Two-Channel Point-Diffraction Interferometer Using Single-Mode Fibers
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Solution Overview
Problem
Existing point-diffraction interferometers face challenges in achieving independent focusing of light channels, stability, and high accuracy due to limitations in focusing directions and mutual interference between working and reference channels, particularly when testing optical systems with uncoated mirrors.
Innovation Solution
A two-channel point-diffraction interferometer design that utilizes single-mode optical fibers for independent focusing of light channels along x, y, z directions, with linear stages for objective movement and a pinhole plate to exclude mutual interference, allowing for precise focusing and high stability in any orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If tilting mirrors are used for focusing light channels, then focusing in z direction is achieved, but focusing in x and y directions cannot be kept strict
Solution Approach 1:
The patent replaces the mechanical tilting mirror system with single-mode optical fibers that guide light to pinholes. This substitution allows independent control of light paths in x, y, z directions through fiber positioning and objective lens movement, achieving strict focusing in all three dimensions without the directional limitations of mirror tilting.
2Volume of moving object
If two pinholes are used in close proximity, then the device is compact, but mutual interference between working and reference channels occurs
Solution Approach 1:
The patent segments the light paths by using single-mode optical fibers to guide light from separate sources to each pinhole. This segmentation allows the pinholes to be positioned close together while maintaining independent control of their respective light channels, preventing mutual interference through spatial and optical path separation.
3Measurement precision
If objectives are moved using complex mechanisms, then focusing accuracy is improved, but stability and vibration sensitivity worsen
Solution Approach 1:
The patent employs linear stages with controlled movement capabilities for positioning objectives, allowing precise adjustment when needed while maintaining stable positions during measurement. The system transitions between dynamic adjustment phase and static measurement phase, achieving both focusing accuracy and stability without excessive vibration sensitivity.
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 design achieves the highest signal-to-noise ratio for fringe patterns and sub-nanometer accuracy in phase shifting measurements, enabling precise testing of optical surfaces and wavefronts without a reference surface, particularly for glass or plastic uncoated mirrors.
Implementation Method 1
single-mode optical fibres for guiding light from laser sources to pinholes
Implementation Method 2
point-diffraction interferometer
Implementation Method 3
calibrated wavefront reference sources (WRS) generating point-diffracted spherical wavefront
Implementation Method 4
linear stages to move objectives in x, y, z directions
Implementation Method 5
phase shifting measurements
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
The present invention is related with the two-channel point-diffraction interferometer for testing the optical systems or optical elements. The two-channel point-diffraction interferometer comprising a laser source [1] inducing a linearly polarized laser beam which is divided by a beamsplitter to a working channel and to a reference channel whereas the one half of light as working channel is directed from the first collimator [7] to the working collimator [9] by a first single-mode optical fibre [8] to keep polarization of light unchanged, and another half of light as reference channel is directed from the second collimator [17] to the reference collimator [19] by a second single-mode optical fibre [18] to keep polarization of light unchanged.