Variable-Wavelength Interferometry Illumination System
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Solution Overview
Problem
Existing interferometric systems face challenges in providing reliable illumination at different wavelengths without mechanical components, leading to vibrations and inaccurate measurements due to non-Gaussian white light spectra produced by combining red, green, and blue LEDs.
Innovation Solution
A system combining a white-light source with narrowband sources and dichroic filters operating in reflection, allowing for switching between wavelengths by adjusting the power ratio to achieve a Gaussian output, eliminating mechanical parts and vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a mechanical switch is used to switch between green LED and white light LED, then wavelength switching is achieved, but vibrations are introduced that are highly undesirable for interferometric measurements
Solution Approach 1:
The patent replaces the mechanical switch with an electronic control system that uses electronic shutters or modulators to switch between green LED and white light LED. This eliminates mechanical vibrations while maintaining wavelength switching capability, directly resolving the contradiction between adaptability and measurement reliability.
Solution Approach 2:
The patent introduces an electronic control system as an intermediary between the light sources and the interferometer. This intermediary uses electronic signals to control the switching of light sources without mechanical contact, thereby eliminating vibrations while preserving the ability to switch wavelengths for different interferometric applications.
2Reliability
If red, green and blue LEDs are combined with two dichroic mirrors to produce white light, then mechanical switching is eliminated, but the intensity spectrum is not sufficiently Gaussian and exhibits ringing
Solution Approach 1:
The patent extracts only the necessary color components (red and green LEDs) needed to produce a Gaussian-shaped white light spectrum, eliminating the blue LED that causes spectral distortion. This selective extraction maintains the benefit of no mechanical switching while achieving the required Gaussian spectrum for high-quality correlograms.
Solution Approach 2:
The patent adjusts the intensity parameters of the red and green LEDs to achieve the optimal Gaussian spectrum shape. By carefully controlling the relative intensities and spectral characteristics of the LED components, the system produces true white light with a Gaussian intensity distribution that eliminates ringing in the correlograms.
3Device complexity
If a single white-light source with a movable green filter is used, then the number of components is reduced, but the filter attenuates the incoming white light beyond a useful level and mechanical movement is still required
Solution Approach 1:
Instead of filtering green light from white light (which causes attenuation), the patent inverts the approach by directly generating green light using a green LED. This eliminates the need for a movable filter and its associated mechanical components while maintaining high green light intensity without unnecessary attenuation.
4Reliability
If red, green and blue LEDs are combined to produce white light, then mechanical switching is eliminated, but the system becomes relatively expensive due to the large number of components
Solution Approach 1:
The patent extracts only the essential LED components needed for the application - specifically red and green LEDs for white light generation, or green LED alone for narrowband work. By eliminating the blue LED and other unnecessary components, the system reduces complexity and cost while maintaining the reliability benefit of no mechanical switching.
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
Enables fast and accurate switching between wavelengths without mechanical delays or vibrations, producing true white light for interferometric measurements by calibrating the power ratio to match the spectral output with a Gaussian curve, improving measurement precision and reducing system complexity.
Implementation Method 1
a dichroic mirror adapted to reflect the green light from the green light source and transmit the white light from the white light source
Implementation Method 2
acquiring light intensity data from correlograms generated by interfering light beams reflected from a test object and a reference surface
Data Source
AI summary
An illumination system for an interferometer combines a white-light source and a green source with a reflective green dichroic filter. When the green source alone is energized for PSI measurements, the output of the illumination system is green only. When a white-light output is desired for VSI measurements, both sources are energized and the intensity of the green light is judiciously calibrated to match the spectral band filtered out by the dichroic mirror. Therefore, the system can switch between green and white light simply by changing the selection of energized sources, without any mechanical switching and attendant delays and vibrations. Multiple narrowband sources may be combined with white light in a similar manner.