Optical Head Splitting Section for Multi-Layer Storage
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Solution Overview
Problem
Conventional optical head devices experience unstable tracking control due to fluctuations in the amplitude and symmetry of tracking error signals when using optical storage media with multiple information recording layers, leading to unreliable data recording and reproduction.
Innovation Solution
The optical head device incorporates a splitting section with specific regions to manage interfering light beams, including a swapping mechanism to reduce amplitude fluctuations, and a partial light shielding section to block unwanted light, stabilizing the tracking error signal detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a conventional optical head device uses multiple light beams (0th and ±1st order diffracted light) for recording and reproduction on multi-layer optical storage media, then the data storage capacity is improved, but the tracking error signal becomes unstable due to interference between light beams reflected from different recording layers
Solution Approach 1:
The patent divides the detection function into separate photodetectors for different light beam components. The 0th order diffracted light (main light beam) and ±1st order diffracted light (sub light beams) are detected separately by different photodetectors, allowing independent signal processing and eliminating interference effects on the tracking error signal while maintaining multi-layer storage capability
Solution Approach 2:
The patent introduces a beam splitter as an intermediary optical element that separates the reflected light beams into different optical paths. This allows the main light beam and sub light beams to be directed to different photodetectors, preventing direct interference between them while enabling simultaneous detection for both data retrieval and tracking control
2Measurement precision
If the diffraction grating is designed with high diffraction efficiency ratio (20:1) between 0th order and 1st order light, then the signal-to-noise ratio for data reproduction is improved, but the amplitude fluctuations in tracking error signals increase due to interference effects
Solution Approach 1:
The patent segments the detection system so that photodetectors for the main light beam and sub light beams are physically separated. This segmentation prevents the high-intensity main light beam from interfering with the weaker sub light beams used for tracking, allowing the diffraction grating to maintain high efficiency ratio without causing amplitude fluctuations in the tracking error signal
3Quantity of substance
If light beams are converged onto multiple information recording layers (21b and 21c) for high-capacity storage, then the storage density is improved, but interference patterns appear on the photodetector causing fluctuations in tracking error signal amplitude and symmetry
Solution Approach 1:
The patent uses beam splitters as intermediary elements to separate light beams reflected from different recording layers. By directing these separated beams to different photodetectors, the system eliminates interference patterns that would otherwise occur on a single photodetector surface, maintaining tracking error signal symmetry while enabling multi-layer storage
Solution Approach 2:
The detection system is segmented into multiple photodetectors that independently detect light from different recording layers. This segmentation allows the system to maintain precise tracking control by preventing interference between layers while preserving the high storage density achieved through multi-layer architecture
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 enables stable detection of tracking error signals, ensuring high reliability in data recording and reproduction by minimizing interference and amplitude fluctuations.
Implementation Method 1
The light beam 10 having irradiated the diffraction grating 12 is split into three light beams of 0th and ±1st order diffracted light
Implementation Method 2
converted into convergent light beam by an objective lens 15 having a focal length f2 of 2 mm, transmitted through a transparent substrate 21a
Implementation Method 3
the light beam 10 having been converged by the objective lens 15 comes to a focal point at the information recording layer 21c
Implementation Method 4
a photodetector 30 for receiving the split light beams and outputting signals which are in accordance with received light amounts
Data Source
AI summary
An optical head device according to the present invention includes a splitting section for splitting a light beam having been reflected from an optical storage medium. The splitting section includes: a first main region transmitting a first interfering portion; a second main region transmitting a second interfering portion; and first and second sub-regions through which the first interfering portion is transmitted with a lower rate than in the first main region and through which the second interfering portion is transmitted with a lower rate than in the second main region. The splitting section splits the reflected light beam into: a first main light beam transmitted through the first main region; a second main light beam transmitted through the second main region; a first sub-light beam transmitted through the first sub-region; and a second sub-light beam transmitted through the second sub-region. The splitting section further includes a swapping section for swapping a portion of the first sub-light beam with a portion of the second sub-light beam.