Blazed Diffraction Grating Angle Optimization for High Efficiency
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Solution Overview
Problem
Existing diffraction gratings do not achieve a perfect blaze effect for both TE and TM polarization directions, with diffraction efficiency limited by manufacturing tolerances and absorption losses, and are unable to direct all light into a single diffraction order without significant losses in other orders.
Innovation Solution
The optical arrangement selects the angle of the blaze flanks relative to the base surface as a function of the Littrow angle to maximize diffraction efficiency in the largest propagating diffraction orders, allowing for deviations beyond traditional manufacturing tolerances, achieving a perfect blaze effect of 100% for ideally conducting materials and near-perfect efficiency for materials with finite conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the blaze flank angle is set according to traditional manufacturing tolerances to achieve high diffraction efficiency, then the diffraction efficiency is improved, but the manufacturing precision requirements become too strict and cannot be met in practice
Solution Approach 1:
The patent changes the blaze flank angle parameter from the traditional Littrow angle to a new angle β that is larger than the Littrow angle. This parameter change allows the diffraction efficiency to remain high while significantly relaxing the manufacturing precision requirements, as the new angle configuration is more tolerant of manufacturing variations.
Solution Approach 2:
The patent introduces an adjustable angle mechanism that allows the blaze flank angle to be dynamically optimized. By making the angle adjustable rather than fixed, the system can adapt to manufacturing tolerances and achieve optimal diffraction efficiency without requiring extremely precise initial manufacturing.
2Loss of energy
If the blaze flank angle is optimized for maximum diffraction efficiency, then the diffraction efficiency is improved, but the angular tolerance decreases making the system more sensitive to alignment errors
Solution Approach 1:
By changing the blaze flank angle from the Littrow angle to a larger angle β, the patent simultaneously achieves high diffraction efficiency and increased angular tolerance. The new angle configuration creates a broader efficiency plateau that is less sensitive to angular deviations.
Solution Approach 2:
The patent uses an angle β that is intentionally larger than the traditional Littrow angle. This excessive action beyond the conventional optimization point creates a more robust system with greater angular tolerance while maintaining sufficiently high diffraction efficiency for practical applications.
3Ease of manufacture
If the blaze flank angle deviates from the Littrow angle by more than traditional tolerances, then manufacturing flexibility is improved, but diffraction efficiency was previously thought to decrease
Solution Approach 1:
Instead of trying to manufacture the grating at the precise Littrow angle and then accepting efficiency losses from deviations, the patent inverts the approach by deliberately designing the blaze flank angle to be larger than the Littrow angle. This inversion allows manufacturing at more accessible angles while maintaining or improving diffraction efficiency.
Solution Approach 2:
The patent fundamentally changes the blaze flank angle parameter from the Littrow angle to a new angle β. This parameter change enables manufacturing flexibility to be improved without sacrificing diffraction efficiency, as the new angle configuration is inherently more tolerant of manufacturing variations.
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 increases diffraction efficiency in the blaze order while reducing light in other orders, achieving high angular tolerance and manufacturing flexibility, refuting the notion that a perfect blaze effect is impossible for both polarization directions.
Implementation Method 1
Light which falls onto a diffraction grating is diffracted at the diffraction grating. When a light beam 112 with light of a wavelength λ is incident on the diffraction grating 102, the light is diffracted in many discrete directions, these directions being termed diffraction orders.
Implementation Method 2
an incident light beam being arranged at a Littrow angle (θL) relative to a grating normal of the diffraction grating
Data Source
AI summary
An optical arrangement includes a light source which emits coherent light of a wavelength λ, and a diffraction grating which has a multiplicity of diffraction structures which follow one another periodically at the spacing of a grating period d and are arranged along a base surface, the individual diffraction structures respectively having a blaze flank and an antiblaze flank, the blaze flanks being arranged at an angle β and the antiblaze flanks being arranged at an angle α to the base surface, and respectively neighbouring blaze and antiblaze flanks enclosing an apex angle γ, and an incident light beam being arranged at a Littrow angle θL relative to a grating normal of the diffraction grating. The angle β of the blaze flanks to the base surface is selected as a function of the Littrow angle θL such that the diffraction efficiency is at least approximately maximal in one of the largest diffraction orders m, which still fulfils the condition (2((m+1)/m)−1)sin θL≧1, and for at least one polarization direction.