Interferometric Distance Measurement Using Spectral Separation
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Solution Overview
Problem
Existing interferometric distance measurement methods face challenges with high measurement rates for moving or vibrating targets, especially on metallic surfaces, due to issues with polarization maintenance and depolarization effects, which reduce accuracy and applicability.
Innovation Solution
The method employs spectral separation of double chirp signals using chromatic or electrical filtering to distinguish between radiation components with different absolute optical frequencies or wavelengths, eliminating the need for polarization-maintaining fibers and allowing precise distance measurements on metallic surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If polarization-maintaining fibers are used to separate radiation components, then the two frequency ramps can be distinguished, but the device complexity increases and alignment errors occur
Solution Approach 1:
The patent changes the separation parameter from polarization state to optical frequency/wavelength. By using two laser sources with different center frequencies (λ1 and λ2) and applying opposite chirps, the radiation components are separated through frequency discrimination rather than polarization maintenance, eliminating alignment errors and device complexity associated with polarization-maintaining fibers
Solution Approach 2:
The patent replaces the mechanical alignment system (polarization-maintaining fiber connections) with an optical filtering system. Chromatic filters or electrical frequency filtering substitute for the precise mechanical alignment of polarization-maintaining fibers, eliminating sensitivity to mutual alignment errors
2Measurement precision
If temporally successive ramps are used to compensate Doppler shifts, then the measurement rate is reduced by half
Solution Approach 1:
The patent implements continuous measurement by emitting both frequency ramps simultaneously rather than successively. The two laser sources with opposite chirps (one increasing frequency, one decreasing) operate at the same time, allowing continuous distance measurement without the measurement rate reduction inherent in sequential ramping methods
Solution Approach 2:
The patent adds a frequency dimension to separate the two radiation components. Instead of using time-se separated ramps, two frequency ramps are emitted simultaneously at different center frequencies, allowing spectral separation and simultaneous measurement, thereby maintaining high measurement rates while compensating Doppler shifts
3Measurement precision
If polarization-based separation is used, then radiation components can be distinguished, but depolarization on metallic surfaces causes errors
Solution Approach 1:
The patent changes the discrimination parameter from polarization state to optical frequency. By using chromatic filtering or electrical frequency filtering on two laser sources with different center frequencies, the method avoids polarization-dependent depolarization effects that occur on metallic surfaces, ensuring reliable measurements regardless of target material
Solution Approach 2:
The patent introduces chromatic filters or electrical frequency filters as intermediaries to separate the radiation components. These filters discriminate based on frequency rather than polarization state, acting as a mediator that is insensitive to depolarization effects on metallic surfaces, thereby ensuring reliable signal separation
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 approach enables robust and precise distance measurements on metallic surfaces without polarization errors, maintaining high measurement rates and eliminating vibration influences, using standard single-mode fibers and chromatic or electrical filtering for signal separation.
Implementation Method 1
spectral separation of double chirp signals using chromatic or electrical filtering to distinguish between radiation components with different absolute optical frequencies or wavelengths
Implementation Method 2
subsequent reception with heterodyne mixing of the radiation scattered back from the target
Implementation Method 3
impresses two opposing chirps on two laser sources (1A, 1B) for generating and emitting chirped laser radiation
Data Source
Figure 1~3b
Figure 4~5
AI summary
In a distance measurement method, chirped laser radiation with two separable radiation components is emitted at at least one target to be measured and via a local oscillator path, wherein the radiation components exhibit opposing chirps as a temporal dependence of the modulated wavelengths (λ1, λ2). After receiving the laser radiation backscattered from the target and guided via the local oscillator path, the received laser radiation is converted into signals, and the distance to the at least one target is determined from the signals based on interferometric mixing, whereby the radiation components are separated according to their spectral characteristics.