Takashi Iwamura

Volumetric Optical Recording Using a 400 nm All-Semiconductor Picosecond Laser

We have demonstrated volumetric optical recording using an all-semiconductor picosecond laser, which generated optical pulses with a duration of 3 ps and a maximum peak power of 100 W at a wavelength of 404 nm and a repetition frequency of 1 GHz. This pulsed laser system efficiently induced multiphoton absorption in the recording media due to its high peak power and high repetition rate. The recording marks were formed as submicrometer voids inside a single thick recording layer by multiphoton absorption. A clear readout signal was obtained from the recorded marks.

Development of Organic Recording Media for Blue High Numerical Aperture Optical Disc System

Organic write once media is developed for the Blu-ray disc format, namely, a system comprising a blue wavelength laser diode of 405 nm and a high numerical aperture (NA) lens of 0.85. The first generation Blu-ray disc format employs phase change media. Thus, the organic write once media was designed with a reflectivity modulation scheme in order to retain compatibility. A very simple layer structure is proposed, SiO2/Dye/SiO2 without any metal reflective layer, and the media showed sufficient modulation amplitude and signal quality. The optical constants before and after the recording were measured to clarify the recording mechanism, and the result matched well with the readout waveform in the optical disc system. The measured jitter level after random pattern recording at a density of 23.3 GB per disc was 6.7% using a limit equalizer, which satisfies the Blu-ray disc format.

Dynamic Recording of 200 Gbytes in Three-Dimensional Optical Disk by a 405 nm Wavelength Picosecond Laser

We present experimental results of our volumetric optical data storage system. To achieve volumetric recording over a wide depth range of 250 µm in a recording medium, we developed a relay lens system for compensating for the spherical aberration of a high-numerical-aperture (0.85) objective lens. The disk employs a single monolithic recording layer and a reference layer for servo control. A 405-nm-wavelength titanium:sapphire laser that exhibits 2 ps pulse duration and a more than 2 kW peak power is used for recording. We adopted void formation and mark position as recording principles. We have experimentally demonstrated 34-layer dynamic recording, corresponding to a capacity of 200 Gbytes.

Volumetric Optical Recording with Void Marks Using an All-Semiconductor Picosecond Laser

We demonstrated volumetric optical recording with void marks in a bulk recording medium using a newly developed all-semiconductor picosecond laser. The laser is compact and has an ultrahigh peak power, which is necessary for practical application of the volumetric optical recording system. We confirmed the laser to be able to record void marks effectively on our recording media. The laser was implemented to our optical drive system as a light source and as much as 30 layer void-mark recording was carried out on the 200-µm-thick bulk recording medium. The total recording capacity was 97 Gbyte and the bit error rates (bERs) were measured to be on the order of 10-4 for most of the layers. We believe that this was a significant step to realize a practical volumetric optical recording system.

Development of organic recording media for blue-high NA optical disc system

We have developed an organic write once media suitable for the DVR-Blue format. By use of organic material with high initial refractive index at 404 rim wavelength, a high density recording of 21 GB per 12 cm diameter single side disc was optimised to a practical level. Further optimisation of the recording pulse strategy and the media in near future promises the achievement of full compatibility with the DVR-Blue format.