Redundant core in multicore optical fiber for safety
An optical fiber includes multiple optical cores configured in the fiber including a set of primary cores and an auxiliary core. An interferometric measurement system uses measurements from the multiple primary cores to predict a response from the auxiliary core. The predicted auxiliary core response is compared with the actual auxiliary core response to determine if they differ by more than a predetermined amount, in which case the measurements from the multiple primary cores may be deemed unreliable.
1. An interferometric measurement system for measuring an optical shape sensor comprising multiple primary cores in the optical shape sensor and an auxiliary core in the optical shape sensor, the system comprising:
interferometric detection circuitry configured to detect measurement interferometric pattern data associated with each of the multiple primary cores and the auxiliary core; and
data processing circuitry configured to:
determine a shape of the optical shape sensor based on the detected measurement interferometric pattern data for the multiple primary cores,
determine a predicted phase or strain value of the auxiliary core based in part on the detected measurement interferometric pattern data for the multiple primary cores,
determine a measurement-based phase or strain value of the auxiliary core based on the detected measurement interferometric pattern data for the auxiliary core,
determine a difference between the predicted phase or strain value of the auxiliary core and the measurement-based phase or strain value of the auxiliary core, and
detect an error associated with the determined shape of the optical shape sensor based on the difference.
2. The system of claim 1 , wherein the optical shape sensor comprises a multi-core optical fiber containing the multiple primary cores and the auxiliary core.
3. The system of claim 1 , wherein the interferometric detection circuitry comprises multiple interferometric interrogators, each interferometric interrogator paired with an associated core to form an associated acquisition channel, wherein the associated core is selected from the group consisting of the multiple primary cores and the auxiliary core, and wherein the interferometric detection circuitry is configured to detect the measurement interferometric pattern data by:
coupling light from a tunable light source into the multiple primary cores and the auxiliary core via the interferometric interrogators;
in each interferometric interrogator of the multiple interferometric interrogators, interfering light reflected in the associated core with reference light to form an interference pattern of the associated acquisition channel; and
converting the interference pattern of the associated acquisition channels associated with the multiple primary cores and the auxiliary core into electrical signals, the electrical signals corresponding to the measurement interferometric pattern data.
4. The system of claim 3 , wherein the light source is scanned through a range of optical frequencies, and wherein the data processing circuitry is configured to:
resample the measurement interferometric pattern data at increments constant in optical frequency, and
transform the resampled measurement interferometric pattern data into a temporal domain, the temporal domain corresponding to length along the optical shape sensor.
5. The system of claim 1 , wherein the data processing circuitry is configured to detect the error by:
determining that the difference exceeds a predetermined amount.
6. The system of claim 1 , wherein the data processing circuitry is further configured to cause a precautionary action in response to the error.
7. The system of claim 1 , wherein the data processing circuitry is further configured to, based on the error, perform at least one action selected from the group consisting of:
labeling the determined shape of the optical shape sensor as unreliable;
generating a fault signal for display;
generating an alarm;
stopping operation of the interferometric measurement system; and
stopping operation of a machine associated with the optical shape sensor.
8. The system of claim 1 , wherein the data processing circuitry is further configured to:
determine an electronic or optical error in the interferometric detection circuitry based on the error.
9. The system of claim 1 , wherein the data processing circuitry is configured to determine the shape of the optical shape sensor by:
determining parameters equal in number to the multiple primary cores.
10. The system of claim 9 , wherein the parameters are selected from the group consisting of pitch bending, yaw bending, twist, common mode strain, and temperature of the optical shape sensor.
11. The system of claim 1 , wherein the predicted phase or strain value of the auxiliary core is a predicted strain value, wherein the measurement-based phase or strain value of the auxiliary core is a measurement-based strain value, and wherein the data processing circuitry is configured to determine the predicted strain value of the auxiliary core by:
determining strains in the multiple primary cores based on the measurement interferometric pattern data for the multiple primary cores; and
calculating the predicted strain value in the auxiliary core based on a physical model of the optical shape sensor and the determined strains in the multiple primary cores.
12. The system of claim 1 , wherein the predicted phase or strain value of the auxiliary core is a predicted phase value, wherein the measurement-based phase or strain value of the auxiliary core is a measurement-based phase value, and wherein the data processing circuitry is configured to determine the predicted phase value of the auxiliary core and the measurement-based phase value of the auxiliary core by:
tracking optical phase signals based on the measurement interferometric pattern data for the multiple primary cores as compared to reference interferometric pattern data determined for the multiple primary cores;
calculating derivatives of the optical phase signals for the multiple primary cores;
determining a predicted optical phase derivative for the auxiliary core based on the calculated derivatives of the optical phase signals for the multiple primary cores; and
integrating the predicted optical phase derivative for the auxiliary core to obtain a predicated optical phase value for the auxiliary core.
13. The system of claim 1 , further comprising the optical shape sensor, wherein the multiple primary cores comprise a center core and peripheral cores at a first radial distance from the center core, and wherein the auxiliary core is at a second radial distance from the center core, the second radial distance different by at least 10% from the first radial distance.
14. A method for measuring an optical shape sensor, the optical shape sensor comprising multiple primary cores and an auxiliary core, the method comprising:
detecting measurement interferometric pattern data associated with each of the multiple primary cores and the auxiliary core;
processing the detected measurement interferometric pattern data for the multiple primary cores to determine a shape of the optical shape sensor;
processing the detected measurement interferometric pattern data for the multiple primary cores to determine a predicted phase or strain value of the auxiliary core;
processing the detected measurement interferometric pattern data for the auxiliary core to determine a measurement-based phase or strain value of the auxiliary core;
determining a difference between the predicted phase or strain value of the auxiliary core and the measurement-based phase or strain value of the auxiliary core; and
detecting an error associated with the determined shape of the optical shape sensor based on the difference.
15. The method of claim 14 , wherein the optical shape sensor comprises a multi-core optical fiber containing the multiple primary cores and the auxiliary core.
16. The method of claim 14 , wherein detecting measurement interferometric pattern data associated with each of the multiple primary cores and the auxiliary core comprises:
coupling light from a tunable light source into the multiple primary cores and the auxiliary core;
for each core of the multiple primary cores and the auxiliary core, interfering light reflected in the core with reference light to form an interference pattern associated with the core; and
converting the interference patterns associated with the multiple primary cores and the auxiliary core into electrical signals.
17. The method of claim 14 , further comprising:
causing a precautionary action in response to the error.
18. The method of claim 14 , wherein the predicted phase or strain value of the auxiliary core is a predicted strain value, wherein the measurement-based phase or strain value of the auxiliary core is a measurement-based strain value, and wherein processing the detected measurement interferometric pattern data for the multiple primary cores to determine the predicted strain value of the auxiliary core comprises:
determining strains in the multiple primary cores based on the measurement interferometric pattern data for the multiple primary cores; and
calculating the predicted strain value in the auxiliary core based on a physical model of the optical shape sensor and the determined strains in the multiple primary cores.
19. The method of claim 14 , wherein the predicted phase or strain value of the auxiliary core is a predicted phase value, wherein the measurement-based phase or strain value of the auxiliary core is a measurement-based phase value, and wherein processing the detected measurement interferometric pattern data for the multiple primary cores to determine the predicted phase value of the auxiliary core and the measurement-based phase value of the auxiliary core comprises:
tracking optical phase signals based on the measurement interferometric pattern data for the multiple primary cores as compared to reference interferometric pattern data determined for the multiple primary cores;
calculating derivatives of the optical phase signals for the multiple primary cores;
determining a predicted optical phase derivative for the auxiliary core based on the calculated derivatives of the optical phase signals for the multiple primary cores; and
integrating the predicted optical phase derivative for the auxiliary core to obtain a predicated optical phase value for the auxiliary core.
20. A system for measuring an optical shape sensor, the optical shape sensor comprising multiple primary cores and an auxiliary core, the system comprising:
means to interferometrically interrogate the multiple primary cores and the auxiliary core to detect measurement interferometric pattern data for the multiple primary cores and the auxiliary core; and
means to process the measurement interferometric pattern data to:
determine a shape of the optical shape sensor from the measurement interferometric pattern data for the multiple primary cores,
determine a predicted phase or strain value of the auxiliary core based in part on the detected measurement interferometric pattern data for the multiple primary cores,
determine a measurement-based phase or strain value of the auxiliary core based on the detected measurement interferometric pattern data for the auxiliary core,
determine a difference between the predicted phase or strain value of the auxiliary core and the measurement-based phase or strain value of the auxiliary core, and
detect an error associated with the determined shape of the optical shape sensor based on the difference.