Optical Pickup Diffraction Grating for Stable Tracking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional optical pickup devices using the in-line DPP method experience asymmetric intensity distribution of convergence spots, leading to shifted phase differences in push-pull signals, which prevents stable tracking error detection on optical information recording media with different guide groove pitches.
Innovation Solution
An optical pickup device with a diffraction grating divided into three regions, where the middle region is further divided into sub-blocks with specific phase differences, ensuring symmetric intensity distribution of convergence spots and maintaining the advantages of the in-line DPP method for stable tracking error detection across various optical information recording media.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional diffraction grating with three regions of different phases is used, then the in-line DPP method can be applied, but asymmetric intensity distribution of convergence spots occurs, causing phase shifts in push-pull signals and preventing stable tracking error detection on media with different guide groove pitches
Solution Approach 1:
The diffraction grating is divided into three regions (first, second, third regions) with different phases, where each region is further segmented into sub-blocks with alternating phases. This segmentation allows the grating to handle different guide groove pitches while maintaining proper intensity distribution through the alternating phase sub-blocks in the second region.
Solution Approach 2:
Different regions of the diffraction grating are assigned different phase characteristics tailored to specific functions. The first and third regions have one phase configuration while the second region has alternating phase sub-blocks, creating local quality variations that resolve the intensity distribution problem and enable both versatility and precision.
2Ease of operation
If the phase of grating grooves is shifted by 90 degrees in the in-line DPP method, then beam separation is achieved, but asymmetric intensity distribution occurs in convergence spots, leading to unstable push-pull signal phase differences
Solution Approach 1:
The patent intentionally introduces asymmetry through alternating phase sub-blocks in the second region of the diffraction grating. This controlled asymmetry compensates for the asymmetric intensity distribution caused by the 90-degree phase shift, restoring symmetry to the convergence spots and stabilizing the push-pull signal phase difference.
Solution Approach 2:
Instead of accepting the asymmetric intensity distribution as inevitable, the patent inverts the approach by introducing alternating phase sub-blocks that actively counterbalance the asymmetry. This inversion strategy transforms the problematic asymmetric intensity distribution into a stable symmetric pattern at the convergence spots.
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 solution enables stable tracking error detection on multiple optical information recording media with different guide groove pitches by reducing phase shifts in push-pull signals, allowing for accurate convergence spots formation and improved tracking error signal detection.
Implementation Method 1
a diffraction grating for separating a light beam emitted from the light source into at least three light beams
Implementation Method 2
converging a light beam emitted from a light source such as a semiconductor laser device on a recording track of the optical disc by using an objective lens
Implementation Method 3
converting reflected light from the optical disc to an electric signal by a photodetector
Data Source
AI summary
An optical pickup device includes a diffraction grating 12 for separating an emitted light beam into at least three light beams. The diffraction grating 12 is divided into three regions by dividing lines D1 and D2 extending in a first direction parallel to a tangent line of a track of an optical information recording medium. A second region 12B is divided into four sub-blocks by a dividing line D3 extending in the first direction and a dividing line D4 extending in a second direction that crosses the first direction. The sub-blocks located diagonally opposite to each other have a same phase, and the sub-blocks located adjacent to each other have a phase difference of approximately 180 degrees. The first region 12A has a phase difference of approximately 90 degrees from each sub-block of the second region 12B, and the first region 12A has a phase difference of approximately 180 degrees from the third region 12C.