Brewster Angle Beam Splitter for Stable Low-Percentage Decoupling
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Solution Overview
Problem
Existing beam splitters face challenges in decoupling a small percentage of an optical beam with minimal spectral fluctuation over a large wavelength range, as partially transparent mirrors exhibit significant reflectivity variations across the desired spectrum, leading to substantial changes in the coupled-out beam fraction.
Innovation Solution
A beam splitter device comprising two interconnected planar plates of different materials, where the angle of incidence is set to the Brewster angle for a refractive index greater than the maximum of one plate and less than the minimum of the other, ensuring minimal total reflection across a specified wavelength range, thereby maintaining a small and stable decoupled beam fraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a partially transparent mirror coating is used to couple out a small beam component (less than 1%), then the beam coupling efficiency is improved, but the spectral fluctuation range increases considerably (varying between 0.1 and 0.4% over the wavelength range)
Solution Approach 1:
The patent divides the beam coupling function into multiple discrete reflective interfaces (first interface, second interface, third interface) rather than using a single partially transparent coating. Each interface contributes a small, controlled reflection, and the cumulative effect achieves the desired beam coupling with reduced spectral fluctuation. The segmentation of the optical path allows precise control over the total reflected beam percentage.
Solution Approach 2:
The patent applies different refractive indices at different interfaces (n1 at first interface, n2 at second and third interfaces) to optimize the reflection characteristics locally at each interface. By selecting materials with specific refractive indices and configuring the local optical properties at each boundary, the system achieves minimal spectral fluctuation while maintaining the desired beam coupling ratio.
2Loss of energy
If the angle of incidence is set to the Brewster angle for a specific refractive index, then the reflectivity is minimized at that wavelength, but the spectral range over which minimal reflection is maintained is limited
Solution Approach 1:
The patent uses a composite structure involving multiple materials with different refractive indices (n1 and n2) arranged in sequence. This composite configuration creates multiple reflective interfaces that collectively broaden the spectral range over which minimal reflection is maintained. The combination of different materials allows the system to achieve low beam reflection loss across a wider spectral range than a single material could provide.
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
The solution achieves a small total percentage of beam decoupling with a low fluctuation range, maintaining less than 10% beam component reflection across the desired spectral range, with exemplary embodiments demonstrating overall percentage reflections of 0.16%, 0.30%, and 0.79% with fluctuation ranges of 2.0%, 1.9%, and 3.2% respectively.
Implementation Method 1
The angle of incidence α corresponds to a Brewster angle for a refractive index na which is greater than the maximum refractive index n2max of the second flat plate 2 and is smaller than the Brewster angle for the maximum refractive index n1max of the first flat plate 1
Implementation Method 2
the first and second optical beams are directed onto the plate in such a way that the first and the second beam impinge in each case at an angle to the respective surface perpendicular which is at least approximately equal to the Brewster angle
Implementation Method 3
The first and second optical beams are linearly polarized, with the plane of polarization of the first beam being parallel to the plane of incidence of the device and that of the second optical beam being perpendicular to the plane of incidence
Data Source
Figure 1~2
Figure 3a~3b
Figure 4a~4b
AI summary
The invention relates to a device having a beamsplitter (0) and to a method in which the device is used. The device has an emission unit and a downstream beamsplitter (0), which is formed of two flat plates (1), (2) of different material, which flat plates adjoin each other. For a specified wavelength range of an optical beam (S) from which a partial beam (SR) should be coupled out by reflection, the material of the first flat plate (1) has a minimum refractive index that is greater than the maximum refractive index of the material of the second flat plate (2) by a refractive index distance. From the optical beam (S), which, collimated and linearly polarized parallel to a plane of incidence (E), hits the beamsplitter (0) at a certain angle of incidence (α), a partial beam (SR) having an only very small summary beam percentage of the optical beam (S) and a small spectral fluctuation range is coupled out.