Multilayer optical bit-oriented memory

1. Multilayer optical bit-oriented memory

2. Multilayer optical bit-oriented memory Abstract The advent of blue-laser (405nm) optical storage in the form of BD,HD DVD,holographic memories, and UDO would seem to signal the end of opticalstorage's technology life. But, in fact, the future of optical storage is stillvery bright. Once theoretical methods of capacity growth, such as multilayer,multi-level, near-field, and holographic are ready to enter the productmainstream. The engineering challenges of these advanced recordingmethods on lasers, media, optical pickups, servos, and read/write channelswill be significant, but achievable. One can confidently predict the future ofoptical storage will be 120-130mm disc media with capacities in the 100 GBto 1 TB range.

3. Multilayer optical bit-oriented memory

4. Multilayer optical bit-oriented memory Classical Optical Storage Classical Optical Storage - I Is the end of the technology line in sight? Is the end of the technology line in sight? • Laser diode (LD) wavelengths (l) have reached the end of the visible spectrum at 405nm. • Conventional objective lens have reached the limit of usable numerical apertures (NAs). • Spot size is a function of l/NA; shorter ls and bigger NAs yield smaller spot diameters and higherareal densities. • The technology life appears ended - but wait! This is only true for linear thinking and design.

5. Multilayer optical bit-oriented memory • Classical Optical Storage - 2 Is the end of the technology line in sight? Is the end of the technology line in sight? • For l fixed at 405nm, classical optical storage can increasecapacity in several ways, alone or in combination. • Architecture Examples: – Multilayer Discs (MLD); 2-N surfaces. – MultiLevel Recording (MLR); replicated, phase change. – Near-Field Recording (NFR); read-only and write/read. – Fluorescent Multilayer Disc (FMD); read and record. • Attractive Combinations: – MLD + MLR (25-50 GB/surface x 2.5 ML gain x N surfacesor 250-500 GB/120mm disc). – NFR + MLR + MLD (50-200 GB/surface x 2.5 ML gain x 1-2surfaces or 125 GB - 1 TB/120mm disc).

6. 3D optical memory: conception Multilayer optical bit-oriented memory Femtosecond lasers Two-photon absorption Single-beam recording Two-beam recording Fluorescent readout Refraction readout Reflection readout Polarization readout

7. 3D optical memory: conception Multilayer optical bit-oriented memory 1-laser, 2-frequency converter, 3- beam splitter, 4-prism, 5-mirrors, 6-delay line, 7-lenses, 8-photochromic recording media, 9-filters, 10-irradiation detector 4 2 1 6 3 5 7 5 5 8 5 7 7 9 10

8. Multilayer optical bit-oriented memory Photochromic compounds Many organic compounds exhibit reversible photochromictransformations between two forms: hv A B hv To develop 3D bitwise working optical memory photochromic compounds must satisfy to the conditions of their application. The concrete requirements are: - large cross-section of light absorption; -high efficiency of photochemical transformations; - thermal stability offorms A and B; -high stability of both forms to irreversible phototransformations; -non-destructive and efficient readout of recorded information by the certain method (fluorescent, refractive, reflective, polarization

9. Multilayer optical bit-oriented memory Photochromic recording media In accordance with the present invention the medium material having the above improved properties comprises a light sensitive photochromic polymeric compositions based polycarbonate or polystyrene and one of new fulgimides.

10. Photochromic recording media Multilayer optical bit-oriented memory The main parameters: -spectral characteristics of recording media provide application of laser radiation with 1064, 532 and 266 nm; -recorded information is retained at room temperature more 10 years; -photoinduced change of refraction index may be over 10-2 at acceptable laser radiation power; -a number of cycles for photoinduced recording- erasure processes may achieve 106. Therefore, it was unexpectedly revealed that above polymer materials based on polycarbonate or polystyrene and photochromic compound from a new fulgimide class undergo photochromic reaction accompanied with photoinduced changes of absorption and refraction which makes them suitable for the purposes of a 2D or 3D working optical memory system. The new fulgimide class was patented.

11. Multilayer optical bit-oriented memory

12. Multilayer optical bit-oriented memoryDiode pumping solid-state laser l = 1064, 532, 266 nm Laser parameters: Pulse duration – 5 ns power (532) – 50 mW Power (266) – 5 mW frequency – 20 kHz

13. Multilayer optical bit-oriented memoryLow voltage multi-channel electro-optical modulators Control voltage – 5-10 V; control frequency – up to 1 MHz

14. Multilayer optical bit-oriented memoryTwo-photon media • Advantage: - Altering of the medium state only in the focal volume • Disadvantage • High threshold • Complicated of the light source miniaturization

15. Multilayer optical bit-oriented memoryOne-photon media • Advantage: - low threshold • simplicity of the light source miniaturization • Disadvantage • darkness of the entire medium volume

16. Multilayer optical bit-oriented memory

17. Multilayer optical bit-oriented memory

18. Multilayer optical bit-oriented memory

19. Multilayer optical bit-oriented memory Numerical model Eout(x.y)=F-1{H(fx,fy) F[Ein(x,y)]} where: transfer function is is considered of the influence of the evanscente modes

20. Transverse structure of the gaussian light beam (w0=25 mm) ) near boundary of the two dielectrics Multilayer optical bit-oriented memory

21. Transverse structure of the gaussian light beam (w0=12.5 mm) ) near boundary of the two dielectrics Multilayer optical bit-oriented memory

22. 1 - w0 =25 mm; 2 - w0 =12.5 mm; 3 - w0 =  (plane wave). Multilayer optical bit-oriented memory Dependence of the reflection coefficient for Gaussian beam from medium’s refraction coefficients

23. Multilayer optical bit-oriented memory Diode pumping solid-state laser l = 1064, 532, 355 nm Beam quality – TEM00 Tripled efficiency – 20%

24. Multilayer optical bit-oriented memoryDiode pumping pig-tail laser with focusing lens

25. Multilayer optical bit-oriented memoryExperimental setup X-Y – 20x20mm, step – 5 mm, Z – 5 mm, step – 10 mm, repeatability – 1 mm

26. Multilayer optical bit-oriented memory System for the fine filtering of the monomers. Filtering particles with sizes up to 0,1 mm with next polimerization in clean conditions in closed volume of the special forming setup.

27. Multilayer optical bit-oriented memory Optical scheme of the experimental setup spatial resolution – 1 mm, depth of field – 10 mm, media thickness – up to 1,5 mm

28. Multilayer optical bit-oriented memory • New photochromic recording media with the best properties providing their application in one- and two-photon 3D bitwise working optical memory have been worked out. • Method for nondestructive readout based on photoinduced changes of refraction index have been developed for working optical memory. • Prototype of the device for one-photon working optical memory based on photochromic recording media has been produced. • Developed media were tested with positive results for application • It was demonstrated that number of photochromic layers up to 30 is possible • It was demonstrated that number of writing-erasing-reading circles is more than 106