Method for data reading/writing using an optical carrier...

Details Method for data reading/writing using an optical carrier... Method for data reading/writing using an optical carrier...

2001-02-12

2003-01-14

Edun, Muhammad (Department: 2653)

Dynamic information storage or retrieval

Control of storage or retrieval operation by a control...

Control of information signal processing channel

C369S047100, C369S059100, C369S275100

Reexamination Certificate

active

06507545

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention.
The invention relates to optical memory systems and more particularly to methods of 2D spatial encoding of information for high-density writing in one- or multilayer optical, especially fluorescent data storage systems.
2. Description of the Prior Art.
The available optical memory systems utilize 2D carriers, generally with one or two information layers. Most of the prior art in the field of optical information recording are based on generating changes in the intensity of reflected laser radiation in local microregions (pits) of the information layer. These changes contain stored information and can result from interference effects on a microrelief surface of optical discs of a CD- Read-Only-Memory (ROM)-type, burning of holes in the metal film, dye bleaching, local melting of dye-containing polymers in widely used CD-Write-Once-Read-Many (WORM) systems, change in reflection coefficient in phase-change CD-Rewritable (RW) systems, etc.
FIG. 1
schematically presents geometry of two-dimensional spatial distribution of information pits on the surface of CD and DVD optical information carriers. Their spatial distribution in CD- and DVD-ROM can be characterized by such parameters as typical pit sizes (shortest pit length l, width w, depth d, and track pitch p) and channel bit length.
Numerical values of these and other CD- and DVD-ROM parameters are given in Table 1. [“Information Storage Materials ”, pp. 36, 42].
TABLE 1
From CD to DVD
Parameter
CD
DVD
Wavelength &lgr;, nm
780
650
Numerical aperture NA
0.45
0.60
Shortest pit length, nm
831
399
Depth, &mgr;m
0.13-0.15
0.11-0.12
Track pitch, &mgr;m
1.6
0.74
Channel bit length, nm
277
133
Modulation code*
EFM
EFM**
Physical bit density, Mbit/cm
2
106
508
Reference velocity CLV, m/s
1.2
4.0
Spot size &lgr;/2NA, &mgr;m
0.9
0.55
Capacity, GB
0.65
4.7
*For EFM (“eight-fourteen modulation”) one has 17 channel bits (14 modulation and 3 merging bits) for 8 data bits. Each channel bit corresponds to 1/3 of the minimum mark length. The physical bit density equals to 1/(track pitch × channel bit length × 17/8). For EFM** the factor 17/8 is replaced by 16/8.
As can be seen from Table 1, transfer to the DVD-format considerably increases the density and consequently the volume of stored information. However, as can be seen from FIG.
1
and Table 1, information pits occupy yet only part of the information layer area which significantly reduces the values of density and volume of stored information as compared to maximum permissible magnitudes.
To increase the writing density such methods are used as transfer to shorter-wavelength radiation sources in combination with high-NA objective lens (see Table 1 and as an example [I. Ichimura et al, SPIE, 3864, 228]), a reduced track pitch and increasing the groove depth of the land groove recording type optical disk [S. Morita et al, SPIE, 3109, 167]. For high-density data storage, new media and techniques for data reading therefrom [T. Vo-Diny et al, SPIE, 3401, 284], pit-depth modulation [S. Spielman et al, SPIE, 3109, 98], and optical discs having square information pits arranged in symmetrical patterns [Satoh et al, U.S. Pat. No 5,572,508].
Data writing density as high as more than several terabits per cubic centimeter can be ensured by three-dimensional (monolithic) photosensitive media exhibiting various photophysical or photochemical non-linear effects at two-photon absorption. The best reading/writing mode for such 3D WORM or WER information carriers is cooperative two-photon absorption by photosensitive components and photoreaction products themselves via an intermediate virtual level as in the case of photochromic [D. Parthenopoulos et al, Science, 245, (1989), 843] or photobleacing [P. Cheng et al, Scanning, 18, (1996), 129] materials or registration of a change in refractive index as in the case of photorefractive crystals [Y. Kawata et al, Opt. Lett., 23, (1998), 756] or polymers [D. Day et al, SPIE, 3864, 103] and photopolymers [R. Borisov et al, Appl. Phys., B 67, (1998), 1].
Generally, such reading/writing mode allows local recording of data as marks (pits) analogous to information pits in conventional CD- or DVD-ROM, with varied optical properties in the volume of information medium.
Practical realization of this principle however is impeded by the large overall size needed for such writing of femtosecond laser radiation sources and the extremely low photosensitivity of the media themselves. The latter is dictated predominantly by the low magnitudes of cross sections of two-photon absorption currently known.
That same reason rules out the application of 1-10-mW small-size semiconductor lasers for two-photon data writing. Besides, the design of the 3D system based on this principle is rather complicated.
To increase the volume of information stored the application of multilayer bilateral information carriers would be technically more justifiable. However, they impose certain restrictions on the design and properties of the recording medium, data reading and writing procedures, especially in the depth, thereby creating additional difficulties.
In the reflection mode operation, each information layer of the multilayer optical data carrier must have a partially reflecting coat. This attenuates the intensity of both reading and reflecting, information-carrying, beams as a result of direct and reverse motion through the carrier up to a specified information carrying layer and back to the photoreceiver. In addition, as both beams are coherent, they are prone to difficult-to-read diffraction and interference distortions on pits and grooves of the information carrying layers occurring on their way.
In this case, preference should be given to multilayer optical information carriers with fluorescent reading that need no partially reflecting coats. Said information carriers ensure considerably reduced diffraction and interference distortions due to the noncoherence of fluorescent radiation, longer wavelength thereof in contrast to reading laser radiation as well as transparence and homogeneity (identity of refraction indices for some layers) of the optical medium with respect to the incident laser and fluorescent radiations. Consequently, multilayer fluorescent optical information carriers have advantages over reflecting ones. In addition, fluorescent reading enables a higher signal-to-noise ratio as compared to the absorption method.
Currently the general demand to all types, in particular fluorescent, of multilayer information carriers as optical discs and cards, tapes or cylinders is that they must ensure maximum possible volume and density of recorded information and maximum possible data reading rate. These requirements are met by minimizing the size of information pits and increasing the recording density thereof in each separate information layer while increasing the total number of layers, as well as by switching over to shorter-wavelength optical radiators as the information density storable in N-dimensional memory systems (N=1, 2, 3) is inversely proportional to the wavelength to the power N. However reducing the size of information pits and accordingly increasing the writing density thereof may lead to a lower intensity of the reading information signal and higher crosstalks due to the “excitation” of the adjacent information layers the reading radiation is passing through. As a result, the reading signal-to-noise ratio goes down.
The purpose of the present invention is to eliminate the above drawbacks through application of a new method of spatial encoding in information layers and parallel data reading therefrom.
SUMMARY OF THE INVENTION
The subject of the present invention is a new ETT (“eight-to-ten”) method of two-dimensional spatial encoding of information stored in two- or three-dimensional, in particular fluorescent optical carriers. The method specifically ensures the same writing density as DVD ca

Affiliated with

Also associated with

Rating

Method for data reading/writing using an optical carrier... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method for data reading/writing using an optical carrier..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for data reading/writing using an optical carrier... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3039063