Tilt Sensor Using Photodetector Segmentation for Optical Disk Drives
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional optical disk drive systems face challenges in accurately detecting the tilt of optical disks, especially at the boundary between tracks with different reflectances, due to the influence of focusing state on the tilt error signal, leading to erroneous tilt measurements.
Innovation Solution
A tilt sensor is developed that uses a photodetector with a photosensitive plane divided into specific areas to detect light intensities and generate push-pull signals, ignoring the zero-order light area to minimize the effects of asymmetric light intensity distribution, allowing for accurate tilt detection irrespective of the focusing state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the conventional photodetector detects all light areas including zero-order light, then the detection system is simple, but the tilt detection precision deteriorates due to asymmetric light intensity distribution at track boundaries
Solution Approach 1:
The photodetector's photosensitive plane is divided into multiple distinct areas: a first area detecting +first-order light, a second area detecting -first-order light, and a third area detecting zero-order light. This segmentation allows selective use of light components for tilt detection, improving precision by excluding the problematic zero-order light from the tilt calculation while maintaining a manageable device structure.
Solution Approach 2:
The invention extracts and separates the zero-order light detection function from the tilt detection process. By providing a dedicated third area for zero-order light and excluding it from the tilt error signal calculation, the system removes the source of asymmetry-induced errors while preserving the essential tilt detection capability through first-order light components.
2Quantity of substance
If the beam spot size is decreased for high-density storage, then the storage capacity increases, but the tilt detection accuracy deteriorates due to increased coma aberration
Solution Approach 1:
The invention applies different quality requirements to different light components: first-order light components are used for tilt detection as they provide sufficient sensitivity, while zero-order light components are excluded to eliminate asymmetry errors. This local quality differentiation allows accurate tilt detection even with small beam spots required for high-density storage.
Solution Approach 2:
The invention changes the parameter selection for tilt detection by using only first-order diffracted light components and excluding zero-order light. This parameter change (selecting specific diffraction orders) maintains tilt detection accuracy while enabling compatibility with small beam spots needed for high storage density.
3Measurement precision
If the photodetector uses all diffracted light components, then the signal strength is high, but the tilt measurement accuracy deteriorates due to asymmetric intensity distribution
Solution Approach 1:
The invention converts the harmful asymmetric intensity distribution of zero-order light into a beneficial separation strategy. By detecting zero-order light in a dedicated third area and excluding it from tilt calculations, the system eliminates the source of measurement errors. Simultaneously, the first-order light components, which provide useful tilt information, are selectively utilized, achieving both accuracy and efficient energy use.
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 precise detection of optical disk tilt, reducing the impact of focusing state variations and ensuring accurate high-density data reading and writing even if the disk is warped.
Implementation Method 1
a beam spot of a light beam for reading and/or writing data from/on such a high-density disk needs to have a further decreased size
Implementation Method 2
The photodetector 107 includes photosensitive areas 107a through 107f, which are irradiated with the light beam that has been reflected from the optical disk 105
Implementation Method 3
The light emitted from the light source 101 and having an optical axis 102 is transmitted through the beam splitter 103 and then focused by the objective lens 104 onto the data storage layer of a given optical disk 105
Implementation Method 4
The light emitted from the light source 101 and having an optical axis 102 is transmitted through the beam splitter 103 and then focused by the objective lens 104
Data Source
AI summary
A tilt sensor includes a photodetector having a photosensitive plane and detecting a light beam in multiple areas and outputting detection signals representing its intensities and a tilt detector for generating a tilt error signal, including information about the tilt of a disk, based on the detection signals. The light beam forms a beam spot on the photosensitive plane. The beam spot includes a +first-order light area in which zero-order and +first-order light rays, diffracted by a track on the disk, are superposed, −first-order light area in which zero-order and −first-order light rays are superposed, and a zero-order light area which is sandwiched between the +first-order and −first-order light areas, includes neither the +first-order nor −first-order light ray, but includes a zero-order light ray. The photodetector generates the detection signals except for light entering an opaque area provided for at least part of the zero-order light area.