Laser Interferometric Wavelength Leverage for Absolute Distance
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Solution Overview
Problem
Current absolute distance measurement methods, such as time-of-flight and laser interferometric techniques, face limitations in accuracy and flexibility, especially for large distances, with millimeter-level precision and ambiguity in measurements, and are prone to errors due to direct-current drift and frequency modulator instability.
Innovation Solution
The use of a laser interferometric wavelength leverage method involving a light source system with two lasers emitting orthogonally polarized beams, a wavelength-leverage laser interferometric system with cube-corner prisms, and an interference signal processing system to establish a leverage relationship between the synthetic wavelength and the moving displacement of a cube-corner prism, allowing for high-accuracy absolute distance measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If time-of-flight measurement with laser pulses is used, then measurement speed is improved, but measurement precision deteriorates to millimeter level
Solution Approach 1:
The patent combines frequency-sweeping interferometry and multiple-wavelength interferometry into a unified wavelength-leverage interferometric system. By merging the frequency modulation capability with multi-wavelength synthesis, the system achieves both high measurement speed (through rapid frequency sweeping) and high precision (through synthetic wavelength interferometry that eliminates ambiguity), resolving the contradiction between speed and precision in traditional time-of-flight methods.
Solution Approach 2:
The patent changes the measurement parameter from direct time-of-flight to optical path difference through frequency modulation. By sweeping the laser frequency and measuring the phase change of interference fringes, the system converts temporal measurement into spatial interferometric measurement, achieving millimeter-level precision while maintaining fast measurement speed through rapid frequency modulation.
2Measurement precision
If phase shifting method is used, then measurement resolution is improved, but measurement range deteriorates due to non-ambiguity distance limitation
Solution Approach 1:
The patent implements a nested measurement structure where multiple synthetic wavelengths are used hierarchically. The system first measures with a long synthetic wavelength to determine the coarse distance (resolving ambiguity), then progressively uses shorter synthetic wavelengths to refine the measurement precision. This nested approach allows the measurement range to extend beyond the non-ambiguity distance of any single wavelength while maintaining high resolution.
Solution Approach 2:
The patent adds the frequency dimension to the traditional single-wavelength interferometry. By modulating the laser frequency and creating multiple synthetic wavelengths through frequency sweeping, the system transforms a one-dimensional phase measurement into a multi-dimensional measurement space, enabling both extended range and high resolution simultaneously.
3Speed
If frequency-sweeping interferometry is used, then measurement speed is improved, but measurement precision deteriorates with relative uncertainty of 10^-6
Solution Approach 1:
The patent introduces synthetic wavelength as an intermediary parameter between direct frequency measurement and distance measurement. Instead of directly converting frequency sweep to distance (which causes errors), the system uses interference fringe phase change as an intermediary that linearly relates to optical path difference. This intermediary approach eliminates the non-linearity and drift errors inherent in direct frequency-sweeping methods, achieving both speed and precision.
4Adaptability or versatility
If heterodyne detection is used, then measurement capability is improved, but synthetic wavelength stability deteriorates due to frequency modulator instability
Solution Approach 1:
The patent implements a self-referential measurement scheme where the system measures its own frequency drift by using the return path of light through the same optical components. The frequency modulator's instability affects both the measurement and reference paths equally, and the interferometric differential measurement automatically compensates for this common-mode error, achieving stable synthetic wavelength without requiring external frequency stabilization.
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 method achieves nanometer-level measurement accuracy for large distances, simplifies the measurement process, and is cost-effective, enabling precise distance measurement in high-precision equipment manufacturing and spatial engineering.
Implementation Method 1
The linearly polarized beam with a constant wavelength λ1 and the linearly polarized beam with a variable wavelength λ2 combine one orthogonally linearly polarized beam
Implementation Method 2
a first laser emits a linearly polarized beam with a constant wavelength λ1; a second laser emits a linearly polarized beam with a variable wavelength λ2, and a polarization direction of the beam from the second laser is perpendicular to that of the beam from the first laser
Data Source
AI summary
An absolute distance measurement apparatus and method using laser interferometric wavelength leverage includes a light source system, a wavelength-leverage laser interferometric system and an interference signal processing and controlling system. The light source system outputs a orthogonally linearly polarized beam with the wavelength λ1 and the wavelength λ2. The orthogonally linearly polarized beam projects onto the wavelength-leverage laser interferometric system to form the interference beam. The interference beam projects onto the interference signal processing and controlling system. In the wavelength-leverage laser interferometric system, the synthetic wavelength and the single wavelength as well as the measured absolute distance and the moving displacement of the cube-corner prism in the reference arm form a wavelength-leverage absolute distance measurement relationship.