Sony has developed a monolithic dual-wavelength laser applicable to writing both a CD-R/RW and a recordable DVD disc.
Sony claims that it is the world's first such development. It is achieved by integrating into a chip both a 780nm-band, high-power infrared laser and a 650nm-band, high-power red laser.
The former laser is for recording/replaying data on CD media, and the latter is for use with DVD media.
Typically, there is a merit in the dual-wavelength laser, compared with separately mounting two semiconductor lasers, in reducing costs and the size of an optical pickup system. Therefore, many DVD players today use the dual-wavelength laser for replay only. However, when a player needs recording, the laser's optical output power needs to be enhanced in a quantum leap.
This has been a difficulty, and thus there has been no such thing as a monolithic laser that supports writing in both CD and DVD media.
With this development, Sony has worked out on a solution to achieving an optical output power during pulse oscillation of 240mW with an infrared laser and 100mW with a red laser. These optical output levels are high enough to enable a 48x-52x speed than the normal CD recording as well as a 4x recording speed than a normal DVD.
The specifications of the two new monolithic lasers are as follows:
The oscillation wavelength is 784nm for the infrared laser and 658nm for the red laser. Until the optical output level during pulse oscillation reaches 240mW and 100mW, respectively, a "kink" phenomena is not confirmed where the linearity between an input electric current and an optical output level is broken.
The aspect ratio of outgoing radiation is 1.92 (that is, 15.0 degrees of the perpendicular divergence angle and 7.8 degrees of the parallel divergence angle) for the infrared laser and 1.94 (that is, 17.5 degrees and 9.0 degrees, correspondingly) for the red laser. The interval between emission points is 110 microns, within an error of 2 microns; the height of an emission point from the substrate surface is identical for both lasers.
However, the above data, as announced in the development presentation, do not indicate real specifications of commercial products of the lasers. It is yet to be decided when to commercialize and at what price to offer them. According to Sony, the monolithic lasers will be first applied to the recordable 9.5mm-thick DVD units. Aiming at this specific type, the company is going to provide a 3mm thin package housing the laser.
Through mass-production of these units, Sony intends to gradually expand application devices using the dual-wavelength laser.