Dual-layer Optical Disk Research Articles

One-Head Near-Field Writing/Erasing on a Rewritable Dual-Layer Optical Disk Having High-Index Cover and Separation Layers

Near-field writing and erasing on a rewritable dual-layer optical disk with a single solid immersion lens (SIL) optical head is demonstrated for the first time. A novel beam expander enabled access to both information layers of the disk without exchanging two individual optical heads. A rewritable dual-layer disk having high-index (n=1.8) cover and separation layers was newly developed. By using the SIL optical system and the disk, an effective numerical aperture (NA) of 1.42 is achieved and a recording capacity of 180 Gbyte for the dual-layer rewritable disk is expected.

One-Head Near-Field Writing/Erasing on a Rewritable Dual-Layer Optical Disk Having High-Index Cover and Separation Layers

One-Head Near-Field Writing/Erasing on a Rewritable Dual-Layer Optical Disk Having High-Index Cover and Separation Layers

Reduction of Interlayer Crosstalk in Dual-Layer Optical Disks Using Patterned Phase Plate

In dual-layer optical disks, light reflected from an adjacent layer overlaps and interferes with light reflected from the target layer on the photodetector. As a result, the signal obtained from outputs of the photodetector fluctuates. In this paper, we propose an optical head which employs a six-segment patterned phase plate in the return path to reduce interlayer crosstalk (fluctuation of a differential push–pull signal) without degrading the readout signal. The patterned phase plate weakens the intensity of the main beam from the adjacent layer which enters the sub-beam detecting sections of the photodetector and restricts the interference between sub-beams from the target layer and the main beam from the adjacent layer. Beam intensity distributions on the photodetector and push–pull signals have been investigated through numerical simulations and experiments. The results demonstrate that interlayer crosstalk can be sufficiently reduced using the patterned phase plate.

Analysis of Disturbance on Differential Push–Pull Tracking with Dual-Layer Optical Disc

In this paper, we analyze the disturbance of tracking error signal caused by layer cross talk on playback of a dual-layer disc. We will reveal the origin of the disturbance by experiments using a special disc. The origin is the groove of the cross-talk layer. Furthermore, we will investigate other related factors that increase the disturbance. Tangential tilt and variation of space layer thickness in one revolution are such factors.

ZrO2-Based Interface Films Realizing a Dual-Layer Phase-Change Optical Disk Utilizing a Blue-Violet Laser

A ZrO2-based dielectric material shows superior properties for interface films of phase-change optical disks, in particular, when utilizing a blue-violet laser. i) The ZrO2-based film possesses a high transparency at a wavelength of 405 nm, ii) it has a superior adhesiveness with phase-change recording films, and iii) it shows no crystallization or decomposition below 1000 °C, as shown by temperature-programmed desorption (TPD) measurement. The film was adopted for interface films of a semitransparent recording layer (L1) that was located on the laser-incident side of a dual-layer optical disk, and a high optical transmittance of more than 50% and a large reflectivity contrast of more than 0.8 were realized. By dynamic evaluation based on the Blu-ray Disc Format version 1.0, the obtained jitter measured with limit equalizer (LEQ jitter) was 6.7% and the cycle number was more than 10,000, whereas those of the reference disk using conventional GeN-based interface films were 7.3% and 2000, respectively. From the optical and thermal simulation, the maximum temperature in the interface film located on the laser-incident side of L1 was around 700 °C.

Towards Cover-Layer Incident Read-Out of a Dual-layer Disc with a NA=1.5 Solid Immersion Lens

We present the status of our efforts to demonstrate the feasibility of recording on a cover-layer protected dual-layer optical disc with a blue laser and NA=1.45 objective lens that is based on a solid immersion lens (SIL). We discuss the potential data density and some practical and theoretical considerations for the light path, the objective lens and the media. In particular, we show a lens design and results of prototype manufacturing for a NA=1.45 lens that focuses on the data layer of an optical disc through a sub-wavelength air gap and a 3 µm spin coated cover-layer that protects the data on the disc.

Analyses of Signals from Dual-Layer Phase Change Optical Disks

The signals obtained from dual-layer optical disks were analyzed experimentally and theoretically with emphasis on reducing layer cross talk (LCT) and spherical aberration (SA). Using the dual-layer phase change optical disk, the DC element of the LCT was measured and phase change marks were written on both layers. Diffraction calculations were used to explain the experimental results and to determine the amount of LCT and signal degradation caused by SA as functions of spacer layer thickness and optical detector size. Analytical methods to estimate LCT and SA were proposed, and their predictions turned out to agree well with the experimental and diffraction calculation results. These findings indicate that for a blue laser, the conventional techniques cannot simultaneously keep the LCT and SA to within practical values. Accordingly, designs for disks and drives for dual-layer optical disks are discussed.

Numerical Simulation Method for a Liquid-Crystal Aberration Compensation Device

We have developed a numerical simulation method on the basis of the ray tracing technique to evaluate a liquid-crystal (LC) spherical aberration compensation device for next-generation high-capacity optical memory devices. We numerically evaluated the performance and the tolerance of the LC device and showed its adequate capability to compensate the spherical aberration due to the nonuniformity of the disc cover layer thickness. Using the simulation method, we numerically examined the possibility of using LC devices to compensate the large spherical aberration due to the layer jump of the dual-layer optical disc and determined that the gradation-type LC device can be used for dual-layer optical recording.

Development of Recording Stacks for a Rewritable Dual-Layer Optical Disc

In this paper results are presented on the development of recording layers for a rewritable dual-layer phase-change optical disc. The disc is based on the digital video recording (DVR) system utilising a blue laser and a high numerical-aperture objective lens. With such a disc the capacity of the DVR system could be increased to about 45 GB. Various stack designs, write strategies and recording characteristics of the media are discussed. For each recording layer a design with a fairly good performance is found.

Semi transparent Recording Stack with Fast-Crystallization Phase-Change Material for Dual-Layer Optical Disk

We report the experimental results of a semi transparent recording stack with a fast-crystallization (FC) phase-change material for a dual-layer optical disk, using a pickup with a blue laser diode at 405 nm and a lens numerical aperture (NA) of 0.85 to achieve the highest capacity. The transmittance of 47% and the clock-to-data jitter of approximately 9% were obtained from the semi transparent recording stack. We confirmed that the FC phase-change material could be applied to a high-capacity dual-layer recording system.

Dual-Layer Optical Disk with Te–O–Pd Phase-Change Film

A recordable dual-layer optical disk that uses a Te–O–Pd phase-change film was studied for high-density recording. In order to reduce thermal influence to adjacent tracks, we selected the optimum composition of Te42O46Pd12 that gives low thermal conductivity. To get equivalent signal amplitude and absorbance of layers, the thicknesses of the laser incident side recording layer (Layer 1) and the other layer (Layer 2) are designed to be 20 nm and 55 nm, respectively. We confirmed that there was less than 10% bottom jitter for both layers under the following recording densities: recording bit length of 0.41 µm and track pitch of 0.74 µm. The laser powers required for recording on Layer 1 and Layer 2 were typically 10 mW and 12 mW, respectively. The jitter was less than 13% for both layers with large power tolerance of 30%p-p.

The characteristics of a dual-layer optical disk with read-only and erasable functions

A dual-layer optical disk comprised of a read only layer and a phase-change layer was designed to perform the read-only and erasable dual-functionality in an optical disk. With the properly designed dual-layer disk structure, 23 mW of write power was adequate to write data marks on the erasable phase-change layer; simultaneously, equal magnitude of sufficient radiofrequency readout signals could be obtained on both its data layers. The analyzes of its recording characteristics demonstrated the feasibility of the dual-functional optical disk.