Optical Pickup Stray Light Offset Reduction via Segmented Detection
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Solution Overview
Problem
Existing optical pickup apparatuses face challenges in obtaining stable servo signals, particularly in reducing the offset of tracking error signals at the boundary between unrecorded and recorded regions on optical discs, which affects writing speed and light use efficiency.
Innovation Solution
The optical pickup apparatus employs a polarizing diffraction grating with specific dividing regions to prevent stray light from other layers, allowing for stable focus and tracking error signal detection by focusing reflective light fluxes on distinct regions of a light detector, thereby reducing DC offset and improving tracking control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional optical pickup apparatus is used to read multilayer optical discs, then the apparatus can access multiple layers, but the tracking error signal contains offset caused by stray light from other layers, reducing measurement precision
Solution Approach 1:
The light receiving element is divided into multiple independent light receiving regions (first through fourth regions) arranged in a specific pattern. Each region receives light from specific track positions, allowing the system to segment the tracking error signal detection and eliminate offset from stray light by using only signals from regions不受affected by other layer interference.
Solution Approach 2:
The invention extracts and eliminates the offset component from the tracking error signal by using a specific calculation method: TES = (S1 - S2) - (S3 - S4), where S1-S4 are signals from the four light receiving regions. This extraction method removes the stray light offset while preserving the useful tracking information.
2Measurement precision
If the light receiving element is divided into multiple regions to eliminate stray light offset, then tracking precision improves, but the device complexity increases
Solution Approach 1:
The light receiving element is divided into four light receiving regions (first through fourth regions) arranged in a specific pattern. Each region receives light from specific track positions, allowing the system to segment the tracking error signal detection and eliminate offset from stray light by using only signals from regions不受affected by other layer interference.
Solution Approach 2:
The divided light receiving element structure serves multiple functions: it detects tracking error signals, eliminates stray light offset, and maintains compatibility with conventional optical pickup systems. The same four regions are used for both tracking error signal detection and for eliminating offset through the specific calculation method.
3Ease of operation
If the objective lens is displaced in the radial direction for tracking adjustment, then the light spot can follow the track, but the focus position shifts, affecting writing speed and light use efficiency
Solution Approach 1:
The light receiving element is divided into multiple independent light receiving regions (first through fourth regions) arranged in a specific pattern. Each region receives light from specific track positions, allowing the system to segment the tracking error signal detection and eliminate offset from stray light by using only signals from regions不受affected by other layer interference.
Solution Approach 2:
The invention uses the cleaned tracking error signal (free from stray light offset) as feedback to control the objective lens displacement. This accurate feedback ensures that the lens is displaced precisely along the track without unnecessary focus position shifts, thereby maintaining writing speed and light use efficiency while achieving proper tracking control.
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 solution enables stable focus and tracking error signal detection, enhances writing speed, and reduces light use inefficiency, effectively addressing the offset issues at the boundary between unrecorded and recorded regions.
Implementation Method 1
a polarizing diffraction grating with specific dividing regions to prevent stray light from other layers
Implementation Method 2
The optical pickup apparatus employs a polarizing diffraction grating with specific dividing regions
Implementation Method 3
an objective lens for focusing a light flux emitted from the light source on the optical disc
Implementation Method 4
a light detector for receiving the light flux condensed by the condenser lens with a plurality of light receiving parts to convert it into an electrical signal
Data Source
AI summary
An optical pickup apparatus is provided with a dividing element having a plurality of regions. The dividing element is capable of dividing a light flux reflected by the optical disc into a plurality of light fluxes having different outgoing directions. Each region of the dividing element and light receiving parts of a light detector are structured such that when a target information recording layer of the optical disc is brought into focus, a light flux reflected from the target information recording layer is focused on the light receiving parts of the light detector, and a light flux reflected from other information recording layer than the target information recording layer is not irradiated onto the light receiving parts of the light detector.