Frequency-Modulated Laser Distance Measurement With Reflected Light Interference
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Solution Overview
Problem
Optical distance meters using frequency-shifted feedback lasers face reduced measurement accuracy due to reflected light occurring at the exit end, which can mix with the reference light and affect the beat signal generation.
Innovation Solution
A measurement apparatus that includes a frequency-modulated laser beam splitter, a beat signal generation part, a frequency analyzing part, and a storage part to subtract the signal level of a reference frequency signal from the beat signal, allowing for accurate calculation of the difference in propagation distances between reference and measurement lights, even when end-face reflected light is present.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the frequency-shifted feedback laser is used to generate beat signals for distance measurement, then the measurement capability is provided, but reflected light at the exit end mixes with reference light and reduces measurement accuracy
Solution Approach 1:
The patent extracts and separates the harmful reflected light component from the measurement signal by using quadrature detection to isolate the reference light interference, then removes it through signal processing to recover the accurate distance measurement signal
Solution Approach 2:
The patent employs feedback mechanisms where the detected reflected light signal is fed back into the signal processing system to dynamically adjust and cancel out the interference, improving measurement accuracy through continuous correction
2Loss of information
If the reference light and measurement light are mixed to generate beat signals, then distance information can be obtained, but the reflected light from the exit end contaminates the reference light and degrades signal quality
Solution Approach 1:
The patent converts the harmful reflected light into a useful reference signal by deliberately measuring the exit end reflection and using it as a basis for generating compensation signals that cancel out the interference in the main measurement channel
3Device complexity
If simple beam splitting is used to separate reference and measurement light, then the system configuration remains simple, but reflected light cannot be distinguished from the actual measurement signal
Solution Approach 1:
The patent introduces quadrature detection as an intermediary mechanism that enables differentiation between reference light and measurement light signals without requiring complex optical path modifications, maintaining system simplicity while achieving signal discrimination
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 configuration effectively suppresses the reduction in measurement accuracy caused by end-face reflected light, ensuring precise distance measurement by isolating the reference and measurement light signals and canceling out image signals through quadrature detection.
Implementation Method 1
a laser apparatus that outputs a frequency-modulated laser beam
Implementation Method 2
a beat signal generation part that generates a beat signal by mixing the reference light and a reflected light
Implementation Method 3
a frequency analyzing part that performs a frequency analysis on the beat signal
Data Source
AI summary
A measurement apparatus including: a laser that outputs a frequency-modulated laser beam; a branch that splits the frequency-modulated laser beam into a reference light and a measurement light; a beat signal generator that generates a beat signal by mixing the reference light and a reflected light that is reflected by radiating the measurement light onto an object to be measured; a frequency analyzer that frequency-analyzes the beat signal; a storage that stores a reference frequency signal which is a frequency signal obtained by converting a reference signal output by the beat signal generator in a state without the object to be measured; and calculation circuitry that calculates a difference between propagation distances of the reference light and the measurement light.