Violet Lasers Begin Mass Production in Japan

Jiro Ono, Nichia Corp.

Nichia and Sony recently announced an agreement for mass production of blue-violet laser diodes for use in optical disc recording and playback. Violet laser development is not new at Nichia Corp. of Tokushima, Japan. In fact, the company is in its third phase of development.

In the first phase, a five-year project that began in 1995, Nichia researchers devoted most of their effort to increasing diode lifetime. This meant increasing output power simultaneously because lifetime and power are always a trade-off. They focused primarily on “improving crystal quality,” which is an important and yet difficult part of development, and found that the mismatch among crystal lattice, the GaN layer and substrate was the largest hurdle. They made a breakthrough by growing high-quality GaN on a sapphire substrate to fabricate the first violet laser diode.

In the second phase, which took place about three years ago, the group worked to fine-tune the laser diode characteristics for application requirements. As the average lifetime exceeded 10,000 hours, Nichia’s goal was to meet other individual requirements such as beam quality or noise.

The first industry that adopted the violet laser diode was the printing industry, where the device increases speed in computer-to-plate printing. Other applications include laser microscopes and disc mastering.

The most demanding application for violet laser diodes is in the optical disc industry, where performance is paramount. Nichia will continue to refine the technology to meet the needs of Sony’s commercial application. One goal is to replace the light source with a semiconductor laser diode, and the group is about to release a >100-mW multimode laser diode for power applications. A new assembled light source unit that bundles 20 pigtailed fiber-coupled laser diodes has a 400-mW limit, and the group expects the out-put power to reach 1.5 to 2.0 W in 2004.

Another direction the Nichia researchers are pursuing is a wide range of wavelengths, including 375, 440 and 473 nm. Each model will produce 5 to 20 mW, depending on the color, and will support medical, biotechnical, sensing and scientific instruments. The 375-nm model will achieve 10 mW. In the past, UV light has been applied to many applications, but existing expensive and bulky laser systems have made them impractical for commercial use.

With these recent advances, 440- and 473-nm laser diodes will replace helium cadmium and argon laser systems, and will create markets for compact and easy-to-use instruments.

The next goal for the Nichia researchers is to develop a 488-nm laser diode and push it into the green range.

Meet the author

Jiro Ono is manager of the optoelectronics division of Nichia Corp. in Tokyo.