nitride semiconductor laser device

Blue-violet semiconductor lasers are used to read digital signals from Blu-ray discs, and the commercial development of Blu-ray products that have enabled millions of consumers to enjoy true HD in their homes would not have been possible without this core component device. Thanks to determined efforts by its engineers racing against time, Sony was able to complete development of the laser within a very tight schedule in time to start the mass-production of millions of PLAYSTATION 3 consoles, the first product to incorporate Blu-ray technology. In this interview with Masao Ikeda of Sony Advanced Materials Labratories, we learn about the numerous failures with deadlines looming in the development of the first 3 in 1 laser (CD, DVD, and BD) for the Playstation 3, and how Masao thought it would never happen.

Masao: During my time with Sony, I have been involved in the development of semiconductor lasers for optical discs, including CD, DVD and BD systems. For me the most exciting achievement, and one that required enormous effort, was the development of the blue-violet semiconductor laser.

A semiconductor laser is to an optical disc what a needle is to an analog record. The surface of an optical disc is covered with minute pits (concave areas) and ridges (convex areas). By bouncing laser beams off these areas and reading information contained in the reflected light, we can play back the content recorded on the disc. If we reduce the wavelength of the laser beam, the spot diameter of the laser is also reduced, allowing us to use smaller pits and ridges on the disc. By recording data using a laser with a short wavelength, we can store more information within the same disc area. The development of semiconductor lasers with progressively shorter wavelengths has driven the evolution of optical discs, from CDs to DVDs, and now to BDs. The laser used when playing a music CD has a wavelength of 780nm (nm=nanometer), while a DVD requires a 650nm red laser. Because the red laser used to write DVDs has a shorter wavelength, the capacity of DVDs is correspondingly greater. To create the BD, which has around five times more recording capacity than a DVD, we needed to develop a blue-violet laser capable of producing light with an even shorter wavelength.

Masao: The development of blue lasers began in the 1980s. Despite the efforts of engineers in many countries, the development of suitable materials was a slow process. Semiconductor lasers emit light when an electrical current is passed through the semiconductor used. To discover suitable materials for semiconductor lasers, we need to find combinations of substances that will produce laser light with the desired wavelength when current passes through them.

Initially Sony tried to develop a semiconductor laser using materials based on zinc selenide, and in 1996 we succeeded in maintaining continuous oscillation for 100 hours. However, Sony changed its development strategy after Nichia Corporation succeeded in developing a gallium nitride semiconductor laser with a shorter wavelength. It was a difficult decision to abandon development of the materials that we had previously been researching. However, we wanted Sony to maintain its leading role in the advancement of optical disc technology, and we saw this as the best decision in terms of ensuring that Sony would be the first to develop next-generation products based on BD technology.

Yet at this stage, we had simply selected the material that we would use. There were still many challenges to overcome before we could turn this into a semiconductor laser that could be used in commercial products. The first of these was the solution of problems surrounding Nichia Corporation's patents relating to gallium nitride. In the second half of the 1990s, there was a patent lawsuit between Nichia Corporation and Toyoda Gosei Co., Ltd. concerning a blue LED made using gallium nitride. There was extensive media coverage about the blue LED that couldn't be marketed because of the patent dispute. Urgent steps were needed to resolve this problem so that Sony could introduce its blue-violet semiconductor laser. However, Nichia Corporation took the position that it would sell products but not the technology, and that it would opt for licensing if there were complementing technologies. Fortunately, Sony had laser manufacturing patents, expertise and commercialization experience dating back to the CD era. We also had manufacturing facilities with world-class technology, including Sony Shiroishi Semiconductor Inc. (Sony Shiroishi), the Sony's Group's semiconductor laser manufacturer.