Instantaneous Phase-Shift Interferometer Using Short Coherence Light
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Solution Overview
Problem
Conventional instantaneous phase-shift interferometers face challenges in accurately measuring optical parameters due to variations in bias and amplitude between interference fringe images captured by different cameras, requiring costly high-accuracy scanning stages and vibration-free environments, which are difficult to maintain over time.
Innovation Solution
The use of a light source with a coherence length shorter than the optical path length difference between reference and measurement beams, combined with a delay optical path allowing for adjustable optical path length changes, enables the capture of phase-shifted interference fringe images and calculation of optical parameters like bias, amplitude, and phase shift without specialized equipment, allowing for accurate shape measurement of objects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-accuracy scanning stage is used to shift the measured object in the optical axis direction, then the measurement precision of optical parameters is improved, but the device complexity and cost increase
Solution Approach 1:
The invention extracts the phase shifting function from the mechanical scanning stage and implements it through optical path length adjustment. By using a movable component (such as a mirror or prism) that can be displaced along the optical path, the system achieves phase shifting without requiring a complex scanning stage to move the measured object itself.
Solution Approach 2:
The invention introduces an intermediary optical path adjustment mechanism between the light source and the measured object. This intermediary component (movable mirror, prism, or delay optical path) serves as a mediator to control the optical path length and induce phase shifts, eliminating the need for direct mechanical coupling between the scanning stage and the measured object.
2Measurement precision
If a vibration-free environment is prepared to eliminate relative shift error, then the measurement precision is improved, but the ease of operation deteriorates
Solution Approach 1:
The invention incorporates feedback mechanisms through the use of reference surfaces and reference beams that continuously monitor and compensate for environmental disturbances. The system adjusts the optical path length dynamically to maintain stable interference patterns, automatically compensating for vibrations and environmental changes without requiring a vibration-free environment.
Solution Approach 2:
The invention changes the optical parameters (optical path length, phase shift amount) dynamically during measurement to compensate for environmental disturbances. By continuously adjusting these parameters, the system maintains measurement precision even in the presence of vibrations, eliminating the need for a controlled vibration-free environment.
3Reliability
If optical parameters are measured periodically to maintain performance, then the reliability is improved, but the loss of time increases
Solution Approach 1:
The invention performs preliminary calibration of optical parameters using a reference surface and reference beam before actual measurements. This preliminary action establishes baseline values for bias, amplitude, and phase shift that can be stored and used during normal operation, eliminating the need for frequent re-calibration and reducing time loss.
Solution Approach 2:
The system performs self-calibration using built-in reference surfaces and reference beams that are always available within the interferometer. The system automatically monitors and adjusts its own optical parameters without requiring external calibration equipment or manual intervention, enabling continuous maintenance of reliability without significant time loss.
4Productivity
If multiple interference optical paths are used to simultaneously measure phase-shifted interference fringes, then the productivity is improved, but the device complexity increases
Solution Approach 1:
The invention segments the optical path into multiple independent channels, each capable of measuring phase-shifted interference fringes simultaneously. By dividing the measurement task across multiple optical paths, the system achieves parallel processing of measurement data, improving productivity without requiring complex interactions between paths.
Solution Approach 2:
The invention designs the optical paths to be modular and interchangeable, with each path capable of performing the same measurement function. This universality allows for flexible configuration and simplifies the overall system design, as the same basic optical components can be reused across multiple paths without requiring specialized equipment for each measurement channel.
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 simplifies the pre-measurement of optical parameters, reducing errors and enabling high-accuracy shape measurement of objects in various environments, including those with vibrations, without the need for special devices or precise measurement setups.
Implementation Method 1
an interferometer which splits a detected light beam into a plurality of light beams or regions, the detected light beam including a reference beam as a measurement reference and a measurement beam obtained by reflecting from or passing through a measured object
Implementation Method 2
relatively shifting a phase difference between the reference beam and the measurement beam, then generating interference fringes
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
An instantaneous phase-shift interferometer uses a light source having a coherence length shorter than a difference in optical path length between the light reflected from a reference surface and the light reflected from a measured surface. A beam from the light source is split and, using an adjustable delay optical path, a first beam is delayed to cause a difference in optical path length and is superimposed on the same optical axis as a second beam, after which the reference beam and the measurement beam are generated. The optical path length of the delay optical path is changed during adjustment, a plurality of interference fringe images are individually captured, and at least one of a bias, amplitude, and phase shift amount of the interference fringes obtained in each of the interference fringe images is calculated. A shape of a measured object is measured based on bias calculation results, amplitude calculation results, and phase shift amount calculation results.