Fluorescent multilayer recording is here: watch out, blu-ray!

CD and DVD technologies have met with phenomenal success, especially in the consumer marketplace for high-quality audio and video entertainment. The next wave may well be fluorescent multiplayer recording, a holographic-like technology using light reflectance rather than metallic reflectance. The earliest effort to bring this technology to market was made in the mid-90s, but the company ultimately faded for reasons unconnected with the technology. The intellectual property was acquired by a new firm, D-Data, which looks to field a product in the next 12 months or so. D-Data's principal scientist, Dr. Eugene Levich, shared thoughts with us.

In discussing multilevel optical recording, what I would like to do is look into some of the operating principles of the technology that you will be offering through D-Data into the marketplace. It uses a very different kind of optical media. I see a transparent disk instead of the usual metallic reflective layer that I would see on a CD or DVD. Can you tell me how you can store without using metallic reflectance?

The response is triggered by a laser beam, exactly in the same way that is done with a CD disk or a DVD disk. So there should be some response, correct? And we have mastered a number of ways to trigger this response; one of them is to accept a fluorescent signal triggered by this laser beam.

A fluorescent signal?

Yes. Fluorescence is a phenomenon where certain substances start to emit radiation-photons when triggered by an outside electro-magnetic signal like a laser beam.

In fluorescent recording, wouldn't you have a shift in the color spectrum?

This is correct. In principle, fluorescent signal has a frequency that is typically higher than the frequency of the triggering radiation. It can be an essential effect, but not necessarily. It helps us diminish the crosstalk in this particular manifestation of our technology, but it is not really fundamental for our technology. In this particular type of technology we are developing, the information pits are sealed with fluorescent substance. It is a proprietary substance, which gives very considerable fluorescent response.

One of the problems we encounter--as everyone who works with fluorescence knows very well--is that generally it is a weak radiation. In order to have a good response signal--a good response signal means a good signal to noise ratio--this ratio should be high enough to give high qualities to an image. There are standards for this. There are two parameters: one is the strength of the signal and the second one is the level of the noise. The level of the noise can be made small but it can't be smaller than a base point. So in order to comply with the standard signal/noise ratio, the signal should be high enough. This is why we invested a lot of effort into making very good fluorescent composition that gives the desirable effect.

Then it is dye-based?

It is based on a fluorescent dye, but it is quite a complicated composition. I'd like to emphasize from the beginning that even though it's a complicated composition doesn't mean it's an expensive composition. It's a tricky composition, however all ingredients are off the shelf.

My understanding is that you are able to record in multiple layers, which historically has had a problem between the different levels of reflectance. How do you handle the multi-layer issue?

We don't have this problem. If there is no reflection, then there is no problem. We have exactly the same signal strength from any layer. Since the disk is practically not absorbing--that is, transparent for fluorescent radiation--we don't encounter the problem. There are two ways to record information on a layer. One is the prerecorded disk, where information is replicated on a polymer substance with stampers, either nickel stampers or glass stampers

Right, that gives you your prerecorded material.

Pre-recorded or ROM disks. The other way is to actually replicate information in a player--these are writeable disks or WORM disks. Our first products were ROM disks. While we work on both technologies, our first priority is recordable disk for high-definition television. These are prerecorded disks, ROM disks. After we stamp the information, we seal the information pits with our fluorescent composition and on the top of it we add another layer of polymer substance. We then cast another set of information pits on this layer, a new layer, then we again seal the pits with fluorescent composition and so forth. We are using so-called 2P technology. There are different ways of doing 2P technology. We have very simple and reliable 2P technology--in fact I believe we are the world leader in 2P technology.

Red Laser vs. Blue Laser

I'm still working on the multilayer nature of the technology. Your current product line, that your going to be introducing, is that a red laser-based technology?

At this time, we focus on red laser technology, even though the principles of technology are applicable to blue laser. With the help of red laser it is possible, in my view, to manufacture disk of up to 30-40 gigs of capacity. After that, we enter the area where the use of blue lasers will become justified. But then again, we have to think in terms of the future necessities. For instance, even now I have been reading an announcement by a Japanese institute that started the development of applications for an ultra high-definition standard.

It may not come in the next 20 years, but people are starting to work on it. In the future, we will need disks with 100 and even 200Gb capacity. The usual reflection approach--the metal reflection that you mentioned in the beginning--may be good for blue lasers delivering up to 50Gb, a dual-layer disk. Anyway, this is what Sony claims.

However, it is absolutely clear to everyone that even they cannot move beyond this. So there will be a necessity to come up with a multi-layer structure for blue lasers for the future everywhere. But, having said this, let me come back to what we are doing now, the red laser approach. Our reasons for this is quite obvious; red lasers are cheap, reliable, and well known. Blue lasers are still a novelty and it will take some time for them to come to the industry in a cheaper way or in a consumer way. This is where we have other advantages in our optics. Our product will be inherently backward compatible with DVD disk. Our players enjoy the same tolerances in terms of production as DVD disks. In some respects, our approach is even simpler than DVD disk technology. Over 90% of the equipment we use is regularly available for DVD production. But we manufacture our disk in very slightly more defined session by comparison with DVD disk now.

And so you will be able to backward read portions of the actual metallized DVDs right now?

Yes.

APPLICATIONS

What applications do you see your technology going into?

Definitely the first application is high definition. High definition is appearing in many applications. Personally, I even call it "DVD Plus" in a way, because the application is exactly the same as the way you view your DVD-ROM disks now; you just see the movie, but the resolution will be higher, the quality incomparable. We will allow effects. I call it cinema-like effects on high-definition screens at home--and really the effects are quite spectacular.

Before we go on, I would like to a make a very important observation. When I described the fluorescent multi-layer technology before, I described only one of the ways we can make this multi-layered disk. We have other technologies which are not fluorescent, as well, and we are achieving about the same result. This is a less well-known technology that we cannot announce yet; but I want to assure you and your readers that fluorescents are not the only way to achieve the results.

There has been an effort for some time to put together a photochromatic approach to recording, using these fluorescent properties.

Yeah, but our approach to fluorescence is not photochromatic, it is based on inorganic substances. What I want to say is that we really understand how to make multi-layer structures of various kinds and use them as recording vehicles.

How many recording layers can you put on a single 120mm disk?

You know, we tried experimentally in our lab for up to 20. It is technologically feasible at this stage, but you know we have to come down to earth to see what is required for consumers. 30Gb disks with 6-8 layers is a very feasible enterprise. We can do it with a very low error rate and a high media yield.

What are your yield concerns?

It is suspected that the more layers you have, the more errors will accumulate. Errors do tend to accumulate with the increase in number of layers. However, the kind of technology that we have developed gives a very high yield indeed.

OPTICAL IN THE DATA CENTER?

Doctor, I would like you to respond to a statement that has been going around the storage industry suggesting that optical technologies of any stripe no longer have a place in the data center--it's more a consumer creature ... a commercial creature. How would you feel about that?

I would, in part, agree with this statement. Optical storage has become a part of consumer technology and there are definite limitations, especially the way it is projected now--it is very much a consumer commodity. On the other hand, if someone succeeds in developing a truly three-dimensional optical memory, then it will be elevated to the status of other magnetic and flash memory devices. I have this dream of elevating optical memory to the level of truly three-dimensional storage. When I speak about multi-layered disk, it is not truly three-dimensional because the spacing between the levels is still quite significant--in our technology, no less than 25 microns. However, even now we are working on another set of materials, nano-materials. There are substances in which we are actively working that would allow us to diminish the distance between the spacing of information layers up to 5 microns. If we achieve this, it would be really quite close to the realization of truly three-dimensional optical memory.

Five microns and still a clean signal?

Without a crosstalk from the layers.

What is the current status of your technology? When do you plan to go to market?

It's a matter of business decision, but I strongly believe we can start limited production by the end of second quarter of 2005 using one or another or both technologies that I described--either the fluorescent or non-fluorescent approach. We plan to offer 15 and 20 Gigabytes disks by the end of second quarter of 2005.

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