Multilayer Optical Disc Base Thickness and Reflectance Optimization
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Solution Overview
Problem
Conventional multilayer optical discs face challenges in maintaining a good Signal-to-Noise Ratio (SNR) during read operations, especially when unintentional layer-to-layer jumps occur, leading to potential data deterioration due to varying reflectance and transmittance of recording layers.
Innovation Solution
The solution involves a multilayer information recording medium with varying readout powers for each layer and a base thickness between layers that ensures the intensity of light remains within a predetermined range, minimizing aberration effects and preventing data deterioration during unintentional jumps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of recording layers is increased to enhance storage capacity, then the storage capacity is improved, but the reflectance of deeper layers decreases making read operations difficult
Solution Approach 1:
The patent applies local quality by setting different reflectance values for different recording layers. Specifically, the L0 layer (deepest layer) has a reflectance of 70% while shallower layers have lower reflectances. This localized differentiation ensures that each layer has sufficient reflectance for reliable read operations, regardless of its depth in the multilayer structure.
Solution Approach 2:
The patent changes the reflectance parameter across different layers to solve the problem. By increasing the reflectance of deeper layers (particularly L0 layer to 70%), the patent compensates for the natural decrease in reflectance with depth, thereby maintaining reliable read operations even as storage capacity increases through additional layers.
2Measurement precision
If the readout power is increased to improve SNR for deep layers, then the SNR is improved, but data deterioration occurs due to unintentional layer-to-layer jumps
Solution Approach 1:
The patent applies beforehand cushioning by setting a safety margin in the base thickness between layers. The base thickness is determined to be 10 μm or more, which provides a cushion against unintentional layer-to-layer jumps. This pre-established protective margin prevents data deterioration even when readout power is increased to improve SNR for deep layers.
Solution Approach 2:
The patent uses the base thickness as an intermediary element between adjacent recording layers. This base thickness acts as a buffer zone that prevents direct optical interference between layers, allowing higher readout powers to be used without causing data deterioration from unintentional jumps to adjacent layers.
3Reliability
If the base thickness between layers is increased to prevent layer-to-layer jumps, then data integrity is improved, but the intensity of light decreases due to aberration
Solution Approach 1:
The patent optimizes the base thickness parameter to a specific range (10 μm or more) that balances two conflicting requirements. At this thickness, the base provides sufficient protection against layer-to-layer jumps while limiting the degradation of light intensity due to aberration. This parameter optimization ensures both data integrity and adequate light intensity for read operations.
4Measurement precision
If the reflectance of deep layers is increased to maintain uniform light reflection, then the SNR is improved, but it becomes difficult to arrange recording layers with appropriate transmittance
Solution Approach 1:
The patent applies local quality by assigning specific reflectance values to specific layers based on their depth. The L0 layer (deepest) is given a reflectance of 70%, while shallower layers have lower reflectances. This localized approach simplifies the layer arrangement process compared to requiring uniform high reflectance across all layers, as each layer's reflectance is optimized for its specific position.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach ensures stable read operations with low error rates and maintains data integrity even if unintentional layer-to-layer jumps occur, by optimizing light intensity and readout powers across the recording layers.
Implementation Method 1
the reflectance TR(L0) of the deepest one (L0 layer) of those layers stacked is given by the following Equation (1): TR(L0)=R0×T12×T22×T32×T42×T52×T62×T72 where T0 through T7 represent the transmittances of the respective layers and R0 through R7 represent their own reflectances
Implementation Method 2
the intensity of the light returning from that layer to the photodetector would decrease, thus also decreasing the SNR
Implementation Method 3
the size of a light beam spot to be condensed by an objective lens provided for an optical head has been decreased year after year by increasing the NA (numerical aperture) of the objective lens
Data Source
AI summary
An information recording medium according to the present invention includes at least three information recording layers. If the readout power of a laser beam in reading information from an information recording layer L(n) is identified by Pw(n), and if the readout power of the laser beam in reading information from an information recording layer L(n+a) is identified by Pw(n+a), then a base thickness between the information recording layers is determined so that the intensity of the light when the information recording layer L(n+a) is irradiated with a laser beam having the readout power Pw(n) becomes equal to or lower than that of the light when the information recording layer L(n+a) is irradiated with a laser beam having the readout power Pw(n+a).