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

Computer Technology Review, June, 2004 by Mark Ferelli

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.