Objective Lens Balancing Thickness and Decentering Sensitivities
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Solution Overview
Problem
The production of objective lenses with a numerical aperture of 0.8 or more for Blu-ray Disc systems is challenging due to increased sensitivity to production tolerance, leading to decreased yield and inferior products, as existing designs struggle to simultaneously minimize decentering and thickness sensitivities, which are interdependent and difficult to optimize independently.
Innovation Solution
The objective lens is designed to satisfy specific equations that balance third- and fifth-order thickness and decentering sensitivities, ensuring a wavefront-aberration deterioration level within acceptable limits, even with maximum allowable decentering and thickness errors, thereby improving production yield and optical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the numerical aperture is increased to 0.8 or more for Blu-ray Disc systems, then the light beam concentration and information recording density are improved, but the sensitivity to production tolerance increases significantly, leading to decreased production yield
Solution Approach 1:
The patent applies parameter changes by carefully selecting and optimizing the refractive index of the lens material and the specific curvature parameters of the aspherical surfaces. By changing these parameters, the lens achieves reduced sensitivity to production tolerances while maintaining the required numerical aperture of 0.8 or more, thus improving production yield without sacrificing optical performance
Solution Approach 2:
The patent employs aspherical surface design for both the object-side and disc-side surfaces of the lens. This curvature approach allows precise control over wavefront aberrations and reduces sensitivity to decentering and thickness errors, enabling high numerical aperture operation with acceptable production yield
2Productivity
If the decentering sensitivity is reduced to improve production yield, then the thickness sensitivity increases, and vice versa, making it difficult to optimize both simultaneously
Solution Approach 1:
The patent uses parameter changes by optimizing the refractive index and aspherical surface coefficients to achieve a balanced design where both decentering and thickness sensitivities are reduced. This simultaneous optimization of multiple parameters allows improvement in production yield while maintaining manufacturing precision
Solution Approach 2:
The patent specifies using glass materials with particular refractive index ranges (1.70 ≤ n < 2.00) to achieve the desired balance between decentering and thickness sensitivities. The selection of specific material properties enables reduction of both sensitivity types simultaneously
3Productivity
If the allowable decentering error and thickness error ranges are maintained at ±2.5 μm and ±1.0 μm respectively for high productivity, then the wavefront aberration increases, but if the ranges are reduced to improve optical quality, then productivity decreases
Solution Approach 1:
The aspherical surface design enables the lens to maintain wavefront aberration within acceptable limits even with the standard tolerance ranges of ±2.5 μm decentering and ±1.0 μm thickness. The aspherical coefficients are specifically optimized to compensate for aberrations introduced by these tolerances, allowing high productivity without sacrificing optical performance reliability
Solution Approach 2:
By changing the refractive index to specific ranges and optimizing the aspherical surface parameters, the patent reduces the lens's sensitivity to manufacturing tolerances. This allows the maintenance of wide tolerance ranges for high productivity while keeping wavefront aberration at acceptable levels for reliable optical performance
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 approach significantly reduces wavefront aberration levels, ensuring desired optical performance and increasing production yield by minimizing the impact of production variations, while maintaining acceptable tolerance ranges for decentering and thickness errors.
Implementation Method 1
an objective lens having a numeric aperture (NA) of about 0.8 or more to concentrate a light beam of about 405 nm in wavelength on the recording layer of the optical disc
Implementation Method 2
The objective lens is a focusing lens that focuses light from a laser beam onto a recording layer of an optical disc
Data Source
AI summary
An objective lens has a numerical aperture of 0.8 or more and focusing a light beam of a wavelength λ of at least 450 nm or less on an optical information recording medium. In this objective lens, a wavefront-aberration deterioration level TOR, accumulative value of aberration deterioration, satisfies the equation (1):TOR=√{square root over (2.52(DCm32+DCm52)+(TSA32+TSA52))}{square root over (2.52(DCm32+DCm52)+(TSA32+TSA52))}≦0.07[λrms] (1)In the equation (1), TSA3 [λrms/μm] and TSA5 [λrms/μm] refer to a third-order thickness sensitivity level and a fifth-order thickness sensitivity level, which are generated when a thickness error from a predetermined thickness is +1 μm, respectively. DCm3 and DCm5 refer to a third-order decentering sensitivity level and a fifth-order decentering sensitivity level, which are generated when a decentering error of each of lens surfaces is 1 μm, respectively.