Optical Head Coma Aberration Symmetric Correction
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Solution Overview
Problem
Conventional optical heads with high numerical aperture objective lenses suffer from deteriorated tilt correcting function due to coma aberration, leading to unstable recording and reproducing operations when the optical recording medium is tilted, as the aberration correction is asymmetric and affects spherical and astigmatism aberrations differently based on the medium's warp direction.
Innovation Solution
The optical head is designed to tilt the objective lens in a manner that the coma aberration of the lens itself is oriented perpendicularly to the tilting direction, ensuring symmetric correction of aberrations generated by the optical recording medium's tilt, with additional features like marking the coma aberration direction on the lens for easy alignment and using a tilt detecting device to adjust the lens position for precise correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the numerical aperture of the objective lens is increased to achieve higher recording density, then the recording density is improved, but the permissible level for characteristic fluctuation becomes stricter and aberration sensitivity increases
Solution Approach 1:
The optical head pre-adjusts the objective lens tilt angle before recording or reproducing operations based on detected medium tilt. This preliminary correction ensures that the optical system is properly aligned before actual data operations, preventing aberration-related failures during critical recording/reproducing moments.
Solution Approach 2:
The system uses tilt detection means to continuously monitor the tilt state of the optical recording medium and provides feedback to the tilt control means. This closed-loop feedback mechanism dynamically adjusts the objective lens tilt angle to compensate for medium variations, maintaining stable recording density and reproduction quality even with high NA lenses.
2Reliability
If the objective lens is tilted to correct medium tilt aberration, then the tilt correcting function is improved, but coma aberration of the lens itself causes asymmetric correction and deteriorates the correcting function
Solution Approach 1:
The patent intentionally introduces a fixed asymmetric tilt angle to the objective lens that compensates for the lens's inherent coma aberration. This predetermined asymmetric adjustment creates a balanced optical system where the lens tilt simultaneously corrects medium tilt effects and compensates for the lens's own optical imperfections, achieving symmetric overall correction.
Solution Approach 2:
The system modifies the tilt angle parameter of the objective lens beyond simple medium tilt compensation. By adding a fixed component to the tilt angle that accounts for the lens's coma aberration characteristics, the system transforms the tilt parameter into a dual-function control variable that addresses both medium tilt and lens aberration simultaneously.
3Reliability
If a tilt sensor and tilt control circuit are added to detect and correct medium tilt, then the aberration correction capability is improved, but the device complexity increases
Solution Approach 1:
The tilt detection means serves multiple functions: it detects medium tilt for aberration correction, and its signal is also used to control the objective lens tilt mechanism. This multi-functional use of the detection system maximizes the utility of added components, reducing the need for separate detection and control elements.
Solution Approach 2:
The tilt control means acts as an intermediary between the tilt sensor and the objective lens positioning mechanism. It processes the tilt detection signal and translates it into appropriate lens adjustment commands, simplifying the overall control architecture by providing a dedicated intermediate control layer that manages the complexity of coordinating sensor data with actuator responses.
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 approach enhances the stability of recording and reproducing operations by ensuring symmetric correction of aberrations, improving the radial and tangential tilt correcting functions and maintaining stability across different tilt directions, thus supporting higher recording densities with reduced aberration margins.
Implementation Method 1
an objective lens (65) converging light to a recording layer of the optical recording medium (66)
Implementation Method 2
a tilt sensor (69) to detect the tilt of the optical recording medium (66)
Data Source
AI summary
An optical head performs recording and/or reproducing of a signal to an optical recording medium and comprises a light source, an objective lens converging the light emitted from the light source to the optical recording medium, and objective lens tilting mechanism for tilting the objective lens in order to correct aberration generated when the optical recording medium is tilted, and the optical head is assembled so that a direction of the coma aberration of the objective lens itself perpendicularly crosses a direction tilted by the objective lens tilting mechanism.