Frequency-Modulated Laser Distance Measurement with Cavity Frequency Feedback
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Solution Overview
Problem
Optical distance meters using frequency-shifted feedback lasers face reduced measurement accuracy due to environmental fluctuations, such as temperature changes, which can increase the apparatus size and cost when attempts are made to mitigate these effects.
Innovation Solution
A measurement apparatus that includes a laser with an optical cavity outputting a frequency-modulated laser beam, branching the beam into reference and measurement lights, generating a beat signal from the reflected measurement light, and analyzing signal components to calculate the propagation distance, while monitoring the cavity frequency to account for environmental fluctuations without the need for extensive temperature stabilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temperature chamber is installed to prevent cavity length change, then measurement accuracy is maintained, but apparatus size and cost increase
Solution Approach 1:
The patent uses feedback by monitoring the cavity frequency (which changes with temperature) and using this information to correct the distance measurement. The system detects the cavity frequency shift and applies compensation to maintain measurement accuracy without requiring a temperature chamber.
Solution Approach 2:
The patent replaces the mechanical/physical temperature chamber system with an optical/electronic solution. Instead of physically stabilizing the temperature, the system uses optical frequency monitoring and electronic signal processing to compensate for temperature effects on the cavity length.
2Measurement precision
If temperature chamber is installed to prevent cavity length change, then measurement accuracy is maintained, but cost increases
Solution Approach 1:
The system implements feedback by continuously monitoring cavity frequency and using this information to correct distance measurements. This eliminates the need for expensive temperature chambers while maintaining measurement accuracy through electronic compensation.
Solution Approach 2:
The patent substitutes the expensive mechanical temperature chamber system with a more cost-effective optical and electronic compensation system that uses frequency monitoring and signal processing to achieve the same measurement accuracy.
3Measurement precision
If cavity length is monitored to compensate for environmental fluctuations, then measurement accuracy is maintained, but device complexity increases
Solution Approach 1:
The patent makes the system multi-functional by using the same optical cavity for both distance measurement and temperature compensation. The cavity serves dual purposes: as the measurement medium and as the sensor for environmental fluctuations, eliminating the need for separate monitoring devices.
Solution Approach 2:
The system uses feedback by detecting cavity frequency changes and applying real-time corrections to the distance measurement calculation, maintaining accuracy while using a unified system rather than adding separate complex monitoring apparatus.
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 allows for accurate distance measurement with a simple setup, reducing the impact of environmental fluctuations on measurement accuracy without increasing the apparatus' scale or cost.
Implementation Method 1
a laser apparatus that has an optical cavity (laser resonator) and outputs a frequency-modulated laser beam with a plurality of modes
Implementation Method 2
a beat signal generation part that generates a beat signal by mixing the reference light and a reflected light
Data Source
AI summary
A measurement apparatus includes a laser apparatus, a branch that branches a 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 the measurement light radiated onto an object to be measured, a first analyzer that analyses a first signal component corresponding to a difference in a propagation distance between the reference light and the measurement light on the basis of the beat signal, a second analyzer that analyses a second signal component corresponding to a cavity frequency of an optical cavity on the basis of the beat signal, and calculation circuitry that calculates the difference in the propagation distance between the reference light and the measurement light.