Optical Shape Sensing Birefringence Correction
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Solution Overview
Problem
Optical shape sensing systems face challenges with polarization fading due to birefringence, which affects the accuracy of shape sensing in medical devices like endoscopes and guidewires, as birefringence changes the polarization state of scattered light and cannot be decoupled from mechanical length changes, leading to unreliable interference signals.
Innovation Solution
The system employs an input polarization controller and an interferometer unit with a polarizing beam splitter to set specific polarization states for the input and output light signals, allowing for orthogonal polarization settings and improved birefringence correction by analyzing interference signals independently of input and output polarization states, thereby reducing signal degradation and increasing signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If optical shape sensing is performed using back scatter reflectometry with a single polarization state, then the system structure is simple, but polarization fading occurs due to birefringence leading to loss of measurement information
Solution Approach 1:
The system dynamically switches between multiple input polarization states (at least two different polarization states) to compensate for birefringence effects. By varying the input polarization state and measuring interference signals for each state, the system ensures that measurement information is not lost due to polarization fading, while maintaining operational simplicity through automated polarization state management
Solution Approach 2:
The system changes the polarization state parameter of the input light to at least two different states. This parameter change allows the system to overcome birefringence-induced polarization fading by ensuring that at least one polarization state will produce a measurable interference signal, thereby preventing information loss without significantly complicating the overall system structure
2Measurement precision
If birefringence effects are present in the optical fiber, then the refractive index changes provide additional measurement information, but the polarization state changes cause polarization fading and unreliable interference signals
Solution Approach 1:
The system dynamically adjusts the input polarization state to at least two different states to compensate for birefringence. By measuring interference signals for multiple polarization states and combining the information, the system maintains reliable interference signals while utilizing birefringence-induced refractive index changes for enhanced measurement precision
Solution Approach 2:
The system uses feedback from interference signal measurements taken at different polarization states to determine the optimal combination of signals. This feedback mechanism ensures that polarization fading is compensated and that the final shape sensing result achieves high precision while maintaining signal reliability
3Reliability
If multiple input polarization states are used to counteract polarization fading, then measurement reliability improves, but device complexity increases
Solution Approach 1:
The system uses dynamic polarization state switching with at least two input polarization states to improve measurement reliability. The polarization controller automatically manages the switching between states, maintaining high reliability while keeping the control system relatively simple through automated operation rather than complex manual intervention
Solution Approach 2:
The system changes the polarization state parameter to at least two different values to improve reliability. This parameter change approach is implemented efficiently using standard polarization controllers and interferometer configurations, avoiding excessive device complexity while achieving the desired reliability improvement through systematic parameter variation
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 effectively counteracts polarization fading, enhances the accuracy of shape sensing, and improves birefringence correction, resulting in more reliable and precise measurements of medical device shapes and orientations.
Implementation Method 1
an optical shape sensing technology is developed based on back scatter reflectometry. The light of a light source is split into a reference signal and a device signal, wherein both signals are guided in fibers through an interferometer. The device signal is guided first to undergo scatterings within the fiber portion that is inserted into a medical device
Implementation Method 2
subsequently to interfere with the reference signal due to their different optical paths. Based on the interference signal, information regarding mechanical strains due to shape deformations of the device can be retrieved
Implementation Method 3
This phenomenon is known as birefringence, which has two effects for the optical shape sensing. First of all, it changes the state of polarization of the scattered, in particular reflected signal dependent on the position of the scattering point within the device
Data Source
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Figure 3~4
Figure 5(A-1)~5(B-2)
AI summary
The present invention relates to an optical shape sensing system for sensing a shape of a medical device (24), comprising an input polarization controller (12) for setting an input polarization state of an input light signal, at least one interferometer unit (18) for dividing said polarized input light signal into a device signal and a reference signal, guiding said device signal to be scattered within an optical fiber (19) inserted into said device (24) and coupling said scattered device signal with said reference signal to form an output light signal, and at least one measurement branch (39) comprising an output polarization controller arrangement (26) for setting an output polarization state of said output light signal, a polarizing beam splitter (30) for splitting said polarized output light signal into two signal portions, each being in a corresponding one of two signal portion polarization states, and a detector arrangement (35) comprising two detectors (32, 34), each for detecting a corresponding one of said two signal portions, wherein said input polarization controller (12) is configured to set two pairs of input polarization states, or said output polarization controller arrangement (26) is configured to set two output polarization states each for enabling a corresponding one of two pairs of signal portion polarization states, wherein each pair of input or signal portion polarization states are representable by a corresponding one of two axes in a Poincaré sphere different from each other.