Two-Material Achromatic Prism for Linear Spectral Dispersion
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Solution Overview
Problem
Conventional dispersive elements, such as prisms, suffer from large variance in dispersion over wide wavelength bands, leading to unwanted distortions and non-linear spectral dispersion, which complicates achieving a desired spectral sampling interval in spectrometers.
Innovation Solution
A spectrometer design utilizing a two-material prism system, where a crystalline crown material is paired with a crystalline flint material, such as Aluminum Oxynitride and Strontium Titanate, to achieve a flat dispersion across visible and infrared wavelength bands by optimizing the refractive index and Abbe number characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-material prism is used, then the device complexity is low, but the dispersion linearity is poor leading to large distortion
Solution Approach 1:
The patent applies composite materials by combining two different optical materials (crown glass and flint glass) with different dispersion characteristics to create a two-material achromatic prism. The crown glass element provides lower dispersion while the flint glass element provides higher dispersion, and their combination produces a net dispersion effect that is more linear across the spectral range, thereby improving spectral dispersion linearity without excessive complexity
Solution Approach 2:
The patent segments the prism into multiple elements made from different materials. Instead of using a single homogeneous prism, the dispersion function is divided among separate crown glass and flint glass elements, each contributing differently to the overall dispersion. This segmentation allows independent optimization of each element's dispersion characteristics to achieve improved overall linearity
2Measurement precision
If multiple materials are combined to reduce dispersion variance, then the spectral sampling interval improves, but the device complexity increases
Solution Approach 1:
The patent uses composite materials (crown glass and flint glass) with complementary dispersion properties to achieve reduced dispersion variance across the spectral range. This material combination directly improves measurement precision by providing more uniform spectral sampling, while the well-established nature of these conventional optical materials helps manage device complexity
Solution Approach 2:
The patent changes material parameters by selecting specific crown and flint glass types with appropriate Abbe numbers and refractive indices. By carefully selecting materials with specific optical parameters, the system achieves reduced dispersion variance and improved spectral sampling uniformity while maintaining practical manufacturability
3Ease of manufacture
If conventional glassy materials are used, then the manufacturing is easier, but the dispersion flatness over wide wavelength band is insufficient
Solution Approach 1:
The patent combines conventional glassy crown and flint materials that are easy to manufacture with complementary dispersion characteristics. The crown glass provides a baseline dispersion while the flint glass adds higher dispersion, and their combination achieves improved dispersion flatness across wide wavelength bands while maintaining the manufacturing advantages of conventional glass materials
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 results in reduced variance of dispersion over a wide wavelength band, providing a more linear and flat spectral dispersion, which improves the spectral sampling interval and reduces the required detector bandwidth, enhancing the performance of spectrometers.
Implementation Method 1
The dispersion of light is conventionally achieved through a dispersive element, such as a diffraction grating or a prism
Implementation Method 2
A prism utilizing only a single material yields a dispersion curve proportional to the change in the material's index of refraction versus wavelength
Data Source
AI summary
A spectrometer comprises a detector array and a prism. The prism comprises a first prism element comprising a substantially crystalline crown material, and a second prism element contacting the first prism element, the second prism element comprising a substantially crystalline flint material. The spectrometer further includes optics configured to direct light at least twice through the prism. The prism is configured to disperse light received from the optics at an incident angle therethrough into constituent spectra in visible and infrared wavelength bands that are dispersed from the prism at angles offset from the incident angle. The constituent spectra are directed onto the detector array with approximately equal dispersion across the visible and infrared wavelength bands. Among other things, desirable material selections for the first and second prism elements are also disclosed.