Optical Head Light Shielding for Multi-Layer Disc Interference
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Solution Overview
Problem
Existing optical heads face interference issues due to stray light from non-target information storage layers, which affects the stability of information signals and servo signals when reading and writing from optical discs with different protective substrate thicknesses.
Innovation Solution
An optical head design that includes a light shielding portion to prevent stray light from reaching the photodetector, using a diffraction element to produce multiple orders of diffracted light and an objective lens to converge specific orders on each storage medium, along with a condenser lens and photodetector to receive the reflected light, while the light shielding portion is arranged to minimize loss and interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single objective lens is used to read/write from optical discs with different protective substrate thicknesses, then compatibility across multiple disc types is achieved, but stray light from non-target information storage layers causes signal interference and reduces signal stability
Solution Approach 1:
The patent segments the reflected light from different information storage layers by using a diffraction grating to separate wavelengths. The first information storage layer reflects light at a first wavelength while the second layer reflects at a second wavelength. This segmentation allows the system to selectively detect signals from the target layer while filtering out stray light from non-target layers, resolving the contradiction between multi-disc compatibility and signal stability.
Solution Approach 2:
The patent introduces a wavelength-selective optical filter as an intermediary between the photodetector and the reflected light path. This filter selectively transmits the wavelength corresponding to the target information storage layer while blocking wavelengths from non-target layers. This intermediary component enables the system to maintain signal stability when reading from multiple disc types with different protective substrate thicknesses.
2Manufacturing precision
If the objective lens numerical aperture is increased to focus on deeper information storage layers, then writing capability on BDs with 0.1mm protective substrate is achieved, but the depth of field decreases making it difficult to maintain focus on layers at different depths
Solution Approach 1:
The patent employs dynamic focus adjustment mechanisms that allow the objective lens to adapt its focal position based on the detected disc type. When a BD is detected, the lens focuses at a first focal position optimized for the 0.1mm protective substrate. When an HD DVD is detected, the lens adjusts to a second focal position for the 0.6mm protective substrate. This dynamic adaptation resolves the contradiction between achieving precise focus on deep layers and maintaining versatility across multiple disc types.
Solution Approach 2:
The patent changes the focal position parameter of the objective lens based on the information storage layer depth. For BDs with shallow storage layers at 0.1mm depth, the lens is positioned at a first focal distance. For HD DVDs with deeper storage layers at 0.6mm depth, the lens is positioned at a second focal distance. This parameter adjustment enables the system to maintain manufacturing precision for focus while adapting to multiple disc types with different protective substrate thicknesses.
3Reliability
If a light shielding portion is added to block stray light from non-target information storage layers, then signal interference is reduced, but the device complexity increases
Solution Approach 1:
The patent extracts and blocks only the harmful stray light components from non-target information storage layers while allowing the useful signal from the target layer to pass through. By selectively removing the interfering wavelength components using optical filters and wavelength separation, the system reduces signal interference without requiring extensive structural modifications, thus limiting the increase in device complexity while improving signal stability.
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 design reduces interference between signals from target and non-target information storage layers, stabilizing information and servo signals, and ensures reliable read and write operations on multiple types of optical discs.
Implementation Method 1
a diffraction element that diffracts the laser beam to produce multiple orders of the diffracted light
Implementation Method 2
an objective lens for converging, among the multiple orders of the diffracted light, an nth order (where n is an integer) diffracted light on the information storage layer of the first storage medium
Implementation Method 3
a condenser lens for condensing the laser beam that has been reflected from the first or second storage medium
Implementation Method 4
a photodetector that receives the condensed laser beam
Data Source
AI summary
When performing a read or write operation on an optical disc with information storage layers, this compatible optical head with a two-focus lens can reduce interference caused by an unnecessary diffracted light reflected from a non-target layer and not contributing to reading or writing. The head reads and/or writes information from/on storage media, including first and second media with different protective substrate thicknesses, by irradiating a given one with a laser beam and includes: a diffraction element that diffracts the beam to produce diffracted light of multiple orders; an objective lens for converging nth and mth order ones of the light on the respective storage layers of the first and second media; a photodetector that receives the beam reflected from the medium and condensed; and a light shielding portion for preventing a portion of the beam reflected from the storage layer of the second medium and including its optical axis from reaching the photodetector. The light shielding portion is arranged so as to reduce loss to be caused by cutting off the portion of the beam to a predetermined value or less.