Interferometric Cavity Distance Measurement Without Tunable Lasers
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Solution Overview
Problem
Existing interferometers using fixed wavelength lasers lack the capability for autofocus and absolute optical distance measurement without requiring a wavelength tunable laser.
Innovation Solution
An interferometer equipped with a dynamic illumination system that moves an illumination spot along a trajectory with a nonzero radial component relative to the optical axis, allowing for the analysis of interferograms to determine the functional dependence of optical path length difference, enabling the extraction of absolute optical distance between cavity surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed wavelength laser is used in the interferometer, then the device complexity is reduced and cost is lowered, but the capability for autofocus and absolute optical distance measurement is lost
Solution Approach 1:
The patent applies dynamics by moving the illumination spot along a trajectory with nonzero radial component in the back focal plane. This dynamic illumination approach enables the system to extract absolute optical distance and enable autofocus capability using a fixed wavelength laser, resolving the contradiction between device simplicity and measurement capability.
Solution Approach 2:
The patent changes the illumination parameter by varying the radial position of the illumination spot along a trajectory. This parameter change allows the system to measure optical path length differences and extract absolute distance information, thereby achieving autofocus and absolute distance measurement with a fixed wavelength laser.
2Measurement precision
If a wavelength tunable laser is used, then absolute optical distance measurement and autofocus capabilities are enabled, but the device complexity and cost increase
Solution Approach 1:
The patent extracts the wavelength tuning function from the laser system and replaces it with a dynamic illumination approach. By moving the illumination spot along a trajectory with nonzero radial component, the system extracts absolute distance information from the interferograms without requiring a tunable laser, thus reducing device complexity while maintaining measurement capability.
Solution Approach 2:
The patent creates an optical copy of the wavelength tuning function through dynamic illumination. Instead of physically tuning the laser wavelength, the system uses a fixed laser and dynamically positions the illumination spot to simulate the effect of wavelength variation, enabling absolute distance measurement without the actual wavelength tuning mechanism.
3Measurement precision
If the illumination spot is moved along a trajectory with nonzero radial component, then absolute optical distance can be extracted from interferograms, but the measurement process becomes more complex
Solution Approach 1:
The patent makes the illumination system multi-functional by having a single dynamic illumination mechanism serve multiple purposes: it enables absolute distance measurement, facilitates autofocus, and maintains compatibility with fixed wavelength lasers. This universal approach reduces overall system complexity while achieving multiple measurement objectives.
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 precise autofocus and absolute optical distance measurement in interferometers, enhancing measurement fidelity and focus accuracy without the need for a wavelength tunable laser.
Implementation Method 1
Laser interferometers are a widely used tool for high-precision measurements of engineered surfaces... observe high contrast interference even with large unequal optical paths between interfering surfaces
Implementation Method 2
a dynamic illumination system configured for moving an illumination spot in a back focal plane of the interferometer along a trajectory
Data Source
AI summary
Disclosed is a method and corresponding apparatus for determining an absolute optical distance between two reflecting surfaces that make up an interferometric cavity, the method comprising: moving an illumination spot in a back focal plane of an interferometer along a trajectory that has a nonzero radial component relative to an optical axis to cause different radial positions for the illumination spot along the trajectory while synchronously acquiring images of interferograms of the interferometric cavity; and using one or more electronic processors to analyze the images to determine a functional dependence of an optical path difference (OPD) for the interferometric cavity versus radial position for the illumination spot and extract the absolute optical distance between the two reflecting surfaces based on the determined functional dependence.