Key technologies for near-field recording/readout systems using a solid immersion lens (SIL) are summarized in this paper. Our system employing a SIL of 1.84 numerical aperture (NA) and a laser diode (LD) of 405 nm wavelength has realized the capacity of a 112 GB in a 12 cm diameter phase-change disc along with a write-power margin of ±11.2% and a data transfer rate of 36 Mbps. Such a larger-capacity data storage system should provide a high data transfer rate. A preliminary result of 1.84 NA dual-channel near-field recording/readout using a monolithic dual-beam LD with 412 nm wavelength is presented.
PACS 42.55.Px, 42.60.Lh, 78.66.Fd, 81.05.Ea, 81.15Gh GaN-based blue-violet lasers with a kink-free output power of higher than 150 mW have been successfully realized by adopting a new ridge structure and appropriately designing the beam divergence. The new ridge structure is a narrow 1.4 µm ridge covered with a stacked layer of Si on SiO 2 and the beam divergence half-angles parallel and perpendicular to the junction plane are set at 8° and 21°, respectively. These lasers have been operating stably for more than 500 h under 130-mW pulsed operation at 60 °C. The empirical activation energy of device lifetime under 30-mW continuous-wave operation is 0.32 eV.Introduction GaN-based high-power blue-violet laser diodes (BV-LDs) operating in the 400-410 nm wavelength band are promising light sources for large-capacity optical storage systems. The characteristics of BV-LDs have been improved remarkably since Nakamura et al. reported the first roomtemperature continuous-wave (CW) operation in 1996 [1]. Reliable BV-LDs with estimated lifetimes exceeding 10,000 h under 30-mW CW operation at 60 °C have been realized in recent years [2][3][4]. Although these devices can be readily used in high-density digital video recording systems [5], reliable BV-LDs capable of much higher output power will be required in the near future as the technology for optical disk systems extends to multi-layer disks and higher data transfer rates to facilitate higher densities and higher recording speeds.In designing a high-power laser suitable for use in optical disk systems, it is essential to maintain both a high kink level and a high catastrophic optical damage (COD) level of output power. These two levels are closely related to the optical confinement in the stripe of the laser structure, and hence to the beam divergence angles. The lifetime of BV-LDs is also governed by the density of dislocations within the stripe [6]. The stripes of current lasers typically contain significantly less than 100 dislocations, reduced from previously much higher numbers through the use of dislocation-reduction techniques such as epitaxial lateral overgrowth (ELO) [7,8], and lifetimes of over 1,000 h at 60 °C have already been achieved. However, even one dislocation in a stripe causes rapid degradation in other III-V laser diodes such as AlGaAs, GaInAsP and AlGaInP lasers. The remarkably long lifetimes and resilient nature of GaN-based lasers is therefore apparently associated with the inherent rigidity of this material system.In this paper, the kink and COD levels of a laser structure optimized for obtaining high output powers of more than 100 mW are described with reference to the most important device parameters. The dependence of the lifetime of these high-power lasers on the ambient temperature and output power are also reported.
AlGaInN‐based blue–violet laser diodes with a single broad‐area stripe emitter were successfully fabricated on GaN substrates. Three stripe widths were examined; 10, 50, and 100 μm, and the maximum light output power of 0.94 W under cw operation at 20 °C was achieved for the sample with a stripe width of 10 μm. A super high‐power laser diode array was fabricated using 11 of these high‐performance laser chips, with a resultant output power of 6.1 W under cw operation at 20 °C. This result represents the highest reported output power for blue–violet laser diodes. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
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