The Imperial Invention Prize was awarded in recognition of the basic patent for the Blu-ray Disc system, which defined the standard for recording HD video on optical discs. It was one of the core inventions by which the Blu-ray Disc was realized. The development of prototypes based on this invention began in 1994. At the time, this initiative was quite simply a unique expedition into the unknown.

Furuki: In 1994, the term "optical disc referred to the compact disc (CD)." I joined Sony that year, and it was around that time that everyone was competing to create a DVD standard which would enable the DVD to become the next-generation disc. Engineers in those days had already envisioned a road map leading from CD to DVD to HD discs, but few at that time were actually involved in efforts to develop an optical disc to succeed the DVD.

One of those engineers was Toshiyuki Kashiwagi. He joined Sony in 1982, the year in which CD production had begun, and ever since then has dedicated his efforts to optical disc technology. Kashiwagi understood the need for a new-generation disc technology to succeed the DVD and had explored various possible structures for the new disc.

kashiwagi: HD broadcasting was scheduled to begin in 2000, and we needed to develop a disc capable of recording those broadcasts. Our goal was to develop a disc that could hold two hours of HD broadcasts. That would require a capacity of 25GB, the equivalent of five DVDs. To achieve that, we wanted to use blue (blue-violet) lasers, which have a shorter wavelength than the red lasers used as the light sources for CDs and DVDs. An operational blue light-emitting diode (LED) laser had been announced in 1993, and we all believed that blue lasers would be used in the new-generation disc that would succeed the DVD. The problem was how to focus a blue laser accurately.

There were three key challenges that had to be met in order to develop a large-capacity optical disc. First, it would be necessary to use blue lasers with a shorter wavelength than conventional red lasers. In other words, the shorter the laser light wavelength, the smaller the focal point of light, and the smaller the point of light, the more densely the laser is able to record data. Another key was the creation of an objective lens with a high numerical aperture to focus the light into a smaller beam. These innovations would reduce the area of the optical point to approximately one-fifth that of a DVD, to increase recording capacity to 25GB, which is equivalent to about five 4.7GB DVDs. However, to record data at five times the density of a DVD, it would be necessary to improve the entire structure of the disc to achieve the precision required for recording and playback. The idea that emerged was to reduce the thickness of the cover layer on the disc surface, through which the laser light must penetrate, to 0.1mm, or about one-sixth the thickness of a DVD cover layer.

Furuki: The basic structure of a DVD consists of a recording layer sandwiched between two 0.6mm discs, for a total thickness of 1.2mm. The new disc would also be 1.2mm thick, but it would consist of a recording layer formed on a 1.1mm substrate, with a 0.1mm cover layer. By reducing the thickness of the cover layer to 0.1mm, it would be possible to reduce spot distortions and focal problems caused by disc warping and tilting during the manufacturing stage.

Kashiwagi: Some people may have had the idea of reducing the cover layer to 0.1mm, but I doubt that anyone actually opted for that approach. Everyone involved in the optical disc field in those days knew just how technologically challenging it would be to create a light penetration layer measuring only 0.1mm. However, in using a blue laser, we realized we couldn't achieve high capacity with a 0.6mm layer, and that future development of multi-layer discs would be difficult if we didn't take on this challenge. These factors coupled with the realization that the HD era was approaching, led us to consider the creation of a 0.1mm cover layer as a challenge we knew we had to address.

Creating a 0.1mm cover layer required the team to explore various engineering approaches. With their sights still set on commercialization and mass-production in the near future, the engineers began working on prototypes.. Eventually this work led to two discoveries: reverse-side recording and playback, and the use of spin-coating to create the cover layer.

Furuki: We first used injection molding of polycarbonate resin to create the substrate, to which we added a reflective film to bounce back the laser light. Up to this point the process was the same as for CDs and other optical discs. However, we took a new approach with the Blu-ray by opting for reverse-side recording and playback, which meant that the laser beam would be projected onto a cover layer created on the reverse side of the disc. Since the laser reads data through the reflective film, accurate reading is impossible unless the reflective film precisely reflects the minute grooves cut into the recording layer. Many refinements were needed before we were able to come up with an extremely thin film capable of tracing the data exactly.

Kashiwagi: We'd decided to use a 0.1mm cover layer, but this was too thin for injection molding, which involves pouring hot resin into a mold from which the product is removed after setting. So, we opted for the spin coating method instead. With this method, UV-curable resin is poured onto a disc, which is then spun at high speed. This spreads the resin into a thin layer just 0.1mm thick while removing any excess. The layer is then hardened (cured) under UV light. However, spin coating technology was originally used to create films measuring a few microns on semiconductors and other products. It was extremely difficult to create a uniformly thick layer measuring 0.1mm, or 100 microns. So, we went through a long trial and error phase.

A long trial-and-error phase was needed before the resin could be spread evenly.

When Blu-ray Discs first went on sale in 2003, a sheet method involving the application of a 0.1mm adhesive film was used instead of the resin spin coating method, since this allowed the product to be developed more quickly.

Furuki: The first Blu-ray Discs sold were manufactured using a sheet method, which reliably provided the precise thickness required. However, there are cost problems with this method, since material is wasted when the film is trimmed to fit the disc, and because of the extra processes involved, such as the application of adhesive. Spin coating with UV-curable resin, on the other hand, provides excellent localized playback performance. We also realized that it would be possible to reuse the excess resin after being spun off and that this manufacturing method could be carried out using existing facilities designed for similar coating processes. Yet, there were still a number of hurdles that needed to be cleared. For one, no suitable material was available at that time, and the discs tended to become extremely warped after hardening. It took a lot of time to perfect a coating process that would provide a uniform layer.

As work on the development and commercialization of the Blu-ray Disc advanced, around 2002 competition to create a new-generation large-capacity optical disc standard to succeed the DVD began to intensify. While the rival camp was committed to keeping the old 0.6mm cover layer, the higher capacity made possible by the 0.1mm layer was an advantage that could not be abandoned.

Kashiwagi: Ultimately the difficulty of creating a 0.1mm layer came down to challenges related to manufacturing technology. We knew it could be done if we were willing to spend enough time and effort. The question was whether the method could be taken to the mass-production stage. In other words, could we produce high-quality products rapidly enough for mass-production? To be honest, I thought it would be extremely difficult. However, I felt a strong sense of mission that drove me to do whatever was necessary to take the Blu-ray Disc forward and ultimately see Japan become the birthplace of a new world standard.

While development work continued, Kashiwagi visited motion picture companies and DVD manufacturers in the US to give lectures and presentations about the performance and potential of Blu-ray Disc technology. He also offered to visit factories in Europe and North America to assist with problems relating to discs and equipment.

Kashiwagi: Engineers are very fair when it comes to evaluating the potential of technology. Even those who were initially skeptical about the 0.1mm cover layer were persuaded to support the Blu-ray Disc when I, as another engineer, provided technical evidence that the process was absolutely feasible and emphasized that support would always be available.

Kashiwagi's reputation is such that he deserves to be called "Mr. Optical Disc." His engineering background in this field and his tireless efforts to promote Blu-ray as a world standard were consistently effective, and his efforts played a key role in bringing the standard war to an end in 2008.

Lectures were held in many countries to provide information about the performance and potential of the Blu-ray Disc.

This invention that won the Imperial Invention Prize is of course the one that ultimately became the Blu-ray standard, and has since become familiar throughout the world as a medium for HD video recording, film music, video games and other content. Patents were registered in 20 countries, and by 2010 a total of 640 million Blu-ray Discs had been manufactured. That number continues to increase with every passing moment. The engineering team's idea that a 0.1mm cover layer was essential to the development of multi-layer discs has also been proven right by recent developments, including the application of this invention to the creation of a Blu-ray device standard for four-layer discs with a capacity of 128GB.

Furuki: The patent itself is extremely simple. While it's quite easy for young engineers to get hooked into focusing on complex technology, from the viewpoint of registering patents and nurturing industries, it's these simple core inventions that offer limitless potential as keys to development and manufacturing. I was extremely lucky to become involved with this sort of project during my first year with the company. My work today is in the field of life electronics (healthcare electronics), which involves the application of many aspects of optical disc technology. In particular, there are opportunities for Sony to achieve a unique leadership position by applying its accumulated knowledge of optical disc technology, including laser optics, servo technologies, micro fabrication and molding techniques, to the development of flow cytometers, which are used in cytological analysis. This is a new field, but I believe that we should not be afraid to take up the challenge.

Kashiwagi: I see the Blu-ray Disc as one of my children. Parents see their children every day and are often unaware of their growth, even though perfect strangers can tell when children have already fully grown into adults. In the same way, I wasn't really aware of the importance of Blu-ray technology. However, after learning that over 600 million discs had been manufactured worldwide, and after receiving this wonderful award, I have gained a new awareness of the growth and evolution of Blu-ray technology, and feel blessed to have been involved in this work for so long. This award recognizes the comprehensive and synergistic power of the united Sony Group including its manufacturing systems for recorders, drives and discs, its factories and sales outlets, and its BD strategy. I see this invention as the embodiment of Sony's accumulated expertise in the field of storage technology of which magnetic recording has served as a key starting point.