Interferometer Spatial Differential Demodulation
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Solution Overview
Problem
Current interferometers in optical coherence tomography face limitations in scan speed and vibration resistance due to reliance on time-domain methods and the use of precise but vibration-sensitive components like PZT for depth scanning and demodulation.
Innovation Solution
An interferometer with a demodulation function that splits a light beam into two paths, uses spatial differential calculations on interference signals generated from a test sample, and employs a stepping motor stage for adjusting optical path differences, eliminating the need for PZT and enabling real-time demodulation of images at different depths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If time-domain OCT methods with PZT are used for depth scanning and demodulation, then measurement precision is improved, but scan speed is limited and vibration resistance deteriorates
Solution Approach 1:
The patent replaces the mechanical PZT-driven depth scanning system with a spatial scanning approach using a scanning mirror and camera. Instead of moving the reference mirror along the optical axis (mechanical movement), the system scans the interference pattern spatially across the camera sensor using a rotating or oscillating mirror, converting temporal domain measurements into spatial domain measurements. This substitution eliminates the mechanical limitations of PZT while maintaining measurement precision.
Solution Approach 2:
The patent transforms the problem from the temporal dimension (time-domain OCT where depth is scanned by moving mirrors over time) to the spatial dimension (spatial-frequency domain OCT where depth information is encoded spatially across the camera sensor). By performing Fourier transform on the spatial interference pattern rather than temporal signals, the system achieves both high precision and fast acquisition simultaneously.
2Measurement precision
If PZT components are used for depth scanning, then measurement precision is improved, but vibration resistance deteriorates
Solution Approach 1:
The patent eliminates PZT components by replacing the mechanical depth scanning mechanism with a spatial scanning approach. The reference mirror remains stationary while a scanning mirror directs the interference pattern across the camera sensor. This removes the vibration-sensitive PZT from the system entirely, significantly improving vibration resistance while maintaining depth scanning capability through spatial rather than temporal methods.
Solution Approach 2:
The patent extracts and removes the problematic PZT component from the interferometer system. By separating the depth encoding function from the mechanical PZT actuator and implementing it through spatial scanning and Fourier transform processing, the system eliminates the vibration-sensitive element while preserving the essential depth measurement functionality.
3Productivity
If spatial differential calculation is used for demodulation, then scan speed is improved and costs are reduced, but measurement precision may be affected
Solution Approach 1:
The patent replaces traditional temporal demodulation methods with spatial-frequency domain processing. Instead of using time-domain Fourier transform or complex demodulation algorithms on temporal signals, the system performs Fourier transform directly on the spatial interference pattern captured by the camera, achieving fast demodulation with a single shot while maintaining high precision through the mathematical properties of the spatial-frequency transformation.
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 enhances scan speed, reduces costs, and increases vibration resistance by performing demodulation using a single interference image and spatial differential calculations, while avoiding the use of vibration-sensitive components.
Implementation Method 1
a beam splitting element being configured to receive and split the light beam from the light source into first incident light and second incident light
Implementation Method 2
If light on the reference arm path and light on the sample arm path has overlap in coherence length, then they are interfered. The interference signal may be measured by the photodetector.
Data Source
AI summary
Provided is an interferometer for inspecting a test sample. The interferometer includes: a light source for providing a light beam; a beam splitting element, splitting the light beam into first and second incident light, wherein the first incident light is reflected by the test sample into first reflection light; a reflecting element, reflecting the second incident light into second reflection light; an optical detection element, receiving the first and the second reflection light into an interference signal; and a signal processing module, coupled to the optical detection element, for performing spatial differential calculation on the interference signal to generate a demodulation image of the test sample.