The realization of a prototype miniaturized 5 mm height optical drive and 28 mm media is reported here. Using the optical light path as a starting point, this presentation will highlight the high degree of miniaturization that is achieved in the field of the optical pickup, optical components and mechanics. Furthermore, the use of newly developed disc media is discussed.

A prototype of ultra small optical drive was studied and developed in order to see the feasibility of mobile application, which is targeted to be attachable into the PCMCIA II slot in small mobile devices. A new design and fabrication technology of optical flying head (OFH) for first surface MO recording was studied, and an effective OFH precisely equipped with high NA lens and MO coil was developed based on miniaturization technology. Design consideration of small form factor optical drive is discussed. Some technical issues and barriers in designing and manufacturing the OFH are introduced. Head-disk interface for reliability and flying stability on plastic disk media was tested and evaluated. Basic tracking and read-write performances in a test bed system were tested.

Optical disc readout uses generally the "Central Aperture Readout" method. We show that "Push Pull Readout" can read efficiently very small phase modulation have good transparency and allow the stacking of many layers. We modified the push pull detection by adding a variable transparency in the far field that reduces the interlayer crosstalk, the system has potential for Terabyte capacity. We have realized a 8 layer DVD like optical disc and demonstrated that Push Pull Readout gives sufficient signal even on highly transparent disc.

A 10 μm free working distance recording head for blue, cover-layer incident MO recording has been developed with NA=0.95 and integrated high bandwidth MFM coil. ZF-MAMMOS recording experiments are described.

RF-MAMMOS is a promising technology to reach storgae densities around 100 Gb/in². Using domain expansion (and collapse) driven by a small, external magnetic field, bits much smaller than the optical spot size can be read out with saturated signal levels. Because these bits are selected by the center of the thermal profile induced by the focused laser spot, it is essential that the readout conditions determining the size of this heated region, the copy window, are controlled very accurately. At the same time, the external field needs to be synchronized to the recorded data. This can be achieved by data dependent field switching: the external field starts in the expansion direction and is only modulated at the bit clock frequency when expansion for a mark is detected. In this way, each first peak of a mark run length contains complete timing information which is used as input for a phase locked loop (PLL). Based on this approach, a method is proposed to solve the readout margin problem. By applying a small, fixed modulation to the laser power or the external field at a frequency above the bandwidth of the PLL, we demonstrate that the induced timing modulation provides a suitable signal to actively control the size of the copy window. First experimental results confirm the feasibility of better than 1% power control accuracy, opening the way to robust readout at the highest densities.

We propose novel ultrafast photonic interfaces for use in storage networking based on all-optical serial-to-parallel and photonic parallel-to-serial conversion. We confirm their operation with 40-Gbit/s 16-bit optical data using compact modules and a potential bandwidth of over 100 Gbit/s. We realize a photonic random access memory (RAM) by sandwiching a CMOS RAM with these two interfaces and achieve the storage and read-out of 40-Gbit/s 16-bit optical data. We also discuss the advantages of the interfaces and their possible applications to storage networking such as the real-time remote back-up of huge quantities of data, disaster recovery and video communication systems.

Recently, there has been much research on high-density recording of phase change optical disc using blue laser. In most research, RLL (Run Length Limited) modulation such as (1,7) RLL and EFM (Eight to Fourteen Modulation) modulation is used for high-density recording and channel clock regenerating. NRZI (Non Return to Zero Inverse) modulation has a wider window width than other modulation methods. This is a superior characteristic for achieving a high-density recording system of optical disc. We introduced NRZI+ modulation to suppress the low frequency components. And we obtained a result of a bER (bit Error Rate) of less than 1×10^-4 at a bit length of 0.13μm using Turbo coding with an objective lens of NA 0.7 and a blue laser of 405 nm wavelength. This result shows that a recording capacity of 20 GB is feasible using NRZI modulation.

We have developed an optical pick up with multi beam laser diode (LD). Multi beam LD has three emitters and individual emitter can control independently. Primary experiment for parallel recording has done and acceptable results for Power Margin, Tilt Margin, Defocus smargin and Detrack margin have measured. After than, possibility of double speed recording has confirmed by dual beam recording method.

Nonlinear properties and response mechanisms of PtO₂ and PdO_1.1 mask layers for optical data storage with super-resolution near-field structure were investigated. The results obtained from Z-scan measurement was supported by microscopic observation studies. The 5.1 mW and 6.5 mW, respectively, as the decomposition threshold of the PdO_1.1 and PtO₂ for leading to metallic nano-particles were confirmed. The scanned PdO_1.1 and PtO₂ mask samples could be retrieved at less than their own threshold values. It was also found for the PdO_1.1 and PtO₂ mask samples that the nonlinear optical response not only came from the metallic particles but also from the bubble deformation.

We describe a photodimerization process in organic thin films, for high capacity optical storage in the blue and UV. Neighboring molecules attached through a short peptide chain can be made to undergo cycloaddition. Preliminary experiments performed with anthracene and thymine dipeptides at 360 and 257 nm respectively show that the photo-induced change in absorption is stable both at room temperature, and at elevated temperatures. Very good optical quality films of the monomers can be fabricated.

We developed a side-wall-annealing technique for land/groove substrates. By applying this technique to our Domain Wall Displacement Detection (DWDD) Magneto-Optical (MO) recording stack formed on a land/groove substrate, even with an NA of 0.6 and a wavelength of 660 nm, we realized a density of 15 Gbit/in² with a sufficiently wide recording tolerance. This density corresponds to a capacity of 4.7 GB mm disc like MiniDisc.

Domain Wall Displacement Detection (DWDD) medium with no annealing method, which we call "anneal-less" DWDD medium, has been improved for practical use. The key technologies of our progress are not only an optimum design of the magnetic film structure but also a deep groove substrate for land-groove recording with a quite unique groove form. The substrate was prepared by using the mastering process with a reactive ion etching (RIE) method. We achieved 15 Gbit/in²-areal density with wide system tolerances using the anneal-less DWDD medium, a 660nm-laser and a 0.60 NA objective lens. The areal density corresponds to 4.7 GB-capacity on a disc like MiniDisc (MD) wiht a 64 mm-diameter.

We have developed dual-layer write-once media with Te-O-Pd based recording films on Blu-ray (BD) format. Recording capacity was 50GB with dual layers on a disk of 120mm in diameter. Rear and Front layers showed jitters of 5.8% and 7.7% at 1x speed, and 6.0% and 8.0% at 2x speed, respectively, which were good enough to satisfy the BD format. Evaluations were carried out with blue-violet laser of 405nm wavelength, objective lens NA of 0.85. Recording linear velocities were 4.92m/s at BD 1x (36Mbps), and 9.84m/s at BD 2x (72Mbps). Characteristics at 4x speed recording were also examined, and it was revealed that carrier to niose ratio at high recording linear velocity of 19.7m/s, which corresponds to BD 4x (144Mbps), was alomst as same as those of 1x and 2x. Recording mechanism was discussed and proposed a model that Te-O-Pd films were not crystallized directly through solid process, but crystallized through melting.

The optical disc with larger capacity and higher speed data recording rate will be required in coming broadband network society. We have developed the inorganic write-once disc with quadruple recording layers for the blu-ray system. We obtained the reflectivity of more than 5% and a jitter value of less than 10% for each recording layer. As a result, we proved the possibility of 100 GB user capacity of 120 mm diameter size.

We have developed a model to simulate the phase-change behavior of GeSbTe thin film alloys. Based on classical nucleation theory we described formation of crystalline clusters using chemical rate equations. Assuming that the phase-change proceeds by interactions of single GeSbTe molecules with growing or decaying crystalline clusters we used a set of differential equations to account for the population density changes of clusters. We defined reaction rates encountered in model equations by considering possible molecular processes during the phase-change process. To validate the model we simulated experiments taken from the literature. It can predict the kinetics of crystallization well, describe transient effectis correctly, and consider influecnes of substrates on crystallization successfully.

The crystallization process of two types of phase change materials (Ge₂Sb₂Te₅ and AgInSbTe) has been studied by in-situ annealing experiments in the column of a transmission electron microscope. Under the same heating rate (7.5K/s), the Ge₂Sb₂Te₅ material starts to nucleate at 170°C, while AgInSbTe starts to nucleate at 250°C. The measured nucleation rate of Ge₂Sb₂Te₅ is 8.2×10¹⁴ cm^-3s^-1 larger than nucleation is dominant for both Ge₂Sb₂Te₅ and AgInSbTe with ZnS-SiO₂ as the dielectric layer in the thinned samples.

We have developed phase change media of 20GB user data capacity for the next generation optical recording system using a blue-violet laser diode with the wavelength of 405nm. An objective lens with the numerical aperture of 0.65 has been used along with mm-thick substrates on which the laser is incident. We have employed the land and groove recording. A transparent film with high thermal conductivity has been adopted at the light incident side of the recording layer in order to improve the carrier to noise ratio and the erase ratio as well as to reduce the cross-erase. Bottom channel bit error rate of less than 1×10^-6 has been obtained and its wide tilt margins have successfully demonstrated the strong feasibility for the next generation rewritable system.

We have investigated the recording characteristics of the dual-layer phase change recording media for the sysetm with the NA of 0.65, the wavelength of 405 nm, and the light incidence on 0.6-mm-thick substrate having the land and groove format. For both L0 and L1 of the dual-layer disc, we have adopted bismuth substituted pseudo-binary GeSbTe alloy film as the recording layer and a novel interface layer material in order to improve overwriting characteristics. Bit error rate measurements have successfully demonstrated the feasibility of the user capacity of 36GB and confirmed 30GB with tilt margins.

The authors are researching and developing a high-density system using a blue-laser diode (LD) and an objective lens numerical aperture (NA) of 0.85, in particular, based on a Blu-ray Disc format, as the next generation of a Digital Versatile DIsc (DVD). In order to win the solid confidence of consumers worldwide in Blu-ray Disc for use at the office and home in the near future, it is most important to realize cost cutting and high-speed recording. Thus, in this paper, a rewritable disc and a dye-type-once disc formed by a spin-coating method, for low-cost and high-speed recording as 36 to 100 Mbps, is proposed.

New recording material with higher crystallization speed and higher thermal stability is required to realize a phase-change disc for higher data recording rate. We have developed a new phase-change material that consists of TbSbTeGe material based on eutectic composition. This new phase-change material improves the crystallization speed and the crystallization temperature simultaneously. We have achieved the practical use characteristic of data recording rate of 216 Mbps (6X-speed of Blu-ray Disc) by using TbSbTeGe new phase-change material.

We worked on an inorganic write-once technology based on hole formation and developed a possible stack for a dual level blu-ray disc with amorphous tellurium alloys. The study was tackled from different point of view: material, optical and thermal aspects.

We have investigated the feasibility of a probe storate technique based on the interaction of a conductive tip with a phase-change (PC) medium. The electro-thermal writing process was modeled using the element method. The crystalline and the amorphous phases were taken into account as a possible initial state of the phase-change material. The analysis of the corresponding current flow and temperature distributions showed that the choice of the initial state of the PC material greatly influences the shape of the written dots, due to the important difference in the electrical properties of these two states. When introducing the kinetics of the phase-change process in the model, the simuation results indicated indeed, that the crystalline dots spread throught the thickness of the PC layer, whereas the amorphous dots are more localized at the top of the layer. One can then expect important effects on the readout process (and contrast) and the erasing mechanism, depending on the initial state of the storage medium.

We have fabricated a new optical storage media using minute spheres arranged on surface relief grating (SRG). By using minute spheres as recording bits, we can limit recordable regions by sphere size, since one mintue sphere becomes one recording bit. We can realize high resolutive reconstruction in the plane direction. We make surface relief structures on a polymer thin fim, and tried to perform diffusion arrangement and adsorptive fixation of minute spheres on it. The stability of arranged spheres was confirmed for heating and washing. Furthermore, we tried dipping method for more simple arranging minute spheres on a large area of the substrate and have made a monolayer sample of the spheres. We are able to realize high sensitive reconstruction of the media using the confocal optical system as record and readout systems. We have also succeeded in doping the recordable dyes in minute spheres.

Ultrafast phase transitions triggered by single femtosecond laser pulse in Ge₁Sb₂Te₄ films were investigated. By proper control of the film thickness, ultrafast crystalline and amorphous phase transformations have been achieved in Ge₁Sb₂Te₄ films. These utlrafast phase transitions were confirmed by reflectivity change and x-ray diffraction measurement.

A method of high-density optical disk structure design using computational electromagnetic FDTD analysis is proposed. A staircase method is used to simulate the realistic sidewall geometrical structure of the land-groove of phase-change optical disk. The phase-change materials appear as different optical characteristics under irradiation of different frequency laser beam. Materials models in the FDTD scheme have been studied to solve the computational instability. Using this FDTD method, the structures of the phase-change optical disk with blue laser and high-NA system are investigated.

Jitter of 9.5% with conventional equalizer and 6.1% with limit equalizer have been achieved on a 23.3GB blue-violet laser write-once optical disc with a recording laeyr formed by spin coating with a dye-based solution. Data transfer speed is 36Mbit/s. The disc is composed of a polycarbonate substrate, a reflective layer, a dye-coated recording layer, a bonding layer, and a polycarbonate protective sheet. Cavities formed in the marks during recording result in large changes in refractive index for signal amplitude. Recording and playback was successful even at 2x drive speeds with data transfer of 72Mbit/s.

We developed a Finite-Difference Time Domain (FDTD) Method based simulator that can analyze Dual-Layered phase-change disc structure. Because of a substrate thickness error, it is necessary to consider spherical aberration. The electric field distributions have been calcuated on Single-Layered and Dual-Layered phase-change discs. We found differences between the electic distributions focused on a groove and on a land. These calculation results can explain the corresponding experimental results clearly.

The paper describes a novel laser beam mastering system with technologies of direct focus servo, high contrast photoresist material, recording signal compensation. Although the optics consists of conventional 266 nm laser with numerical aperture (NA) 0.9 objective lens, it successfully realizes an over 20 Gbytes capacity Read-Only-Memory (ROM) disc.

Near-field mastering process with a 266 nm laser was improved in the stability for long time exposure and in the performance for ROM exposure. The exposure stability was achieved by using a chemically amplified type photoresist and by setting the air gap large. The exposure performance was achieved by reducing the aberration of the objective lens and by adjusting the focal position precisely. As a result, 100 nm narrow width was obtained in the groove structure, and good signal quality was obtained from a 25 gigabyte (GB) read only memory (ROM) disc. A full area exposure for a 25 GB ROM disc was also achieved.

We have demonstrated the capability of 100GB density recording by the electron beam mastering and readout by a near-field optical pick-up with an effective NA of 2.05 and a blue LD of 405 nm wavelength. The Si disc of 100GB density was fabricated by the optimized Si etching process condition to form suitable pit pattern shape for the near-field readout.

We developed a high-speed simulator for partial response (PR) channels employing low density parity check (LDPC) codes. Bit error rate (BER) performances for channels employing PR(1,1) and PR(1,2,2,1) targets wtih blue laser and 0.85 numerical aperture (NA) are estimated by simulating up to 10¹¹ data sampled which allowed us to estimate BERs as low as 10^-10. Three data detection methods (namely, a simple slicer, soft-output Viterbi algorithm or SOVA, and maximum a posteriori probability or MAP detector) followed by LDPC decoder are compared. We also show BER performance of our one-chip hardware LDPC decoder on additive white Gaussian noise channel.

We have developed a turbo codes module for zero field MAMMOS and a simulation system to examine the performance of a turbo codes module for the zero field MAMMOS readout signal. In the zero field MAMMOS readout channel, issues such as dropouts and edge-shifts may determine the bottom of the error rate when the recording density reaches a certain height, and also reduce the performance of turbo codes. In order to improve the performance of turbo codes to deal with these issues, we propose an improved turbo codes. We first confirmed the performance of the turbo codes module, simulated for the additive white Gaussian noise channel modesl, and then we investigated the performance for the zero field MAMMOS readout channel. With respect to code rates and number of iterations, the turbo decoding results of zero field MAMMOS readout channel against the conventional binarization method are presented. Finally, we present the performance of improved turbo codes and confirm the effectiveness of the improvement.

No abstract available.

Spectroscopic properties of new aluminum oxide crystals for volumetric optical data storage are investigated. Magnesium impurity and double oxygen vacancy defects are responsible for the main optical properties of the new material. Sequential two-photon absorption and ionization of color centers followed by capture of a free electron on a deep trap is a suggested mechanism for writing information. One-photon absorption and non-destructive readout using reconstruction of recorded holograms or a confocal fluorescence detection scheme are proposed.

Two-photon absorption in new aluminum oxide single crystals is used for recording single bits in multiple layers while one-photon absorption and a confocal fluorescence detection scheme is applied for data readout.

Holographic recording is tested using new Al₂O₃:C,Mg single crystals. Plane holograms were recorded using 442 nm pulsed laser light from an optical parametric oscillator and were read non-destructively with a 442 nm He-Cd laser.

The feasibility of multilayered optical data storage is examined in glass, quartz, polycarbonate and a rhodamine B and Au (III) doped PMMA medium by using a focused 800 nm, 100-fs pulsed laser. Refractive-index or fluorescent data patterns are recorded by use of an objective to focus laser pulses inside these transparent medium. The laser pulse produces a submicrometer-diameter structurally altered region in the material. For glass, quartz and polycarbonate materials, we record binary information by writing such bits in multiple planes and read it out with a microscope. We demonstrate data storage and retrieval with 0.6-μm in-plane bit spacing and 10-μm interplane spacing (100 Gbits/cm3). Scanning electron microscopy (SEM) are used to characterize structural changes in these materials. For the rhodamine B and Au (III) doped PMMA medium, fluorescent spectra are measured before and after laser treatment. Writing three-dimensional data bit inside the transparent medium based on a multi-photon absorption process is expected to become a useful method used to fabricate optical memory with both an ultra-high storage density and an ultra-high storage density and an ultra-high recording speed.

Volumetric media have great potential for meeting future optical data storage demands, but homogeneous media lack internal features for tracking. A novel method of tracking inside homogeneous media is described that uses external reference tracks attached to the media. Several possible configurations for implementing the "slave-servo" concept are described and compared. An optical design for the most promising configuration is presented. This desing utilizes a diffractive optical element for dispersion compensation. Modeling describes the limits of device performance and alignment. Early prototype results are presented.

A method of uniform illumination for digital volume holographic storage system is proposed based on the speckle modulation technique by using a band-limited diffuser. The special diffuser is placed at a distance before the object plane to make the illumination light uniform, with approximate 4% rms power variation. Furthermore, vibrating the diffuser can help to reduce the speckle noise that roots in the Fourier imaging and recording system. The experimental results are given and it is shown that this method can reach a low raw bit error rate for the stored binary pages.

We report playback performance results of volumetric optical data storage disks that are made from a new class of light-absorbing (photo-chromic) compounds. The disks are first exposed to a simulated space environment. In order to simulate the space environment, a vacuum oven bakes the disks for certain amount of time at a designated temperature. Test results in this temperature study are fit into an Arrhenius model. Disks are also exposed to radiation doses similar to those found in a space environment. Disks fail in high temperature and large proton-dose conditions. Heavy ions do not cause significant disks failure. The prevention of disk failure due to harsh space environments is also discussed.

Ten thousand data pages, each containing 768×768 pixels, have been stored in a single section of a disk-shaped, iron-doped LiNbO³ crystal using spatioangular multiplexing with a convergent spherical reference beam, leading to an areal density of 33.7bits/μm2 and a volumetric density of 6.7Gbits/cm³. The system design considerations for the achievement of the goals ensure the success of the experiment. Customer-designed Fourier transform and imaging optics with short focal length provide tightly confined object beam at the crystal and good iamge quality in the detector array. An optimized reflection configuration avoids the detrimental scattering from the crystal surface to enter the detector array. An optimzied reflection configuration avoids the detrimetnal scattering from the crystal surface to enter the detector. The images were reconstructed with good fidelity. The signal to noise ratio (SNR) was measured to be 3.6 for the worst-case in the sampled retrieved images, from which, a raw bit error rate of 1.6×10^-4 before error correction could be estimated.

A multi-information-layer optical disk system using electrochromism for layer selection has been proposed and studied. Promising advantages of the disk are in its large capacity, high sensitivity in recording, and relative simplicity regarding hardware. PEDOT, a polythiophene derivative was selected as an electrochromic material. As a result of our fundamental investigation, DVD-like write/read has been achieved using DVD-RAM disk substrates and optics as DVD on a colored layer.

We have achieved high density near field readout of a 100 GB capacity (69.5 Gbit/in²) disc by using a solid immersion lens with numerical aperture of 2.05. In order to realize the solid immersion lens wtih numerical aperture of 2.05, the solid immersion lens was made from Bi₄Ge₃O₁₂ mono-crystal. The refractive index of Bi₄Ge₃O₁₂ is 2.23 at the wavelegnth of 405 nm. A conventional optical pick-up actuator with the solid immersion lens was used for the near field optical disc system. We confirmed that the near field readout system is promising method of realizing a high density optical disc system.

We have investigated nano-apertures with different geometries on VSALs using far-field measurements, near-field measurements, and finite difference time domain (FDTD) simulation methods. We were able to quantitatively verify the aperture geometry dependent power throughput in all three methods. From both far-field measurements and FDTD simulation results, we conclude that for the apertures of the same area, a rectangular aperture with the long side perpendicular to the active layer has the largest throughput, while a circular aperture has the second largest, and the rectangular aperture with the long side parallel to the active layer has the least throughput among the three. We have attempted to correlate the relationship between far-field power and near-field power. Employing an apertureless near-field scanning optical microscopy (NSOM), we found that for the two rectangular apertures being studied, the near-field power throughput results was consistent to that of far-field measurement. Using VSALs as a near-field aperture testbed was also proposed and demonstrated.

The optical characteristics of probe of near-field optical microscope operating on TEM-wave based on two trapeziform metallic strips on the surface of a dielectric cone are investigated by mathematic simulation. It was shown that this probe has large near-field and far-field transmission coefficient. The mathematic simulation also shown that this probe has large electrical field enhancement and broad bandwidth. The theoretical modeling of field structure of quasi TEM in optical waveband has shown that spatial resolution of 10 nm can be achieved. The probe design with low background radiation is proposed. The method of distance measurement from scanned surface based on detection of amplitude of microwave radiation excited by mechanical vibration of contrarily charged part of bifurcate probe apex is proposed. Large transmission coefficient, high spatial resolution and broad bandwidth of operation make this probe promising for using it in data storage, spectroscopy and nonlinear optic of nano-object. The characteristics of bulk metal were used in digital simulation. The obtianed theoretical results must be validated by experiments.

We have explored the optical near-field technology for the fabrication of subwavelength-size binary bit by the combination of the femtosecond laser of the second harmonic output with the near-field scanning optical microscopy (NSOM). The photosensitive polymer material was exposed, and the nanopatterns with feature size smaller than the laser wavelenght can be generated. It was found that the feature size depends strongly on the gap between the fiber probe tip and substrate surface. The approach offers the advantages of high precision, speed and selectivity in nanopatterning, and is promising to be used in data storage device manufacture for high density data storage.

For the application to the 5mm height optical drive, we have developed a small optical pick-up module within its dimension of 3.0×2.0×5.5mm, by integrating refractive and diffractive optical elements with laser diode and photo diodes assembly.

The efficiency of end-fire coupling between a light delivery system and a planar waveguide for optical and hybrid recording heads is calculated using amode matching technique.

A micro-optical pickup has been implemented by using a focusing waveguide grating coupler. The grating coupler was designed and fabricated on a single mode BPSG (boron phosphor silica glass) waveguide layer. The coupling area was 1×1mm² containing more than 1,500 grating lines, where the maximum and minimum grating pitch were 296nm and 811nm, respectively. The focal length and the numerical aperture of the present grating coupler were 530 μm and 0.68 with 632.8nm He-Ne red laser. The full width half maximum diameter of the focal spot was measured to be 450 nm and 510 nm in x and y direction.

A focusing grating coupler (FGC) using a blue laser of a wavelength of 400 nm as a light source was fabricated for the first time. The FGC was designed to have a numerical aperture of 0.48 and a focusing angle of zero. The focal length and the grating area were 900 μm and 1×1mm², respectively. Grating pattern of a minimum period of 0.2μm was fabricated on a single mode waveguide based on the boron phosphor silicate glass (BPSG) material by electron-beam lithography process using the vector scan method. The spot size at the full width (1/e²) was measured at 0.85 and 0.92μM in x and y direction, respectively, and these values are nearly same as the diffraction limited size.

A new dynamic test stand is built to test coupon samples for volumetric bit wise optical data storage applications. An unconventional rotating head and fixed sample design is employed. Results from media samples are reported that illustrate pulse-length/power optimization and focus sensitivity. One sample is shown to be appropriate for volumetric applications based in its focus sensitivity.

We made improvements on the previously reported hard-coat for cartridge-free Blu-ray disc from a viewpoint of an anti-fingerprint property. As a result of this study, two types of the hard-coat have been obtained. One is for Blu-ray discs of ROM and write-once types, and the other is for that of rewritable type. The former well inhibited a deterioration of bit error rate (bER) of the signal written prior to the fingerprint adhesion. The later exhibited low bER for the data signals written both before and after the fingerprint adhesion. These results are attributable to the area ratio of drops of fingerprint-ingredient on the disc surface, and the low area ratio resulted in a low bER. Moreover, it was confirmed that the disc with higher contact angle of oily compound exhibited the lower area ratio of the fingerprint.

Combining Data Detection using Pattern Recognition (DDPR) with LSB (Least Significant Bit) Limited Modulation (LLM) effectively reduces data errors in a blue laser optical disc system. We confirmed that a recording capacity of 25 GB is feasible for a system by using a laser diode of 405-nm wavelength and a 0.65 numerical aperture objective lens was effective to reduce data errors in a blue laser optical disc system.

In this paper we consider theoretical and practical aspects of a multilevel, re-writable and write-once optical recording system with compact disc parameters. A linear time invariant channel model is presented. We compare fixed-length and variable length runlength limited (RLL) coding and find that for the mark lengths of interest (600 nm for CD) M=4 is the optimum number of levels for RLL coding. For fixed-length modulation M=8 is the optimum number of levels and it is superior to RLL overall. We also show that M-ary RLL is a practical alternative if stronger coding can be applied to it.

We have previously reported on the performance of Multilevel ML technology on a wide variety of systems including CD-, DVD-, and blue-based systems. ML technology enables increased capacity and performance over traditional binary-modulation systems. Implementing this technology requires the addition of a single integrated circuit or IC core to the standard electronics of current drives, so manufacturers can provide ML capacity without altering existing optics, mechanics, or manufacturing infrastructure. In this paper, we describe precompensation and postcompensation, key Calimetrics' technologies that enable ML recording. These technologies enable ML recording by making the native nonlinear recording channel behave as a simple linear channel as well as by dynamically adjusting for nonlinear channel variations among different media and drives.

Can complex 3D subwavelength-sized structures molded in plastic optical ROM media be interrogated by a diffraction-limited focused spot for the retrieval of multilevel information? Finite-difference time-domain (FDTD) methods are used to examine the reflected intensity fields from such structures. The results presented show that such information retrieval is possible.