Phase Shift Interferometer Using Polarization Beam Splitter
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Solution Overview
Problem
The existing Fizeau-type phase shift interferometers face difficulties in achieving a wide opening quarter wavelength plate, which is necessary for measuring wide surfaces, due to the challenges in manufacturing high-quality double refraction crystals with large openings, leading to high costs and impractical configurations.
Innovation Solution
The proposed solution involves an optical system that emits first and second polarized lights with orthogonal polarizing directions, using a pinhole plate to separate and direct the reference and object lights to interfere at different phases, eliminating the need for a quarter wavelength plate by ensuring the lights do not interfere initially, thus allowing for the acquisition of multiple interference fringes with different phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a quarter wavelength plate with large opening is used to measure wide surfaces, then the measurement area is improved, but the manufacturing difficulty and cost increase significantly
Solution Approach 1:
The invention extracts and eliminates the quarter wavelength plate from the optical system. By using a polarization beam splitter to separate reference light and object light into different polarization states, the system removes the need for a large-opening quarter wavelength plate, thereby solving the manufacturing difficulty while maintaining wide surface measurement capability
Solution Approach 2:
The invention introduces a polarization beam splitter as an intermediary element. This device mediates the separation of reference light and object light by polarization state, replacing the function previously performed by the quarter wavelength plate. The polarization beam splitter directs differently polarized lights into separate optical paths, enabling wide area measurement without requiring large-opening wavelength plates
2Area of stationary object
If a quarter wavelength plate with large opening is used to measure wide surfaces, then the measurement area is improved, but the cost increases extremely high
Solution Approach 1:
The invention extracts and eliminates the quarter wavelength plate from the optical system. By using a polarization beam splitter to separate reference light and object light into different polarization states, the system removes the need for a large-opening quarter wavelength plate, thereby solving the manufacturing difficulty while maintaining wide surface measurement capability
Solution Approach 2:
The invention replaces the expensive, difficult-to-manufacture large-opening quarter wavelength plate with more affordable optical components including a polarization beam splitter and standard wavelength plates used in smaller openings. This substitution significantly reduces manufacturing cost while achieving the same functional outcome of wide area surface measurement
3Reliability
If the object light passes through the quarter wavelength plate two times to become orthogonal polarized, then the reference light and object light can be separated, but the structure becomes impracticable
Solution Approach 1:
The invention extracts and eliminates the quarter wavelength plate from the optical system. By using a polarization beam splitter to separate reference light and object light into different polarization states, the system removes the need for a large-opening quarter wavelength plate, thereby solving the manufacturing difficulty while maintaining wide surface measurement capability
Solution Approach 2:
The invention replaces the optical mechanism of double-passing through a quarter wavelength plate with a polarization beam splitter-based separation system. Instead of relying on the birefringent properties of a large crystal plate, the system uses polarization-dependent beam splitting to achieve light separation, simplifying the overall device structure and making it more practical
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 configuration enables the measurement of surface shapes with wide light beams, reduces the complexity and cost of the interferometer, and shortens measurement time by allowing the reference and object lights to interfere in different phases without requiring a quarter wavelength plate, resulting in a more practical and efficient Fizeau-type phase shift interferometer.
Implementation Method 1
an illuminating optical system for emitting a first polarized light and a second polarized light having polarizing directions orthogonal to each other
Implementation Method 2
a pinhole plate provided with a pinhole located at a focus position of the collimator lens on the side opposite to the surface-to-be-measured
Implementation Method 3
making, in an object light reflected by the surface-to-be-measured and a reference light reflected by the reference half mirror, a portion of the object light and the reference light that have been passed through the pinhole interfere with each other in three or more different phases to obtain interference fringes with different phases
Data Source
AI summary
A phase shift interferometer (100) has an illuminating optical system (200) that emits a P-wave and an S-wave, a collimator lens (110), a reference half mirror (120), a pinhole plate (130) having a pinhole (131), and a phase shift interference fringe acquiring section (300) that allows an object light and a reference light contained in the light beam passed through the pinhole (131) interfere with each other in four different phases to acquire interference fringes with different phases. In the S-wave, only the reference light (SR) reflected by the reference half mirror (120) is passed through the pinhole (131), and the object light (SM) reflected by a surface-to-be-measured is blocked by the pinhole plate (130). In the P-wave, only the object light (PM) reflected by the surface-to-be-measured is passed through the pinhole (131), and the reference light (PR) reflected by the reference half mirror (120) is blocked by the pinhole plate (130).