Five-Area Diffraction Grating for Multi-Wavelength Tracking
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Solution Overview
Problem
Conventional optical pickup devices using the in-line differential push-pull method struggle with stable tracking error detection when employing two or more adjacent laser light sources, as the diffraction grating configuration is optimized for one light source, leading to inadequate phase shifts and convergence spot formation for the second light source on optical information recording media with different guide groove pitches.
Innovation Solution
An optical pickup device is designed with a diffraction grating partitioned into five areas, each with a specific periodic structure, allowing two semiconductor lasers with different wavelengths to form convergence spots on optical information recording media, enabling stable tracking error detection across multiple media types by adjusting the phase differences of the diffracted beams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional diffraction grating optimized for one laser light source is used, then stable tracking error detection is achieved for that specific light source, but inadequate phase shifts and convergence spot formation occur for a second light source with different wavelength
Solution Approach 1:
The diffraction grating is divided into five distinct areas (first area, second area, third area, fourth area, and fifth area), each with specific periodic structures optimized for different wavelengths. This segmentation allows each area to handle diffraction for specific laser sources, enabling stable tracking error detection for multiple wavelengths simultaneously.
Solution Approach 2:
Different areas of the diffraction grating are assigned different local qualities (phase structures) tailored to specific wavelengths. The first and fifth areas have phase structures optimized for one wavelength range, while the second and fourth areas have phase structures optimized for another wavelength range, allowing each region to perform its specialized function effectively.
2Adaptability or versatility
If the diffraction grating is designed with five areas and specific phase structures, then stable tracking error detection is achieved for multiple wavelengths, but the device complexity increases
Solution Approach 1:
Multiple functional areas are merged into a single integrated diffraction grating component. The five areas with different phase structures are combined in one grating element, eliminating the need for separate gratings for different wavelengths and reducing overall system complexity despite the increased internal structure.
Solution Approach 2:
The diffraction grating is designed as a universal component that handles multiple wavelengths and serves multiple functions (diffraction for both first and second light sources, tracking error detection for both wavelengths) within a single device, reducing the need for multiple specialized components.
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
The modified diffraction grating configuration ensures proper phase shifts for tracking error signal detection, allowing the device to form convergence spots on a single guide groove even with two adjacent laser sources, thus enabling stable recording and playback on optical information recording media with different guide groove pitches.
Implementation Method 1
a diffraction grating for separating one of the light beam with the first wavelength and the light beam with the second wavelength into at least three light beams
Implementation Method 2
an object lens for causing each of the at least three light beams separated by the diffraction grating to converge and causing the at least three light beams to form at least three separate convergence spots on a recording surface
Implementation Method 3
a photodetector for receiving light beams respectively reflected from the at least three convergence spots on the optical information recording medium
Implementation Method 4
a first semiconductor laser emitting a light beam having a first wavelength; a second semiconductor laser placed in parallel with the first semiconductor laser and emitting a light beam having a second wavelength different from the first wavelength
Data Source
AI summary
An optical pickup device includes a diffraction grating for separating a light beam from a semiconductor laser into at least three light beams. The diffraction grating is partitioned into five areas each having a given periodic structure: a first area; a second area adjacent to the first area in a first direction; a third area adjacent to the first and second areas in a second direction; a fourth area sandwiching the third area with the first area; and a fifth area adjacent to the fourth area in the first direction and sandwiching the third area with the second area. The phase of the periodic structure of each of the first and fifth areas is ahead of that of the third area by substantially 90°. The phase of the periodic structure of each of the second and fourth areas is behind that of the third area by substantially 90°.