Diffractive Optical Element with Curved Ridge Portions
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Solution Overview
Problem
The challenge in manufacturing diffractive optical elements lies in forming precise diffraction gratings with microscopic features, particularly the valley bottom portions, which are difficult to process due to the limitations of cutting tools and grinding processes, leading to deformation of ridge portions and degradation of diffraction efficiency and wavelength characteristics.
Innovation Solution
A diffractive optical element is designed with a first optical member having raised portions with a curved surface defined by vertical and inclined surfaces, and a second optical member with recessed portions, where the curvature radius of the raised portions is optimized to maintain high diffraction efficiency by satisfying specific expressions relating the refractive index difference and pitch of the gratings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a turning tool or grindstone is used to process the valley bottom portion of the inverted shape in the mold, then the mold can be manufactured, but the valley bottom portion cannot be formed in an ideal sharpened shape due to tool size limitations
Solution Approach 1:
Instead of attempting to directly form the sharpened valley bottom portion in the mold using cutting tools, the invention inverts the approach by forming the diffraction grating with rounded ridge portions directly in the optical member. The rounded shape that would normally be considered a manufacturing imperfection is instead made the intentional design feature, eliminating the need for difficult sharpened valley formation in the mold while achieving the desired optical performance.
Solution Approach 2:
The invention changes the critical parameter from valley bottom sharpness to ridge portion curvature radius. By controlling the curvature radius R of the rounded ridge portions to satisfy R≦A1×P3+B1×P2+C1×P, the patent transforms the manufacturing challenge into a controllable parameter specification that can be achieved through standard molding processes with appropriate mold design.
2Ease of manufacture
If the valley bottom portion of the inverted shape is not processed in a sharpened shape, then manufacturing is easier, but the ridge portion of the crest of the diffraction grating becomes deformed
Solution Approach 1:
The invention inverts the traditional diffraction grating geometry by making the ridge portions rounded instead of sharp. This inversion allows the mold to be easily manufactured without requiring precision sharpening of valley bottoms, while the rounded ridge portions are intentionally designed to prevent deformation during the molding process.
Solution Approach 2:
The rounded ridge portions act as a cushioning design feature that prevents stress concentration and deformation during molding. By preemptively designing the ridge portions with rounded shapes and controlling their curvature radius, the patent prevents deformation before it can occur during the molding process, rather than attempting to correct it afterward.
3Reliability
If a sharpened ridge portion of the crest of the diffraction grating is formed, then diffraction efficiency is maximized, but chipping is likely to occur
Solution Approach 1:
The invention applies curvature to the ridge portions by forming them with a rounded shape instead of sharp edges. By controlling the curvature radius R to satisfy the specified relationship with pitch P, the patent maintains sufficient diffraction efficiency while eliminating stress concentration points that would lead to chipping, thereby improving durability.
Solution Approach 2:
The patent changes the physical state of the ridge portions from sharp to rounded by controlling the curvature radius parameter. This parameter change maintains the optical functionality for diffraction while fundamentally improving the mechanical strength and resistance to chipping of the ridge portions.
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 configuration ensures high diffraction efficiency, with the diffraction efficiency maintained at or above 85% for the blaze wavelength, and up to 95% by adhering to specific curvature and pitch relationships, even when the ridge portions are rounded, thereby preventing deformation-related efficiency losses.
Implementation Method 1
a diffractive optical element in which two optical members are stacked, and a diffraction grating is formed at an interface between the two optical members
Data Source
AI summary
A diffractive optical element includes first and second optical members which are stacked. The first optical member includes a diffraction grating in which a plurality of raised portions each having a vertical surface and a surface inclined to the vertical surface are arranged. The second optical member includes a diffraction grating in which a plurality of recessed portions are arranged, to which the raised portions are fitted. The diffraction grating of the first optical member and the diffraction grating of the second optical member are in close contact with each other. A ridge portion of the raised portion defines a curved surface. A curvature radius R (μm) of the curved surface, a pitch P (mm) of the raised portions, and a refractive index difference Δnd between the first and second optical members satisfy a predetermined relationship.