Patent ID: 12188762

Throughout this description, elements appearing in figures are assigned three-digit reference designators, where the most significant digit is the figure number, such as where the element is first introduced, and the two least significant digits are specific to the element. An element that is not described in conjunction with a figure may be presumed to have the same characteristics and function as a previously-described element having a reference designator with the same least significant digits.

DETAILED DESCRIPTION

Structural devices and objects can undergo shape changes when exposed to certain environments or conditions, in which case it may be beneficial to know the degree of such shape changes in order to adapt to or compensate for such changes. For this purpose, a fiber optic sensor embedded in or attached to the structure may monitor the dynamic shape or relative position of the structure and, in certain instances, may do so without inaccuracies being introduced due to temperature or load effects. In a similar manner, the specific state of intentionally flexible structures may be determined at any point in time by measuring the dynamic shape of such structures at such time.

Fiber optic sensors utilize one or more fiber optic components to measure shape changes. Compared to other sensors, fiber optic sensors are particularly useful in smart structures, health monitoring, and other applications because of their relatively small size, low cost, multiplexing capabilities, immunity to electromagnetic interference and vibration, intrinsic safety, and ability to be embedded within or attached to many types of structures operating in a variety of different physical conditions.

Fiber optic sensing enables precise measurement of full strain fields, load distributions, temperature distributions, and other parameters, and thus is becoming pervasive across multiple industries including manufacturing, mechanical, medical, automotive, aerospace and energy.

For “intrinsic” fiber optic sensing—where the fiber optic cable itself is the sensor-changes in a light signal are measured as propagates along an optical fiber's waveguide. These optical sensors can measure temperature, strain, twist, pressure, and other parameters by monitoring the resulting changes in the intensity, phase, polarization, wavelength and/or transit time of light within the fiber. Sensors that vary the reflected wavelength of light based on strain and/or temperature within the fiber are the simplest to measure as only one source and detector are required. These fiber optic sensors can also provide distributed sensing along the entire length of the fiber.

Fiber optic sensors of this kind typically use one of two techniques—based on inherent scattering or based on use of fiber Bragg gratings (FBGs)—for analyzing the changes in the way the light reflects in the optical fiber's waveguide and making calculations with this information to provide accurate measurements. However, each technique has advantages and disadvantages. For example, scattering techniques offer fully distributed data points along a fiber using naturally occurring random imperfections in the fiber optic cable, but this dependence on inherent imperfections is limited as such imperfections are rarely optimal for such purposes. FBGs, on the other hand, can also be fully distributed but only by using a fiber having continuously inscribed FBGs which can be difficult and costly to produce. Nevertheless, because FBGs are purposefully fabricated as well-defined sensors—and thus are much more optimal than imperfections that occur naturally—FBGs have a much higher signal-to-noise ratio and are therefore much more reliable, which in turn enables FBG “interrogators” (the data acquisition hardware) to obtain precise measurements when using continuously inscribed FBGs. Specifically, FBGs use periodic perturbations in refractive index inscribed into the optical fiber to reflect only a specific wavelength of light (described further below), and strain, twist and temperature changes cause spectral shifts in the reflected wavelength and optical frequency domain reflectometry (OFDR) phase changes which are detectable by an interrogator. Stated differently, FBGs exhibit periodic variations in the fiber's index of refraction (the speed of light within the fiber) such that a single FBG consists of a finite length of fiber which contains these perturbations and the entire FBG acts as a wavelength selective mirror. As such, most fiber optic sensing systems on the market today use FBGs to reflect light back to an interrogator.

By operating as wavelength selective mirrors, FBGs reflect a single specific wavelength of light and transmit all others, and the wavelength reflected by the FBG is referred to as the Bragg wavelength. When an FBG (and the optical fiber in which it is located) is stretched, compressed, and/or undergoes changes in temperature, the Bragg wavelength (i.e., the reflected wavelength) changes. The interrogator—using a demodulation technique—can observe this change in the wavelength and translate it into strain, phase and/or temperature measurements based on the relationship between mechanical strain, phase, twist, temperature change, and the resulting Bragg wavelength. Notably, FBGs have inherent sensitivity to both mechanical strain and temperature change, so it is not just the thermal expansion (mechanical) which gives sensitivity to temperature, but also some optical properties change as well, which have an effect on the Bragg wavelength. FBGs are sensitive to twist through the inherent sensitivity to strain. In an interrogation system that uses OFDR, each array of FBGs contained within a single fiber may require a single reference reflector located on a second fiber “arm” whereby the single fiber gets split into two fibers such that one of the two splits contains the array of FBGs and the other split arm contains a single reference reflector. This setup would then be copied for each array which must be interrogated, such as each individual sensing fiber contained in a 3-dimensional (3D) shape sensing bundle or a multi-fiber bundle (an MFB).

Both scattering and FBG technologies use various demodulation techniques-used to obtain and make calculations with the optical signal provided by the sensors—with wavelength division multiplexing (WDM) being the most common for FBG-based optical sensors. However, OFDR offers significant advantages over WDM in many circumstances, primarily because OFDR technology can utilize an order-of-magnitude more sensors on a single fiber than WDM. Optical time domain reflectometry (OTDR) may also provide advantages in certain circumstances.

In WDM systems each FBG must reflect a different Bragg wavelength. Because laser light includes only a finite number of distinguishable wavelengths, WDM systems are limited to the number of sensors they can interrogate on a single fiber. Furthermore, in WDM the range of potentially reflected wavelengths for each FBG cannot be too close to those used by another FBG in the same optical fiber because one FBG under strain could shift so much as to reflect the same wavelength as another grating (strained or unstrained) and thereby render the data indistinguishable as to the FBG source (making the data unusable).

In contrast, in OFDR systems each FBG reflects the same wavelength where the return reflections are measured for changes in wavelength as a function of modulation frequency and that can be plotted as indicators of fiber length corresponding to the locations of each FBG (even among a continuous array of FBGs). In this manner, OFDR is able to provide spatially continuous information along one or more fibers (while WDM cannot), making OFDR well-suited for applications that require spatially continuous monitoring of strain, phase, temperature, stress, distributed loads, twist and/or shape-changes in real-time. And because OFDR allows each FBG to reflect the same wavelength, there is no limit on the total number of FBG sensors incorporated into an optical fiber (enabling continuous arrays of FBGs) that are used to provide spatially continuous measurements along the optical fiber. Indeed, the measurement distance for such FBG sensors is only limited by the coherence length of the tunable light source.

Accordingly, one approach for achieving continuous measurements using an optical fiber (e.g., to collect fully distributed strain, phase and temperature data) is to inscribe FBGs continuously along the entire length of the optical fiber. The FBGs must be incorporated into the core of the optical fiber when the optical fiber is manufactured or written through the coating post-manufacturing. The FBGs then act as miniscule mirrors in the core of the optical fiber. As a light-based signal travels down the optical fiber, each FBG reflects a portion of the signal back to the system. The system recognizes changes in the returning signal and makes calculations with this information to provide accurate strain, phase and temperature measurements. As such, when an FBG optical fiber is bonded to a material and interrogated with light, the FBGs will reflect different wavelengths and phase as the fiber is strained concurrent with the material onto which it is bonded.

Fiber optic position and/or shape sensing devices generally include a multicore optical fiber for determining position and shape of an object. Multicore optical fiber includes two or more cores within a common cladding, positioned in relative relationship to one another, and spaced apart from each other to reduce mode coupling (i.e., distortions) between the fiber cores. Such devices further include an interrogator that transmits light to, and receives reflected light from, the multicore optical fiber.

An MFB such as a multi-fiber shape sensor bundle is a helically twisted bundle of at least three single-core optical fibers wrapped around a single-core central fiber. Such an MFB can be used when calculating MFB twist distribution data along a MFB using OFDR phase interrogation data.

The bundle may be rigidly bonded with an adhesive to form a unitary multi-fiber bundle (“rigidly” meaning where all fibers in the multi-fiber bundle deform together due to a change in position or shape). In this MFB configuration- and because each fiber has its own core, cladding, and coating—the fiber cores are spaced apart and separated from each other such that mode coupling between the fiber cores is substantially eliminated. By definition, in structure, in operation and in output, an MFB and a MOF are very different.

An interrogator may be coupled to each individual optical fiber in order to obtain data associated with each of the multiple fiber segments of each individual optical fiber and, collectively, all of the fiber segments of all of the optical fibers. This data, in turn, can then be used to determine a strain parameter and/or phase signal for the core of each of the multiple fiber segments and, based on predetermined baseline strain parameters for each fiber in the multi-fiber bundle, information regarding shape (including position and bend as well as twist) of a portion of the multi-fiber may also be determined. These determinations, in turn, enable the strain parameters and/or phase signals to be converted into local shape measurements defining shape in the multi-fiber bundle at a particular location along the bundle that represent a change in position, bend, or twist. A particular side effect and enhanced benefit to the MFB is that it can be used to get a larger twist signal in a different way compared to the traditional straightforward approaches (such as those based on MOF designs). The interrogator may be part of an optical network.

FIG.1illustrates a representative shape sensing device (SSD)100for calculating MFB twist distribution data along the MFB using OFDR phase data of the interrogation data. InFIG.1, the shape sensing device100includes an MFB120operationally coupled to an interrogator110(reflectometer) via an integrated connection interface (ICI)112. In a general sense, the interrogator110may include a laser and an optical network. The interrogator110may also include an OFDR, an OTDR, or both (among other options such as those based on WDM for example), and/or any other device suitable for processing light signals received from the MFB120to produce interrogation data with regard to shape sensing as known and appreciated by skilled artisans. The interrogator110, in turn, may be operationally coupled by coupling123to a special-purpose computing system140capable of making calculations with the interrogation data to determine position, bend, and/or twist of the MFB and/or presenting this information to an end-user. The components of SSD100other than system140may be or be part of an optical network.

With specific regard to the interrogator110, optical transduction may be utilized that involves monitoring the reflected FBG signal and correlating that information to strain, phase and/or temperature. Changes in the FBG length and optical properties due to changes in strain and/or temperature result in changes to the Bragg wavelength and phase of the FBG. In this manner, mechanical strain and temperature can be measured directly-based on changes to the Bragg wavelength and/or phase of the FBG- and various temperature compensation techniques can then be employed to decouple these measurements.

InFIG.1, MFB120further includes a helically-twisted132main section122for shape sensing (including detecting shape, position, bend, and/or twist), an interrogator-side unbonded section124for coupling to the integrated connection interface (ICI)112, and a terminal portion126constituting the terminus of the main section122and the MFB120opposite the unbonded section124. The coupling of124to ICI112may be a direct connection or a connection through a coupling point. The MFB may also include optional boundary reinforcement121at the boundary between the helically-twisted132main section122and the unbonded section124. As shown inFIG.1, the main section122may include single-core optical fibers128, and these optical fibers128may be rigidly bonded such that all fibers in the MFB120deform together due to a change in position, shape, bend or twist of the MFB120.

The MFB120may include a set of seven single-core optical fibers128and these single-core optical fibers128may be arranged such that, from the boundary between the rigidly bonded helically-twisted main section122and the unbonded section124to the terminal portion126, one fiber runs linearly through the center of the MFB120while the remaining six fibers are helically twisted132around and bonded to the center fiber.

The use of Bragg gratings, Bragg wavelengths, strain and temperature for generating interrogation data of an MFB can each be used to calculate curvature, bending direction and twist of the MFB. In some cases, phase can be used in addition to these techniques, and replace a very small subset of the calculations within strain to calculate twist of an MFB. Phase can be calculated from the same optical interrogation data as strain, but they can be and use separate calculations. Strain or phase data can be used to calculate curvature, bending direction and twist of the MFB.

Interrogator110and/or system140may be for or be part of a system for calculating MFB twist distribution data along an MFB using OFDR phase data of interrogation data. This calculating may be or include measuring and/or determining MFB twist distribution data along a multi-fiber 3D shape sensor bundle using OFDR phase interrogation data. Also, MFB120or other MFBs herein may be considered a 3D shape sensing bundle or a 3D MFB shape sensor.

System100may be a fiber optic shape-sensing system having optical fibers helically twisted and rigidly bonded to form a linearly-running MFB120for calculating position, bend and twist of the shape-sensing MFB120, wherein each optical fiber has a single core. Interrogator110is operationally coupled to MFB120and is for transmitting light to, and receiving reflected light from the MFB120to produce interrogation data. Interrogator110includes inputs each of which is operationally coupling with each of the optical fibers of MFB120. Computing system140is operationally coupled to the interrogator110and is for calculating MFB twist distribution data along the MFB using OFDR phase data of the interrogation data. Calculating the MFB twist distribution data may include making calculations with the phase difference data of each of the optical fibers over time using the OFDR phase data to determine the MFB twist distribution data. Calculating the MFB twist distribution data might not include calculating position or bend using the phase difference data of the interrogation data. The OFDR difference phase data might not include intensity, polarization, wavelength or transit time of light in each of the optical fibers; or calculating might not include using interrogation data having intensity, polarization, wavelength or transit time of light for the optical fibers. Interrogator110may be configured to produce the OFDR interferometric interrogation data using a laser that scans a frequency range into the MFB, which is a multi-fiber 3D shape sensor bundle. MFB120can be integrated into a guidewire that is configured to be registered to and visualized with anatomical imaging to display in real-time a location and shape of the guidewire within a patient; and the location and shape may be used for feedback control of robotically controlled medical devices.

An array of FBGs can be disposed within the core of each single-core optical fiber from among the single-core optical fibers, where: a) at least a subset of FBGs from among the FBGs in at least one optical fiber from among the optical fibers overlaps a subset of gaps between FBGs from among the FBGs in at least one other optical fiber from among the optical fibers, b) at least a subset of FBGs from among the FBGs in each optical fiber from among the optical fibers overlaps a subset of gaps between FBGs from among the FBGs for each of the other optical fiber from among the optical fibers in the shape-sensing bundle, or c) the array of FBGs disposed within the core of each single-core optical fiber comprises a single elongated FBG running the entire length of a shape-sensing region of the shape-sensing bundle. The optical fibers may comprise at least seven optical fibers with a first fiber running linearly and six other optical fibers helically twisted around and rigidly adhered to the first fiber, and the first optical fiber remains centrally-positioned with respect to the six other optical fibers. The optical fibers may have at least three optical fibers that are helically twisted around each other to form a triple-helix strand running linearly.

Device100, interrogator110and/or system140can calculate MFB twist distribution data along the MFB using OFDR phase data of the interrogation data, such as using a subnetwork of device100or interrogator110. The MFB twist distribution data or distributed twist may be or include the cross sectional rotation of the sensor due to torsional deformation relative to an initial, untwisted state. This MFB twist distribution data may be a calculation along part of or along the entire length L ofFIG.1's main section122for shape sensing. It may exclude the interrogator-side unbonded section124.

Device100, interrogator110and/or system140can be used to receive optical radiation at a first coupling point of an optical subnetwork of interrogator110for at least partially removing birefringence from a subnetwork measurement arm. Removing may be done at a location of this subnetwork at which polarization fading effects are reduced and birefringence effects are mitigated. At the location, polarization fading effects are minimized and birefringence effects are maximally mitigated. Removal of birefringence may include minimizing polarization fading effects and maximally mitigating birefringence effects.

FIG.2Aillustrates the ICI112of the interrogator110shown inFIG.1. InFIG.2A, the ICI112includes optical fiber engagement points210where each point is capable of operationally coupling with the core of a single-core optical fiber. Each engagement point210may be designated for a specific single-core optical fiber from unbonded section124of the MFB120, and may also be designated or labeled accordingly such that, for example, the engagement point for the central-running optical fiber might be labeled as “C” while the six other points corresponding to the other six optical fibers helically twisted and surrounding the central-running optical fiber may be numbered, by way of example, in a clockwise fashion as “1”, “2”, “3”, “4”, “5”, and “6” accordingly (in reference to the MFB120illustrated inFIG.2Band described below). Moreover, the ICI112may further include an additional engagement point (not shown) for interfacing with an additional single-core optical fiber or other sensor for temperature determinations along the MFB120or for other purposes (described later herein). The connection point (e.g., of section124to ICI112) may also be a single connector that contains all individual connections in a single interface. In some case, Multi-fiber Push On (MPO) connectors, Multi-fiber Termination Push-on (MTP) connectors, multiple dual-fiber SN (e.g., SN® (Senko Nano) Push-Pull-Boot Duplex plug connectors) fiber connectors may be linked together into the single connector.

FIG.2Billustrates the terminal portion126of the main section122of the MFB120providing a representative cross-section of the MFB120. InFIG.2B, the MFB120includes optical fibers128which are shown to be seven single-core optical fibers including one central optical fiber220running linearly through the MFB122and enclosed within the other six additional optical fibers222,224,226,228,230, and232, the latter of which (as shown inFIG.1) are helically twisted132around the central-running optical fiber220.

FIG.3Aillustrates the composition of a representative single-core optical fiber226′ from among the optical fibers128including the main section122of the MFB120. InFIG.3A, the single-core optical fiber226′ includes a core312, cladding314, and a coating316. The core and cladding may be both made from silica glass, although the optical properties of each differ. Specifically, the refractive index of the core—which describes the speed at which light travels through a material—is slightly increased during the manufacturing process in order to form the waveguide that enables light to be transmitted over long distances in the core with very low attenuation. The outermost layer, the coating, is applied to the outside of the cladding to increase the robustness of the fiber while protecting the exterior of the cladding from mechanical damage and contaminants, such as dirt and moisture. For strain and/or phase sensing applications, this coating must be sufficiently stiff in order to provide a load path for strain to transfer into the core. These three primary layers of the optical fiber structure are depicted inFIG.3A. For additional environmental protection, fiber may be encased within auxiliary buffer tubes or jackets to form a fiber optic cable, otherwise known as a “patch cord”. In a typical patch cord, the optical fiber is packaged in a tight buffer jacket and loosely incorporated into an outer jacket filled with strength members such as Kevlar® strands.

FIG.3Bfurther illustrates the composition of a representative single-core optical fiber226′ from among the optical fibers128including the main section122of the of the MFB120. InFIG.3B, the core312of the single-core optical fiber226′ further includes FBGs352separated by inter-FBG gaps354.

Referring now toFIG.4, there is shown a schematic embodiment of an optical network400which includes optical network410and the MFB420. The optical network410may be or include the interrogator110and the MFB420may be or include MFB120ofFIG.1. The optical network400has a number of optical devices interconnected with optical fibers. In general, the lengths of fiber are selected so that reflections move into an area of the OFDR reflection spectrum data where they will not interfere with the desired data. The lengths of fiber may also be selected such the reflections from the MFB420appear in a desired section of the OFDR reflection spectrum data. A laser415sends a laser light signal to isolator418which may isolate laser light from laser415as a passive device that allows isolated light to pass through in one direction towards splitter425while blocking light in the opposite direction back from splitter425, thus reducing back reflections in the laser optical fiber and reducing backscattering of light which may be highly desirable. Light from isolator418continues to 1×2 splitter425which splits that light and sends split light to clock network415and 1×4 splitter430. Splitter425splits light received from isolator418into two fibers to network415and 1×4 splitter430. This particular splitter may not split with even amplitude. The split amplitude may be with 70 to 95% going to the 1×4 splitter and 30 to 5% going to the clock network. One arm of the laser light from splitter425is sent to network415to create a clock signal at clock photodiode (PD)405. Clock network415is a clock subnetwork which modulates the signal received from splitter425, and this modulated signal is sent to the clock photodiode PD402to create a clock signal for network400and System PDDs450. The signal received at clock PD405can be used to control the timing for sampling the OFDR data with the data acquisition system. The clock photodiode (PD)405may receive timing signals in the form of modulated optical radiation through a subnetwork such as a clock network415which provides appropriate sampling timing to the system/photo diodes (PDDs)450.

The other arm of the laser light from splitter425is sent by the 1×2 splitter425to be distributed by splitter 1×4430into 4 split signals which are each modified (e.g., by probes 1-4) to appropriately interrogate the MFB420. The laser light from splitter 1×2125is split by a 1×4 splitter430into a channel subnetwork460having four optical subnetworks that include respective probes441,442,443,444. MFB420may be MFB120. Probes441-444are optically connected to and output light signals to optical fibers428a-d, respectively, which are each a fiber128. Although 4 probes and fibers are shown there can be various number of both, such as for the 7 fibers previously shown. Each subnetwork of subnetworks460and/or probe441-444of network400may be part of MFB120or of a fiber128of that MFB. Each subnetwork of subnetworks460may be part of network110and each of probes441-444may be part of MFB120, such as by being a fiber128of that MFB. Probes441-444are also optically connected to and output light signals to system/photo diodes (PDDs)450, such as by fibers. Although 4 fibers are shown there can be various numbers, such as for the 7 fibers of fibers128previously shown.

Referring now toFIG.5there is shown a schematic embodiment of an optical subnetwork500having birefringence mitigation. The optical subnetwork500may be representative of or part of the four optical subnetworks ofFIG.4which make up the network110, a channel of subnetwork460, each of probes 1-4 and/or MFB420. The optical subnetwork500may be representative of each of probes441-444such as where splitter515receives light from a channel (e.g., 1 of the 4) of 1×4 splitter430(not shown inFIG.5) that was sent by light from laser415(not shown inFIG.5) through isolator420(not shown inFIG.5) to subnetwork460(not shown inFIG.5) for one of the probes 1-4. That is, input505may be the light from a channel of splitter430to a probe 1-4, PDD510may be a received channel of output at PDD450from a probe 1-4, and sensor585may be a probe 1-4 channel to/from a fiber428a-dof MFB420. Subnetwork500may represent one of 4 channels as inFIG.4, 7 channels as inFIG.1-3B, or another number of channels or fibers. The various optical devices within the optical subnetwork500are interconnected with SM fiber segments, such as either polarization insensitive or polarization-maintaining (PM). SM can be polarization insensitive segments which do not maintain light polarization and/or polarization maintaining (PM) fiber segments can be segments that do maintain polarization of light. All fiber segments withFIG.5are polarization insensitive unless otherwise stated (such those shown with solid lines), and the PM segments are shown inFIG.5as dashed lines. The optical subnetwork500may include delay elements (not shown) to achieve appropriate timing of signals at given points within the optical subnetwork500.

An input505provides laser light provided by the 1×4 splitter430(FIG.4). The signal input505is connected or coupled to a 2×2 splitter515. The 2×2 splitter515is a connection point which divides the laser light from the input505to a reference arm520and a measurement arm550. In some cases, the split is even in amplitude. In other cases, it is not. The 2×2 splitter515also combines optical radiation back from the reference arm520and the measurement arm550, and provides this combined optical radiation to a polarization diversity detector (PDD)510which converts the optical radiation into electrical signals which themselves are used to produce interrogation data. This is the same interrogation data described above with respect toFIG.1.

The reference arm520produces a reference signal with which a measurement signal from the measurement arm550is superimposed. The reference arm520has a half wave plate525and a mirror530. Optical radiation from the 2×2 splitter515passes through the half wave plate525and then is reflected back by the mirror530. The half wave plate525rotates the state of polarization of the optical radiation travelling through the reference arm520such that the incident signal on the PDD510is optimized. The half wave plate525is used to evenly split the reflected optical power from the reference arm520across the two orthogonal polarization states that are received by the PDD510. PDD510may be designed to receive two or more polarization orientations, and the half wave plate525may be used to maximize power reflected from reference arm520across all polarization orientations of the PDD510.

The measurement arm550is distinct from the reference arm520. The combination of the measurement arm550and the reference arm520and the splitter515between them collectively make up or include a Michelson interferometer. The measurement arm550includes an outbound path590and a return path595connected by respective optical circulators555,580on either end.

The outbound path590is for sending optical radiation from the input505to a sensor585and has a number of optical devices565,570,575which reduce polarization fading effects and enable birefringence mitigation. In the outbound path590, the polarization of the optical radiation is delayed and rotated. Delay may be achieved by providing an appropriate length of fiber in the segment. The outbound path contains two subpaths such as shown at segments571and572, created by the PBS565, and recombined in the PBC575. In one of these subpaths such as shown at segments572, the signal is delayed and the state of polarization is rotated at rotator570relative to the other sub path such as shown at segments571. The outbound path590includes a first optical device560such as a half wave plate which rotates polarization of the optical radiation from the circulator555. A second optical device565such as a polarization beam splitter then splits the polarization-rotated optical radiation into a first polarization maintaining segment571and into a second segment572which delays and further rotates polarization of the optical radiation using, for example, an inline Faraday rotator570. Instead of a Faraday rotator there may be a circulator and a Faraday mirror. The first optical device560may be outside of the outbound path590, such as between the 2×2 splitter515and the circulator555.

Rotator570may rotate the polarization of light in segment572to be orthogonal the polarization of light in segment571. That is, light in segment572may be rotated to have polarity that is 90 degrees different than or at a right-angle as compared to light in segment571. Rotator570may rotate the polarization of segment572by 90 degrees or 270 degrees as compared to 0 or 180 degrees of segment571. In some cases, the polarization maintaining optical segment572is for rotating a polarization of the optical radiation received from splitter565, and polarization maintaining optical segment571is for maintaining the polarization of the optical radiation received from splitter565. In some cases, the polarization maintaining optical segment572is for rotating the polarization of the optical radiation received from splitter565an arbitrary number of times such that it is orthogonal to the state of polarization in the polarization maintaining optical segment271, in this case, the polarization maintaining optical segment571may also rotate the polarization of the optical radiation (e.g., by a rotator or rotators not shown). In some cases, there are two rotations on the segment572path, and one on the segment571path, such that they are still orthogonal” relative to each other, but both see an initial and identical rotation. This can be expanded to be one arm571having N rotations (faraday mirrors/in line rotators), and the other arm572having N+1. For this case,FIG.5shows where N=0.

A third optical device575such as a polarization beam combiner then combines the optical radiation from the first polarization maintaining segment, having a first state of polarization, and from the second segment, having a different state of polarization, and one path being delayed relative to the other, for transmission to the sensor585. The outbound path590is therefore a location at which polarization fading effects are reduced and birefringence effects may be mitigated. For example, the phase of the signal at a location of the return path595may be adjusted based on data from the PDD510, sensor585or both. In other cases, the phase of the signal at a location of another fiber, path or segment of arm550may be adjusted based on data from the PDD510, sensor585or both to reduce polarization fading effects and mitigate birefringence effects. The adjustment may be made by interrogator110and/or system140using that data. Furthermore, within the outbound path590polarization fading effects may be minimized and birefringence effects may be maximally mitigated.

In some cases, outbound path590generates OFDR interrogation data that can be used to mitigate polarization fading effects and birefringence effects through additional calculations. In this case, the effects are not mitigated by the network design alone. The network generates the data that can be processed such that they are mitigated, such as by interrogator110and/or system140.

The return path595receives optical radiation from circulator580which receives it from combiner575, and path595passes that received optical radiation to the PDD510. Circulator580receives optical radiation from combiner575, sends and receives radiation from combiner575to and from the MFB sensor585, and then sends the light received from the MFB sensor585to the PDD510. In some cases, the return path595receives optical radiation from the sensor585and also passes that received sensor optical radiation to the PDD510. The return path595is a polarization insensitive single mode fiber segment between the two optical circulators555,580.

The optical subnetwork500may be or be part of the interrogator110, such as where input505is from the laser (e.g., light goes from laser415to the 1×2 splitter425then to the 1×4 splitter430then to 2×2 splitter515of subnetwork500), and the sensor (e.g., MFB120or420) connects to the subnetwork500between 580 and 585. Input505may be from the laser415that goes from the laser through the 1×2 splitter425then through the 1×4 splitter430as part of subnetwork500. The sensor may connect to the subnetwork between 580 and 585. Subnetworks of networks400and500may be or be part of an optical network and/or be part of the interrogator110and of the MFB120ofFIG.1. For example, splitter430or another splitter may split signals from splitter515as input505; circulator580may circulate signals to and from the probes or fibers of the MFB420as or as well as sensor585; and PDD510may be one channel of input to PDD450. The PDD510and/or PDDs450may be part of interrogator110or an OFDR system, such as for feeding their data to system140for adjusting the polarization and/or delays of the signal at a location of a fiber, path or segment of arm550based on that data to reduce polarization fading effects and mitigate birefringence effects.

Interconnections ofFIGS.4-5may be optical connections. They may be direct connections without other optical devices in between. In other cases, they are optical couplings that may have other optical devices not shown in between that do not change the functions or descriptions herein.

FIG.6is a block diagram of a computing device600or environment that may be used in conjunction with examples and embodiments disclosed herein. Device600may be or be a part of interrogator110and/or of system140. As shown inFIG.6, the computing device600includes a processor610, memory620, a communications interface630coupled to interrogator110which is connected to MFB120, along with storage640, and an input/output interface650. MFB120operationally coupled to interrogator110via an integrated connection interface (ICI)112which may be or include comm interface630.

The processor610may be or include one or more microprocessors, microcontrollers, digital signal processors, application specific integrated circuits (ASICs), or a systems-on-a-chip (SOCs). The memory620may include a combination of volatile and/or non-volatile memory including read-only memory (ROM), static, dynamic, and/or magnetoresistive random access memory (SRAM, DRM, MRAM, respectively), and nonvolatile writable memory such as flash memory.

The memory620may store software programs and routines for execution by the processor, such as for dynamically transitioning of a simulating host of a portion or all of network interactive environments. These stored software programs may include an operating system software. The operating system may include functions to support the input/output interface650, such as protocol stacks, coding/decoding, compression/decompression, and encryption/decryption. The stored software programs may include an application or “app” to cause the computing device to perform portions of the processes and functions described herein, such as the process of dynamically transitioning of a simulating host of a portion or all of network interactive environments. The word “memory”, as used herein, explicitly excludes propagating waveforms and transitory signals. The application can perform the functions described herein.

Connections of communications interface630to and from interrogator110are shown. The communications interface630may include one or more wired interfaces (e.g. a universal serial bus (USB), high definition multimedia interface (HDMI)), one or more connectors for storage devices such as hard disk drives, flash drives, or proprietary storage solutions. The communications interface630may also include a cellular telephone network interface, a wireless local area network (LAN) interface, and/or a wireless personal area network (PAN) interface. A cellular telephone network interface may use one or more cellular data protocols. A wireless LAN interface may use the Wi-Fi® wireless communication protocol or another wireless local area network protocol. A wireless PAN interface may use a limited-range wireless communication protocol such as Bluetooth®, Wi-Fi®, ZigBee®, or some other public or proprietary wireless personal area network protocol. The cellular telephone network interface and/or the wireless LAN interface may be used to communicate with devices external to the computing device600.

The communications interface630may include radio-frequency circuits, analog circuits, digital circuits, one or more antennas, and other hardware, firmware, and software necessary for communicating with external devices. The communications interface630may include one or more specialized processors to perform functions such as coding/decoding, compression/decompression, and encryption/decryption as necessary for communicating with external devices using selected communications protocols. The communications interface630may rely on the processor610to perform some or all of these functions in whole or in part.

Storage640may be or include non-volatile memory such as hard disk drives, flash memory devices designed for long-term storage, writable media, and proprietary storage media, such as media designed for long-term storage of data. The word “storage”, as used herein, explicitly excludes propagating waveforms and transitory signals.

The input/output interface650may include a display and one or more input devices such as a touch screen, keypad, keyboard, stylus or other input devices. The processes and apparatus may be implemented with any computing device. A computing device as used herein refers to any device with a processor, memory and a storage device that may execute instructions including, but not limited to, personal computers, server computers, computing tablets, set top boxes, video game systems, and telephones. These computing devices may run an operating system, including, for example, variations of the Linux, Microsoft Windows, and Apple Mac operating systems.

The techniques may be implemented with machine readable storage (e.g., non-transitory) media in a storage device included with or otherwise coupled or attached to a computing device600, such as, when executed, for performing dynamically transitioning of a simulating host of a portion or all of network interactive environments. That is, the software may be stored in electronic, machine readable media. These storage media include, for example, magnetic media such as hard disks, optical media such as compact disks (CD-ROM and CD-RW) and digital versatile disks (DVD and DVD+RW), flash memory cards and other storage media. As used herein, a storage device is a device that allows for reading and/or writing to a storage medium. Storage devices include hard disk drives, DVD drives, flash memory devices, and others.

Device600, interrogator110and/or system140may each be or include an apparatus having a non-transitory machine readable medium storing a program having instructions which when executed by a processor will cause the processor to perform the actions, function and/or processes described herein, such as to measure MFB twist distribution data along a multi-fiber shape sensor bundle using OFDR phase interrogation data.

The computing system environment is only one example of a suitable computing environment and is not intended to suggest any limitation as to the scope of use or functionality. As for replacing device600, numerous other general purpose or special purpose computing system environments or configurations may be used, including those implementing cloud and artificial intelligence (AI). Examples of well-known computing systems, environments, and/or configurations that may be suitable for use include, but are not limited to, personal computers (PCs), server computers, handheld or laptop devices, multiprocessor systems, microprocessor-based systems, network PCs, minicomputers, mainframe computers, embedded systems, distributed computing environments that include any of the above systems or devices, and the like.

Computer-executable instructions, such as program modules, being executed by a computer may be used. Generally, program modules include routines, programs, objects, components, data structures, and so forth that perform particular tasks or implement particular abstract data types. Distributed computing environments may be used where tasks are performed by remote processing devices that are linked through a communications network or other data transmission medium. In a distributed computing environment, program modules and other data may be located in both local and remote computer storage media including memory storage devices.

FIG.7is a flow chart of a process flow700for calculating MFB twist distribution data along a multi-fiber shape sensor bundle using optical frequency domain reflectometry phase interrogation data. Flow may also be for birefringence mitigation. Process700may be performed by device600, interrogator110and/or system140. The process700starts at step710and ends at step780, but the process may be cyclical in nature, such as by returning to step710or720after step780. Certain steps may not be shown in flow700. Flow700may measure, determine or calculate the MFB twist distribution data along the length ofFIG.1's main section122for shape sensing, or along the length of section122and section124. The MFB twist distribution data may be a distributed twist that is or includes the cross sectional rotation of the MFB sensor due to torsional deformation relative to an initial, untwisted state. This MFB twist distribution data may be a calculation along part of or along the entire length L orFIG.1's main section122for shape sensing.

Process700begins with step710at which the OFDR interrogation data is acquired from an MFB. Step710may be interrogator110and/or system140acquiring OFDR interferometric interrogation data for each of the fibers of MFB120or an MFB herein. The OFDR interrogator may use a variable frequency laser beam that is coupled to an optical interferometer. The output of a tunable laser source (TLS) is split between the reference and measurement arms of an interferometer which may be the fibers of the MFB. In the MFB fiber measurement path, the light is further split to interrogate a length of fiber under test (FUT) of MFB and return the reflected light. The reflected interference signal between the measurement and reference arms is recorded using optical detectors. The auxiliary interferometer used to trigger the data acquisition in equal optical frequency increments and a portion of the network where a gas cell is used to monitor the absolute wavelength of the tunable laser are not shown in the figure. The acquiring may include receiving light signals from the MFB and processing them to produce interrogation data.

OFDR systems can be classified in two main classes: coherent and incoherent OFDR. The OFDR herein may be either, or another applicable class. Most OFDR systems based on Rayleigh scattering are classified as coherent OFDR, while incoherent OFDR is mainly used for systems based on Raman or Brillouin scattering. The OFDR configuration can be used to detect temperature, phase, strain, beat length and high order mode coupling in optical fibers. It is an excellent choice for short sensing lengths (<100 m).

The MFB may have at least three single core radially offset fibers helically wrapped about and rigidly adhered to a central single core fiber, wherein the at least three radially offset fibers and the central single core fiber include fiber Bragg gratings (FBGs). Acquiring at step710may be receiving OFDR interferometric interrogation data for all of the at least three radially offset fibers and the central fiber of the MFB. The MFB may be MFB120, or any other MFB herein. The MFB may include six single core fibers helically wrapped about and rigidly adhered to a central single core fiber. The MFB is not a multicore optical fiber (MOF).

After step710, at step720current phase signal data is calculated from the OFDR interferometric interrogation data. Calculating at720may be extracting the current phase signal data for each of the at least three radially offset fibers and the central fiber of the MFB. Calculating at step720(or steps720-730) may include the following routine for each fiber of the MFB:1. Calculate a Fast Fourier Transform (FFT) data of the OFDR interrogation data of step710;2. Calculate a phase angle of the FFT data;3. Calculate the phase angle difference relative to an initial reference state;4. Unwrap the phase angle difference data;5. Account for FBG gaps/correct FBG gap unwrapping discontinuities in the phase data.

In some cases, after710the interrogation data, or after720the current phase signal data does not include intensity, polarization, wavelength, or transit time of light in each of the optical fibers.

After step720, at step730a phase difference of the current phase signal data is calculated relative to previously acquired reference phase signal data for the MFB. The previously acquired reference phase signal data at step730may be the prior phase of the fiber that the phase difference is being calculated for.

Step730may be calculating phase difference data that is a change in phase data between the current phase signal data and previously acquired reference phase signal data from the OFDR interferometric interrogation data, for each of the at least three radially offset fibers and the central fiber of the MFB. The step730phase difference calculation may be just a subtraction calculation of subtracting the previously acquired reference phase signal data from the current phase signal data.

Steps710-730may include monitoring over time the resulting changes in the intensity, phase, polarization, wavelength, and/or transit time of light within the fibers of an MFB herein. In some cases, steps710-730are only monitoring phase data. In some cases, steps710-730are monitoring resulting changes in phase, but not monitoring the resulting changes in the intensity, polarization, wavelength, and/or transit time of light within the fibers of an MFB herein. In some cases, steps710-730are monitoring resulting changes in strain and/or bend in addition to phase using the interrogation data.

After steps710-730, at step770birefringence is mitigated. The optical network causes two instances, or “images” of the sensor to be present in the sampled interferometric data. The processed OFDR data from these two images is averaged to generate a birefringence (and polarization fading) mitigated result. The mitigating may include using signals from subnetwork500, PDD510and/or sensor585as noted herein. The mitigating may include adjusting the polarization and/or delays of the light signal at a location of arm550as noted herein. A nonlimiting embodiment of this mitigation or design may also comprise one or more locations within the described Michelson interferometer of optical subnetwork500or at which the state of polarization of the light signal at that location is controlled and able to be changed for the purpose of minimizing polarization fading effects and maximizing the degree to which birefringence effects may be mitigated.

After step770, calculating at step780may be or include converting units of the OFDR interferometric interrogation data to units of MFB twist distribution data. In some cases, step780includes calculating MFB twist distribution data along the length L of the MFB. In some cases, step780includes converting the bend-compensated twist phase difference distribution data from the OFDR interferometric interrogation data units to 3D twist units to calculate MFB twist distribution data for the at least three radially offset fibers (and optionally for the central fiber), or for the entire MFB.

In some cases, step780includes inputting the bend-compensated twist phase difference distribution data or difference between an average of all of the at least three radially offset fibers and a central fiber of an MFB into a 3D algorithm to calculate shape and/or the MFB twist distribution data along the length of the MFB. In some cases, step780includes inputting the MFB twist distribution data for each of the at least three radially offset fibers (and optionally for the central fiber) of an MFB into a 3D algorithm to calculate shape and/or the MFB twist distribution data along the length of the MFB. In some cases, calculating at step780or process700does not include calculating using interrogation data for, of or having intensity, polarization, wavelength, or transit time of light within the optical fibers. Calculating at step780or process700may be calculating shape of the MFB by calculating the position and orientation of every point along the MFB, which requires the calculation of twist first. Calculating at step780may be a single step that can be described as multiplying the bend-compensated twist-phase difference data by a scaling factor.

The MFB twist distribution data along an MFB may be or include a 3D location from the base or proximal end of the MFB main section122or section124to a twist location at the distal end or terminal portion126of the MFB.

In some cases, process700includes obtaining the gap-mitigated phase difference data of all radial offset fibers and the center fiber; then averaging the radial results, and subtracting the center fiber result. Then the bending component is removed to calculate a final result “twist-phase” distribution data along part or all of length L of the MFB.

After step780the shape of the sensor MFB, the MFB twist distribution data and/or a device the MFB can be integrated into (such as a guidewire) is then registered to and visualized with anatomical imaging to display in real-time the location and shape of the entire device within the patient during surgery. Shape, MFB twist distribution data and other calculated data may also be used for feedback control of robotically controlled medical devices. This shape includes or is the MFB twist distribution data along the MFB.

In some cases, step780and/or process700includes calculating MFB twist distribution data along the MFB using MFB twist distribution data of the OFDR phase data of the interrogation data. In some cases, step780and/or process700includes acquiring, measuring and/or calculating the MFB twist distribution data along an MFB while inputting a laser that scans a frequency range into the MFB.

Process700may be using optical sensors to monitor the changes in the intensity, phase, polarization, wavelength, and/or transit time of light within the MFB (e.g.,710-730) that result from and thus are used to determine, measure or calculate temperature, strain, twist, pressure, and other parameters (e.g.,7780).

Process700may be repeated over time to calculate MFB twist distribution data in each of the optical fibers over time using the OFDR phase data to determine position, bend, and/or the MFB twist distribution data along the length of the MFB.

Applications of birefringence mitigation include mitigating nonzero strain and phase measurements which result from inherent and induced birefringence effects. This technique may be used to mitigate birefringence effects stemming from inherent and induced birefringence occurring within the MFB as well as the non-sensorized lead fibers which connect the MFB to the OFDR optical network. With these nonzero strain and phase measurements being mitigated, 3D accuracy is significantly improved.

The technology herein may include OFDR optical network design for mitigating inherent and induced birefringence effects in OFDR interrogation data. The technology herein may include birefringence mitigation optical network designs for OFDR-based 3D fiber optic shape sensing.

The technology herein improves the functioning of computers and provides a specialized computing device by being or including a specialized MFB and/or interrogator110(and optionally system140) capable of performing a number of steps of process700, such as step710and/or birefringence mitigation, such as step770.

Descriptions herein of being “for” doing an action may mean that they are configured to and/or adapted to perform that action, such as for calculating MFB twist distribution data along an MFB using optical frequency domain reflectometry (OFDR) phase interrogation data and/or for birefringence mitigation.

Closing Comments

Throughout this description, the embodiments and examples shown should be considered as exemplars, rather than limitations on the apparatus and procedures disclosed or claimed. Although many of the examples presented herein involve specific combinations of method acts or system elements, it should be understood that those acts and those elements may be combined in other ways to accomplish the same objectives. With regard to flowcharts, additional and fewer steps may be taken, and the steps as shown may be combined or further refined to achieve the methods described herein. Acts, elements and features discussed only in connection with one embodiment are not intended to be excluded from a similar role in other embodiments.

As used herein, “plurality” means two or more. As used herein, a “set” of items may include one or more of such items. As used herein, whether in the written description or the claims, the terms “comprising”, “including”, “carrying”, “having”, “containing”, “involving”, and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of”, respectively, are closed or semi-closed transitional phrases with respect to claims. Use of ordinal terms such as “first”, “second”, “third”, etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements. As used herein, “and/or” means that the listed items are alternatives, but the alternatives also include any combination of the listed items.