Polarization-Sensitive OCT Using Non-PM Fiber and Waveplate Encoding
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Solution Overview
Problem
Conventional optical coherence tomography (OCT) systems face challenges in maintaining polarization due to fiber imperfections and temperature fluctuations, leading to undesirable static and dynamic polarization effects, which complicates the use of non-polarization-maintaining single-mode fibers in polarization-sensitive OCT applications.
Innovation Solution
A polarization-sensitive OCT method is implemented by retrofitting a conventional fiber-optic OCT interferometer with a polarizer and an addressable waveplate in the sample arm, allowing for polarization-sensitive measurements by encoding polarization data in signal amplitude and using a minimum number of components, thereby minimizing the need for dual detection channels and maintaining flexibility in sample arm designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If non-polarization-maintaining single-mode fiber is used in OCT systems, then cost is reduced and alignment flexibility is improved, but polarization stability deteriorates due to fiber imperfections and temperature fluctuations
Solution Approach 1:
The system divides the detection process into multiple polarization channels (dual orthogonally polarized detection channels) to separately measure different polarization components. This segmentation allows the system to compensate for polarization effects in non-PM fibers by analyzing each polarization component independently and reconstructing the original polarization state.
Solution Approach 2:
The patent uses bulk optics components (waveplates, polarizers) to create a reference polarization path that copies and controls the polarization state. By implementing polarization control in the bulk optics rather than relying on fiber polarization maintenance, the system achieves predictable polarization states despite using non-PM fibers.
2Reliability
If bulk optics are used to maintain predictable polarization, then polarization stability is improved, but device complexity and cost increase
Solution Approach 1:
The patent applies polarization control components (waveplates, polarizers) only in the sample arm of the interferometer where polarization manipulation is needed, rather than throughout the entire optical path. This localized application reduces overall system complexity while achieving the necessary polarization control for PS-OCT measurements.
3Measurement precision
If dual orthogonally polarized detection channels are implemented, then polarization measurement capability is improved, but device complexity and cost increase
Solution Approach 1:
The patent combines the dual polarization detection channels at the detector to measure both orthogonal polarization components simultaneously. By merging the detection of S and P polarized light into a unified measurement process, the system achieves polarization sensitivity without requiring completely separate detection systems, thereby reducing complexity.
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 enables accurate measurement of reflectance, sample retardance, and fast axis, while reducing the complexity and cost of polarization maintenance, allowing for effective polarization-sensitive imaging without the limitations of bulk optics and dual orthogonally polarized detection channels.
Implementation Method 1
polarization-sensitive OCT (PS-OCT) systems have been developed to add the capability of controlling the polarization state of light incident upon the sample and measuring the reflectivity of light returning in particular polarization states
Implementation Method 2
Such selectivity allows for the measurement of birefringence and/or dichroism
Implementation Method 3
Optical coherence tomography (OCT) is an emerging technique for in-vivo microscopy which obtains micron-scale cross-sectional images of subsurface structure in biological tissues
Data Source
AI summary
A method and apparatus for extracting the vector optical properties of biological samples with micron-scale resolution in three dimensions, using polarization-sensitive optical coherence tomography (PS-OCT). The method measures net retardance, net fast axis, and reflectivity. Polarization sensing is accomplished by illuminating the sample with at least three separate polarization states, using consecutive acquisitions of the same pixel, A-scan, or B-scan. The method can be implemented using non-polarization-maintaining fiber and a single detector. This PS-OCT method reported measures fast axis explicitly. In a calibration test of the system, net retardance was measured with an average error of 7.5° (standard deviation 2.2°) over the retardance range 0° to 180°, and fast axis with average error of 4.8° over the range 0° to 180°.