Common-Path Interferometer Using Pinhole Spatial Filtering
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Solution Overview
Problem
Existing interferometric microscopy setups face challenges with stability due to environmental conditions like mechanical vibrations and air perturbations, and they require complex alignment and high-coherence light sources, limiting their portability and accessibility for commercial use, especially in clinical settings.
Innovation Solution
A novel interferometric device with a common-path geometry that splits and combines the sample beam after it has interacted with the sample, using spatial filtering through a pinhole and lenses to create a reference beam, allowing for stable and high-quality interference patterns with low-coherence light sources, and can be easily integrated into existing microscopes without requiring advanced optical skills.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional interferometric setups are used with high-coherence light sources and complex alignment, then measurement precision is improved, but device complexity and ease of operation deteriorate
Solution Approach 1:
The patent extracts the reference beam generation from the conventional interferometric setup by using a pinhole spatial filter in the Fourier plane to create a reference beam from the sample beam itself. This eliminates the need for separate reference beam paths and complex alignment, reducing device complexity while maintaining measurement precision through the common-path geometry.
Solution Approach 2:
The patent makes the sample beam serve multiple functions: it first passes through the sample to carry quantitative phase information, then uses the same beam (after spatial filtering) as the reference beam for interference. This multi-functionality eliminates the need for separate reference beam generation components, simplifying the overall system.
2Measurement precision
If conventional interferometric setups are used with high-coherence light sources, then measurement precision is improved, but adaptability to different environments deteriorates
Solution Approach 1:
The patent changes the coherence parameter requirement by using low-coherence light sources (e.g., LEDs) instead of high-coherence sources like lasers. The common-path geometry and pinhole spatial filter compensate for the lower coherence, enabling portable operation while maintaining sufficient measurement precision for biological and material science applications.
Solution Approach 2:
The patent removes the requirement for high-coherence light sources by extracting the coherence function from the light source itself and replacing it with spatial filtering through the pinhole. This allows the system to operate with inexpensive, portable low-coherence sources while maintaining interference pattern quality.
3Ease of manufacture
If conventional interferometric setups are used with open geometry, then ease of manufacture is improved, but stability against environmental factors deteriorates
Solution Approach 1:
The patent merges the sample beam and reference beam into a common path after the sample plane, using a beam splitter to combine them before the detector. This common-path geometry eliminates differential environmental effects (vibrations, air currents) between the two beams, improving stability while maintaining ease of manufacture through simple optical elements.
Solution Approach 2:
The patent introduces a pinhole spatial filter as an intermediary element in the Fourier plane that processes the sample beam to create the reference beam. This intermediary component enables the common-path geometry and provides spatial filtering that compensates for environmental disturbances, improving both stability and manufacturability.
4Measurement precision
If conventional interferometric setups are used with separated reference and sample beams, then measurement precision is improved, but device complexity and alignment difficulty deteriorate
Solution Approach 1:
The patent merges the reference and sample beams into a common path after the sample, using a beam splitter to recombine them before detection. This eliminates the need for separate reference beam alignment, greatly simplifying operation while maintaining quantitative phase measurement precision through the preserved spatial frequency information.
Solution Approach 2:
The patent moves the reference beam generation from the spatial domain (separate beam paths) to the frequency domain (Fourier plane spatial filtering). By processing the beam in the Fourier domain through the pinhole filter, the system creates a reference beam without requiring separate spatial paths, simplifying alignment and operation.
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
The device achieves sub-nanometric precision and low noise levels, enabling label-free imaging of live cells and quality testing with high-resolution, wide-field, and dynamic measurements, while being portable, inexpensive, and easy to align, even with low-coherence sources.
Implementation Method 1
a beam splitter/combiner unit for receiving an input beam of the amplitude and phase modulation indicative of a quantitative phase profile of a sample and splitting the input beams into first and second light beams
Implementation Method 2
a spatial filter comprises a pinhole accommodated in front of the other one of the first and second reflective surfaces and a Fourier optics assembly comprising two lenses
Implementation Method 3
a Fourier optics assembly comprising two lenses, one being in a 4f configuration with respect to each other
Implementation Method 4
one of the first and second reflective surfaces comprises a retro-reflector configured and operable to direct the first light beam and shift a Fourier plane center of the reflected light beam, so that an off-axis angle is created
Implementation Method 5
an interference pattern resulting from the interaction of the first and second optical beams being thereby indicative of the amplitude and phase modulation
Data Source
Figure 1A
Figure 1B
Figure 2~3
AI summary
The present invention provides a novel simple, portable, compact and inexpensive approach for interferometric optical thickness measurements that can be easily incorporated into an existing microscope (or other imaging systems) with existing cameras. According to the invention, the interferometric device provides a substantially stable, easy to align common path interferometric geometry, while eliminating a need for controllably changing the optical path of the beam. To this end, the inexpensive and easy to align interferometric device of the invention is configured such that it applies the principles of the interferometric measurements to a sample beam only, being a single input into the interferometric device.