Optical Reading System PRML Constraint Length Optimization
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Solution Overview
Problem
Optical recording media face challenges in maintaining signal reading quality due to surface scratches and extraneous matters, especially when the information recording layer is close to the light incident surface, leading to decreased reading efficiency and recording capacity.
Innovation Solution
An optical reading method that sets the constraint length in the PRML detection method to a specific range, ensuring stable signal reading by adjusting the wavelength, numerical aperture, and channel bit frequency, allowing for effective decoding even with surface imperfections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the information recording layer is positioned close to the light incident surface to increase recording capacity, then the recording capacity is improved, but the signal reading quality deteriorates due to surface scratches and extraneous matters
Solution Approach 1:
The patent applies parameter changes by optimizing the constraint length parameter in the PRML detection method. By setting the constraint length to a specific value based on the relationship between beam spot diameter and channel bit length, the system achieves both high recording capacity and reliable signal reading even when the information recording layer is close to the light incident surface. This parameter optimization resolves the contradiction between increased recording capacity and maintained signal reading quality.
2Measurement precision
If the constraint length in PRML detection is increased to improve decoding precision, then the decoding precision is improved, but the resistance to surface imperfections deteriorates
Solution Approach 1:
The patent determines the optimal constraint length parameter by establishing a specific relationship between the beam spot diameter (λ/NA) and the channel bit length (LV/f). By setting the constraint length to approximately half of the number of channel bits contained in the beam spot, the system achieves both high decoding precision and robust resistance to surface imperfections. This parameter optimization resolves the contradiction between decoding precision and resistance to fingerprints and scratches.
3Quantity of substance
If the linear recording density is increased by reducing recording mark size, then the recording capacity is improved, but the read signal amplitude decreases to near zero at the resolution limit
Solution Approach 1:
The patent addresses the resolution limit problem by optimizing the constraint length parameter in PRML detection. By setting the constraint length to approximately half of the number of channel bits in the beam spot, the system can successfully decode signals even when recording marks are reduced to sizes at or below the theoretical resolution limit (λ/NA)/4. This parameter optimization enables high linear recording density while maintaining sufficient read signal amplitude through enhanced signal processing capability.
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 stabilizes signal reading characteristics and rationally increases recording capacity by optimizing the constraint length in the PRML detection method, enhancing resistance to fingerprints and scratches while maintaining high decoding precision.
Implementation Method 1
irradiating an optical recording medium with a laser beam through an objective lens to read information recorded on an information recording layer
Data Source
AI summary
An optical reading system is provided to improve read signal quality with increasing its linear recording density. An optical recording medium in which the distance from a light incident surface to an information recording layer is less than 100 μm is irradiated with a laser beam through an objective lens and information stored in the information recording layer is read by means of a PRML detection method. At this time, the constraint length n in the PRML detection method is set to an integer which satisfies 0.5×(λ/NA)/(LV/f)−1<n<0.5×(λ/NA)/(LV/f)+1, wherein λ represents the wavelength of the laser beam, NA represents the numerical aperture of the objective lens, LV represents the linear velocity of the optical recording medium when recording, and f represents a channel bit frequency when recording.