KR20040054660A - Multilayer optical disc - Google Patents

Abstract

To reduce the loss of reading light, a multilayer optical disc (FIG. 1, disk), like a disc in CD or DVD format, includes a multilayer with only pits or tracks and only reflective material within the pits or tracks. This disk can be used as a ROM or WORM disk. Also disclosed is a method of making this disc.

Description

Multilayer optical disc

Multilayer optical discs are known which are proposed in US Pat. No. 6,039,898, March 21, 2000, B. Glushko and in the US patents (reference is to IBM multilayer disc patents). Factors limiting the number of layers in a multilayer disk include the loss of data signals picked up by the lens or incident on the layer read as light passes through the multilayer disk. In this case there are other losses related to the data reading method besides the ones that can be minimized, such as process losses associated with light reflections from the layers of the multilayer disk and caused by their different refractive indices. For example, IBM's patent suggests using a partially reflective layer with phase modulation of the data signal received from the pit. The incident I _N signal of the N layer will be equal to I _N = (1-R) ^N , where R is the reflection coefficient of a single layer. In order to reduce the losses incurred as light passes between the multi-layer discs, we propose the following record structure on each layer: The reflector is only a track-forming data element, i.e., while light penetrates the inner-track space without loss. It is located in a pit (ROM) or groove (WORM). In this case, the loss of each layer is reduced by about 70% in the CD format and 50% in the DVD format. This method also makes it possible to increase the number of layers in a multilayer disk.

Various methods are used to form the reflective pit or groove system on the layer surface into the desired system.

Method 1

For example, by the state of the art CD method, a data relief pattern is formed on the disk surface. Next, the surface is coated with a reflective material having a reflection coefficient R. As these materials, for example, metal (ROM) or metal alloys or their oxides (WORM) whose transfer coefficients change when heated like ITO is used. Next, using a selective etching technique that leaves them in the recesses to remove metal from the flat surface, the reflective material is left only in the pit or track. Selective etching techniques that can be used are ion etching techniques with angled surfaces.

Method 2

First, a mask is produced that contains data in the form of pits or grooves (in fact, they are hollows made in metal). Next, a lift-off photolithography technique is used to form a matching system of reflective pits or grooves on the layer surface. Finally, the reflective material described in the above embodiment is used.

Method 3

The layer surface is coated with metal alloys or their oxides whose transfer coefficients change when heated, for example, ITO. A stationary laser unit is then used to format the reflective layer between the track and the pit with light.

Multilayer discs can already be produced by the methods proposed by other inventors.

Claims (6)

Multiple transparent layers; Pits or groove patterns for storing information in each of the plurality of layers; And And a reflective material disposed only on the pits or grooves. The method of claim 1, And said disk is a ROM disk. The method of claim 1, And said disk is a WORM disk. The method of claim 1, comprising depositing and etching the reflective material over the layer such that the reflective material remains only in a pit or groove pattern. The method of claim 1, wherein the reflective material is applied using a lift-off photolithography technique. In each of the layers, a method of manufacturing a disc according to claim 1 comprising applying a material that changes the transfer coefficient when heated, and heating the material with a laser to define a pit or groove pattern.