Lynn Savage, email@example.com
SENDAI, Japan – Numerous research labs are looking for ways to increase the amount
of information one can store on a CD-ROM or related optical disc, but the equipment
needed to push past the boundaries of Blu-ray technology is exceedingly large and
expensive. Recently, investigators affiliated with Tohoku University and with Sony
Corp. in Atsugi have made a huge leap toward a laser that is portable yet potent
enough to drive optical storage up to 1 TB.
Researchers at Tohoku University and at Sony Corp. have developed
a semiconductor blue-violet laser that emits 100-W, 3-ps pulses at 1 GHz, perhaps
ushering in a new generation of large-capacity optical storage devices. Images courtesy
of Sony Corp.
The next iterations of large-capacity optical storage devices
– as well as nano-scale photolithography systems, novel noninvasive biological
imagers and other useful tools on the horizon – require cumbersome Ti:sapphire
lasers to operate in the labs where they are being developed. To get them out of
the laboratory and into consumers’ hands, the lasers powering such devices
must shrink while maintaining the ability to generate picosecond-long high-energy
pulses at high repetition rates.
Hiroyuki Yokoyama of Tohoku University and his colleagues there
and at Sony have been studying the behavior of GaInN laser diodes that are placed
under intense electronic excitement. In the July 12, 2010, issue of Applied Physics
Letters, Yokoyama’s team reported that it achieved better than 100 W of output
power from a GaInN laser diode operating at 405 nm. The experimental device provides
peak power of 103 to 119 W at 1050-mA electrical input, doing so with 3-ps pulses
at a rate of 1 GHz. The university reported that the peak power achieved is 100
times higher than that supplied by other lasers in the blue-violet emission range.
Schematic depiction of the new semiconductor
The researchers achieved the large power and short pulses without
extraneous pulse compression techniques. Instead, they developed a master oscillator
power amplifier (MOPA), using a single-stage GaInN semiconductor optical amplifier
(SOA) to increase the power of a mode-locked laser diode. The MOPA comprises a 600-μm-long
bisectional laser diode, an optical filter designed to pass 404-nm light and an
external mirror with 5 percent reflectivity. The researchers passively mode-locked
the MOPA to generate clean pulses without noticeable subpulse components.
“Tohoku University is responsible for the device physics
controlling nonlinear-optic effects and optical noise problems, etcetera, while
Sony has the excellent GaInN laser diode device technologies,” Yokoyama said.
Sony tested the laser for possible use in large-capacity optical
storage, finding good results when creating 300-nm-diameter void marks at a 3-µm
pitch inside a plastic substrate.
Besides optical storage, the semiconductor laser system may find
utility in two-photon absorption experiments such as those used in biological imaging.
“The present stage is still a kind of basic research to
confirm the novel device operation function,” Yokoyama said. “Therefore,
low-cost production technologies and reliability evaluation for semiconductor laser
devices would be important toward commercialization.”