Fizeau Interferometer On-Axis Polarization Beam Separation
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Solution Overview
Problem
Fizeau interferometers face challenges in integrating parallel or spatial phase-shifting techniques due to the need for encoding opposite polarizations from reflections of light off common optical path components, which introduces aberrations and requires alterations or coatings, limiting their spatial range and measurement accuracy.
Innovation Solution
A Fizeau interferometer system that uses an optical retarder with an uncharacteristically small thickness, allowing for orthogonal polarization states between reference and test beams without tilt or thin-film coatings, enabling single-shot surface profiling without the need for coherence length adjustments or spatial translation, and maintaining high measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If thin-film polarization reflection coating is used to separate object and reference beams in a Fizeau interferometer, then beam separation is achieved, but the system requires significant spatial angle between incident and reflected wavefronts and only works over a narrow spectral band
Solution Approach 1:
The patent removes the thin-film polarization reflection coating from the system entirely. Instead of using coated surfaces for beam separation, the invention employs a different mechanism that does not require altering the optical surfaces, thereby eliminating the spatial angle and spectral bandwidth limitations imposed by the coating approach.
Solution Approach 2:
The patent introduces a polarizing beamsplitter as an intermediary component placed outside the Fizeau cavity to separate the object and reference beams. This intermediary device enables beam separation without requiring spatial angles or spectral restrictions, as the polarizing beamsplitter can handle orthogonal polarizations directly along the optical axis.
2Ease of manufacture
If tilt is introduced in the Fizeau cavity to separate or recombine polarization components, then beam separation is achieved, but aberrations are introduced into the measurement
Solution Approach 1:
The patent extracts the polarization separation function from the Fizeau cavity itself by placing a polarizing beamsplitter outside the cavity. This removes the need to introduce tilt within the cavity, thereby preventing the introduction of aberrations that would degrade measurement precision.
Solution Approach 2:
The patent replaces the mechanical tilt-based separation method with a polarization-based separation method using a polarizing beamsplitter. This substitution allows beam separation without altering the optical paths within the Fizeau cavity, maintaining measurement accuracy.
3Productivity
If spatial phase-shifting methods are used with orthogonal polarization beams, then simultaneous measurement is achieved, but the system requires precise polarization encoding which is difficult in Fizeau interferometers
Solution Approach 1:
The patent introduces a polarizing beamsplitter as an intermediary that automatically separates orthogonal polarization components into different spatial channels. This mediator simplifies the polarization encoding process, making it feasible to implement spatial phase-shifting methods in a Fizeau interferometer configuration.
Solution Approach 2:
The patent segments the optical path by using the polarizing beamsplitter to direct orthogonally polarized beams into separate detection channels. This segmentation enables simultaneous capture of multiple phase-shifted interferograms, achieving high-speed measurement while simplifying the polarization management.
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
Enables precise, single-shot surface profiling and opto-geometrical parameter measurement without introducing optical aberrations, overcoming previous limitations by maintaining beams on-axis and avoiding the need for tilt, coatings, or coherence length adjustments, thus enhancing measurement accuracy and flexibility.
Implementation Method 1
an optical retarder with an uncharacteristically small thickness, allowing for orthogonal polarization states between reference and test beams
Implementation Method 2
partially reflecting light from an input beam of light, having an axis, at a reference surface of an interferometer to form a reference beam of light having a first state of polarization and partially transmitting the input beam through the reference surface
Implementation Method 3
the combination of the reference and test beams is further propagated from the reference surface to an optical detection system to derive spatial profile of the test surface
Data Source
AI summary
An optical device for characterizing a workpiece combines an interferometer with a polarization rotation pellicle, installed in a stand-alone fashion in a spatial gap between the mirrors of the interferometer, and a polarization based phase-shift sensor.