Interferometric Distance Measurement Using Delayed Chirp Signals
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Solution Overview
Problem
Existing interferometric distance measurement methods face challenges with moving or vibrating targets, as they require two laser sources for opposite chirps, reducing measuring rate and being sensitive to target acceleration and vibrations, and also involve complex device setups.
Innovation Solution
A single laser source generates two radiation components with opposing frequency curves, with one component delayed optically to create a phase-shifted virtual source, allowing separation by polarization or signal processing, reducing the need for polarization-maintaining fibers and simplifying the device structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two laser sources are used to generate opposing chirps for moving targets, then measurement accuracy is improved, but device complexity increases and measuring rate decreases
Solution Approach 1:
The patent merges the function of two separate laser sources into a single laser source that generates both opposing chirp signals. The single laser source produces a first radiation component with a first chirp and a second radiation component with a second chirp, eliminating the need for two separate laser sources while maintaining the capability to measure moving targets accurately.
Solution Approach 2:
The patent segments the single laser source output into two separate radiation components with opposing chirps. By dividing the laser output and applying different chirp characteristics to each component, the system achieves the functionality of two laser sources while using only one physical source, thereby reducing device complexity.
2Measurement precision
If two laser sources are used for opposite chirps, then compensation for target movement is achieved, but measuring rate is reduced
Solution Approach 1:
The patent enables continuous operation at high measuring rates by using a single laser source that can generate both opposing chirps simultaneously or in rapid succession. This eliminates the time penalty associated with switching between two separate laser sources, maintaining continuous measurement capability without reducing the measuring rate.
3Ease of operation
If polarization-maintaining fibers are used to separate radiation components, then separation is achieved, but device complexity and cost increase
Solution Approach 1:
The patent creates a virtual copy of the laser source through optical delay. By delaying one radiation component relative to the other, the system creates an apparent second source that is in fixed phase relationship with the first, enabling separation and processing without requiring polarization-maintaining fibers.
Solution Approach 2:
The patent introduces an optical delay as an intermediary mechanism to separate the two radiation components. Instead of using complex polarization-maintaining fibers, the optical delay provides a simpler method to distinguish between the first and second radiation components, reducing device complexity and cost.
4Device complexity
If standard single-mode fiber is used instead of polarization-maintaining fiber, then device complexity is reduced, but maintaining signal integrity becomes more difficult
Solution Approach 1:
The optical delay creates a virtual copy of the laser signal that maintains a fixed phase relationship with the original. This approach preserves signal integrity without relying on polarization-maintaining properties, allowing the use of standard single-mode fiber while maintaining measurement reliability.
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 maintains high measurement rates, reduces device complexity, and effectively compensates for target movements and vibrations without requiring two laser sources, while allowing for standard single-mode fiber use in interferometers.
Implementation Method 1
one component delayed optically to create a phase-shifted virtual source
Implementation Method 2
create a phase-shifted virtual source
Implementation Method 3
allowing separation by polarization or signal processing
Implementation Method 4
interferometric distance measuring method
Implementation Method 5
subsequent reception with heterodyne mixing of the radiation scattered back from the target
Implementation Method 6
Constant movement of the target leads to opposite Doppler shifts for the different directions of the frequency ramp during tuning
Data Source
Figure 1~3b
Figure 4~6
Figure 7~8
AI summary
In a distance measurement method with a distance measuring device comprising at least one frequency-modulated laser source for generating chirped laser radiation. The laser radiation exhibits radiation components with opposing chirps as a temporal dependence of the modulated wavelengths, the simultaneous opposing of the frequency response being achieved for one of the two radiation components via an optical delay line (3). The generated radiation is directed onto a target (6) in a measuring interferometer (5) and simultaneously guided through a local oscillator. After receiving the laser radiation backscattered from the target (6) and guided through the local oscillator line, the received laser radiation is converted into signals, and the distance to the at least one target (6) is determined from the signals based on interferometric mixing.