Optical Pick-Up Stray Light Subtraction for Multi-Layer Discs
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Solution Overview
Problem
Existing optical pick-up systems for multi-layer optical discs face challenges with interlayer cross talk, particularly in detecting servo signals due to stray light from out-of-focus layers, which affects the accuracy of focus and tracking error signals, and require additional components like separate HOEs for SSD, increasing the system's size and complexity.
Innovation Solution
The optical pick-up system employs multiple photodetectors and a diffracting optical element with switchable functions to selectively detect and subtract stray light components, allowing for accurate alignment and stable signal generation without the need for additional HOEs, using a main and dummy photodetector to adjust the position of the HOE and photodetector for improved signal clarity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple photodetectors are used to detect and subtract stray light components, then measurement precision of servo signals is improved, but device complexity increases
Solution Approach 1:
The photodetector is divided into multiple independent detection regions: a first photodetection part for detecting diffracted light from the target layer, and a second photodetection part for detecting stray light from out-of-focus layers. This segmentation allows separate detection and subtraction of stray light components, improving servo signal precision without requiring entirely separate detector systems.
Solution Approach 2:
The patent combines multiple detection functions into a single integrated photodetector structure. The first and second photodetection parts are merged into one device, allowing simultaneous detection of both target layer signals and stray light components. This reduces the need for multiple separate detectors and associated optical paths, thereby reducing device complexity while maintaining measurement precision.
2Reliability
If separate HOE is added for SSD to remove stray light, then reliability of servo signals is improved, but device complexity and size increase
Solution Approach 1:
The patent makes the existing HOE multi-functional by designing it to simultaneously perform its original diffraction function and an additional function of directing stray light to the second photodetection part. This eliminates the need for a separate HOE dedicated to SSD, reducing device complexity while maintaining servo signal reliability through effective stray light removal.
Solution Approach 2:
The patent merges the stray light detection function into the existing HOE and photodetector system. By configuring the HOE to direct stray light components to appropriate detection regions and combining multiple detection functions into a single photodetector, the system achieves reliable servo signals without adding separate HOE components, thereby reducing overall device complexity.
3Manufacturing precision
If feedback control is implemented for HOE and photodetector positioning, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent implements a self-alignment mechanism where the HOE and photodetector automatically position themselves relative to each other through feedback control based on detected light signals. The system uses the detected diffracted light and stray light signals to generate feedback that adjusts the relative positioning, eliminating the need for complex external alignment equipment and reducing manufacturing complexity while achieving high precision.
Solution Approach 2:
The patent employs feedback control where the signals detected by the photodetector (both from the target layer and stray light) are used to adjust the relative positioning of the HOE and photodetector. This feedback mechanism ensures accurate alignment during assembly and operation, improving manufacturing precision while using a relatively simple control system that leverages the existing detection capabilities.
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 accurate positioning of the HOE and photodetector during assembly, minimizes the influence of stray light on servo signals, and maintains stable RF, FES, and TES generation, even in multi-layer discs with three or more layers, while reducing the system's size and complexity.
Implementation Method 1
The reflected light from the optical disc is divided and diffracted into multiple light beams by a diffracting optical element, such as HOE (Holographic Optical Element)
Implementation Method 2
the resulting light beams are received by a photodetector and the signals detected in response to the amount of light received generate reproducing RF signal
Data Source
AI summary
An optical pick-up which permits the relative position of a diffracting optical element and a photodetector to be adjusted by feedback control with signals which are generated when more than one kind of diffracted light differing in order is received, the diffracted light occurring as the reflected light from the optical disc is divided and diffracted by the diffracting optical element having multiple regions. The photodetector which detects the light beam passing through the central region of the diffracting optical element and generates RF signals is juxtaposed with sub-photodetectors, so that they receive reflected stray light from out-of-focus layers and perform computation to calculate the reflected stray light component which the RF signal detector receives, thereby detecting only the component of signals of the reflected light from a target layer.