Optical Head Aberration Correction for Multi-Layer Discs
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Solution Overview
Problem
Conventional optical heads face challenges in accurately correcting third-order astigmatism and coma aberrations when recording or reproducing information from multi-layer optical discs with varying light transmitting layer thicknesses, leading to increased aberrations and interference issues.
Innovation Solution
The optical head design includes a diffraction-grating fitted mirror and a flat-plate mirror that reflect and transmit laser light at specific ratios, with a collimator lens actuator moving to correct spherical aberrations by adjusting the light path, and a compatible objective lens for each disc type to minimize astigmatism and coma aberrations, ensuring accurate laser power control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional optical head design is used to record or reproduce information from multi-layer optical discs with varying light transmitting layer thicknesses, then the basic recording and reproduction function is maintained, but third-order astigmatism and coma aberrations increase, leading to decreased recording and reproduction accuracy
Solution Approach 1:
The patent employs dynamic adjustment mechanisms including a collimator lens actuator that moves the collimator lens in the optical axis direction to correct spherical aberration, and an objective lens actuator that tilts the objective lens in the radial direction to correct coma aberration. These dynamic adjustments allow the optical system to adapt to varying light transmitting layer thicknesses across multiple disc layers, maintaining focus accuracy and minimizing aberrations during recording and reproduction operations.
Solution Approach 2:
The patent changes key optical parameters including the numerical aperture (NA) of the objective lens and the wavelength of the laser light source to optimize performance across different disc types and layers. By adjusting the NA and wavelength parameters, the system can compensate for variations in light transmitting layer thickness and reduce the impact of third-order astigmatism and coma aberrations, thereby improving recording and reproduction accuracy.
2Reliability
If means for correcting third-order spherical aberration are added to the optical head, then spherical aberration correction capability is improved, but the optical head size increases and complexity increases
Solution Approach 1:
The patent combines multiple aberration correction functions into integrated actuator assemblies. The collimator lens actuator integrates spherical aberration correction with focus control, while the objective lens actuator combines coma aberration correction with tracking control. This merging of functions reduces the number of separate components needed and simplifies the overall optical head structure while maintaining comprehensive aberration correction capability.
Solution Approach 2:
The patent designs the collimator lens actuator and objective lens actuator to perform multiple functions simultaneously. These actuators not only correct spherical and coma aberrations but also maintain focus and tracking accuracy across different disc layers. This multi-functionality eliminates the need for separate dedicated correction mechanisms, thereby reducing device complexity while ensuring reliable aberration correction.
3Adaptability or versatility
If multiple objective lenses with different numerical apertures are used to support different disc types, then compatibility with various disc formats is improved, but the optical head size and structural complexity increase
Solution Approach 1:
The patent employs a single objective lens with adjustable numerical aperture through dynamic control mechanisms. The objective lens actuator can tilt the lens to effectively change the NA, allowing the same physical lens to serve multiple disc types (CD, DVD, BD) with different required NAs. This dynamic adjustment replaces the need for multiple fixed NA lenses, reducing optical head complexity while maintaining broad disc format compatibility.
Solution Approach 2:
The patent changes the effective numerical aperture parameter of the objective lens through mechanical adjustment rather than replacing the lens itself. By tilting the objective lens at different angles, the system can optimize the NA for different disc types and layers, achieving multi-format compatibility with a single lens design and avoiding the complexity of managing multiple objective lenses with different specifications.
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 effectively suppresses third-order astigmatism and coma aberrations across different optical discs, enhancing recording and reproduction accuracy and reducing interference, while maintaining a compact optical head size.
Implementation Method 1
a diffraction-grating fitted mirror 25...separates blue-violet laser light passing through the second surface 25b into 0th-order light and ±1st-order diffracted light
Implementation Method 2
The blue-violet laser light reflected by the diffraction-grating fitted mirror 25...passes through the objective lens 8
Implementation Method 3
A part of the blue-violet laser light incident on the flat-plate mirror 15 is reflected toward the quarter-wave plate 6
Implementation Method 4
The blue-violet laser light reflected by the flat-plate mirror 15 passes through the quarter-wave plate 6 after being converted into circularly polarized light
Implementation Method 5
The blue-violet laser light reflected by the diffraction-grating fitted mirror 25 is focused to be incident as a light spot on a specified information recording surface...by the objective lens 8
Implementation Method 6
a photodetector for receiving reflected light from the information recording surface of the first information recording medium
Data Source
AI summary
An optical head, an optical disc device and an information processing device are capable of suppressing the amount of third-order astigmatism created upon recording or reproducing information on or from a multi-layer optical disc including at least three information recording surfaces. An objective lens satisfies a relationship of tc>(t0+tn)/2 assuming that t0 denotes the thickness of a light transmitting layer from the outer surface of the multi-layer optical disc to an information recording surface having the largest light transmitting layer thickness, tn denotes the thickness of a light transmitting layer from the outer surface of the multi-layer optical disc to an information recording surface having the smallest light transmitting layer thickness and tc denotes the thickness of a virtual light transmitting layer at which the absolute value of a third-order spherical aberration is minimum when blue-violet laser light is incident as parallel light on the objective lens.