Optical Coherence Tomography Microscopy Adaptive Sampling
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Solution Overview
Problem
Existing optical coherence tomography microscopy apparatuses are unsuitable for use in environments with vibrations and disturbances, as they rely on precise control of path length differences which are affected by mechanical inertia and phase shifts, leading to inaccurate displacement measurements.
Innovation Solution
The apparatus uses a displacement sensor to generate a detection reference signal with a period corresponding to a fraction of the sense signal's period, allowing for adaptive sampling and accurate demodulation of interference patterns, even in the presence of vibrations, by measuring interference in a narrower bandwidth than the emission bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard demodulation techniques with large RC constants are used, then demodulation accuracy is improved, but compatibility with CMOS processes deteriorates
Solution Approach 1:
The patent replaces the traditional electronic RC filtering system with a time-domain sampling and digital processing system. Instead of using large RC constants for filtering, the invention uses precise timing control to sample the interferogram at specific intervals (every N-th zero-crossing of the reference signal), then applies digital filtering and demodulation algorithms. This substitution eliminates the need for large physical RC components while achieving equivalent or superior filtering performance, making the system CMOS-compatible.
Solution Approach 2:
The invention changes the fundamental parameter from continuous analog filtering (characterized by RC time constants) to discrete time-domain sampling characterized by sampling intervals and digital filter coefficients. By transforming the filtering operation from the frequency domain (analog RC filters) to the time domain (digital sampling and processing), the system achieves the required filtering performance without being constrained by physical component values, enabling integration in standard CMOS processes.
2Measurement precision
If precise control of path length difference is maintained, then measurement accuracy is improved, but susceptibility to vibrations and environmental disturbances worsens
Solution Approach 1:
The patent implements a feedback mechanism where the reference signal (derived from a separate interferometer measuring path length differences) is continuously monitored and used to dynamically adjust the sampling timing. The system detects zero-crossings of the reference signal and samples the measurement interferogram at predetermined intervals relative to these zero-crossings. This feedback loop compensates for path length drifts and vibrations by continuously adapting the sampling points to the actual interferometer state, thereby maintaining measurement accuracy despite environmental disturbances.
Solution Approach 2:
The invention introduces a reference interferometer as an intermediary system that measures path length differences independently. The reference signal generated by this separate interferometer serves as a mediator to synchronize and adapt the sampling of the measurement interferogram. By using this intermediary reference measurement, the system can distinguish between actual sample displacement and spurious effects from vibrations or environmental changes, improving measurement robustness.
3Device complexity
If sampling is performed at fixed intervals, then system simplicity is improved, but accuracy in vibrating environments deteriorates
Solution Approach 1:
The patent transitions from static fixed-interval sampling to dynamic adaptive sampling. Instead of sampling at predetermined fixed time intervals, the system continuously monitors the reference signal for zero-crossings and adjusts the sampling timing dynamically based on the actual state of the interferometer. This dynamic approach ensures that sampling always occurs at physically meaningful points in the interferogram cycle, maintaining high measurement accuracy even when vibrations cause variations in the interferometer's operating conditions.
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 provides more reliable detection of three-dimensional images of optically translucent or reflective samples, reducing systematic errors and standard deviations in measurements, making the system more robust against environmental disturbances.
Implementation Method 1
a light source which comprises one or more light emitting elements to emit a beam of light having an emission bandwidth
Implementation Method 2
splitting the emitted beam BS into a first beam B1 and a second beam B2 to be directed along respective first and second optical paths
Implementation Method 3
measuring a temporal change in interference in a bandwidth narrower than the emission bandwidth
Implementation Method 4
sensing a light intensity in a sensing region and generating a sense signal indicative for the light intensity
Data Source
Figure 1
Figure 2~3
Figure 4~4A
AI summary
An optical coherence tomography microscopy apparatus (1) is presented for detecting a three-dimensional image of an optically translucent or reflective sample object (OS), the apparatus comprising an interferometric optical setup including a photo sensor unit (20). A sense signal Si from the photo sensor unit (20) is detected using a detection reference signal. The detection reference signal is derived from a signal indicative for a relative displacement of the sample object (OS) with respect to a reference object.