An interview with Haruki Tokumaru of NHK Science & Technical Research Laboratories

In the field of TV broadcasting, VCRs and video cameras that record images on magnetic tape are still dominant even as DVD players, which use optical-disk technology, are becoming more common as a home-use imaging device. Research and development efforts are in progress to apply such optical-disk technologies to record images for broadcasts. The following article is based on an interview with Haruki Tokumaru, senior researcher for Recording Technology & Mechanical Engineering at NHK Science & Technical Research Laboratories, who is working on the development of high-definition (HDTV) optical-disk camera for newsgathering activities.

It was 1930, five years after the launch of Japan's first radio broadcasting service, when NHK Science & Technical Research Laboratories were established in Setagaya, Tokyo. Since then, the Laboratories have been engaged in various research activities involving comprehensive broadcasting technologies in Japan, including the start of TV broadcasting. Today, their focus is on ISDB (Integrated Services Digital Broadcasting), a technology to enable diversified broadcasting through digitization, based on which many other research projects are being developed. One such project is their research and development of a HDTV optical-disk camera.

Advantages to Optical Disks

Replacing conventional magnetic video recording media, such as videotapes, with optical disks will be beneficial in many aspects, according to Tokumaru.

"Optical disks provide high-speed access and, unlike hard disks, mobility so that camera crew members can edit and send images while they are still on site. Endless recording is also available when they want to keep the camera running at an ongoing incident site. When transmitting the captured images, disk rotation speed can be adjusted to correspond to each network's transmission speed.

Also, unlike the current tape medium that requires maintenance such as cleaning every three years and is prone to damage as it physically contacts with the head during playback, optical disks allow non-contact reproduction ensuring scratch-free playback with virtually no degradation."

Thus, digitalization of recording media is also deeply related to storage and reproduction issues.

In the area of broadcasting, digitization began in the satellite broadcasting sector in December 2000, while the same change is expected for terrestrial broadcasting starting from 2003. As digitization allows the storing and handling of various forms of data, such as images, audio and text, in a package, irrespective of the contents. NHK is planning to launch ISDB as a means to enable diverse use of such material. Need for producing material available for ISDB is prompting the broadcaster to digitize its recording medium. Meanwhile, NHK announced that, jointly with Saitama Prefecture, it plans to build an archive facility in Kawaguchi City, Saitama in 2003, which mainly stores NHK's past video material.

"NHK has more than 1.5 million video programs - with respect to only complete programs that have been aired - stored in NHK's local broadcasting stations and broadcasting center, and the number is still growing [Fig. 1]. Besides, making a 60-minute program usually requires raw footage that is 10 to 20 times longer. In terms of making the most of the expensive material gathering process, preferably such footage should be maintained for secondary use. Storing video programs and material on optical disks would save cost and space, while making them easy to search and reuse."

In addition, he mentions that these archives will be made available to the public so that people can view or use past broadcasts and material.

Using Parallel Recording and a Blue Laser

We then asked about the technical challenges his research team faces in commercializing an optical-disk camera.

"What we need to do is to increase the recording rate (speed) and recording capacity. Recording HDTV material and news requires a recording rate nearly ten times greater and a recording capacity more than five times larger than commercial rewritable DVDs." [Fig. 2]

In the first phase of development, his team tackled enhancement of the recording rate and successfully achieved a recording rate of 1,100 megabits per second (100 Mbps) per channel. This technological achievement was displayed during the Laboratories' open house technology exhibition held in May 2001. This is currently the highest-level rate for this kind of medium in the world. Also on exhibition was the parallel two-channel recording technology, in which two optical heads (the equivalent of a pen to write down information) are used to write data onto two adjacent tracks simultaneously. A blue laser was employed as the light source. By using a blue laser, which has a 405 nanometer wavelength, instead of a red laser with a 635 nanometer wavelength currently used for DVDs, more data can be stored within the same area. Since a shorter wavelength generates a beam with a smaller diameter - in this case, 0.5 microns for the blue laser compared with 0.9 microns for the red laser - the blue-laser based technology allows multiplied storage density, thus significantly enhancing recording capacity and speed.

Other technologies under development include a signal processing method to support high-density/high-speed recording and a control technology to allow high-accuracy tracking of an optical disk rotating at high speeds. By 2005, through the improvement of these technologies, the researchers at the Laboratories seek to provide a 200-Mbps recording rate and offer a 20 minute or more recording capacity (equivalent to a 30-GB storage capacity in total) on a single side of a CD size optical disk.

What Can We Expect from Optical-Disk Technology?

You may be wondering what impact the development of optical disks will have on our life, aside from its effect on news images we watch on TV.

"People will most likely see the technology incorporated into PCs and home storage (memory) devices. A 20-minute recording time is just our first-round target. When thinking about studio use, we should expand it to at least two hours [Fig. 2]. As such technology would allow extremely massive data recording, it would find applications in increasing PC storage capacity and dramatically raising speeds for data writing and retrieving.

The technology would also enable home video recorders to record much longer hours and play back recorded parts of a program while still recording it. When a device with a recording rate of 20 Mbps is recording data at 10 Mbps, it is using only half of its total capability. As such, it could afford to return to previously recorded data and play it back."

NHK Science & Technical Research Laboratories make internally developed technologies open to the public once they are patented, in an attempt to share the technological benefits with society. Similarly, regarding a variety of techniques linked to optical disks, Tokumaru and his associates hope to develop a standard under an agreement with manufacturers and others concerned, so that the technology can be widely applied not only to broadcasting but also to PCs and other home electronics.