Range-Finding Apparatus Using Michelson Interferometer
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Solution Overview
Problem
Existing range-finding methods, such as time-of-flight and triangulation, face limitations in accuracy due to the speed of timing circuitry and signal-to-noise ratio, especially at larger distances, and struggle to provide precise measurements beyond the limitations of pulse duration and timing resolution.
Innovation Solution
A method involving the division of pulsed radiation into two portions, one directed to a remote target and the other to a local retro-reflector, with adjustable repetition rates to achieve spatial coincidence of pulses, allowing for the detection of frequency differences and phase modulation to enhance range measurement accuracy, utilizing a Michelson interferometer setup with phase-modulation and heterodyne signal detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If time-of-flight measurement using pulsed radiation is used, then large distances can be measured, but the accuracy is limited by the speed of timing circuitry and signal-to-noise ratio
Solution Approach 1:
The patent replaces the mechanical timing circuitry system with an optical interference system. Instead of measuring time directly with electronic circuits, the invention uses optical path length differences and interference patterns to determine range, thereby eliminating the speed limitations of timing circuitry while maintaining the ability to measure large distances.
Solution Approach 2:
The invention changes the measurement parameter from time domain to optical path domain. By measuring optical path length differences through interference rather than time intervals, the system achieves higher precision without being constrained by timing circuitry speed, while still capable of measuring large distances through the interference pattern analysis.
2Length of stationary object
If triangulation metrology is used, then range can be determined from angle measurement, but range-accuracy decreases with increasing range
Solution Approach 1:
The patent replaces the angular measurement system with an optical path length measurement system. Instead of measuring angles and using trigonometric calculations, the invention directly measures optical path length differences through interference, providing accuracy that does not degrade with increasing range.
3Measurement precision
If optical interferometry is used, then very high range resolution can be achieved, but the absolute distance to the target remains unknown due to wavelength ambiguity
Solution Approach 1:
The patent introduces a reference beam as an intermediary that travels a known stable reference distance. By comparing the optical path length of the return beam with the reference beam through interference, the system determines the absolute distance to the target while maintaining sub-wavelength resolution, resolving the wavelength ambiguity problem.
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 approach enables accurate range measurement over large distances without the limitations of timing circuitry speed, achieving sub-wavelength resolution and improved signal-to-noise characteristics, allowing for precise determination of target range with enhanced light-gathering capabilities.
Implementation Method 1
The two beams are interfered to indicate the difference in optical path length traveled by the two beams
Implementation Method 2
phase-modulating one of said first and second portions (to frequency-shift that portion) and observing a heterodyne signal
Implementation Method 3
directing the second portion from the division point to a local retro-reflector along a second path
Data Source
AI summary
Range-finding apparatus comprises a source of pulsed radiation of variable repetition rate and a beam-splitter for dividing the pulsed radiation into two portions which are directed respectively to a local retro-reflector and to a retro-reflector co-located with a remote target the range of which is to be determined. The source, beam-splitter and retro-reflectors are arranged in the form of Michelson interferometer together with a detector. The repetition rate of the source is tuned to frequencies f such that round-trip distance to the remote target is mc/f where m is an integer, this condition being detected by observing a heterodyne signal at the detector. Two such frequencies enable range to be determined. The precision with which range is determined may be increased by carrying out interferometry using the two portions. The accuracy of the method does not depend on absolute range (as with triangulation) and is not limited by the speed of timing electronics, as is the case for time-of-flight techniques.