Semiconductor Laser Position Measuring Device
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Solution Overview
Problem
Current position measuring devices in semiconductor production face challenges with increasing accuracy requirements and refractive index fluctuations in air, making traditional laser interferometers inadequate for high-precision measurements.
Innovation Solution
A position measuring device utilizing a semiconductor laser with fiber grating feedback and temperature adjustment means, enabling pulsed operation with large coherence lengths and high wavelength stability, allowing for asymmetrical partial beam paths and reduced phase noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional laser interferometers are used for position measurement, then the measurement system is simple and cost-effective, but the measurement precision deteriorates due to refractive index fluctuations in air
Solution Approach 1:
The patent introduces a reference beam path that travels through the same air environment as the measurement beam but does not interact with the moving object. By comparing the measurement beam with this reference beam, the system compensates for refractive index fluctuations in air, effectively using the reference beam as an intermediary to cancel out environmental disturbances.
Solution Approach 2:
The patent combines laser interferometry with environmental compensation techniques, creating a composite measurement system that integrates both the interferometric measurement path and the reference path. This composite approach allows the system to maintain simplicity while achieving high precision by accounting for air fluctuations.
2Length of stationary object
If asymmetrical partial beam paths are used to increase measurement range, then the coherence length requirement increases, but the device complexity increases
Solution Approach 1:
The patent employs pulsed laser operation where the laser emits light in periodic pulses rather than continuous operation. This periodic action allows the use of asymmetrical beam paths with larger path differences, as each pulse provides a fresh coherence window. The timing of the pulses is synchronized with the measurement cycle, enabling complex optical paths without requiring continuously high coherence.
Solution Approach 2:
The patent changes the operational parameters of the laser system by using pulsed operation mode instead of continuous wave. This parameter change allows the system to tolerate larger path length differences in asymmetrical configurations, as the coherence length requirement is effectively reset with each pulse, reducing the overall complexity constraints.
3Reliability
If semiconductor lasers with large coherence length are used, then the wavelength stability improves, but the ease of manufacture deteriorates due to technical effort required
Solution Approach 1:
The patent makes the laser operation dynamic by implementing pulsed operation mode with adjustable pulse width and repetition rate. This dynamic operation allows the system to achieve large coherence lengths during the pulse duration while keeping the overall system design flexible and manufacturable. The dynamic timing control compensates for the complexity of maintaining wavelength stability.
Solution Approach 2:
By using periodic pulsed operation, the system achieves wavelength stability during each pulse without requiring continuous stabilization mechanisms. The periodic nature allows for simpler manufacturing as the stability is maintained only during the measurement window, reducing the overall complexity of the light source implementation.
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 solution provides stable, high-precision position measurements with larger permissible path differences and tilting tolerances, minimizing measurement inaccuracies and maintaining stability over time.
Implementation Method 1
an optical waveguide arranged downstream of the coupling optics, a reflection Bragg grating integrated in the optical waveguide
Implementation Method 2
The light source is in the form of a semiconductor laser with fiber grating feedback means
Implementation Method 3
Interfering partial beams of rays from the partial beam paths impinge on a plurality of optoelectronic detector elements, so that displacement-dependent position signals can be detected via the detector elements
Implementation Method 4
The semiconductor laser and the fiber grating feedback means are at least partially coupled to temperature adjustment means
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The present invention relates to a position measuring device for detecting the position of two objects that are arranged to be movable relative to each other in at least one measuring direction. The position measuring device comprises a light source and splitting means by which a light beam supplied by the light source is split into two or more partial beam bundles. The partial beam bundles pass through at least two partial beam paths. Interfering partial beam bundles from the partial beam paths strike several optoelectronic detector elements, so that displacement-dependent position signals can be detected via the detector elements. The light source is designed as a semiconductor laser with fiber grating feedback means (Figure 3).