Makoto Itonaga

Single objective lens having numerical aperture of 0.85 for a high density optical disk system

For the optical disk systems in the next generation, a GaN laser and a high numerical aperture lens are key components. This paper describes the first single objective lens that have the numerical aperture of 0.85. The lens form, which is the most important factor in realizing the lens, is analyzed. The measured wavefront aberration was 0.027λ which is was well below the diffraction limit of 0.07λ. The lens was installed in an optical pickup and write/read characteristics of the pickup with phase-change disks were investigated on a drive. Data-to-clock jitter of a read back signal was 9.5% of channel clock at a disk capacity of 25 Gbytes per 120-mm-diameter disk. The direct overwrite (DOW) characteristic was also measured. The jitter remained stable up to 1×105 cycles. These results confirm the performance of the objective lens.

Optical Disk System Using a High-Numerical Aperture Single Objective Lens and a Blue LD

An optical disk system using a blue laser diode and a single objective lens that has a numerical aperture of 0.7, is proposed. A sufficiently low jitter value was obtained with a read-only disk having 17-Gbyte capacity. The paper also includes discussion on the influence of the laser noise and RF modulation method on the playback signal.

Master Recording Using Kr Ion Laser

Resolution of a master recorder using Kr ion laser was investigated by means of computer simulation and experimentation. Limitary pit length PLmin was indicated by the k factor: PLmin=k×(wavelength)/(numerical aperture). When the duty of the write pulse DT was 0.5, k was 0.56 in simulation. For DT=0.36, k was 0.57. In the experiment pit widths were measured from scanning electron micrographs. Experimental results showed the same tendency as the simulated results. K factors in the experiment were 15.8 percent (DT=0.5) or 20.7 percent (DT=0.36) worse than those in the simulation. The optical system of the recorder is tested using the Twyman-Green interferometer and the knife-edge method. An interferogram shows a good performance. Measured half-width of the spot was 0.24 µm. It was close to the ideal diameter of 0.23 µm.

Investigation of the General Design Principle of a Single Lens and the Development of a New NA=0.85 Single Lens

An aspherical single lens is widely used as an objective lens for optical discs. These lenses are designed as aplanats or are very close to an aplanat design. We have analyzed the lens with NA of 0.85 and determined general equations that predict paraxial parameters of such lenses. The equations are very useful for determining lens specifications. Applying the equations we have determined the specifications of a new lens whose focal length is 2 mm. The wavefront aberration was 24 mλ and well below the diffraction limit. The experimental results on an optical pickup with a 405 nm LD are also shown. The jitter value of the read-back signal using a 23.3 Gbytes phase change disk was as small as 9.0%. This jitter value is sufficient for achieving a low error rate after decoding.

A Format of High-Density Rewritable Optical Disk using Groove Recording

A new physical format using groove recording and new signal processing techniques is discussed. The signal reproduction of shallow pre-embossed pits was confirmed with a technique utilizing tangential push-pull (TPP) and a compatible partial response (PR) equalizing system. An evaluation in terms of the bit error rate by hardware experiments is demonstrated.

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.

Polarization-free blu-ray disc/digital versatile disc compatible optical pick-up

We have developed Blu-ray disc (BD)/digital versatile disc (DVD) compatible technology employing a polarization-free wavefront correction element. The polarization-free wavefront correction elements have high diffraction efficiencies for both BD and DVD. Also, this element has a large decentering tolerance for the objective lens. The effectiveness of this element was confirmed by examining wavefront aberrations for DVD and readout signal waveforms for both BD and DVD.

High-Density Rewritable Optical Disk Using Groove Recording

For an optical disk system using an objective lens of numerical aperture (NA) 0.7 and a GaN laser, the performances of the groove-recording scheme were investigated. A disk having 17 GB capacity showed the initial jitter of 11.9% with an equalizer for digital versatile disks (DVD). With an adaptive equalizer and a Viterbi decoder, sufficiently low bit error rates and wide tilt margins were obtained.

High density optical disk system using D8-15 modulation code and new signal-processing techniques

A new 8-15 RLL(2,10) modulation code and a new 2D adaptive equalizer are combined with a 0.7 NA objective lens and a violet LD. Bit error rates are measured with a 19.8 GB ROM disk.

19.8 GBytes ROM disc readout using a 0.7 NA single objective lens and a violet laser diode

The performance of the proposed system with the noise reduced ROM optical storage disc and the error feedback (EF)-partial response maximum likelihood (PRML), composed of the error-select type adaptive equalizer and the adaptive Viterbi decoder, is demonstrated. The reproduced signal of the 19.8 GBytes ROM disc shows a sufficient low error characteristic.