Lidar Spatial Resolution via Interferometric Path Length Control
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Solution Overview
Problem
Existing lidar systems face limitations in achieving high spatial resolution and accurately determining wind speed over large distances due to the quadratic increase in effective focal length and interference from scattered light from particles outside the focus area, leading to poor signal-to-noise ratios and incorrect assignment of measured wind speeds.
Innovation Solution
A lidar measurement system utilizing a continuous-wave laser source with a Mach-Zehnder interferometer arrangement, where the optical path length of the measurement branch is determined by the distance to particles or objects, and a synthetic laser source with adjustable coherence length and phase modulation to achieve high spatial resolution independently of distance, allowing for flexible and quick detection of particle movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If continuous-wave laser sources with focusing optical systems are used, then spatial resolution can be achieved, but the effective focal length increases quadratically with distance resulting in poor spatial resolution at large distances
Solution Approach 1:
The patent replaces the mechanical focusing system (lenses or telescopes that require physical adjustment) with an optical path length control mechanism in an interferometer arrangement. By adjusting the optical path length of the reference beam through electronic or mechanical means within the interferometer, spatial resolution is achieved without requiring mechanical refocusing of the laser beam, thus avoiding the quadratic increase in effective focal length with distance.
Solution Approach 2:
The patent changes the parameter being controlled from physical focus position to optical path length difference in the interferometer. By varying the optical path length of the reference arm to match the measurement arm's path length to particles at different distances, the system achieves spatial resolution through parameter adjustment rather than mechanical focusing, eliminating the distance-dependent focal length problem.
2Measurement precision
If focusing is used to achieve spatial resolution, then scattered light from particles outside the focus area can be received, leading to signal obscuration and incorrect wind speed assignment
Solution Approach 1:
The patent replaces the mechanical focusing approach with an interferometric measurement method where spatial resolution is achieved through optical path length matching. The interferometer arrangement with controlled optical path lengths selectively measures light from particles at specific distances by creating interference conditions that only occur when the optical path lengths match, thereby rejecting scattered light from particles at other distances.
Solution Approach 2:
The patent introduces the interferometer arrangement as an intermediary system between the laser source and the particles. The interferometer acts as a selective filter that uses optical path length differences to distinguish signals from particles at different distances, preventing scattered light from outside the measurement area from obscuring the signal.
3Adaptability or versatility
If mechanical focus changing is implemented, then different distance sections can be examined, but additional equipment and considerable time are required
Solution Approach 1:
The patent replaces the mechanical focus adjustment system with an optical path length control system within the interferometer. Different distance sections are examined by adjusting the optical path length of the reference arm through simple mechanical or electronic means in the interferometer, rather than requiring complex mechanical refocusing of the entire optical system. This significantly reduces the time and equipment complexity required.
4Measurement precision
If pulsed laser sources with time of flight measurement are used, then spatial resolution can be achieved, but poor signal-to-noise ratios and limited frequency resolution result
Solution Approach 1:
The patent uses continuous-wave laser sources instead of pulsed lasers, providing continuous illumination rather than periodic pulses. This continuous action allows for longer integration times and better signal-to-noise ratios while achieving spatial resolution through interferometric optical path length matching rather than time-of-flight measurement, thus improving reliability without sacrificing spatial resolution.
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
The system provides high spatial resolution and accurate detection of particle movement over extended remote areas without mechanical changes, reducing interference from outside particles and enabling precise wind speed measurement without complex equipment or time-consuming focus adjustments.
Implementation Method 1
a continuous-wave laser source (2), in particular a laser diode
Implementation Method 2
the light guided along the measurement branch (4) and the light guided along the reference branch (5) are spatially coherently superimposed
Implementation Method 3
a photodetector arrangement (7) to output a detector signal which is characteristic of incident light originating from the continuous-wave laser source (2)
Implementation Method 4
Known lidar systems for determining wind speeds are based on the detection of the Doppler frequency shift of the scattered light caused by the scattering of laser light by particles moving with the wind
Implementation Method 5
optical components (3, 6) for guiding light from the continuous-wave laser source (2) along predetermined optical paths
Implementation Method 6
optical components (3, 6) for guiding light from the continuous-wave laser source (2) along predetermined optical paths
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a lidar measuring system for detecting the presence and/or movement of particles and/or objects in a spatial region remote from the lidar measuring system, comprising an interferometer arrangement, and to a corresponding method using such a measuring system. The interferometer arrangement has a continuous-wave laser source (2), a photodetector arrangement (7), and optical components that are adapted so as to split light (23) emitted by the continuous-wave laser source (2), guide the light along a first optical path which forms a measuring branch (4) and along a second optical path which is separate from the first optical path and which forms a reference branch (5), and finally allow the light to strike the photodetector arrangement (7) in a spatially coherently superimposed manner. The reference branch (5) has a specified optical path length, and the measuring branch (4) has a measuring section (16), wherein the light is directed away from the measuring system in the measuring section in the direction of a spatial region remote from the measuring system and passes through the spatial region, and light scattered back in the direction of the measuring system by particles that can be found in the spatial region is received at the measuring system. Furthermore, an analyzing unit (9) is provided which is coupled to the photodetector arrangement (7) and which is adapted so as to receive the detector signal of the photodetector arrangement and detect the presence and/or movement of particles in the remote spatial region on the basis of the detector signal. The continuous-wave laser source (2) has a coherence length ranging from 0.1 to 100 m.