Optical Recording Medium Layer Thickness Asymmetry
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Solution Overview
Problem
Optical recording media with multiple information recording surfaces face issues with back focus problems and signal quality deterioration due to coherence between reflected light from different surfaces, leading to poor servo and reproduction signals.
Innovation Solution
The method involves calculating and setting the thicknesses of the cover layer and intermediate layers in an optical recording medium such that the difference between the sum of certain thicknesses is 1 μm or more, using a specific formula to convert shape-wise thicknesses into thicknesses with a predetermined refractive index, which prevents light from forming images on the backside and reduces coherence between reflected light surfaces, thereby improving signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the thicknesses of intermediate layers are made equal to simplify manufacturing, then manufacturing precision is improved, but back focus problems and signal quality deterioration occur due to coherence between reflected light from different surfaces
Solution Approach 1:
The patent applies asymmetry by making the thicknesses of intermediate layers non-uniform. Specifically, the first intermediate layer has a thickness of 11-15 μm while the second intermediate layer has a thickness of 16-21 μm, creating intentional asymmetry that prevents coherent reflection between different recording surfaces while maintaining manufacturing feasibility through clear thickness specifications.
Solution Approach 2:
The patent changes the thickness parameter of intermediate layers to resolve the contradiction. By setting specific thickness ranges (11-15 μm for the first layer, 16-21 μm for the second layer) and ensuring their difference is 1 μm or more, the patent eliminates back focus problems and improves signal quality while maintaining manufacturing precision through well-defined parameters.
2Reliability
If the distance between the medium surface and the closest information recording surface is increased to reduce signal deterioration from damage or smears, then reliability is improved, but the overall disc thickness increases
Solution Approach 1:
The patent optimizes the thickness parameter of the cover layer and intermediate layers to achieve the desired balance. By setting the cover layer thickness to 50-60 μm and intermediate layers to specific ranges, the patent increases the distance between the surface and recording surfaces to improve signal resistance to damage, while controlling the overall disc thickness through precise parameter management.
3Productivity
If multiple information recording surfaces are added to increase recording capacity, then productivity is improved, but coherence between reflected light from different surfaces causes back focus problems
Solution Approach 1:
The patent uses asymmetry in intermediate layer thicknesses to prevent coherent reflection between multiple recording surfaces. The first intermediate layer is 11-15 μm thick while the second is 16-21 μm thick, creating non-uniform spacing that eliminates back focus problems and maintains servo signal quality even with multiple recording surfaces, thereby enabling increased recording capacity.
Solution Approach 2:
The patent applies local quality by creating different thickness characteristics in different regions of the disc structure. The intermediate layers have distinct thickness ranges (11-15 μm and 16-21 μm) that are optimized for their specific positions, preventing coherent reflection at each interface while maintaining overall disc performance and enabling multiple recording surfaces.
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 enhances the quality of servo and reproduction signals by minimizing coherence between reflected light surfaces and allowing for a larger distance between the medium surface and the closest information recording surface, reducing signal deterioration from damage or smears.
Implementation Method 1
the thicknesses tr1, tr2, . . . and trN are converted into thicknesses t1, t2, . . . and tN of layers having a predetermined refractive index 'no' which makes a divergent amount equal to a divergent amount of a light beam resulting from the thicknesses tr1, tr2, . . . and trN
Implementation Method 2
A focus error (hereinafter, called as FE) signal by an astigmatism method, a tracking error (hereinafter, called as TE) signal by a push-pull method, and an information (hereinafter called as RF) signal recorded in the optical recording medium 401 are generated, based on the current signals
Data Source
AI summary
Shape-wise thicknesses of a cover layer and first through (N−1)th intermediate layers of an optical recording medium having refractive indexes nr1, nr2 are converted into thicknesses t1, t2 of the respective layers having a predetermined refractive index which makes a divergent amount equal to a divergent amount of a light beam resulting from the thicknesses tr1, tr2, a difference DFF between the sum of a thickness “ti” through a thickness “tj”, and the sum of a thickness “tk” through a thickness “tm” is set to 1 μm or more (where i, j, k, and m are each any positive integer satisfying i≦j≦k≦m≦N), and the thicknesses t1, t2 are calculated by products of a function f(n) expressed by the following formula (1), and the thicknesses tr1, tr2:f(n)=−1.088n3+6.1027n2−12.042n+9.1007 (1)in the formula (1), n=nr1, nr2, . . . , and nrN.