MULTILAYER OPTICAL DISC BACKGROUND OF THE INVENTION Field of the Invention There are known multilayer optical discs that were proposed in the following patents: US Patent 6,039, 898, Mar. 21,2000, B. Glushko and US Patent (reference is made to the IBM multilayer disc Patent). A factor limiting the number of layers in a multilayer disc is loss of the data signal that is picked up by the lens or is incident on the layer that is being read as the beam passes through the multilayer disc. In this case, in addition to the loss that can be minimized, for example, the process losses that are related to light reflection from the multilayer disc layers and are caused by their different refractive indexes, there are also other losses that are related to the data reading method. For instance, the IBM Company Patent proposes the use of partially reflective layers with phased modulation of the data signal received from pits. The IN signal incident on Layer N would then equal IN = (1-R) N, where R is the reflection coefficient on a single layer. To reduce losses that occur as the beam passes within a multilayer disc, we propose the following record layout on each layer : the reflective material is positioned only either in the track-forming data elements, i. e. pits (ROM), or the grooves (WORM), while light penetrates the inter-track space without any losses.

In this case the losses in each layer are reduced by about 70% in the CD-format and by 50% in the DVD-format. This method also allows to increase the number of layers in the multiple layer disc.

Several methods can be used to form the required system of reflective pits or groves on the layer surface: Method 1. A data relief pattern is formed on the disc surface by, for example a state-of-the-art CD method. Next, the surface is coated with a reflective material with a reflection coefficient of R. As this material, a metal (ROM) or an alloy of metals or their oxides (WORM) is used whose transmission coefficients can

change when they are heated, for example, ITO. Next, using selective etching methods that allow metal removal from the flat surface while leaving it in the recesses, the reflective material is left only in pits or tracks. A selective etching technique that can be used is ion etching of the surface at angle.

Method 2. First, a mask is made containing data in the form of pits or grooves (actually, they are hollows made in the metal). Next, a matching system of reflective pits or grooves is formed on the layer surface using the lift-off photolithography technique. To this end, the reflective materials referenced in the previous example are used Method 3. The layer surface is coated with an alloy of metals or their oxides whose transmission coefficients can change when they are heated, for example, ITO. Next, the layer is formatted with a stationary laser unit, by lightening the reflective layer between tracks and pits.

The multilayer disc can be fabricated by the methods previously proposed by the authors.