Multi-core optical fiber and elongated instrument for medical intervention applications

Abstract

A multicore optical fiber (10) configured for shape sensing. The fiber (10) includes an elongated body segment (40) and a distal tip segment (42) connected to the body segment (40). The body segment (40) includes a first cladding (12a) and a plurality of first cores (14a, 16a, 18a, 20a) embedded in the first cladding (12a), and the distal tip segment (42) includes a second cladding (12b) and a plurality of second cores (14b, 16b, 18b, 20b) embedded in the second cladding (12b). The first and second cores (14a, 14b, 16a, 16b, 18a, 18b, 20a, 20b) include reflective strain sensitive structures (21) configured for distributed shape sensing along the body segment (40) and the distal tip segment (42). The body segment (40) includes a first material and the distal tip segment (42) includes a second material different from the first material, wherein a first strain-to-failure of the body segment (40) is lower than a second strain-to-failure of the distal tip segment (42).

Description

Technical Field

[0001] This invention relates generally to the field of fiber optic shape sensing technology, also known as fiber optic shape sensing (FORS) technology. Specifically, this invention relates to a multi-core optical fiber and an elongated device comprising the multi-core optical fiber for medical interventional applications. Background Technology

[0002] Fiber Optic Shape Sensing (FORS) technology is a shape sensing and reconstruction technique applied to slender instruments such as guidewires. It enables precise, real-time three-dimensional visualization of the instruments, allowing for efficient navigation in minimally invasive vascular interventional surgeries without the need for X-ray guidance. Reducing X-ray radiation exposure in these procedures benefits patients, surgeons, and healthcare professionals.

[0003] FORS technology uses shape-sensing, elongated instruments (such as guidewires) for surgery, as well as a measurement system that typically includes a light source and optical detector compatible with the shape-sensing, elongated instruments, a signal processing unit, and a user interface for visualizing and tracking the elongated instruments.

[0004] Instruments with FORS functionality typically include an integrated twisted multi-core optical fiber with sensors, which can be configured as distributed fiber Bragg grating (FBG) sensors. Light emitted from a source is used to read signals from each sensor, and the local deformation of each fiber segment is obtained by analyzing the reflected light, thereby reconstructing the overall three-dimensional shape. In this way, the complete shape of a slender instrument can be reconstructed and visualized in real time during surgery. By overlaying it onto images acquired before or during surgery (such as CT or X-ray images), FORS-enabled instruments can be visualized within the patient's anatomy. Compared to X-ray-guided surgery, which requires a new X-ray image every time a slender instrument needs to be visualized, the number of images is significantly reduced, thus significantly reducing the X-ray dose.

[0005] The applicant of this application has developed guidewires and catheters with FORS functionality, which have been successfully used in complex aortic interventional procedures, particularly fenestrated endovascular aortic aneurysm repair (FEVAR) and / or branched endovascular aortic aneurysm repair (BEVAR), as well as endovascular peripheral lesion repair (EVPLR).

[0006] In complex aortic surgeries, the mechanical requirements for the tip of commonly used guidewires do not limit the use of brittle glass fiber optic sensors. These fiber optic sensors can extend to the distal tip of slender instruments because navigation is usually performed within large blood vessels (such as the aorta), where the guidewire can travel freely and typically does not encounter blockages.

[0007] In other surgical procedures, such as various peripheral surgeries used to treat peripheral artery disease (PAD), slender instruments with FORS functionality can also help reduce radiation dose. However, in these procedures, the vessel diameter is much smaller, and the navigation path is often very tortuous, involving many bends and potentially navigating numerous bifurcations to reach the target location, often involving sharp angles that the slender instrument must traverse. Furthermore, these smaller vessels are more fragile and can be damaged by the tip of the slender instrument. Especially in PAD, angioplasty techniques require traversing narrowed or occluded segments of the vessel. For more severe occlusions, force is applied to traverse these segments, and sometimes the instrument tip prolapses, forming a loop and bending backwards—a phenomenon known as "knuckling"—causing very sharp bending at the tip, with a bending radius of less than 1 mm. In these cases, the instrument tip must also be strong enough to withstand this deformation.

[0008] For devices with FORS functionality used in peripheral interventional procedures (such as guidewires), their tips must be sufficiently soft and flexible to allow for smooth navigation through sharp bends and acute-angled bifurcations. For example, the tip load of the combination of the internal fiber optic cable and the outer casing tip must not exceed the limits required for safe navigation (i.e., without damaging blood vessels), which is approximately 2-4 grams of force for guidewires used in peripheral procedures.

[0009] Furthermore, during these procedures, the curvature of the optical fiber may become too high, hindering shape sensing, and may even exceed the maximum curvature that the glass fiber can withstand, causing the glass material to fail during use, i.e., break or shatter.

[0010] Especially in surgeries requiring the guidance of tortuous anatomy and / or passage through narrow lesions or occluded segments, the forces acting on the instrument tip can cause deformation exceeding the tolerance of the glass fiber, particularly when the tip forms a ring or prolapses. Glass fiber breakage not only hinders the use of FORS technology but can also raise patient safety concerns, as glass fragments can damage the internal structure of the instrument tip, thereby altering its mechanical properties.

[0011] At the same time, even under such challenging conditions, including severe deformation due to the formation of rings and prolapse, resulting in extremely small bending radii, the shape and orientation of the slender instrument tip must still be reconstructed as accurately as possible using FORS technology, so as to avoid the need for X-ray guidance.

[0012] Polymer optical fibers are known to be more flexible than glass optical fibers, but they also exhibit higher optical loss compared to glass optical fibers. Summary of the Invention

[0013] One object of the present invention is to provide a multi-core optical fiber configured for optical shape sensing, particularly for use in a slender instrument for a medical interventional application, the slender instrument being suitable for procedures that must guide tortuous anatomical structures and / or must pass through narrow lesions or occluded segments, while allowing for the reconstruction of the shape and orientation of the fiber's end region.

[0014] Another object of the present invention is to provide an elongated instrument for medical interventional applications, which has shape sensing capabilities and is suitable for procedures that require guidance through tortuous anatomical structures and / or passage through narrow lesions or occluded segments, while allowing for reconstruction of the shape and orientation of the tip region of the elongated instrument with sufficient precision using FORS technology.

[0015] In a first aspect of the invention, a multi-core optical fiber configured for shape sensing is provided, comprising an elongated body segment and a distal end segment connected to the body segment. The body segment includes a first cladding and a plurality of first cores embedded within the first cladding. The distal end segment includes a second cladding and a plurality of second cores embedded within the second cladding. The first and second cores include a reflective strain-sensitive structure configured to achieve distributed shape sensing along the body segment and the distal end segment. The body segment includes a first material, and the distal end segment includes a second material different from the first material.

[0016] This invention achieves its objective by providing a multi-core optical fiber, wherein the distal end segment of the multi-core optical fiber comprises a material that is different from the material in the main body segment.

[0017] In the first embodiment, the first fracture strain of the body segment is lower than the second fracture strain of the distal end segment. According to this first embodiment, the material in the distal end segment differs from the material in the body segment, resulting in a higher fracture strain in the distal end segment than in the body segment. In other words, in the distal end segment of the optical fiber, where a lower bending radius (i.e., a higher curvature) is expected during fiber use, a material with higher mechanical strength is used instead of the material in the body segment, allowing the optical fiber to mechanically withstand higher curvature without risk of breakage. The core and / or cladding material of the distal end segment may differ from the core and / or cladding material of the body segment. The material of the body segment, where small bending radii or high curvatures are not expected during use, may be selected to provide high-quality optical shape sensing. Furthermore, the material of the body segment may be selected to have limited optical loss and low temperature sensitivity. The distal end segment may be optimized for high deformation, meaning the material of the distal end segment may be selected to provide higher mechanical robustness for small bending radii (or, in other words, high curvature). As a result, the risk of fiber breakage at the distal end is reduced. At the same time, even in challenging situations where the distal end region of a slender instrument involving optical fibers experiences large deformation due to the formation of loops and drooping, the shape and orientation of the distal end segment can still be accurately reconstructed using FORS technology, thereby avoiding the need for X-ray guidance.

[0018] This reflective strain-sensitive structure may include fiber Bragg gratings (FBGs).

[0019] Other preferred embodiments of the invention are defined in the dependent claims and / or described herein.

[0020] In a more specific embodiment, the second fracture strain is at least 2 times, preferably at least 5 times, more preferably at least 10 times, or about 10 times the first fracture strain.

[0021] The higher the fracture strain of the distal end segment, the more elastic the distal end segment, and the more mechanically robust it is when subjected to high curvature. For example, the material of the distal end segment of the optical fiber can be selected to withstand a bending radius of less than 2 mm, preferably less than 1 mm.

[0022] In the second embodiment, which can be considered alone or in combination with the first embodiment, the distal end segment may have a lower bending strain sensitivity than the main body segment, such that the first minimum bending radius of the distal end segment, measurable by fiber optic interrogation within a defined scanning wavelength range, is less than the second minimum bending radius of the main body segment, measurable by fiber optic interrogation within the defined scanning wavelength range.

[0023] In optical shape sensing, fiber optic interrogation is typically performed by emitting light into the fiber, with the wavelength of the light scanned within a specific wavelength range. For example, this wavelength range could be centered at 1550 nm, with a scan range of 30 nm (i.e., a scan wavelength range of, for example, 1535 nm to 1565 nm). If the curvature of the fiber exceeds a certain value, the wavelength shift of the reflected light caused by strain may exceed the scan range, making such high curvature undetectable optically, leading to shape reconstruction failure. In other words, there exists a minimum bending radius of the fiber that can still be measured by optical shape sensing, while bends below this minimum bending radius cannot be measured. Since the distal end segment of a slender instrument may experience extremely small bending radii when guided through sharp bends, it is advantageous if the bending strain sensitivity of the distal end segment is lower than that of the fiber body segment. This allows the optical interrogation system to still measure the minimum bending radius of the distal end segment, which is smaller than, or even much smaller than, the minimum measurable bending radius in the fiber body segment.

[0024] In the third embodiment, which can be considered alone or in combination with the first and / or second embodiments, the first fiber core includes an outer fiber core arranged at a first radial distance from the central axis of the main body segment, and the second fiber core includes a second outer fiber core arranged at a second radial distance from the central axis of the distal end segment, wherein the second radial distance is less than the first radial distance.

[0025] As the radial distance from the fiber core to the central axis decreases, the bending strain sensitivity decreases accordingly. The advantage is that the distal end section is not only more mechanically robust to withstand high curvature, but also capable of measuring such high curvature.

[0026] In the fourth embodiment, the first material may be quartz glass.

[0027] In this embodiment, the main body segment may be made wholly or at least the major portion along its length from quartz glass. Quartz glass has been shown to provide high-quality shape sensing, with characteristics including limited optical loss and low temperature sensitivity, especially when the reflective strain-sensitive structure is a fiber Bragg grating. In this embodiment, both the core and cladding of the fiber main body segment may be made of quartz glass.

[0028] In another embodiment, the second material may be a polymer.

[0029] As is well known, polymers have higher elasticity than quartz glass, thus exhibiting significantly higher strain and fracture tolerance. The distal end segment incorporating polymer can bend to a smaller radius before failure. In this embodiment, at least the cladding of the distal end segment may be made of polymer, while the core of the distal end segment may be made of the same polymer or a different material. When the distal end segment is short, the higher optical loss of polymer fiber compared to quartz fiber does not significantly affect the shape-sensing performance of the distal end segment. Shorter distal end segments are sufficient for highly flexible end regions of elongated instruments that experience high curvature during guidance.

[0030] In conjunction with the foregoing embodiments, the optical fiber may include a combination of quartz glass in the main body and polymer in the distal end.

[0031] The distal end segment of the polymer can be connected to the main body segment of the quartz glass by means of welding, splicing, bonding, etc. For example, after aligning the core of the distal end segment with the core of the main body segment, a UV-curable adhesive is applied around the interface between the distal end segment and the main body segment for connection.

[0032] The polymer contained in the distal end segment may include one or more of the following: PMMA, polystyrene, polycarbonate, TOPAS polymer, CEONEX polymer, CYTOP polymer.

[0033] TOPAS, CEONEX, and CYTOP are special fiber polymers that exhibit lower optical loss than PMMA at higher wavelengths while maintaining mechanical robustness.

[0034] In another embodiment, the second fiber core may be made of quartz glass.

[0035] Therefore, within the scope of this invention, the quartz glass body segment can be combined with a polymer distal end segment, wherein only the cladding of the distal end segment is made of polymer, while the core of the distal end segment is made of quartz glass. Thus, the distal end segment can be a quartz glass / polymer hybrid. The polymer cladding provides mechanical robustness, while the quartz glass core provides lower optical loss and superior shape-sensing performance compared to a polymer-made core.

[0036] The lower mechanical strength of quartz glass cores compared to polymer cores can be at least partially compensated by combining them with the above-described embodiments, according to which the core of the distal end segment has a reduced radial distance from the central axis of the distal end segment.

[0037] In manufacturing the distal end segment, a porous polymer cladding can be produced into which a quartz glass fiber core is inserted. Optionally, an annealing step can then be performed to eliminate air gaps between the core and the cladding. One advantage is that, due to the low melting or softening temperature of the polymer, a fiber Bragg grating (FBG) can be written into the core before the core is clad and embedded in the polymer cladding, without the risk of the grating fading during subsequent processing.

[0038] In another embodiment, which may be considered alone or in combination with any of the foregoing embodiments, the core of the distal end segment may be made of a first polymer, and the cladding of the distal end segment may comprise a second polymer different from the first polymer, wherein the elastic modulus of the second polymer is lower than that of the first polymer.

[0039] In this embodiment, both the core and cladding of the distal end segment can be made of polymer, wherein the polymer of the cladding of the distal end segment is different from the polymer of the core. In particular, the polymer of the cladding of the distal end segment may be more elastic than the polymer of the core, exhibiting a lower elastic modulus in the cladding of the distal end segment.

[0040] One advantage of this embodiment is that it reduces the manufacturing complexity of the distal end segment, or at least allows for different manufacturing processes, because the elastomeric cladding material can be processed as a liquid at room temperature, or at least at temperatures well below the decay of the fiber Bragg grating (FBG), allowing the grating to be written in before further processing of the elastomeric cladding. This also allows the core to be positioned as needed before the liquid cladding is backfilled onto the core structure, thus allowing for taper and other structural variations along the length of the distal end segment, such as a smaller radial distance of the core from the central axis or a torsional distribution of the core.

[0041] In conjunction with the foregoing embodiments, the fiber core can be made of conventional polymer fiber materials compatible with fiber Bragg gratings (FBGs), such as PMMA, TOPAS, CYTOP, or PC, while the cladding can be made of an elastomer, such as a thermosetting elastomer material like polydimethylsiloxane or polyurethane methacrylate. The cladding can also be made of a UV-curable polymer.

[0042] In another embodiment, the second material contained in the distal end segment may be a polymer modified to reduce its strain sensitivity.

[0043] Typically, fiber cores containing fiber Bragg gratings (FBGs) and made of polymers tend to have higher strain sensitivity than silica glass fibers due to their lower strain-optic coefficient. An advantage of this embodiment is that it allows for lower bending strain sensitivity at the distal end, mitigating the higher strain sensitivity of the polymer. Modification of the polymer at the distal end may include, for example, removing material from the distal end by etching (e.g., etching PMMA with acetone), shortening the write time of the reflective strain-sensitive structure, or annealing, i.e., a combination of temperature and humidity treatment. Alternatively or in combination, the end may be mechanically flattened.

[0044] In this way, the strain sensitivity of the highly flexible polymer distal end segment can be adjusted to match the maximum measurable bending strain, thereby matching the minimum bending radius of the local curvature of the main segment with the smaller measurable minimum bending radius of the high curvature distal end segment.

[0045] In all of the above embodiments, the distal end segment can be spliced, glued, or fused to the main body segment.

[0046] In another embodiment, the distal end segment may have a length ranging from 1 to 5 centimeters.

[0047] In another embodiment, the width or diameter of the tip can be reduced by, for example, material removal (such as etching) and / or mechanical flattening.

[0048] According to a second aspect of the present invention, an elongated instrument for medical interventional applications is provided, comprising: The main body segment and the distal terminal segment together define the lumen along the length of the slender instrument; And the multi-core optical fiber according to the first aspect, which is arranged in the cavity, wherein the distal end segment of the optical fiber is arranged in the distal end segment of the elongated instrument.

[0049] Slender instruments, including those containing multi-core optical fibers according to the invention, are particularly suitable for surgeries that require guiding tortuous anatomical structures and / or passing through narrow lesions or occlusions. The advantages stem from the favorable properties of the optical fibers of the invention, particularly the enhanced elasticity and mechanical robustness of their distal end segments.

[0050] In one embodiment of the slender device, the bending stiffness of the distal end segment may be lower than that of the main body segment.

[0051] In particular, the distal end segment of a slender instrument may include a coil, which is advantageously flexible for interventional applications where the slender instrument must conform to a tortuous structure due to its high flexibility. Attached Figure Description

[0052] The above and other aspects of the present invention will become clear and detailed in conjunction with the embodiments described below. In the following figures: Figure 1 An exemplary length of multi-core twisted optical fiber is shown; Figure 2 An embodiment of a distal region of an elongated instrument for medical interventional applications is shown, wherein the distal region of an optical fiber embodiment is disposed within the elongated instrument; Figure 3 A graph depicting the optical loss of polymer optical fiber and quartz glass optical fiber is shown. Figure 4 A longitudinal cross-section of the distal region of an optical fiber according to another embodiment is shown; and Figure 5A and Figure 5B The cross-sections of optical fibers with different core radial distances to the fiber's central axis are shown. Detailed Implementation

[0053] Figure 1 A segment of multi-core optical fiber 10 is shown, configured for distributed shape sensing along the fiber 10. The multi-core optical fiber 10 includes a cladding 12 and multiple cores 14, 16, 18, and 20. Core 14 is a central core disposed on and extending along the central axis of the fiber 10. Cores 16, 18, and 20 are outer cores arranged radially spaced from the central core 14. As shown, the outer cores 16, 18, and 20 may be helically wound around the central core 14. The outer cores 16, 18, and 20 are angularly spaced from each other around the longitudinal central axis of the fiber 10. In the case of three outer cores, the angular spacing between adjacent cores is typically 120°. The multi-core optical fiber 10 may have fewer than four cores or more than four cores. For example, the multi-core optical fiber 10 may include seven cores, of which three are radially outer cores, one is a central core, and the other three cores are located in a mid-radial position between the three outer cores and the central core.

[0054] Each fiber core 14, 16, 18, and 20 includes a reflective strain-sensitive structure 21. Figure 1 The fiber core 20 is illustrated as an example. This reflective strain-sensitive structure may include one or more fiber Bragg gratings (FBGs). The reflective strain-sensitive structure 21, such as one or more FBGs, responds to strain in the fiber 10. The multi-core fiber 10 can sense strain, which may be axial strain, bending strain, or torsional strain, thereby enabling the three-dimensional shape reconstruction of the fiber 10 using an optical interrogation system (not shown) known in the art. When the multi-core fiber 10 is used in elongated instruments such as guidewires or catheters, it can provide a three-dimensional shape reconstruction of the elongated instrument.

[0055] The optical interrogation system emits a laser beam into the cores 14, 16, 18, and 20 of optical fiber 10, and then receives and analyzes the reflected light from the reflective strain-sensitive structure 21. The wavelength of the laser beam emitted through the fiber is typically scanned within a certain wavelength range, for example, from 1535 nm to 1565 nm. Twists and bends in the fiber affect the wavelength spectrum of the light returning to the optical interrogation system. By analyzing the wavelength spectrum of the reflected light from the cores 14, 16, 18, and 20, the entire length of optical fiber 10 and the three-dimensional shape of elongated instruments disposed within it can be reconstructed. Therefore, radiation-free, real-time three-dimensional visualization of elongated instruments, such as guidewires introduced into a patient's vascular system, becomes possible.

[0056] Typical multi-core optical fibers made of quartz glass with an outer cladding diameter ranging from, for example, 100 μm to 125 μm have proven to have good strain sensitivity, making them well-suited for FORS (Fiber Optic Rectangular Sensing) technology. In interventional medical applications, such as peripheral surgeries (e.g., treatment of peripheral artery disease), slender instruments equipped with multi-core optical fibers and featuring Fiber Optic Rectangular Sensing (FORS), especially guidewires with FORS functionality, are beneficial for reducing radiation dose. However, in such procedures, the vessel diameter is very small, the guide trajectory is often very tortuous (i.e., with many bends), and it may be necessary to navigate through many bifurcations to reach the target location, which typically involves slender instruments and acute angles that the multi-core optical fibers must pass through. Furthermore, these smaller vessels are more fragile and can be damaged by the tips of slender instruments. Particularly in peripheral artery disease (PAD), angioplasty requires traversing narrowed or occluded segments of the vessel. For more severe occlusions, force is usually required, and sometimes the guidewire tip will prolapse, i.e., the guidewire forms a loop and the tip bends in the opposite direction to itself. This phenomenon is also called "knuckling," which can cause the instrument tip to bend very sharply, for example, with a bending radius of less than 1 mm.

[0057] Wang, Jian-Bo, et al., in their article "An Effective Guidewire Looping Technique for the Recanalization of Occlusive Segments of Infrapopliteal Vessels," published in Volume 11 (2010), pp. 441-448, describe a transluminal angioplasty technique. As described, a hydrophilic guidewire is inserted into a proximal branch of the vessel, and then a "U" shape is formed by continuous rotation and advancement of the guidewire. The looped guidewire is then advanced into and across the occluded segment of the vessel, after which a catheter is advanced along the guidewire across the occluded segment. The guidewire described in the article is not equipped with an optical fiber.

[0058] When elongated instruments such as guidewires include optical fibers made of quartz glass that extend to the distal end of the instrument (e.g., Figure 1 The optical fiber 10 in the fiber may become too curved when the fiber undergoes the above-mentioned loop formation, resulting in shape sensing impedance. Alternatively, when the curvature of the fiber becomes even higher than the maximum curvature that the glass fiber can withstand, the glass material of the fiber will fail, that is, the fiber may break or shatter.

[0059] These technical problems are solved by a newly designed multi-core optical fiber, embodiments of which will be described below. The invention addresses these technical problems by replacing the material of this segment of optical fiber 10 in regions where a smaller bending radius (or in other words, higher curvature) is expected, particularly the distal end segment, with a material that is better suited to high curvature, at least in terms of mechanical robustness and optionally in terms of strain sensing capability. By selecting a material with greater mechanical robustness, the optical fiber can mechanically withstand higher curvatures. In some embodiments, the distal end segment of the optical fiber may be additionally configured to reduce its bending strain sensitivity, thereby increasing the maximum curvature that the distal end segment can sense during optical interrogation of the optical fiber.

[0060] Figure 2 The distal region of an elongated instrument 100 for medical interventional applications is shown. The elongated instrument 100 includes a housing 112 defining an inner cavity 114 extending longitudinally along the length of the instrument 100. An optical fiber 10, particularly a multi-core optical fiber 10, is disposed within the inner cavity 114. The optical fiber 10 is free to slide and rotate within the inner cavity 114. Therefore, the optical fiber 10 can be a free-floating optical fiber within the inner cavity 114.

[0061] The device 100 includes a distal terminal segment 118 and a body segment 120 disposed proximal to the distal terminal segment 118. The distal terminal segment 118 of the device 100 terminates at a distal end 122. The distal terminal segment 118 may include a coil 124 embedded in a coating 126 (e.g., a polyurethane coating). The body segment 120 of the device 100 may include a tube 128, such as a nitinol tube, or a tube whose peripheral walls may have slits.

[0062] The distal terminal segment 118 of the device 100 may have a lower, preferably much lower, bending stiffness than the main body segment 120 of the device 100. In other words, the distal terminal segment 118 is softer / more flexible than the main body segment 120, such that the distal terminal segment 118 may prolapse when the slender device 100 is advanced in a blood vessel and encounters an occlusion or lesion. The optical fiber 10 will be described in more detail below.

[0063] Optical fiber 10 includes a main body segment 40 and a distal end segment 42. The distal end segment 42 is a section of the optical fiber that may withstand high bending curvature (or small bending radius). The main body segment 40 and the distal end segment 42 may each include, as described above... Figure 1 The cladding, commonly indicated by reference numeral 12, and the core, commonly indicated by reference numerals 14, 16, 18, and 20, are as follows. Figure 4 For example, the cladding of the main body segment 40 is also designated by reference numeral 12a, and the core of the main body segment 40 is designated by reference numerals 14a, 16a, 18a, and 20a. The cladding of the distal end segment 42 is also designated by reference numeral 12b, and the core of the distal end segment 42 is designated by reference numerals 14b, 16b, 18b, and 20b. The number of cores may be less than or more than four, for example, 2, 3, 5, 6, or 7. The distal end segment 42 of the optical fiber 10 comprises or is made of a material different from that of the main body segment 40. The materials of the cladding 12b and / or the cores 14b, 16b, 18b, and 20b of the distal end segment 42 are selected such that the distal end segment 42 has greater elasticity than the main body segment 40. In other words, the material of the distal end segment 42 is selected such that it is mechanically more robust than the main body segment 40. Specifically, the material of the distal end segment 42 is selected such that the fracture strain of the distal end segment 42 is higher than that of the main body segment 40. Preferably, the fracture strain of the distal end segment 42 is at least twice that of the fracture strain of the main body segment 40, more preferably at least five times, and even more preferably at least ten times.

[0064] In one embodiment, the body segment 40 of the optical fiber 10 may be made of quartz glass, i.e., the material of the cladding 12a and the cores 14a, 16a, 18a, and 20a may be quartz glass, while the distal end segment 42 may be made entirely of or contain polymers, particularly optical polymers, whose fracture strain can be much higher (more than 10 times higher) than that of glass optical fibers, thus allowing it to bend to a smaller radius before failure. In this embodiment, the cladding 12b and the cores 14b, 16b, 18b, and 20b of the distal end segment 42 may all be made of the same polymer.

[0065] Polymers with stronger mechanical strength can be fused, spliced, or bonded to the body segment 40 of the optical fiber 10. For example, after aligning the core of the distal end segment 42 with the core of the body segment 40, a UV-curable adhesive 46 can be used around the joint 44 between the distal end segment 42 and the body segment 40.

[0066] It is well known that polymers (such as optical PMMA) exhibit high optical loss per unit length near a wavelength of 1550 nm, making it disadvantageous to fabricate a complete optical fiber 10, including the main body segment 40, using this material. However, the distal termination segment 118 of elongated instruments such as guidewires is typically short, for example, 2-4 cm, so even with high optical loss, the short length of the distal end segment 42 (ranging from 1 to 5 cm, preferably 2 to 4 cm) in the distal termination segment 118 of the elongated instrument 100 limits the absolute signal loss to an acceptable level. Like most other polymers, PMMA exhibits significantly better mechanical robustness than quartz glass. The maximum mechanical strain limit of glass optical fibers is less than about 2% (equivalent to 20,000 με), while polymers such as PMMA can be stretched to much higher elongation before breakage, typically more than 10 times higher. Furthermore, polymer fibers yield before failure, rather than undergoing brittle fracture like glass fibers. While this affects sensing characteristics (leading to any combination of hysteresis, increased noise, or signal loss), it is still possible to reconstruct the shape of fiber 10 up to the distal end, albeit with lower precision. For fractured glass fibers, shape reconstruction would be completely impossible. The strain sensing characteristics of polymer fibers are linear or nearly linear up to the yield point (above 20,000 με). In effect, these improved mechanical properties of the polymer used for the distal end segment 42 of fiber 10 make the distal end segment 42 of fiber 10 mechanically more robust, preventing fiber breakage during drooping or loop formation of the distal terminal segment 118 of device 100.

[0067] Other materials that can be used for the cladding 12b and / or core z14b, 16b, 18b, 20b of the far-end segment 42 of fiber 10 may include polystyrene, polycarbonate, and special fiber polymers such as TOPAS, ZEONEX, and CYTOP polymers. These special materials exhibit improved optical loss at higher wavelengths while maintaining high mechanical robustness. Figure 3 The curves showing the optical loss of PMMA fiber, CYTOP fiber, and quartz glass fiber as a function of wavelength are displayed.

[0068] When both are equipped with fiber Bragg gratings, the strain sensitivity of polymer fiber is typically about 20-40% higher than that of silica glass fiber (i.e., 1.4-1.7 pm / με for polymer fiber and 1.2 pm / με for glass fiber). This is due to the improved strain-optic coefficient of optical polymers.

[0069] When employing a single optical interrogation system to simultaneously sense both the glass body segment 40 and the polymer distal end segment 42 within a fixed wavelength scanning range, it is more advantageous if the distal end segment 42, subjected to high curvature bending, has reduced bending strain sensitivity—that is, a lower wavelength shift per unit curvature in the distal end segment 42. Although this may seem counterintuitive, the advantage of the lower curvature sensitivity of the fiber distal end segment 42 is that the wavelength scanning range of the interrogation light source can remain constant, while the wavelength shift caused by the larger maximum curvature of the high-curvature distal end segment 42 still falls within that scanning range. Therefore, the minimum bending radius of the distal end segment 42 that can be measured by optically interrogating the fiber 10 within a defined scanning wavelength range is smaller than the minimum bending radius of the body segment that can be measured by optically interrogating the fiber 10 within the same defined scanning wavelength range.

[0070] To reduce the bending strain sensitivity of the distal end segment 42, Figure 4 Another embodiment, illustrated schematically, proposes an outer optical core ( Figure 4 The outer cores 16b and 20b are shown in the figure (the helical nature is not shown for simplicity). The radial distance from the neutral line or center core 14b is variable, for example, as shown in the figure. Figure 4 The value decreases towards the far side. When the radial distance of the outer fiber core, i.e., the radial distance r of the outer fiber core from the neutral line of fiber 10... core As the curvature decreases, the bending strain sensitivity also decreases; that is, the strain induced in the outer core by the same bending curvature varies with the core distance. R core,2 / R core,1 Decrease, of which R core,2 < R core,1 (See Figure 5A and 5B This is because the average strain caused by bending in the fiber core follows the relationship... ε core = r core / R bend ,in R bend The radius of curvature is denoted as .

[0071] In manufacturing with such Figure 4Regarding the reduced radial distances of the outer core 16b, 18b, and 20b in the distal end segment 42, it should be noted that polymer fibers, due to their flexibility and lower melting temperature, are easier to stretch during processing than silica (glass) fibers to achieve a reduction in the radial distance of the core. Therefore, this method can be more easily applied to polymer fibers rather than glass fibers. At interface 44, the radial distance of the outer core in the distal end segment 42 must match the radial distance of the outer core in the main body segment 40, such as... Figure 4 As shown.

[0072] Another advantage of the reduced strain per unit curvature of the outer fiber core in the distal end segment 42 due to the reduced radial distance of the outer fiber core is that the birefringence effect is limited, which is beneficial to the accuracy of strain sensing and corresponding shape calculation.

[0073] In an alternative embodiment, the optical fiber 10 may be designed such that the cores 14b, 16b, 18b, and 20b of the distal end segment 42 are made of glass, which preserves low optical loss characteristics, while the cladding 12b surrounding the cores 14b, 16b, 18b, and 20b is made of a polymer material, which is more elastic and therefore more robust or tougher than glass in mechanical properties. Although this design is not as mechanically robust as the aforementioned reference due to the glass material in the cores 14b, 16b, 18b, and 20b. Figure 2 The far-end segment 42 is designed as described, but the cores 14b, 16b, 18b, and 20b are not typically located on the outer diameter of the fiber 10, so the bending strain in the core is slightly lower than the strain in the outer region of the cladding 12b.

[0074] For a typical optical fiber geometry, the cladding diameter D cladding (See Figure 5A and 5B The core diameter is 100 μm. core The diameter is 8 μm, the radial distance of the outer core is approximately 35 μm, and the maximum strain in cladding 12 is equal to... D cladding / 2 R bend = 50 μm / R bend However, the maximum strain in the outer fiber core is ( D core / 2 + R core ) / R bend = (4 μm + 35 μm) / R bend This means a reduction of approximately 25%, which will allow for a smaller bending radius before the fiber core glass breaks.

[0075] For shorter segments in fiber 10, such as the far-end segment 42, the fiber can be manufactured by fabricating a porous polymer cladding 12b, inserting glass cores 14b, 16b, 18b, and 20b into it, and optionally subsequently performing an annealing step to eliminate air gaps between the cores 14b, 16b, 18b, and 20b and the cladding 12b. Fabricating porous polymer fibers is a known technique for producing microstructured polymer fibers. Therefore, this embodiment is an alternative when applications require low-loss signals but still need higher mechanical robustness (i.e., a smaller bending radius) than conventional glass fibers. It should be noted that this applies only to pure bending deformation and not to axial strain. Under axial strain, the strain on each core is the same and is independent of radial distance from the center.

[0076] Another advantage of this embodiment (where cores 14b, 16b, 18b, and 20b are made of quartz glass, and cladding 12b is made of polymer) is that, due to the low melting or softening temperature of the polymer, reflective strain-sensitive structures (such as fiber Bragg gratings) can be incorporated into cores 14b, 16b, 18b, and 20b before embedding the cores into the polymer cladding 12b, without the risk of grating fading during subsequent processing. For example, most polymers are processable, or at least deformable, at temperatures around 100°C, at which gratings in quartz glass are stable. This allows for the addition or adjustment of the torsion ratio of the outer core and the deformation of the fiber 10, for example, increasing the bending angle without straining the core.

[0077] In addition, as mentioned above Figure 4 As described above, the radial distance of the outer core of the high-curvature distal end segment 42 can be reduced compared to the low-curvature main body segment 40. In this case, in addition to the advantage of locally reducing bending sensitivity, the strain induced in the outer core during bending is further reduced. R core,2 / R core,1 The coefficient decreased (see Figure 5A and 5B Therefore, the breaking radius of fiber cores 14, 16, 18, and 20 is further reduced.

[0078] While the fiber cores 14b, 16b, 18b, and 20b of the distal end segment 42 in the above embodiments are quartz (glass) fiber cores, another embodiment proposes that the fiber cores 14b, 16b, 18b, and 20b are made of a first polymer, particularly conventional polymer fiber materials compatible with fiber Bragg gratings (e.g., PMMA, TOPAS, CYTOP, or PC), while the cladding 12b is made of a second polymer, particularly an elastomer, whose elastic modulus is lower than that of the first polymer contained in the fiber cores 14b, 16b, 18b, and 20b. For example, the cladding 12b may contain a thermosetting elastomer material, such as polydimethylsiloxane or polyurethane methacrylate, or even a UV-curable polymer.

[0079] As an additional benefit, this material choice reduces manufacturing complexity, or at least allows for different manufacturing processes, because the elastomeric material of cladding 12b can be processed as a liquid at room temperature, or at least at temperatures well below the decay of the fiber Bragg grating, allowing the fiber Bragg grating to be written in before further processing of the elastomeric cladding 12. This also allows cores 14b, 16b, 18b, and 20b to be positioned as needed before the liquid cladding material is backfilled onto the core structure, thus allowing for tapering along the length of the distal end segment 42 (see [link to original text]). Figure 4 ) and other structural changes, such as Figure 4 The variable radial distance or torsional distribution of the fiber cores 14b, 16b, 18b, and 20b is shown. This type of processing is feasible because the length of the distal end segment 42 is typically much smaller than that of the main body segment 40.

[0080] As mentioned above, optical fibers with shape sensing capabilities, such as those containing fiber Bragg gratings, typically exhibit higher strain sensitivity than silica (glass) fibers when made of polymers due to their lower strain-optic coefficient. This higher strain sensitivity may offset the aforementioned reference... Figure 4 and 5B The described effect of reducing the radial distance of the outer fiber core may be necessary to avoid wavelength shifts outside the interrogator's wavelength scanning range caused by bending of the fiber Bragg grating.

[0081] However, the distal end segment 42 can also be provided with a polymer material that is less sensitive to strain than typical silica (glass) optical fibers. For example, an optical fiber made of PMMA may exhibit a strain sensitivity of less than 1 pm / με, while the strain sensitivity of CYTOP optical fiber may be 1.1 pm / με.

[0082] The inherent strain sensitivity of polymer optical fibers can be affected by several factors, thereby reducing their inherent strain sensitivity. Therefore, in another embodiment, the distal end segment 42 (which comprises polymer as the material of cladding 12b and / or core 14b, 16b, 18b, 20b) can be modified, wherein the modification may include: etching the polymer distal end segment 42 (e.g., etching PMMA with acetone); shortening the writing time for writing fiber Bragg gratings into the core; and / or annealing, i.e., a combination of temperature and humidity environmental treatment.

[0083] In this way, the strain sensitivity of the highly flexible polymer distal end segment 42 of the optical fiber 10 can be adjusted to match the maximum measurable bending strain, thereby matching the minimum bending radius of the low curvature body segment 40 of the optical fiber 10 with the smaller minimum bending radius of the high curvature distal end segment 42.

[0084] By utilizing the above-mentioned technique for reducing the strain sensitivity of the distal end section 42, preferably in combination with the above-mentioned technique for reducing the radial distance between the outer core and the center core of the optical fiber 10, a reduction of 60-70% in the measurable minimum bending radius of the distal end section 42 can be achieved, for example, from 2.5 mm in glass optical fiber to less than 1 mm in polymer optical fiber.

[0085] Although the invention has been described in detail with reference to the accompanying drawings and the foregoing description, such descriptions should be considered illustrative or exemplary, not restrictive; the invention is not limited to the disclosed embodiments. Other variations of the disclosed embodiments can be understood and implemented by those skilled in the art in practicing the claimed invention through study of the drawings, the disclosure, and the appended claims.

[0086] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude multiple. A single element or other unit can perform several functions recited in the claims. The fact that certain technical means are recited in mutually different dependent claims does not mean that a combination of these technical means cannot be used to obtain an advantage.

[0087] Any reference numerals in the claims should not be construed as limiting the scope.

Claims

1. A multi-core optical fiber (10) configured for shape sensing, the optical fiber (10) comprising an elongated body segment (40) and a distal end segment (42) connected to the body segment (40), the body segment (40) comprising a first cladding (12a) and a plurality of first cores (14a, 16a, 18a, 20a) embedded in the first cladding (12a), the distal end segment (42) comprising a second cladding (12b) and a plurality of second cores (14b, 16b, 18b, 20b) embedded in the second cladding (12b), the first and second cores (14a, 14b, 16a, 16b, 18a, 18b, 20a, 20b) comprising a reflective strain-sensitive structure (21), the reflective strain-sensitive structure being configured to perform distributed shape sensing along the body segment (40) and the distal end segment (42), wherein, The main body segment (40) comprises a first material, and the distal end segment (42) comprises a second material different from the first material. The first fracture strain of the main body segment (40) is lower than the second fracture strain of the distal end segment (42).

2. The multi-core optical fiber according to claim 1, wherein, The second fracture strain is at least twice the first fracture strain, preferably at least five times, and more preferably at least ten times.

3. The multi-core optical fiber according to claim 1 or 2, wherein, The distal end segment (42) has a lower bending strain sensitivity than the main body segment (40), such that the first minimum bending radius of the distal end segment (42), which can be measured by optically interrogating the fiber (10) within a defined scanning wavelength range, is smaller than the second minimum bending radius of the main body segment (40), which can be measured by optically interrogating the fiber (10) within the defined scanning wavelength range.

4. The multi-core optical fiber according to any one of claims 1 to 3, wherein, The first fiber core (14a, 16a, 18a, 20a) includes an outer fiber core (16a, 18a, 20a) arranged at a first radial distance from the central axis of the main body segment (40), and the second fiber core (14b, 16b, 18b, 20b) includes a second outer fiber core (16b, 18b, 20b) arranged at a second radial distance from the central axis of the distal end segment (42), wherein the second radial distance is smaller than the first radial distance.

5. The multi-core optical fiber according to any one of claims 1 to 4, wherein, The first material is quartz glass.

6. The multi-core optical fiber according to any one of claims 1 to 5, wherein, The second material is a polymer.

7. The multi-core optical fiber according to claim 6, wherein, The polymer includes one of PMMA, polystyrene, polycarbonate, TOPAS polymer, ZEONEX polymer, and CYTOP polymer.

8. The multi-core optical fiber according to any one of claims 5 to 7, wherein, The second fiber core (14b, 16b, 18b, 20b) is made of quartz glass.

9. The multi-core optical fiber according to any one of claims 1 to 4, wherein, The second core (14b, 16b, 18b, 20b) is made of a first polymer, and the second cladding (12b) comprises a second polymer different from the first polymer, wherein the elastic modulus of the second polymer is lower than that of the first polymer.

10. The multi-core optical fiber according to claim 9, wherein, The first polymer includes one of PMMA, polystyrene, polycarbonate, TOPAS polymer, ZEONEX polymer, and CYTOP polymer, and the second polymer includes an elastomer, particularly a thermosetting elastomer, particularly polydimethylsiloxane, polyurethane methacrylate, or a UV-curable polymer.

11. The multi-core optical fiber according to any one of claims 1 to 10, wherein, The second material is a polymer that has been modified to reduce its strain sensitivity.

12. The multi-core optical fiber according to any one of claims 1 to 11, wherein, The distal end segment (42) is spliced, glued to or fused to the main body segment.

13. The multi-core optical fiber according to any one of claims 1 to 12, wherein, The distal end segment (42) has a length ranging from 1 to 5 centimeters.

14. An elongated instrument for medical interventional applications, comprising: A main body segment (120) and a distal terminal segment (118), the main body segment and the distal terminal segment together defining an inner cavity (114) along the length of the elongated instrument (100); and According to any one of claims 1 to 13, the multi-core optical fiber (10) is arranged in the inner cavity (114), wherein the distal end segment (42) of the optical fiber (10) is arranged in the distal end segment (118) of the elongated instrument (100).

15. The elongated device according to claim 14, wherein, The bending stiffness of the distal terminal segment (118) is lower than that of the main body segment (120).

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