Interferometer Phase Digitizing with Multi-Frequency Error Separation
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Solution Overview
Problem
Conventional phase digitizing systems in optical heterodyne interferometers face challenges in accurately tracking multiple frequencies due to leakage in polarization, leading to cyclic errors in phase digitization, especially when frequencies are close or identical, resulting in inaccurate displacement measurements.
Innovation Solution
A phase digitizing system that includes multiple phase accumulators, sine and cosine tables, and data accumulators to process composite input signals from both measurement and reference channels, allowing for simultaneous tracking of multiple frequencies and correcting for cyclic errors by isolating and removing contaminant components from the signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional phase digitizing systems track multiple frequencies simultaneously, then cyclic errors are reduced, but tracking accuracy deteriorates when frequencies are close or identical
Solution Approach 1:
The patent divides the frequency tracking task into separate dedicated trackers: a first frequency tracker for the Doppler-shifted measurement signal and a second frequency tracker for the reference signal. This segmentation allows each tracker to optimize for its specific frequency without interference, resolving the contradiction by maintaining tracking precision while eliminating cyclic errors through separate processing paths.
Solution Approach 2:
The patent introduces an intermediary processing stage where the Doppler-shifted measurement signal is mixed with the reference signal to generate an intermediate frequency signal. This intermediary approach transforms the close or identical frequencies into a separable intermediate representation, enabling accurate tracking of both frequencies simultaneously while eliminating cyclic errors in the final phase measurement.
2Speed
If polarization separation is used to separate optical frequencies, then frequency separation is achieved, but leakage causes cyclic errors in phase digitization
Solution Approach 1:
The patent extracts the reference signal component from the composite measurement signal through dedicated frequency tracking and subtraction. By separating the reference frequency component mathematically from the Doppler-shifted measurement signal, the system eliminates cyclic errors caused by polarization leakage while maintaining the speed benefits of polarization-based frequency separation.
3Reliability
If batch processing is used to compensate cyclic error, then cyclic error compensation is achieved, but latency increases to at least one millisecond
Solution Approach 1:
The patent performs preliminary frequency tracking and signal separation continuously during signal acquisition, rather than waiting for batch processing intervals. By maintaining continuous tracking of both frequencies and continuously subtracting the reference component, the system achieves real-time cyclic error elimination with microsecond latency, eliminating the need for millisecond-scale batch processing delays.
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 effectively eliminates cyclic errors with low latency, providing accurate phase progression data independent of object velocity, and reduces latency to microseconds, ensuring precise displacement measurements.
Implementation Method 1
An optical heterodyne interferometer combines signals output from a laser or other light source in measurement and reference channels
Implementation Method 2
In the measurement channel, a Doppler shifted first optical beam, having optical frequency OF1, mixes with an un-modulated second optical beam
Implementation Method 3
The ADC is configured to generate multiple sample segments of digital signal waveform samples based on an analog composite input signal received in a measurement channel
Implementation Method 4
multiple phase accumulators... configured to output... digital phase progression values... representing an instantaneous phase of the first signal, the second signal, or the third signal
Data Source
AI summary
A phase digitizing system includes an analog-to-digital converter (ADC), multiple phase accumulators and a processing device. The ADC generates sample segments of digital signal waveform samples based on an analog composite input signal received in a measurement channel, the composite input signal includes a first signal having a first frequency F1 and a second signal imported from a reference channel having a second frequency F2. The processing device is coupled to the phase accumulators, and digitally processes each sample segment with outputs of the phase accumulators, and continually generates digital phase data The processing device further provides increment values to each of the phase accumulators based on the digital phase data, causing an output of a first phase accumulator to represent an instantaneous phase of the first signal, and an output of a second phase accumulator to represent an instantaneous phase of the second signal.