Concave Diffraction Grating Spectrometer Folium Mirror Placement
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Solution Overview
Problem
Current spectrometers with cylindrical mirrors suffer from reduced optical resolution due to beam path lengthening and complex adjustment challenges, while also being costly and difficult to align, especially when dealing with large light sources and limited photodetector height.
Innovation Solution
The optimization of cylindrical mirror placement along a 'folium' curve, allowing for focused light collection on photodetectors without lengthening the beam path, combined with identical mirror and detector positioning to simplify alignment and reduce mechanical bulk, and the use of alternate mirror radii to cover the entire spectral range without trapezoidal mirror requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If cylindrical mirrors are used to focus diffracted beams onto photodetectors, then light collection sensitivity is improved, but optical resolution is reduced due to beam path lengthening
Solution Approach 1:
The patent replaces cylindrical mirrors with curved focal surfaces (spheroidal or elliptical geometry) that naturally focus diffracted beams without requiring long optical paths. The curved surface geometry provides the necessary focusing power while maintaining compact beam paths, thereby preserving optical resolution while improving light collection sensitivity.
Solution Approach 2:
The patent transitions from using cylindrical mirrors (2D curved surfaces) to spheroidal or elliptical focal surfaces (3D curved surfaces). This dimensional change allows the focal surface to better match the curved wavefronts of diffracted beams, providing superior focusing capability in multiple dimensions simultaneously, thus improving light collection without compromising resolution.
2Adaptability or versatility
If cylindrical mirrors with different radii are used to cover the entire spectral range, then spectral coverage is improved, but device complexity and alignment difficulty increase
Solution Approach 1:
The patent employs a single spheroidal or elliptical focal surface that can focus diffracted beams of all wavelengths onto a planar detector array. This universal focal surface replaces multiple cylindrical mirrors with different radii, providing full spectral coverage while significantly reducing device complexity and alignment requirements.
Solution Approach 2:
The patent uses a planar detector array that copies the spectral information across multiple detection elements. Each element on the planar array receives focused light at its specific position, eliminating the need for multiple curved mirrors while maintaining full spectral coverage through the spatial distribution of detection elements.
3Measurement precision
If the focal surface is curved to match the Rowland circle, then optical resolution is improved, but coupling to planar photodetector arrays becomes difficult
Solution Approach 1:
The patent introduces a curved focal surface as an intermediary optical element that receives the curved diffracted beams and redirects them to a planar detector array. This intermediary surface performs the focusing function while adapting the beam geometry to match the planar detector, thereby maintaining optical resolution while enabling easy coupling to standard photodetector arrays.
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 enhances light collection sensitivity, maintains high spectral resolution, simplifies spectrometer adjustment, and reduces costs by allowing for easier assembly and alignment, while enabling the use of larger light sources and continuous spectral range detection.
Implementation Method 1
The light beam is diffracted by the grating 1, each wavelength λ that makes up the polychromatic incident beam is deviated by an angle β with respect to the normal to the grating
Implementation Method 2
and focused by the grating 1 at a distance Lb
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention relates to an optical spectrometer having concave diffraction grating including an input slot (3) suitable for receiving and forming an incident beam (5) including at least one wavelength ?, a concave diffraction grating (1) suitable for receiving the incident beam (5) with an angle of incidence a and for diffracting said beam in order to form a diffracted beam forming an angle ß(?) with the normal of the grating (1), at least one concave mirror (8, 8a, 8b, 8c) made up of a portion of a cylinder with a circular cross-section having a radius rcy?, said mirror (8, 8a, 8b, 8c) being suitable for receiving the diffracted beam (6, 6a, 6b, 6c) in the direction ß(?) and for focusing said beam on at least one output slot (4, 4a, 4b, 4c), and at least one photodetector (9, 9a, 9b, 9c) optically coupled to an output slot (4, 4a, 4b, 4c) in order to measure the beam diffracted and focused by a cylindrical mirror (8, 8a, 8b, 8c). According to the invention, said mirror (8, 8a, 8b, 8c) is located on a folium curve at a distance d(?) in the direction of the diffraction grating (1) relative to the focus point of the diffracted beam (6, 6a, 6b, 6c) in the direction ß(?) on the Rowland circle (2), such that: d(?) = rcyl, / 23/2 / cos(ß).