Tunable Laser Distance Measurement via Frequency Sweeping
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current laser interferometer systems face challenges in achieving high-precision distance measurements due to limitations in frequency accuracy, stability, and calibration, particularly in harsh environments, which restricts their ability to measure distances with specified accuracy beyond a wavelength and is affected by environmental disturbances.
Innovation Solution
A tunable laser module stabilized to an atomic or molecular reference using sub-Doppler spectroscopy, emitting a test signal with a tunable frequency that is beaten against a reference signal to produce a measurable beat frequency, allowing for high-precision interferometric measurements without mechanical references and fringe counting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple wavelengths are used to eliminate uncertainty in absolute distance measurement, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent changes the frequency parameter of the laser beam dynamically during measurement. By sweeping the frequency and measuring the phase shift at different frequency points, the system resolves the ambiguity of absolute distance without requiring multiple wavelengths. This parameter change approach simplifies the system while maintaining high measurement accuracy.
2Measurement precision
If laser frequency is calibrated to high accuracy, then measurement precision is improved, but device complexity and calibration difficulty increase
Solution Approach 1:
The system uses the laser beam's own frequency modulation to create a measurable signal. By sweeping the laser frequency and detecting the phase shift in the interferometric signal, the system self-calibrates without requiring external reference standards or complex calibration procedures. The laser's frequency sweep serves as its own reference mechanism.
3Difficulty of detecting and measuring
If modern detection systems measure optical signal frequency, then measurement capability is improved, but measurement accuracy deteriorates due to limited frequency resolution
Solution Approach 1:
The patent employs periodic frequency sweeping of the laser beam. By measuring the phase shift at multiple discrete frequency points within one period of the sweep, the system accumulates sufficient information to determine absolute distance with high accuracy. This periodic sampling approach transforms the limited frequency resolution into accurate measurements through multiple measurements.
4Measurement precision
If mechanical references are used for calibration, then measurement accuracy is improved, but reliability decreases in harsh environments
Solution Approach 1:
The patent replaces mechanical calibration references with an optical frequency sweep mechanism. Instead of using physical artifacts or mechanical interferometers for calibration, the system uses frequency-modulated light and electronic detection to achieve calibration. This substitution eliminates mechanical components that would be vulnerable to environmental damage in harsh conditions.
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 distance measurements with accuracy greater than 1 part per billion (ppb) by determining the test frequency with specified accuracy, reducing measurement errors and maintaining stability across environmental changes, suitable for long-term monitoring in harsh conditions.
Implementation Method 1
The object beam and reference beam constructively or destructively interfere, depending on the relative phase of the object beam compared to the reference beam
Implementation Method 2
determining at least two values of the test frequency corresponding to particular values of the interferometric signal by beating the test signal with a reference signal having a reference frequency
Data Source
AI summary
A method determines a distance with a specified accuracy. The method transmits to an interferometer a test signal oscillating with a test frequency and receives, in response to the transmitting, an interferometric signal formed by interfering the test signal with a delayed signal produced by delaying a copy of the test signal over the distance equal to a path length difference in the interferometer. The test frequency is varying such that the test signal oscillates with different values of the test frequency. The method determines at least two values of the test frequency corresponding to particular values of the interferometric signal by beating the test signal with a reference signal having a reference frequency, wherein a value of the reference frequency is an absolute value predetermined with the specified accuracy. The method determines the distance using the two values of the test frequency.