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.
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.
We negotiated persistently with Nichia Corporation for four-and-a-half years, with strong backing from the Patent Department and other units. This hard work eventually paid off, and we reached the conclusion that the quickest way to bring commercial products to market was to link Sony's semiconductor laser manufacturing technology with Nichia Corporation's basic patents for gallium nitride. In late 2002, the two companies began to collaborate on the development of a blue-violet semiconductor laser for use in optical disc applications. In April 2004, we signed a cross-licensing agreement relating to patents for a blue-violet semiconductor laser.
I was absolutely determined to develop a semiconductor laser for use in BD products. We had an unbroken history of involvement in the optical disc business. That heritage began with basic research carried out in the 1960s by a previous generation of Sony engineers and continued through to the commercialization of the CD products in the 1980s, and then to the DVD era. I could not allow that history to end, and I had to keep working until we ultimately achieved success. Both the product engineers and the device (parts) engineers were also determined to ensure that Sony would lead the development of a next-generation optical disc to succeed the DVD.
My commitment to the development project became even stronger because of the presence of another standard that was competing with Blu-ray for dominance in the next-generation optical disc market. Our determination to popularize BD technology as quickly as possible drove us to overcome the many obstacles that lay in our path.
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