Interferometric Rotary Encoder Using Injection-Locked Lasers
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Solution Overview
Problem
Optical metrology systems face limitations in accuracy due to high uncertainties in multi-axis pointing angle measurements, particularly for large-scale objects like airplanes, as existing rotary encoders are intrinsically limited in accuracy and lack direct traceability to standards, leading to inconsistent measurements across different locations.
Innovation Solution
An interferometric rotary encoder that uses injection-locked lasers to provide rotation angle measurements traceable to a primary optical frequency standard, utilizing a rotatable component with reflective elements, interferometers, and optical waveguides to compute rotation angles based on phase shift information from photodetectors, ensuring direct traceability and enhanced accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing rotary encoders with pattern sensors are used, then the device complexity is low, but the measurement precision is limited and not traceable to standards
Solution Approach 1:
The patent replaces the traditional mechanical/optical pattern sensor encoder system with an interferometric measurement system using lasers and photodetectors. This substitution enables direct traceability to the speed of light constant while achieving higher measurement precision through optical interference patterns rather than mechanical encoding disks.
Solution Approach 2:
The patent changes the fundamental measurement parameter from electrical signal encoding to optical phase measurement. By measuring the phase of light waves in an interferometric setup, the system achieves direct traceability to the speed of light constant, fundamentally improving the measurement paradigm rather than merely enhancing existing encoder technology.
2Reliability
If traditional encoders are used, then ease of manufacture is good, but reliability of measurements across different locations is poor due to lack of traceability
Solution Approach 1:
The patent replaces traditional mechanical encoders with an interferometric system that uses optical waves and photodetectors. This substitution eliminates the need for mechanically manufactured encoding patterns, replacing them with a system traceable to the speed of light constant, thereby ensuring consistent measurements across different locations and manufacturers.
Solution Approach 2:
The patent creates a universal measurement system based on fundamental physical constants (speed of light) that can be replicated anywhere in the world. The interferometric encoder uses optical waves and standard photodetectors that can be manufactured using consistent processes, ensuring that measurements from different manufacturers and locations are directly comparable and traceable to the same standard.
3Measurement precision
If gimbals with rotary encoders are used for multi-axis measurements, then the device complexity is manageable, but measurement precision deteriorates due to angle measurement uncertainties
Solution Approach 1:
The patent replaces the rotary encoders in gimbal systems with interferometric angle sensors. This substitution eliminates the accumulated angle measurement uncertainties that limit traditional gimbal systems, providing direct traceability to the speed of light constant for each axis measurement and significantly improving overall measurement precision.
Solution Approach 2:
The patent changes the measurement parameter from electrical encoder signals to optical phase measurements in the gimbal system. This fundamental parameter change enables direct traceability to fundamental constants, eliminating the chain of calibration uncertainties that exist in traditional multi-axis gimbal systems with multiple encoders.
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 solution provides highly accurate, standards-traceable rotation angle measurements, reducing uncertainties and enabling consistent measurements globally, suitable for complex structures and multi-axis gimbals, thereby expanding the range of applications and improving quality verification.
Implementation Method 1
The light source comprises a reference laser and an injection-locked laser which is injection locked to the reference laser, wherein the reference laser has an optical frequency which conforms to an optical frequency standard.
Implementation Method 2
a first interferometer having a first absolute reference length; a second interferometer having a second absolute reference length greater than the first reference length
Implementation Method 3
first and second photodetectors optically coupled to the first and second optical waveguides for receiving light from the first and second interferometers respectively; third and fourth photodetectors optically coupled to the third and fourth optical waveguides for receiving light from the light reflecting means
Data Source
AI summary
A precision optical encoder that utilizes interferometric measurements of displacement to provide angle measurements using a laser which is injection locked to a reference laser having a secondary optical frequency which has been verified with respect to a primary optical frequency standard. The encoder shape encodes distance to rotation angle. By utilizing a laser source locked to a reference laser having a standardized (i.e., verified) secondary optical frequency for fundamental measurements of the encoder surface and real-time interferometer measurements, the encoder reports rotation angle measurements that are directly traceable to a primary optical frequency standard through the injected secondary optical frequency.