Optical Pickup Device Stray Light Reduction via Magnification Control
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Solution Overview
Problem
In optical pickup devices for multilayer discs, stray light from non-target recording layers interferes with signal light, causing fluctuations in tracking error signals, leading to unstable tracking control and increased costs due to complex and enlarged optical systems.
Innovation Solution
An optical pickup device with a laser diode emitting 405 nm wavelength light and an objective lens with a numerical aperture of 0.85, featuring a detector with optical magnification between 10× to 15×, and an optional grating that branches the beam into a main and sub-beams, with a light shielding zone on the detection parts to reduce stray light interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical systems are used to separate signal light from stray light in multilayer discs, then signal accuracy is improved, but device complexity and size are increased
Solution Approach 1:
The patent changes the optical magnification parameter from the conventional high value (20×-24×) to a lower value (10×-15×). This parameter change allows the detection part to be positioned where signal light is incident while minimizing stray light interference, achieving signal separation without complex optical components.
Solution Approach 2:
Instead of using complete optical separation systems, the patent applies partial action by selectively positioning the detection part to receive only the necessary signal light portion. The detection part is placed in a specific region where signal light intensity is sufficient while stray light from other layers is minimized, avoiding the need for full optical isolation.
2Measurement precision
If high optical magnification (20×-24×) is used to detect tracking error signals, then detection sensitivity is improved, but stray light interference increases causing signal fluctuation
Solution Approach 1:
The patent optimizes the optical magnification parameter to a specific range (10×-15×) that balances detection sensitivity with stray light rejection. This intermediate magnification value provides sufficient tracking error signal detection while positioning the detection part in a region where stray light from other recording layers is minimized, ensuring stable tracking control.
3Illumination intensity
If the detection part is positioned to receive signal light from the target layer, then signal light detection is improved, but stray light from other layers also incidents causing interference
Solution Approach 1:
The patent applies local quality by creating a specific detection region with favorable light incident characteristics. The detection part is positioned at a location where signal light from the target layer is strongly incident while stray light from other layers is weak. This spatial differentiation in light quality allows simultaneous signal detection and stray light rejection.
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 significantly reduces the fluctuation of tracking error signals, stabilizes recording and reproducing performance, and achieves size reduction and cost-effectiveness by minimizing the optical magnification from the disc to the detector.
Implementation Method 1
a laser diode emitting laser light of about 405 nm in wavelength
Implementation Method 2
an objective lens irradiating the optical disc with an optical beam emitted from the laser diode and having a numerical aperture of about 0.85
Implementation Method 3
an optical magnification from the optical disc to the detector is set within a range from about 10× to 15×
Data Source
AI summary
Provided is an optical pickup device that suppresses a fluctuation of a tracking error signal caused by stray light when recording/reproducing information on/from an optical disc including a plurality of recording layers and attains size reduction. It includes a laser diode emitting laser light of about 405 nm in wavelength, an objective lens irradiating the optical disc with an optical beam emitted from the laser diode and having a numerical aperture of about 0.85, and a detector including a detection part receiving the optical beam reflected from the optical disc. An optical magnification from the optical disc to the detector is set within a range from about 10× to 15×.