Optical Recording Medium Refractive Index Interference

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Solution Overview

Problem

Existing optical information recording media face challenges in achieving excellent reproduction output without requiring highly accurate film thickness for the recording layer, and struggle with weak fluorescent light emission leading to poor modulation.

Innovation Solution

An optical information recording medium with multiple recording layers and intermediate layers of different refractive indices, where the refractive index difference between the recording layer and the intermediate layers is minimal, allowing for information recording and reading without interference and enabling thicker recording layers for increased storage capacity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the interference effect of reflected beams is utilized to achieve excellent reproduction output, then the reproduction quality is improved, but the film thickness must be highly accurate which increases manufacturing cost

Engineering Contradiction:

Improvereproduction qualityVSAvoidfilm thickness accuracy

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent introduces an intermediate layer with refractive index n2 between the recording layer (n1) and the reflective layer (n3). This intermediate layer acts as a mediator to control light reflection and interference. By carefully selecting n2 such that (n3-n1)/(n3+n1) ≤ 0.001, the patent achieves excellent reproduction output while allowing the recording layer thickness to be relaxed from the strict λ/4n requirement, thus reducing manufacturing precision requirements and cost.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the recording layer thickness is reduced to around 5-50 nm to achieve λ/4n thickness, then the interference effect is optimized, but the manufacturing complexity and cost increase due to high precision requirements

Engineering Contradiction:

Improveinterference effect optimizationVSAvoidmanufacturing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The intermediate layer with refractive index n2 serves as a mediator that decouples the strict thickness requirement from the system performance. This allows the recording layer to be thicker (50-200 nm) while still achieving optimized interference effect through the combined optical path of recording layer + intermediate layer, thereby reducing manufacturing complexity.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of manufacture

If a fluorescent light emission layer is provided under the recording layer to read out information, then the reading method is simplified, but the reproduction output becomes weak due to very weak fluorescent light emission

Engineering Contradiction:

Improvereading method simplicityVSAvoidreproduction output

Core Design Contradiction:

Ease of manufactureVSIllumination intensity

Solution Approach 1:

The patent replaces the fluorescent light emission mechanism (optical mechanism) with a reflective interference mechanism. Instead of relying on weak fluorescent emission to modulate light, the system uses the interference of reflected beams from the intermediate layer and reflective layer to achieve strong modulation of the readout beam, thereby significantly improving reproduction output while maintaining ease of manufacture.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 configuration allows for excellent reproduction output without the need for precise film thickness, reduces manufacturing costs, and increases the number of recording layers, enhancing storage capacity and readout efficiency.

Implementation Method 1

a recording material contained in the optical information recording medium to produce an optical change using a multi-photon absorption reaction such as two-photon absorption

Methodology Applied

Scientific EffectMulti-photon absorption: Absorption (EM radiation)

Implementation Method 2

reflected beams of light reflected at both upper and lower interfaces of the recording layer interfere with each other upon reading out the information (this is called interference effect)

Methodology Applied

Scientific EffectInterference effect: Interference

Implementation Method 3

the difference between the reflectivity at a recorded portion and the reflectivity at a non-recorded portion

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS8980396B2Optical information recording medium

Publication Date: 2015.03.17 FUJIFILM CORP

AI summary

An optical information recording medium 10 includes a plurality of recording layers 14, and intermediate layers 15 each provided between the recording layers 14. The optical information recording medium 10 is configured such that first and second intermediate layers 15A, 15B having different refractive indices are arranged alternately with one recording layer 14 interposed therebetween, that ((n3−n1)/(n3+n1))2≦0.001 is satisfied, where n1 represents a refractive index of the recording layer 14, and n3 represents a refractive index of the second intermediate layer 15B, and that when a recording layer 14 is irradiated with a recording beam RB and generates heat by absorption of the recording beam RB, an interface (reflection interface 18A) between the recording layer 14 and the first intermediate layer 15A adjacent to this recording layer 14 undergoes a change of shape to record information (recording spot M).