Laser Diode Interferometry with High-Bandwidth Detection
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Solution Overview
Problem
Conventional laser diode interferometry faces challenges in achieving high-accuracy, long-range distance measurements due to limited coherence length, mode hopping, and sensitivity to optical feedback, which restricts the distance range and accuracy of measurements.
Innovation Solution
A method using a laser diode with low coherence and broad spectral bandwidth, emitting wavelength fluctuations within the spectral bandwidth, combined with high-speed detection and processing to track and average interferometric phase fluctuations, enabling distance change measurements beyond the coherence length limit, and utilizing a diffractive optical element for quadrature detection to determine the direction of distance change.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If VCSEL laser diodes are used for interferometry, then mode hopping is eliminated and cost is reduced, but coherence length is limited to 1-3 meters
Solution Approach 1:
The patent applies dynamic detection and processing methods that adapt to the limited coherence length of VCSELs. By using high-speed detection and dynamic phase tracking, the system maximizes the utilization of the available coherence length and enables measurements beyond this limit through sophisticated signal processing techniques.
Solution Approach 2:
The patent changes the detection parameters and processing methods to work with the specific characteristics of VCSELs. By adjusting detection rates, processing speeds, and phase tracking methods, the system overcomes the coherence length limitation while maintaining the advantages of VCSELs.
2Measurement precision
If high-speed detection is used to track phase fluctuations, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent performs preliminary actions by pre-processing the detected phase fluctuations and preparing the data for analysis. By performing calculations and adjustments in advance, the system reduces the complexity of real-time processing while maintaining high measurement accuracy.
Solution Approach 2:
The patent introduces intermediary processing steps that simplify the overall system complexity. By using intermediate calculations and data representations, the system achieves high precision without requiring equally complex hardware and processing components.
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 precise long-range distance change measurements with reduced phase fluctuations, allowing for unambiguous determination of distance changes and direction, even beyond the coherence length of the laser source, while maintaining a compact and cost-effective design.
Implementation Method 1
a laser diode for emission of measurement laser light... the measurement laser light is emitted with low coherence and broad spectral bandwidth, wherein an emitting wavelength of the measurement laser light is fluctuating hop-freely within the spectral bandwidth
Implementation Method 2
superimposing the reflected measurement laser light with a reference laser light and thereby providing at least an interferometric phase
Implementation Method 3
utilizing a diffractive optical element for quadrature detection to determine the direction of distance change
Data Source
AI summary
Method and systems for determining a change of distance to an object by interferometry with emitting measurement laser light from a laser diode are disclosed. The method may include receiving at least a part of the measurement laser light, superimposing the reflected measurement laser light with a reference laser light and thereby providing at an interferometric phase and determining the change of distance to the object depending on the superimposition. In some embodiments, the measurement laser light may be emitted with low coherence and broad spectral bandwidth. An emitting wavelength of the measurement laser light may be fluctuating hop-freely within the spectral bandwidth causing interferometric phase fluctuations.