Interferometric Distance Measuring Assembly with Wavelength Multiplexing
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Solution Overview
Problem
Current interferometric distance measuring methods face challenges in efficiently scanning large surfaces without moving the probe head, resulting in reduced speed and increased complexity due to limitations in coherence length and thermal loading, particularly in industrial metrology applications.
Innovation Solution
The implementation of a wavelength-modulated laser source with chromatic multiplexing and frequency multiplexing allows for parallel measurement channels using a single monomode fiber, enabling the probe head to remain passive and reducing thermal stress, while maintaining high accuracy and measurement speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple parallel measurement channels are implemented using mirror-based scanning, then measurement speed is improved, but device complexity increases and coherence length is reduced
Solution Approach 1:
The measurement system is segmented into multiple parallel channels, each handling a specific portion of the wavelength ramp. This allows simultaneous measurement of multiple points on the surface without requiring complex mirror-based scanning mechanisms, thereby improving measurement speed while keeping the setup relatively simple.
Solution Approach 2:
Instead of using spatial scanning mirrors to achieve parallel measurement, the invention transitions to a spectral dimension by assigning different wavelength ranges to different channels. This dimensional shift from spatial to spectral domain eliminates the need for complex mechanical scanning while enabling parallel measurement capability.
2Productivity
If multiple parallel measurement channels are implemented, then measurement speed is improved, but coherence length is reduced
Solution Approach 1:
The available wavelength range is segmented into multiple non-overlapping sub-ranges, with each channel assigned a specific sub-range. This segmentation allows parallel measurement channels to operate simultaneously without interfering with each other's coherence, thus maintaining measurement precision while improving speed.
Solution Approach 2:
The system changes the operating parameter from a single wavelength to multiple wavelength ranges assigned to different channels. By adjusting the wavelength parameter across different channels, the system achieves parallel measurement capability while preserving the coherence length required for precise measurements.
3Measurement precision
If probe head is moved sequentially over each measurement point, then measurement accuracy is maintained, but measurement speed is reduced
Solution Approach 1:
Instead of sequential measurement where the probe head moves between points, the system implements continuous parallel measurement across multiple points simultaneously. Each channel continuously measures its assigned wavelength range while the probe head remains stationary, eliminating idle movement time and maintaining both accuracy and speed.
Solution Approach 2:
The measurement approach transitions from temporal sequencing (measuring points one after another) to spatial parallelism (measuring multiple points simultaneously). By using multiple channels with different wavelength ranges, the system achieves parallel measurement without moving the probe head sequentially, thus improving speed while maintaining accuracy.
4Productivity
If active probe head with multiple channels is used, then measurement speed is improved, but thermal loading increases
Solution Approach 1:
The active electronic components and laser sources are extracted from the moving probe head and relocated to the stationary measurement system. Only the passive optical elements remain in the probe head, eliminating thermal generation at the measurement point while preserving the parallel measurement capability through the distributed channel architecture.
Solution Approach 2:
Optical fibers serve as intermediaries to transmit measurement radiation from the stationary laser sources to the passive probe head. This intermediary approach allows the probe head to remain thermally passive while still enabling parallel measurement through the fiber-optic transmission of multiple wavelength channels.
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 rapid and accurate measurement of multiple points without moving the probe head, reducing complexity and thermal loading, and achieving high spatial resolution and coherence length, suitable for industrial metrology applications.
Implementation Method 1
a wavelength-modulated, i.e., variable-wavelength emitting laser source (1), with measurements performed in the frequency domain. Herein, the laser radiation generated by the laser (1) is modulated by traversing a wavelength ramp
Implementation Method 2
the laser radiation generated by a laser (1), e.g., a laser diode, is modulated by traversing a wavelength ramp, thereby changing the radiation's optical frequency
Implementation Method 3
The distance measurement methods disclosed therein use a frequency-modulated laser beam to provide measurement radiation, which is emitted onto the surface, for measuring surfaces. The measurement radiation backscattered from the surface is received again and used for interferometric distance measurement
Implementation Method 4
at least one chromatic beam splitter defines channels for the parallel emission of measurement radiation, to which a different sub-range of the wavelength ramp is assigned for a given emission time
Implementation Method 5
the probe head and signal processing can be separated and connected via a single single-mode fiber
Data Source
Figure 1~3
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Figure 6~7
AI summary
The invention relates to an interferometric distance measuring arrangement for measuring surfaces, using at least one laser which can be tuned for generating measurement radiation modulated by a wave length ramp, an optical beam path with an optical transmitting system for emitting the measurement radiation to the surface and an optical capturing system for capturing the measurement radiation back-scattered by the surface, comprising a measuring arm and a reference arm and a radiation detector and an evaluation unit for determining the distance from a reference point of the distance measuring device to the surface. Channels are defined by at least one beamsplitter (13, 29) n ≥ 2 for the parallel emission of measurement radiation, respectively, one different sub area of the wave length ramp is allocated to said channels at a predetermined emission time point.