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Holography system rides single beam

Posted: 01 May 2006 ?? ?Print Version ?Bookmark and Share

Keywords:Yoshiko Hara? holography? Hideyoshi Horimai? Yoshio Aoki? Optware?

Along with its promise of storing mammoth amounts of data, conventional holography technology presents developers with one big problem!it requires two light beams that must be exposed from different directions. Hideyoshi Horimai and Yoshio Aoki of Optware Corp. think they have a better way. Their Holographic Versatile Disc (HVD) is based on the company's Collinear technology, which does away with that pesky second light beam. Optware's first Collinear system!with 200Gbytes of storage for the professional broadcast and movie industries!is scheduled to sample this year.

Horimai, who founded Optware in 1999 and is now its CTO, broke through the hindrances holding back holography by sticking to the idea of a one-beam system using a disk medium that contains address information. The beam in his Collinear technology combines the information and reference beams on the same axis, while a disk with addressing information comes preformatted. Collinear technology makes it possible to build a terabyte-level disk system with a structure quite similar to today's optical-disk systems, he said.

President and CEO Aoki!like Horimai, a Sony Corp. veteran!handles standardization, alliances and management, which are indispensable if Optware's HVD is to establish a position in the industry. A European Computer Manufacturers Association technical committee is already working on standardizing the holographic information systems. And the HVD Alliance that Optware formed a year ago has expanded its membership from six companies to 18.

EE Times: How did you come up with the idea for your Collinear holography system?
Hideyoshi Horimai: When Dennis Gabor invented the first holography system about 60 years ago, it was called in-line holography, in which the beams came from the same direction. Then, about 40 years ago, two-axis holography was invented and became the mainstream. At that time, crystal was the medium used for recording, so two-axis holography was suitable. But it was not suitable for disk applications.
The problem in a one-beam system was that the information and reference beams merged, and two-axis holography was a solution to separate them.
I studied magnetic holography and my master's thesis was on holography. In magnetic holography, I could cut the reference light and extract the information light by polarizing the two beams. Since then, I had been thinking that there might be no need for two axes in holography.

Yoshio Aoki: In other words, engineers who have been developing holography systems started from the precondition that two beams were mandatory. We were newcomers and knew only about optical disks. For us, the decision from the start was to let there be one beam.

When did the idea for the Collinear technology come to you?Horimai: I got the idea in 1995 when I joined a research team that was sent to the United States by an optoelectronics industry association to study large-capacity storage. At that time, holography recording technology was gathering attention again over there. Since I had studied holography at university, I was assigned to report back about holography recording.
We visited various laboratories. I remember that I saw a 1cm crystal cube at Stanford. A researcher said that it could contain vast amounts of data equivalent to the contents of one national library. I tried to pick it up to examine it more closely, but the researcher told me not to touch it. The cube did not have addresses in it, so it had to be kept precisely aligned and positioned. Once it was moved, data could not be read out, he said.
That was quite different from disks [disks rotate and are removable]. I wrote a report saying that if the holographic media had to be kept still, that is a defect for memory applications, despite the large capacity.
Several years later, the holographic medium changed form!from a cube to a disk. But the limitation was the same: The disk could not be moved.
Why not put in the address information, I wondered. Surely, the problem was that if the address pits were added, light scattered. Even in our experiments on the Collinear holography system, light blurred at the address pits. Generally speaking, diffraction noise increases because of address pits and makes it difficult to increase capacity. So it was widely believed that holography media couldn't have addresses.
We cleared this problem by introducing a dichronic-mirror layer that selectively passes the light beam to physically separate the red beam for servo and tracking, which is based on the address pits, and the green beam for information recording and reading.
Aoki: The research activities in conventional holography in the mid-'90s did not solve holography's disadvantages, but spurred big progress in peripheral technologies such as high-speed special light modulators, high-speed CMOS sensors and high-quality photopolymers that can be used for disks. Without such technologies, it would have been difficult to develop the Collinear holography technology.

Optware's first product will be a 200Gbyte system?
Horimai: Yes. It is called Magnum, an archival data-storage system with 200Gbyte capacity for broadcasting stations. We'll introduce the system this year.
Our system is based on the concept of "selectable capacity." The disks have a manufacturer's zone in an inner track that users cannot access. It indicates the capacity that the disk can store. The drives read the area when a disk is loaded.
Using the same page format, the disk capacity can be increased just by changing the recording pitch. When the recording pitch is 13m, the capacity per disk is 200Gbytes. When the pitch is squeezed to 8m, the capacity increases to 500Gbytes. An even smaller pitch, 6m, delivers a capacity of 1Tbyte and at 3m, the disk capacity grows to 3.9Tbytes.

Can customers use the different-capacity disks without worrying about the data format?
Aoki: We are now working on how to include this feature in the standard.
Horimai: Backward-compatibility is often touted in the industry, but our drives are compatible with capacities available in the future. We will introduce a 200Gbyte system this year, but if we introduce, say, a 500Gbyte disk in 2007, the drive introduced in 2006 can read and write the 500Gbyte disk.
Aoki: There is no need to upgrade the system or update software.
If a disk is written as 200Gbyte capacity in its manufacturer zone, the drive treats it as a 200Gbyte disk, and if the capacity is marked as 1Tbyte, the drive uses the disk as a 1Tbyte disk. This means that the system can also handle a smaller-capacity disk. It may sound extreme, but the drive can support capacities from 0byte to 3.9Tbytes. So if a disk maker wants to sell a quite inexpensive disk with, say, just 100Gbytes, it works.

What is the biggest challenge at present?
Horimai: The light source. The system uses a green 732nm laser, which is a solid laser that is bulky and expensive. It is really a challenge to make the light source compact.

Will the solution be a semiconductor laser?
Horimai: We cannot wait until a semiconductor laser satisfies our requirements. So the nearest candidate is a microchip laser. We were looking for the candidate all around the world and found last year that Japan was the most advanced in this field.
Government-affiliated labs are developing palm-size lasers that emit a megawatt-level output. Such a laser can penetrate an aluminum plate.
We do not need the megawatt output!kilowatt output is enough, with a pulse width of 10-20ns.

How are you progressing on the standardization front?
: Friends from my Sony days and overseas are helping us with standardization. We have had close talks with Microsoft and with Hollywood studios. Through these talks, we have growing confidence in the demand for applications in post-production areas. However, the system is not yet compact enough for consumer applications.

Will the HVD system be an open standard?
: Yes. The medium is open. It's totally dependent on media manufacturers!how good a material they develop for disks. But it is another story whether we license the drive technology or not.

- Yoshiko Hara
EE Times

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