflection surface is eliminated and replaced with a disposable, 
inexpensive, precision transducer. However, an oil immersion objective 
must still be oil-contacted to the transducer. This invention takes the 
flexible transducer a step further, and eliminates the oil immersion 
objective by incorporating integral micro-aplanatic lenses, arranged in a 
close-packed array into the upper transducer surface. With this flexible 
optical sheet placed on the sample in the teaching of the transducer 
patents, a dry long working distance objective of numerical aperture 0.6 
will function together with the integral aplanatic lenses as an oil 
immersion objective of NA 1.25 or higher. In this way photon tunneling, or 
even just immersion microscopy, is accomplished without oil and with a 
large working distance. Of course, what is lost is the ability to move the 
aplanat with respect to the sample, but with the close packed array most 
of the sample will be made visible by moving the dry objective relative to 
the micro-lenses. 
This flexible lens array brings affordable photon tunneling and immersion 
microscopy to the classroom, for example, or to applications where the 
immersion oil is thought to be a problem, such as in the semi-conductor 
industry. It is easily molded or embossed into web, or the lenses can be 
holographic elements. Polaroid is world-class in all of these 
technologies. 
If in the future the pixel size in CCD arrays is made smaller to the point 
where optical resolution is exceeded, a micro-optic array integral to the 
CCD would increase the resolution accordingly. (Now just used for fill 
efficiency, back thinned too.) 
Recording media can be for optical data recording or for image recording. 
Harmonic generation 
For most of the evanescent field applications discussed thus far, the 
wavelength, or quasi-wavelength, of the evanescent field is the same as 
that of the parent wave in the denser medium, which in these cases are the 
integral micro-optics or the integral resonance structure. The frequency 
of the evanescent field, however, is invariant with the index of the 
medium. If, however, the total internal reflection occurs within a 
photo-refractive non-linear material, second harmonics can be generated 
when the incidence of the light it close to the critical angle, such that 
the frequency of the evanescent field is doubled. In this case, it becomes 
possible to consider other active optical layers in which the mechanism 
for change is molecular in nature, in the form of photo-dissociation of 
bonds. (This can be seen to have impact on a scope wider than optical data 
storage, if, for example, the integral near-field optics are used with 
water as the active optical layer and the illumination is sunlight made 
sufficiently coherent, such that the hydrogen to hydrogen bonds in the 
water are broken to release hydrogen for fuel (with desalination a useful 
byproduct when ocean water is used).) Further discussion is provided in 
Bloembergen and Lee. 
Vertical Storage: Multilayer, Multilevel 
Integrating the near-field optics with the medium also, by definition, 
makes the near-field part of the medium. The stability that this imparts 
compared to a flying near-field head that is part of the drive rather than 
the medium, for example, facilitates the full use of the evanescent field 
component. Thus, for example, diffraction-born evanescent fields with 
their very short decay become more practical to use, as already discussed. 
The stable evanescent field may also be better applied for vertical 
storage in two forms. The first is multilevel, where varying the intensity 
of the illumination causes a corresponding variable change in the optical 
bit in the active optical layer, such that rather than a binary-encoded 
data set one may encode in many levels. The high optical contrast (signal 
to noise) that results from evanescent field illumination of, for example, 
either magneto-optical or phase change active layers, allows many more 
levels to be achieved than with the normal propagating light for reasons 
stated earlier. 
A second form of vertical storage made possible with the integral 
evanescent field is called multi-layer (see FIG. 39), because the total 
reflection interface at which the evanescent field arises can be repeated 
vertically with the addition of subsequent layers of high-low-high 
refractive index materials, where the refractive index may even be complex 
if the absorber is thin enough. In this way, refocusing the external 
objective lens or array causes information stored at each of these total 
reflection interfaces to rapidly come into focus. The number of vertical 
data layers is restricted by the scattering properties of the layers, 
particularly the active layers, in addition to the accumulation of 
unfocussed light from the nearest active layers, so that in practice the 
signal to noise ratio is too low if four or more active layers are used. 
In the example provided, three signals 202, 204, and 206 are returned from 
three such layer configurations. 
See FIG. 40 for an example of signals returned from a storage medium having 
a four-layer configuration. Trace 202t represents the signal from the 
first high-low interface, trace 204t represents the signal from the second 
high-low interface, trace 206t represents the signal from the third 
high-low interface, and trace 208t represents the signal from the fourth 
and most distant high-low interface. 
If the vertical periodicity of the high-low layer elements is on the order 
of 20 microns or less, with the low index being less than a micron thick, 
there is an interesting but unexplained equal splitting of the signal from 
each of the active layers, rather than the expected progressive splitting, 
or halving, of the signal from each of the preceding active layers. For 
greater vertical periodicity, the signal splits as expected such that the 
signal from the lowest is quite weak. In this case it is useful to make 
the vertical periodicity non-linear by making the furthest low index 
layers progressively thinner to compensate for the weaker return signal. A 
greater vertical periodicity, although adding somewhat to the layer 
structure complexity, allows better separation of the signal from each of 
the active layers by the depth of focus of the external objective combined 
with the integrated near-field optics. 
Integral micro-optics can also be used when the method of optical storage 
is holographic in nature. 
While the invention has been described with reference to particular 
embodiments, it will be understood that the present invention is by no 
means limited to the particular constructions and methods herein disclosed 
and/or shown in the drawings, but also comprises any modifications or 
equivalents within the scope of the claims.